Initial commit: Linux kernel 4.19 for Unplugged OS

Documentation/driver-api/80211/cfg80211.rst

@@ -0,0 +1,354 @@
+==================
+cfg80211 subsystem
+==================
+
+.. kernel-doc:: include/net/cfg80211.h
+   :doc: Introduction
+
+Device registration
+===================
+
+.. kernel-doc:: include/net/cfg80211.h
+   :doc: Device registration
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_channel_flags
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_channel
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_rate_flags
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_rate
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_sta_ht_cap
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_supported_band
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_signal_type
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wiphy_params_flags
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wiphy_flags
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wiphy
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wireless_dev
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wiphy_new
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wiphy_read_of_freq_limits
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wiphy_register
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wiphy_unregister
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wiphy_free
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wiphy_name
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wiphy_dev
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wiphy_priv
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: priv_to_wiphy
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: set_wiphy_dev
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wdev_priv
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_iface_limit
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_iface_combination
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_check_combinations
+
+Actions and configuration
+=========================
+
+.. kernel-doc:: include/net/cfg80211.h
+   :doc: Actions and configuration
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_ops
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: vif_params
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: key_params
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: survey_info_flags
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: survey_info
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_beacon_data
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_ap_settings
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: station_parameters
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: rate_info_flags
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: rate_info
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: station_info
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: monitor_flags
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: mpath_info_flags
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: mpath_info
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: bss_parameters
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_txq_params
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_crypto_settings
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_auth_request
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_assoc_request
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_deauth_request
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_disassoc_request
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_ibss_params
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_connect_params
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_pmksa
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_rx_mlme_mgmt
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_auth_timeout
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_rx_assoc_resp
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_assoc_timeout
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_tx_mlme_mgmt
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_ibss_joined
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_connect_resp_params
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_connect_done
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_connect_result
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_connect_bss
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_connect_timeout
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_roamed
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_disconnected
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_ready_on_channel
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_remain_on_channel_expired
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_new_sta
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_rx_mgmt
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_mgmt_tx_status
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_cqm_rssi_notify
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_cqm_pktloss_notify
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_michael_mic_failure
+
+Scanning and BSS list handling
+==============================
+
+.. kernel-doc:: include/net/cfg80211.h
+   :doc: Scanning and BSS list handling
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_ssid
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_scan_request
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_scan_done
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_bss
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_inform_bss
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_inform_bss_frame_data
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_inform_bss_data
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_unlink_bss
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_find_ie
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_bss_get_ie
+
+Utility functions
+=================
+
+.. kernel-doc:: include/net/cfg80211.h
+   :doc: Utility functions
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_channel_to_frequency
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_frequency_to_channel
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_get_channel
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_get_response_rate
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_hdrlen
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_get_hdrlen_from_skb
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_radiotap_iterator
+
+Data path helpers
+=================
+
+.. kernel-doc:: include/net/cfg80211.h
+   :doc: Data path helpers
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_data_to_8023
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: ieee80211_amsdu_to_8023s
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_classify8021d
+
+Regulatory enforcement infrastructure
+=====================================
+
+.. kernel-doc:: include/net/cfg80211.h
+   :doc: Regulatory enforcement infrastructure
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: regulatory_hint
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wiphy_apply_custom_regulatory
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: freq_reg_info
+
+RFkill integration
+==================
+
+.. kernel-doc:: include/net/cfg80211.h
+   :doc: RFkill integration
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wiphy_rfkill_set_hw_state
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wiphy_rfkill_start_polling
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: wiphy_rfkill_stop_polling
+
+Test mode
+=========
+
+.. kernel-doc:: include/net/cfg80211.h
+   :doc: Test mode
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_testmode_alloc_reply_skb
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_testmode_reply
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_testmode_alloc_event_skb
+
+.. kernel-doc:: include/net/cfg80211.h
+   :functions: cfg80211_testmode_event

Documentation/driver-api/80211/conf.py

@@ -0,0 +1,10 @@
+# -*- coding: utf-8; mode: python -*-
+
+project = "Linux 802.11 Driver Developer's Guide"
+
+tags.add("subproject")
+
+latex_documents = [
+    ('index', '80211.tex', project,
+     'The kernel development community', 'manual'),
+]

Documentation/driver-api/80211/index.rst

@@ -0,0 +1,17 @@
+=====================================
+Linux 802.11 Driver Developer's Guide
+=====================================
+
+.. toctree::
+
+   introduction
+   cfg80211
+   mac80211
+   mac80211-advanced
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`

Documentation/driver-api/80211/introduction.rst

@@ -0,0 +1,17 @@
+============
+Introduction
+============
+
+Explaining wireless 802.11 networking in the Linux kernel
+
+Copyright 2007-2009 Johannes Berg
+
+These books attempt to give a description of the various subsystems
+that play a role in 802.11 wireless networking in Linux. Since these
+books are for kernel developers they attempts to document the
+structures and functions used in the kernel as well as giving a
+higher-level overview.
+
+The reader is expected to be familiar with the 802.11 standard as
+published by the IEEE in 802.11-2007 (or possibly later versions).
+References to this standard will be given as "802.11-2007 8.1.5".

Documentation/driver-api/80211/mac80211-advanced.rst

@@ -0,0 +1,295 @@
+=============================
+mac80211 subsystem (advanced)
+=============================
+
+Information contained within this part of the book is of interest only
+for advanced interaction of mac80211 with drivers to exploit more
+hardware capabilities and improve performance.
+
+LED support
+===========
+
+Mac80211 supports various ways of blinking LEDs. Wherever possible,
+device LEDs should be exposed as LED class devices and hooked up to the
+appropriate trigger, which will then be triggered appropriately by
+mac80211.
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_get_tx_led_name
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_get_rx_led_name
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_get_assoc_led_name
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_get_radio_led_name
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_tpt_blink
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_tpt_led_trigger_flags
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_create_tpt_led_trigger
+
+Hardware crypto acceleration
+============================
+
+.. kernel-doc:: include/net/mac80211.h
+   :doc: Hardware crypto acceleration
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: set_key_cmd
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_key_conf
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_key_flags
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_get_tkip_p1k
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_get_tkip_p1k_iv
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_get_tkip_p2k
+
+Powersave support
+=================
+
+.. kernel-doc:: include/net/mac80211.h
+   :doc: Powersave support
+
+Beacon filter support
+=====================
+
+.. kernel-doc:: include/net/mac80211.h
+   :doc: Beacon filter support
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_beacon_loss
+
+Multiple queues and QoS support
+===============================
+
+TBD
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_tx_queue_params
+
+Access point mode support
+=========================
+
+TBD
+
+Some parts of the if_conf should be discussed here instead
+
+Insert notes about VLAN interfaces with hw crypto here or in the hw
+crypto chapter.
+
+support for powersaving clients
+-------------------------------
+
+.. kernel-doc:: include/net/mac80211.h
+   :doc: AP support for powersaving clients
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_get_buffered_bc
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_beacon_get
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_sta_eosp
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_frame_release_type
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_sta_ps_transition
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_sta_ps_transition_ni
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_sta_set_buffered
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_sta_block_awake
+
+Supporting multiple virtual interfaces
+======================================
+
+TBD
+
+Note: WDS with identical MAC address should almost always be OK
+
+Insert notes about having multiple virtual interfaces with different MAC
+addresses here, note which configurations are supported by mac80211, add
+notes about supporting hw crypto with it.
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_iterate_active_interfaces
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_iterate_active_interfaces_atomic
+
+Station handling
+================
+
+TODO
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_sta
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: sta_notify_cmd
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_find_sta
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_find_sta_by_ifaddr
+
+Hardware scan offload
+=====================
+
+TBD
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_scan_completed
+
+Aggregation
+===========
+
+TX A-MPDU aggregation
+---------------------
+
+.. kernel-doc:: net/mac80211/agg-tx.c
+   :doc: TX A-MPDU aggregation
+
+.. WARNING: DOCPROC directive not supported: !Cnet/mac80211/agg-tx.c
+
+RX A-MPDU aggregation
+---------------------
+
+.. kernel-doc:: net/mac80211/agg-rx.c
+   :doc: RX A-MPDU aggregation
+
+.. WARNING: DOCPROC directive not supported: !Cnet/mac80211/agg-rx.c
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_ampdu_mlme_action
+
+Spatial Multiplexing Powersave (SMPS)
+=====================================
+
+.. kernel-doc:: include/net/mac80211.h
+   :doc: Spatial multiplexing power save
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_request_smps
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_smps_mode
+
+TBD
+
+This part of the book describes the rate control algorithm interface and
+how it relates to mac80211 and drivers.
+
+Rate Control API
+================
+
+TBD
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_start_tx_ba_session
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_start_tx_ba_cb_irqsafe
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_stop_tx_ba_session
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_stop_tx_ba_cb_irqsafe
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_rate_control_changed
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_tx_rate_control
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: rate_control_send_low
+
+TBD
+
+This part of the book describes mac80211 internals.
+
+Key handling
+============
+
+Key handling basics
+-------------------
+
+.. kernel-doc:: net/mac80211/key.c
+   :doc: Key handling basics
+
+MORE TBD
+--------
+
+TBD
+
+Receive processing
+==================
+
+TBD
+
+Transmit processing
+===================
+
+TBD
+
+Station info handling
+=====================
+
+Programming information
+-----------------------
+
+.. kernel-doc:: net/mac80211/sta_info.h
+   :functions: sta_info
+
+.. kernel-doc:: net/mac80211/sta_info.h
+   :functions: ieee80211_sta_info_flags
+
+STA information lifetime rules
+------------------------------
+
+.. kernel-doc:: net/mac80211/sta_info.c
+   :doc: STA information lifetime rules
+
+Aggregation
+===========
+
+.. kernel-doc:: net/mac80211/sta_info.h
+   :functions: sta_ampdu_mlme
+
+.. kernel-doc:: net/mac80211/sta_info.h
+   :functions: tid_ampdu_tx
+
+.. kernel-doc:: net/mac80211/sta_info.h
+   :functions: tid_ampdu_rx
+
+Synchronisation
+===============
+
+TBD
+
+Locking, lots of RCU

Documentation/driver-api/80211/mac80211.rst

@@ -0,0 +1,216 @@
+===========================
+mac80211 subsystem (basics)
+===========================
+
+You should read and understand the information contained within this
+part of the book while implementing a mac80211 driver. In some chapters,
+advanced usage is noted, those may be skipped if this isn't needed.
+
+This part of the book only covers station and monitor mode
+functionality, additional information required to implement the other
+modes is covered in the second part of the book.
+
+Basic hardware handling
+=======================
+
+TBD
+
+This chapter shall contain information on getting a hw struct allocated
+and registered with mac80211.
+
+Since it is required to allocate rates/modes before registering a hw
+struct, this chapter shall also contain information on setting up the
+rate/mode structs.
+
+Additionally, some discussion about the callbacks and the general
+programming model should be in here, including the definition of
+ieee80211_ops which will be referred to a lot.
+
+Finally, a discussion of hardware capabilities should be done with
+references to other parts of the book.
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_hw
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_hw_flags
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: SET_IEEE80211_DEV
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: SET_IEEE80211_PERM_ADDR
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_ops
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_alloc_hw
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_register_hw
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_unregister_hw
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_free_hw
+
+PHY configuration
+=================
+
+TBD
+
+This chapter should describe PHY handling including start/stop callbacks
+and the various structures used.
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_conf
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_conf_flags
+
+Virtual interfaces
+==================
+
+TBD
+
+This chapter should describe virtual interface basics that are relevant
+to the driver (VLANs, MGMT etc are not.) It should explain the use of
+the add_iface/remove_iface callbacks as well as the interface
+configuration callbacks.
+
+Things related to AP mode should be discussed there.
+
+Things related to supporting multiple interfaces should be in the
+appropriate chapter, a BIG FAT note should be here about this though and
+the recommendation to allow only a single interface in STA mode at
+first!
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_vif
+
+Receive and transmit processing
+===============================
+
+what should be here
+-------------------
+
+TBD
+
+This should describe the receive and transmit paths in mac80211/the
+drivers as well as transmit status handling.
+
+Frame format
+------------
+
+.. kernel-doc:: include/net/mac80211.h
+   :doc: Frame format
+
+Packet alignment
+----------------
+
+.. kernel-doc:: net/mac80211/rx.c
+   :doc: Packet alignment
+
+Calling into mac80211 from interrupts
+-------------------------------------
+
+.. kernel-doc:: include/net/mac80211.h
+   :doc: Calling mac80211 from interrupts
+
+functions/definitions
+---------------------
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_rx_status
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: mac80211_rx_flags
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: mac80211_tx_info_flags
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: mac80211_tx_control_flags
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: mac80211_rate_control_flags
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_tx_rate
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_tx_info
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_tx_info_clear_status
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_rx
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_rx_ni
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_rx_irqsafe
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_tx_status
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_tx_status_ni
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_tx_status_irqsafe
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_rts_get
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_rts_duration
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_ctstoself_get
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_ctstoself_duration
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_generic_frame_duration
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_wake_queue
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_stop_queue
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_wake_queues
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_stop_queues
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_queue_stopped
+
+Frame filtering
+===============
+
+.. kernel-doc:: include/net/mac80211.h
+   :doc: Frame filtering
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_filter_flags
+
+The mac80211 workqueue
+======================
+
+.. kernel-doc:: include/net/mac80211.h
+   :doc: mac80211 workqueue
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_queue_work
+
+.. kernel-doc:: include/net/mac80211.h
+   :functions: ieee80211_queue_delayed_work

Documentation/driver-api/basics.rst

@@ -0,0 +1,129 @@
+Driver Basics
+=============
+
+Driver Entry and Exit points
+----------------------------
+
+.. kernel-doc:: include/linux/module.h
+   :internal:
+
+Driver device table
+-------------------
+
+.. kernel-doc:: include/linux/mod_devicetable.h
+   :internal:
+
+Delaying, scheduling, and timer routines
+----------------------------------------
+
+.. kernel-doc:: include/linux/sched.h
+   :internal:
+
+.. kernel-doc:: kernel/sched/core.c
+   :export:
+
+.. kernel-doc:: kernel/sched/cpupri.c
+   :internal:
+
+.. kernel-doc:: kernel/sched/fair.c
+   :internal:
+
+.. kernel-doc:: include/linux/completion.h
+   :internal:
+
+.. kernel-doc:: kernel/time/timer.c
+   :export:
+
+Wait queues and Wake events
+---------------------------
+
+.. kernel-doc:: include/linux/wait.h
+   :internal:
+
+.. kernel-doc:: kernel/sched/wait.c
+   :export:
+
+High-resolution timers
+----------------------
+
+.. kernel-doc:: include/linux/ktime.h
+   :internal:
+
+.. kernel-doc:: include/linux/hrtimer.h
+   :internal:
+
+.. kernel-doc:: kernel/time/hrtimer.c
+   :export:
+
+Workqueues and Kevents
+----------------------
+
+.. kernel-doc:: include/linux/workqueue.h
+   :internal:
+
+.. kernel-doc:: kernel/workqueue.c
+   :export:
+
+Internal Functions
+------------------
+
+.. kernel-doc:: kernel/exit.c
+   :internal:
+
+.. kernel-doc:: kernel/signal.c
+   :internal:
+
+.. kernel-doc:: include/linux/kthread.h
+   :internal:
+
+.. kernel-doc:: kernel/kthread.c
+   :export:
+
+Reference counting
+------------------
+
+.. kernel-doc:: include/linux/refcount.h
+   :internal:
+
+.. kernel-doc:: lib/refcount.c
+   :export:
+
+Atomics
+-------
+
+.. kernel-doc:: arch/x86/include/asm/atomic.h
+   :internal:
+
+Kernel objects manipulation
+---------------------------
+
+.. kernel-doc:: lib/kobject.c
+   :export:
+
+Kernel utility functions
+------------------------
+
+.. kernel-doc:: include/linux/kernel.h
+   :internal:
+
+.. kernel-doc:: kernel/printk/printk.c
+   :export:
+
+.. kernel-doc:: kernel/panic.c
+   :export:
+
+.. kernel-doc:: kernel/rcu/tree.c
+   :export:
+
+.. kernel-doc:: kernel/rcu/tree_plugin.h
+   :export:
+
+.. kernel-doc:: kernel/rcu/update.c
+   :export:
+
+Device Resource Management
+--------------------------
+
+.. kernel-doc:: drivers/base/devres.c
+   :export:
+

Documentation/driver-api/clk.rst

@@ -0,0 +1,307 @@
+========================
+The Common Clk Framework
+========================
+
+:Author: Mike Turquette <mturquette@ti.com>
+
+This document endeavours to explain the common clk framework details,
+and how to port a platform over to this framework.  It is not yet a
+detailed explanation of the clock api in include/linux/clk.h, but
+perhaps someday it will include that information.
+
+Introduction and interface split
+================================
+
+The common clk framework is an interface to control the clock nodes
+available on various devices today.  This may come in the form of clock
+gating, rate adjustment, muxing or other operations.  This framework is
+enabled with the CONFIG_COMMON_CLK option.
+
+The interface itself is divided into two halves, each shielded from the
+details of its counterpart.  First is the common definition of struct
+clk which unifies the framework-level accounting and infrastructure that
+has traditionally been duplicated across a variety of platforms.  Second
+is a common implementation of the clk.h api, defined in
+drivers/clk/clk.c.  Finally there is struct clk_ops, whose operations
+are invoked by the clk api implementation.
+
+The second half of the interface is comprised of the hardware-specific
+callbacks registered with struct clk_ops and the corresponding
+hardware-specific structures needed to model a particular clock.  For
+the remainder of this document any reference to a callback in struct
+clk_ops, such as .enable or .set_rate, implies the hardware-specific
+implementation of that code.  Likewise, references to struct clk_foo
+serve as a convenient shorthand for the implementation of the
+hardware-specific bits for the hypothetical "foo" hardware.
+
+Tying the two halves of this interface together is struct clk_hw, which
+is defined in struct clk_foo and pointed to within struct clk_core.  This
+allows for easy navigation between the two discrete halves of the common
+clock interface.
+
+Common data structures and api
+==============================
+
+Below is the common struct clk_core definition from
+drivers/clk/clk.c, modified for brevity::
+
+	struct clk_core {
+		const char		*name;
+		const struct clk_ops	*ops;
+		struct clk_hw		*hw;
+		struct module		*owner;
+		struct clk_core		*parent;
+		const char		**parent_names;
+		struct clk_core		**parents;
+		u8			num_parents;
+		u8			new_parent_index;
+		...
+	};
+
+The members above make up the core of the clk tree topology.  The clk
+api itself defines several driver-facing functions which operate on
+struct clk.  That api is documented in include/linux/clk.h.
+
+Platforms and devices utilizing the common struct clk_core use the struct
+clk_ops pointer in struct clk_core to perform the hardware-specific parts of
+the operations defined in clk-provider.h::
+
+	struct clk_ops {
+		int		(*prepare)(struct clk_hw *hw);
+		void		(*unprepare)(struct clk_hw *hw);
+		int		(*is_prepared)(struct clk_hw *hw);
+		void		(*unprepare_unused)(struct clk_hw *hw);
+		int		(*enable)(struct clk_hw *hw);
+		void		(*disable)(struct clk_hw *hw);
+		int		(*is_enabled)(struct clk_hw *hw);
+		void		(*disable_unused)(struct clk_hw *hw);
+		unsigned long	(*recalc_rate)(struct clk_hw *hw,
+						unsigned long parent_rate);
+		long		(*round_rate)(struct clk_hw *hw,
+						unsigned long rate,
+						unsigned long *parent_rate);
+		int		(*determine_rate)(struct clk_hw *hw,
+						  struct clk_rate_request *req);
+		int		(*set_parent)(struct clk_hw *hw, u8 index);
+		u8		(*get_parent)(struct clk_hw *hw);
+		int		(*set_rate)(struct clk_hw *hw,
+					    unsigned long rate,
+					    unsigned long parent_rate);
+		int		(*set_rate_and_parent)(struct clk_hw *hw,
+					    unsigned long rate,
+					    unsigned long parent_rate,
+					    u8 index);
+		unsigned long	(*recalc_accuracy)(struct clk_hw *hw,
+						unsigned long parent_accuracy);
+		int		(*get_phase)(struct clk_hw *hw);
+		int		(*set_phase)(struct clk_hw *hw, int degrees);
+		void		(*init)(struct clk_hw *hw);
+		void		(*debug_init)(struct clk_hw *hw,
+					      struct dentry *dentry);
+	};
+
+Hardware clk implementations
+============================
+
+The strength of the common struct clk_core comes from its .ops and .hw pointers
+which abstract the details of struct clk from the hardware-specific bits, and
+vice versa.  To illustrate consider the simple gateable clk implementation in
+drivers/clk/clk-gate.c::
+
+	struct clk_gate {
+		struct clk_hw	hw;
+		void __iomem    *reg;
+		u8              bit_idx;
+		...
+	};
+
+struct clk_gate contains struct clk_hw hw as well as hardware-specific
+knowledge about which register and bit controls this clk's gating.
+Nothing about clock topology or accounting, such as enable_count or
+notifier_count, is needed here.  That is all handled by the common
+framework code and struct clk_core.
+
+Let's walk through enabling this clk from driver code::
+
+	struct clk *clk;
+	clk = clk_get(NULL, "my_gateable_clk");
+
+	clk_prepare(clk);
+	clk_enable(clk);
+
+The call graph for clk_enable is very simple::
+
+	clk_enable(clk);
+		clk->ops->enable(clk->hw);
+		[resolves to...]
+			clk_gate_enable(hw);
+			[resolves struct clk gate with to_clk_gate(hw)]
+				clk_gate_set_bit(gate);
+
+And the definition of clk_gate_set_bit::
+
+	static void clk_gate_set_bit(struct clk_gate *gate)
+	{
+		u32 reg;
+
+		reg = __raw_readl(gate->reg);
+		reg |= BIT(gate->bit_idx);
+		writel(reg, gate->reg);
+	}
+
+Note that to_clk_gate is defined as::
+
+	#define to_clk_gate(_hw) container_of(_hw, struct clk_gate, hw)
+
+This pattern of abstraction is used for every clock hardware
+representation.
+
+Supporting your own clk hardware
+================================
+
+When implementing support for a new type of clock it is only necessary to
+include the following header::
+
+	#include <linux/clk-provider.h>
+
+To construct a clk hardware structure for your platform you must define
+the following::
+
+	struct clk_foo {
+		struct clk_hw hw;
+		... hardware specific data goes here ...
+	};
+
+To take advantage of your data you'll need to support valid operations
+for your clk::
+
+	struct clk_ops clk_foo_ops {
+		.enable		= &clk_foo_enable;
+		.disable	= &clk_foo_disable;
+	};
+
+Implement the above functions using container_of::
+
+	#define to_clk_foo(_hw) container_of(_hw, struct clk_foo, hw)
+
+	int clk_foo_enable(struct clk_hw *hw)
+	{
+		struct clk_foo *foo;
+
+		foo = to_clk_foo(hw);
+
+		... perform magic on foo ...
+
+		return 0;
+	};
+
+Below is a matrix detailing which clk_ops are mandatory based upon the
+hardware capabilities of that clock.  A cell marked as "y" means
+mandatory, a cell marked as "n" implies that either including that
+callback is invalid or otherwise unnecessary.  Empty cells are either
+optional or must be evaluated on a case-by-case basis.
+
+.. table:: clock hardware characteristics
+
+   +----------------+------+-------------+---------------+-------------+------+
+   |                | gate | change rate | single parent | multiplexer | root |
+   +================+======+=============+===============+=============+======+
+   |.prepare        |      |             |               |             |      |
+   +----------------+------+-------------+---------------+-------------+------+
+   |.unprepare      |      |             |               |             |      |
+   +----------------+------+-------------+---------------+-------------+------+
+   +----------------+------+-------------+---------------+-------------+------+
+   |.enable         | y    |             |               |             |      |
+   +----------------+------+-------------+---------------+-------------+------+
+   |.disable        | y    |             |               |             |      |
+   +----------------+------+-------------+---------------+-------------+------+
+   |.is_enabled     | y    |             |               |             |      |
+   +----------------+------+-------------+---------------+-------------+------+
+   +----------------+------+-------------+---------------+-------------+------+
+   |.recalc_rate    |      | y           |               |             |      |
+   +----------------+------+-------------+---------------+-------------+------+
+   |.round_rate     |      | y [1]_      |               |             |      |
+   +----------------+------+-------------+---------------+-------------+------+
+   |.determine_rate |      | y [1]_      |               |             |      |
+   +----------------+------+-------------+---------------+-------------+------+
+   |.set_rate       |      | y           |               |             |      |
+   +----------------+------+-------------+---------------+-------------+------+
+   +----------------+------+-------------+---------------+-------------+------+
+   |.set_parent     |      |             | n             | y           | n    |
+   +----------------+------+-------------+---------------+-------------+------+
+   |.get_parent     |      |             | n             | y           | n    |
+   +----------------+------+-------------+---------------+-------------+------+
+   +----------------+------+-------------+---------------+-------------+------+
+   |.recalc_accuracy|      |             |               |             |      |
+   +----------------+------+-------------+---------------+-------------+------+
+   +----------------+------+-------------+---------------+-------------+------+
+   |.init           |      |             |               |             |      |
+   +----------------+------+-------------+---------------+-------------+------+
+
+.. [1] either one of round_rate or determine_rate is required.
+
+Finally, register your clock at run-time with a hardware-specific
+registration function.  This function simply populates struct clk_foo's
+data and then passes the common struct clk parameters to the framework
+with a call to::
+
+	clk_register(...)
+
+See the basic clock types in ``drivers/clk/clk-*.c`` for examples.
+
+Disabling clock gating of unused clocks
+=======================================
+
+Sometimes during development it can be useful to be able to bypass the
+default disabling of unused clocks. For example, if drivers aren't enabling
+clocks properly but rely on them being on from the bootloader, bypassing
+the disabling means that the driver will remain functional while the issues
+are sorted out.
+
+To bypass this disabling, include "clk_ignore_unused" in the bootargs to the
+kernel.
+
+Locking
+=======
+
+The common clock framework uses two global locks, the prepare lock and the
+enable lock.
+
+The enable lock is a spinlock and is held across calls to the .enable,
+.disable operations. Those operations are thus not allowed to sleep,
+and calls to the clk_enable(), clk_disable() API functions are allowed in
+atomic context.
+
+For clk_is_enabled() API, it is also designed to be allowed to be used in
+atomic context. However, it doesn't really make any sense to hold the enable
+lock in core, unless you want to do something else with the information of
+the enable state with that lock held. Otherwise, seeing if a clk is enabled is
+a one-shot read of the enabled state, which could just as easily change after
+the function returns because the lock is released. Thus the user of this API
+needs to handle synchronizing the read of the state with whatever they're
+using it for to make sure that the enable state doesn't change during that
+time.
+
+The prepare lock is a mutex and is held across calls to all other operations.
+All those operations are allowed to sleep, and calls to the corresponding API
+functions are not allowed in atomic context.
+
+This effectively divides operations in two groups from a locking perspective.
+
+Drivers don't need to manually protect resources shared between the operations
+of one group, regardless of whether those resources are shared by multiple
+clocks or not. However, access to resources that are shared between operations
+of the two groups needs to be protected by the drivers. An example of such a
+resource would be a register that controls both the clock rate and the clock
+enable/disable state.
+
+The clock framework is reentrant, in that a driver is allowed to call clock
+framework functions from within its implementation of clock operations. This
+can for instance cause a .set_rate operation of one clock being called from
+within the .set_rate operation of another clock. This case must be considered
+in the driver implementations, but the code flow is usually controlled by the
+driver in that case.
+
+Note that locking must also be considered when code outside of the common
+clock framework needs to access resources used by the clock operations. This
+is considered out of scope of this document.

Documentation/driver-api/conf.py

@@ -0,0 +1,10 @@
+# -*- coding: utf-8; mode: python -*-
+
+project = "The Linux driver implementer's API guide"
+
+tags.add("subproject")
+
+latex_documents = [
+    ('index', 'driver-api.tex', project,
+     'The kernel development community', 'manual'),
+]

Documentation/driver-api/device-io.rst

@@ -0,0 +1,201 @@
+.. Copyright 2001 Matthew Wilcox
+..
+..     This documentation is free software; you can redistribute
+..     it and/or modify it under the terms of the GNU General Public
+..     License as published by the Free Software Foundation; either
+..     version 2 of the License, or (at your option) any later
+..     version.
+
+===============================
+Bus-Independent Device Accesses
+===============================
+
+:Author: Matthew Wilcox
+:Author: Alan Cox
+
+Introduction
+============
+
+Linux provides an API which abstracts performing IO across all busses
+and devices, allowing device drivers to be written independently of bus
+type.
+
+Memory Mapped IO
+================
+
+Getting Access to the Device
+----------------------------
+
+The most widely supported form of IO is memory mapped IO. That is, a
+part of the CPU's address space is interpreted not as accesses to
+memory, but as accesses to a device. Some architectures define devices
+to be at a fixed address, but most have some method of discovering
+devices. The PCI bus walk is a good example of such a scheme. This
+document does not cover how to receive such an address, but assumes you
+are starting with one. Physical addresses are of type unsigned long.
+
+This address should not be used directly. Instead, to get an address
+suitable for passing to the accessor functions described below, you
+should call :c:func:`ioremap()`. An address suitable for accessing
+the device will be returned to you.
+
+After you've finished using the device (say, in your module's exit
+routine), call :c:func:`iounmap()` in order to return the address
+space to the kernel. Most architectures allocate new address space each
+time you call :c:func:`ioremap()`, and they can run out unless you
+call :c:func:`iounmap()`.
+
+Accessing the device
+--------------------
+
+The part of the interface most used by drivers is reading and writing
+memory-mapped registers on the device. Linux provides interfaces to read
+and write 8-bit, 16-bit, 32-bit and 64-bit quantities. Due to a
+historical accident, these are named byte, word, long and quad accesses.
+Both read and write accesses are supported; there is no prefetch support
+at this time.
+
+The functions are named readb(), readw(), readl(), readq(),
+readb_relaxed(), readw_relaxed(), readl_relaxed(), readq_relaxed(),
+writeb(), writew(), writel() and writeq().
+
+Some devices (such as framebuffers) would like to use larger transfers than
+8 bytes at a time. For these devices, the :c:func:`memcpy_toio()`,
+:c:func:`memcpy_fromio()` and :c:func:`memset_io()` functions are
+provided. Do not use memset or memcpy on IO addresses; they are not
+guaranteed to copy data in order.
+
+The read and write functions are defined to be ordered. That is the
+compiler is not permitted to reorder the I/O sequence. When the ordering
+can be compiler optimised, you can use __readb() and friends to
+indicate the relaxed ordering. Use this with care.
+
+While the basic functions are defined to be synchronous with respect to
+each other and ordered with respect to each other the busses the devices
+sit on may themselves have asynchronicity. In particular many authors
+are burned by the fact that PCI bus writes are posted asynchronously. A
+driver author must issue a read from the same device to ensure that
+writes have occurred in the specific cases the author cares. This kind
+of property cannot be hidden from driver writers in the API. In some
+cases, the read used to flush the device may be expected to fail (if the
+card is resetting, for example). In that case, the read should be done
+from config space, which is guaranteed to soft-fail if the card doesn't
+respond.
+
+The following is an example of flushing a write to a device when the
+driver would like to ensure the write's effects are visible prior to
+continuing execution::
+
+    static inline void
+    qla1280_disable_intrs(struct scsi_qla_host *ha)
+    {
+        struct device_reg *reg;
+
+        reg = ha->iobase;
+        /* disable risc and host interrupts */
+        WRT_REG_WORD(&reg->ictrl, 0);
+        /*
+         * The following read will ensure that the above write
+         * has been received by the device before we return from this
+         * function.
+         */
+        RD_REG_WORD(&reg->ictrl);
+        ha->flags.ints_enabled = 0;
+    }
+
+In addition to write posting, on some large multiprocessing systems
+(e.g. SGI Challenge, Origin and Altix machines) posted writes won't be
+strongly ordered coming from different CPUs. Thus it's important to
+properly protect parts of your driver that do memory-mapped writes with
+locks and use the :c:func:`mmiowb()` to make sure they arrive in the
+order intended. Issuing a regular readX() will also ensure write ordering,
+but should only be used when the 
+driver has to be sure that the write has actually arrived at the device
+(not that it's simply ordered with respect to other writes), since a
+full readX() is a relatively expensive operation.
+
+Generally, one should use :c:func:`mmiowb()` prior to releasing a spinlock
+that protects regions using :c:func:`writeb()` or similar functions that
+aren't surrounded by readb() calls, which will ensure ordering
+and flushing. The following pseudocode illustrates what might occur if
+write ordering isn't guaranteed via :c:func:`mmiowb()` or one of the
+readX() functions::
+
+    CPU A:  spin_lock_irqsave(&dev_lock, flags)
+    CPU A:  ...
+    CPU A:  writel(newval, ring_ptr);
+    CPU A:  spin_unlock_irqrestore(&dev_lock, flags)
+            ...
+    CPU B:  spin_lock_irqsave(&dev_lock, flags)
+    CPU B:  writel(newval2, ring_ptr);
+    CPU B:  ...
+    CPU B:  spin_unlock_irqrestore(&dev_lock, flags)
+
+In the case above, newval2 could be written to ring_ptr before newval.
+Fixing it is easy though::
+
+    CPU A:  spin_lock_irqsave(&dev_lock, flags)
+    CPU A:  ...
+    CPU A:  writel(newval, ring_ptr);
+    CPU A:  mmiowb(); /* ensure no other writes beat us to the device */
+    CPU A:  spin_unlock_irqrestore(&dev_lock, flags)
+            ...
+    CPU B:  spin_lock_irqsave(&dev_lock, flags)
+    CPU B:  writel(newval2, ring_ptr);
+    CPU B:  ...
+    CPU B:  mmiowb();
+    CPU B:  spin_unlock_irqrestore(&dev_lock, flags)
+
+See tg3.c for a real world example of how to use :c:func:`mmiowb()`
+
+PCI ordering rules also guarantee that PIO read responses arrive after any
+outstanding DMA writes from that bus, since for some devices the result of
+a readb() call may signal to the driver that a DMA transaction is
+complete. In many cases, however, the driver may want to indicate that the
+next readb() call has no relation to any previous DMA writes
+performed by the device. The driver can use readb_relaxed() for
+these cases, although only some platforms will honor the relaxed
+semantics. Using the relaxed read functions will provide significant
+performance benefits on platforms that support it. The qla2xxx driver
+provides examples of how to use readX_relaxed(). In many cases, a majority
+of the driver's readX() calls can safely be converted to readX_relaxed()
+calls, since only a few will indicate or depend on DMA completion.
+
+Port Space Accesses
+===================
+
+Port Space Explained
+--------------------
+
+Another form of IO commonly supported is Port Space. This is a range of
+addresses separate to the normal memory address space. Access to these
+addresses is generally not as fast as accesses to the memory mapped
+addresses, and it also has a potentially smaller address space.
+
+Unlike memory mapped IO, no preparation is required to access port
+space.
+
+Accessing Port Space
+--------------------
+
+Accesses to this space are provided through a set of functions which
+allow 8-bit, 16-bit and 32-bit accesses; also known as byte, word and
+long. These functions are :c:func:`inb()`, :c:func:`inw()`,
+:c:func:`inl()`, :c:func:`outb()`, :c:func:`outw()` and
+:c:func:`outl()`.
+
+Some variants are provided for these functions. Some devices require
+that accesses to their ports are slowed down. This functionality is
+provided by appending a ``_p`` to the end of the function.
+There are also equivalents to memcpy. The :c:func:`ins()` and
+:c:func:`outs()` functions copy bytes, words or longs to the given
+port.
+
+Public Functions Provided
+=========================
+
+.. kernel-doc:: arch/x86/include/asm/io.h
+   :internal:
+
+.. kernel-doc:: lib/pci_iomap.c
+   :export:

Documentation/driver-api/device_connection.rst

@@ -0,0 +1,43 @@
+==================
+Device connections
+==================
+
+Introduction
+------------
+
+Devices often have connections to other devices that are outside of the direct
+child/parent relationship. A serial or network communication controller, which
+could be a PCI device, may need to be able to get a reference to its PHY
+component, which could be attached for example to the I2C bus. Some device
+drivers need to be able to control the clocks or the GPIOs for their devices,
+and so on.
+
+Device connections are generic descriptions of any type of connection between
+two separate devices.
+
+Device connections alone do not create a dependency between the two devices.
+They are only descriptions which are not tied to either of the devices directly.
+A dependency between the two devices exists only if one of the two endpoint
+devices requests a reference to the other. The descriptions themselves can be
+defined in firmware (not yet supported) or they can be built-in.
+
+Usage
+-----
+
+Device connections should exist before device ``->probe`` callback is called for
+either endpoint device in the description. If the connections are defined in
+firmware, this is not a problem. It should be considered if the connection
+descriptions are "built-in", and need to be added separately.
+
+The connection description consists of the names of the two devices with the
+connection, i.e. the endpoints, and unique identifier for the connection which
+is needed if there are multiple connections between the two devices.
+
+After a description exists, the devices in it can request reference to the other
+endpoint device, or they can request the description itself.
+
+API
+---
+
+.. kernel-doc:: drivers/base/devcon.c
+   :functions: device_connection_find_match device_connection_find device_connection_add device_connection_remove

Documentation/driver-api/device_link.rst

@@ -0,0 +1,307 @@
+.. |struct dev_pm_domain| replace:: :c:type:`struct dev_pm_domain <dev_pm_domain>`
+.. |struct generic_pm_domain| replace:: :c:type:`struct generic_pm_domain <generic_pm_domain>`
+
+============
+Device links
+============
+
+By default, the driver core only enforces dependencies between devices
+that are borne out of a parent/child relationship within the device
+hierarchy: When suspending, resuming or shutting down the system, devices
+are ordered based on this relationship, i.e. children are always suspended
+before their parent, and the parent is always resumed before its children.
+
+Sometimes there is a need to represent device dependencies beyond the
+mere parent/child relationship, e.g. between siblings, and have the
+driver core automatically take care of them.
+
+Secondly, the driver core by default does not enforce any driver presence
+dependencies, i.e. that one device must be bound to a driver before
+another one can probe or function correctly.
+
+Often these two dependency types come together, so a device depends on
+another one both with regards to driver presence *and* with regards to
+suspend/resume and shutdown ordering.
+
+Device links allow representation of such dependencies in the driver core.
+
+In its standard or *managed* form, a device link combines *both* dependency
+types:  It guarantees correct suspend/resume and shutdown ordering between a
+"supplier" device and its "consumer" devices, and it guarantees driver
+presence on the supplier.  The consumer devices are not probed before the
+supplier is bound to a driver, and they're unbound before the supplier
+is unbound.
+
+When driver presence on the supplier is irrelevant and only correct
+suspend/resume and shutdown ordering is needed, the device link may
+simply be set up with the ``DL_FLAG_STATELESS`` flag.  In other words,
+enforcing driver presence on the supplier is optional.
+
+Another optional feature is runtime PM integration:  By setting the
+``DL_FLAG_PM_RUNTIME`` flag on addition of the device link, the PM core
+is instructed to runtime resume the supplier and keep it active
+whenever and for as long as the consumer is runtime resumed.
+
+Usage
+=====
+
+The earliest point in time when device links can be added is after
+:c:func:`device_add()` has been called for the supplier and
+:c:func:`device_initialize()` has been called for the consumer.
+
+It is legal to add them later, but care must be taken that the system
+remains in a consistent state:  E.g. a device link cannot be added in
+the midst of a suspend/resume transition, so either commencement of
+such a transition needs to be prevented with :c:func:`lock_system_sleep()`,
+or the device link needs to be added from a function which is guaranteed
+not to run in parallel to a suspend/resume transition, such as from a
+device ``->probe`` callback or a boot-time PCI quirk.
+
+Another example for an inconsistent state would be a device link that
+represents a driver presence dependency, yet is added from the consumer's
+``->probe`` callback while the supplier hasn't started to probe yet:  Had the
+driver core known about the device link earlier, it wouldn't have probed the
+consumer in the first place.  The onus is thus on the consumer to check
+presence of the supplier after adding the link, and defer probing on
+non-presence.  [Note that it is valid to create a link from the consumer's
+``->probe`` callback while the supplier is still probing, but the consumer must
+know that the supplier is functional already at the link creation time (that is
+the case, for instance, if the consumer has just acquired some resources that
+would not have been available had the supplier not been functional then).]
+
+If a device link with ``DL_FLAG_STATELESS`` set (i.e. a stateless device link)
+is added in the ``->probe`` callback of the supplier or consumer driver, it is
+typically deleted in its ``->remove`` callback for symmetry.  That way, if the
+driver is compiled as a module, the device link is added on module load and
+orderly deleted on unload.  The same restrictions that apply to device link
+addition (e.g. exclusion of a parallel suspend/resume transition) apply equally
+to deletion.  Device links managed by the driver core are deleted automatically
+by it.
+
+Several flags may be specified on device link addition, two of which
+have already been mentioned above:  ``DL_FLAG_STATELESS`` to express that no
+driver presence dependency is needed (but only correct suspend/resume and
+shutdown ordering) and ``DL_FLAG_PM_RUNTIME`` to express that runtime PM
+integration is desired.
+
+Two other flags are specifically targeted at use cases where the device
+link is added from the consumer's ``->probe`` callback:  ``DL_FLAG_RPM_ACTIVE``
+can be specified to runtime resume the supplier upon addition of the
+device link.  ``DL_FLAG_AUTOREMOVE_CONSUMER`` causes the device link to be
+automatically purged when the consumer fails to probe or later unbinds.
+
+Similarly, when the device link is added from supplier's ``->probe`` callback,
+``DL_FLAG_AUTOREMOVE_SUPPLIER`` causes the device link to be automatically
+purged when the supplier fails to probe or later unbinds.
+
+If neither ``DL_FLAG_AUTOREMOVE_CONSUMER`` nor ``DL_FLAG_AUTOREMOVE_SUPPLIER``
+is set, ``DL_FLAG_AUTOPROBE_CONSUMER`` can be used to request the driver core
+to probe for a driver for the consumer driver on the link automatically after
+a driver has been bound to the supplier device.
+
+Note, however, that any combinations of ``DL_FLAG_AUTOREMOVE_CONSUMER``,
+``DL_FLAG_AUTOREMOVE_SUPPLIER`` or ``DL_FLAG_AUTOPROBE_CONSUMER`` with
+``DL_FLAG_STATELESS`` are invalid and cannot be used.
+
+Limitations
+===========
+
+Driver authors should be aware that a driver presence dependency for managed
+device links (i.e. when ``DL_FLAG_STATELESS`` is not specified on link addition)
+may cause probing of the consumer to be deferred indefinitely.  This can become
+a problem if the consumer is required to probe before a certain initcall level
+is reached.  Worse, if the supplier driver is blacklisted or missing, the
+consumer will never be probed.
+
+Moreover, managed device links cannot be deleted directly.  They are deleted
+by the driver core when they are not necessary any more in accordance with the
+``DL_FLAG_AUTOREMOVE_CONSUMER`` and ``DL_FLAG_AUTOREMOVE_SUPPLIER`` flags.
+However, stateless device links (i.e. device links with ``DL_FLAG_STATELESS``
+set) are expected to be removed by whoever called :c:func:`device_link_add()`
+to add them with the help of either :c:func:`device_link_del()` or
+:c:func:`device_link_remove()`.
+
+Sometimes drivers depend on optional resources.  They are able to operate
+in a degraded mode (reduced feature set or performance) when those resources
+are not present.  An example is an SPI controller that can use a DMA engine
+or work in PIO mode.  The controller can determine presence of the optional
+resources at probe time but on non-presence there is no way to know whether
+they will become available in the near future (due to a supplier driver
+probing) or never.  Consequently it cannot be determined whether to defer
+probing or not.  It would be possible to notify drivers when optional
+resources become available after probing, but it would come at a high cost
+for drivers as switching between modes of operation at runtime based on the
+availability of such resources would be much more complex than a mechanism
+based on probe deferral.  In any case optional resources are beyond the
+scope of device links.
+
+Examples
+========
+
+* An MMU device exists alongside a busmaster device, both are in the same
+  power domain.  The MMU implements DMA address translation for the busmaster
+  device and shall be runtime resumed and kept active whenever and as long
+  as the busmaster device is active.  The busmaster device's driver shall
+  not bind before the MMU is bound.  To achieve this, a device link with
+  runtime PM integration is added from the busmaster device (consumer)
+  to the MMU device (supplier).  The effect with regards to runtime PM
+  is the same as if the MMU was the parent of the master device.
+
+  The fact that both devices share the same power domain would normally
+  suggest usage of a |struct dev_pm_domain| or |struct generic_pm_domain|,
+  however these are not independent devices that happen to share a power
+  switch, but rather the MMU device serves the busmaster device and is
+  useless without it.  A device link creates a synthetic hierarchical
+  relationship between the devices and is thus more apt.
+
+* A Thunderbolt host controller comprises a number of PCIe hotplug ports
+  and an NHI device to manage the PCIe switch.  On resume from system sleep,
+  the NHI device needs to re-establish PCI tunnels to attached devices
+  before the hotplug ports can resume.  If the hotplug ports were children
+  of the NHI, this resume order would automatically be enforced by the
+  PM core, but unfortunately they're aunts.  The solution is to add
+  device links from the hotplug ports (consumers) to the NHI device
+  (supplier).  A driver presence dependency is not necessary for this
+  use case.
+
+* Discrete GPUs in hybrid graphics laptops often feature an HDA controller
+  for HDMI/DP audio.  In the device hierarchy the HDA controller is a sibling
+  of the VGA device, yet both share the same power domain and the HDA
+  controller is only ever needed when an HDMI/DP display is attached to the
+  VGA device.  A device link from the HDA controller (consumer) to the
+  VGA device (supplier) aptly represents this relationship.
+
+* ACPI allows definition of a device start order by way of _DEP objects.
+  A classical example is when ACPI power management methods on one device
+  are implemented in terms of I\ :sup:`2`\ C accesses and require a specific
+  I\ :sup:`2`\ C controller to be present and functional for the power
+  management of the device in question to work.
+
+* In some SoCs a functional dependency exists from display, video codec and
+  video processing IP cores on transparent memory access IP cores that handle
+  burst access and compression/decompression.
+
+Alternatives
+============
+
+* A |struct dev_pm_domain| can be used to override the bus,
+  class or device type callbacks.  It is intended for devices sharing
+  a single on/off switch, however it does not guarantee a specific
+  suspend/resume ordering, this needs to be implemented separately.
+  It also does not by itself track the runtime PM status of the involved
+  devices and turn off the power switch only when all of them are runtime
+  suspended.  Furthermore it cannot be used to enforce a specific shutdown
+  ordering or a driver presence dependency.
+
+* A |struct generic_pm_domain| is a lot more heavyweight than a
+  device link and does not allow for shutdown ordering or driver presence
+  dependencies.  It also cannot be used on ACPI systems.
+
+Implementation
+==============
+
+The device hierarchy, which -- as the name implies -- is a tree,
+becomes a directed acyclic graph once device links are added.
+
+Ordering of these devices during suspend/resume is determined by the
+dpm_list.  During shutdown it is determined by the devices_kset.  With
+no device links present, the two lists are a flattened, one-dimensional
+representations of the device tree such that a device is placed behind
+all its ancestors.  That is achieved by traversing the ACPI namespace
+or OpenFirmware device tree top-down and appending devices to the lists
+as they are discovered.
+
+Once device links are added, the lists need to satisfy the additional
+constraint that a device is placed behind all its suppliers, recursively.
+To ensure this, upon addition of the device link the consumer and the
+entire sub-graph below it (all children and consumers of the consumer)
+are moved to the end of the list.  (Call to :c:func:`device_reorder_to_tail()`
+from :c:func:`device_link_add()`.)
+
+To prevent introduction of dependency loops into the graph, it is
+verified upon device link addition that the supplier is not dependent
+on the consumer or any children or consumers of the consumer.
+(Call to :c:func:`device_is_dependent()` from :c:func:`device_link_add()`.)
+If that constraint is violated, :c:func:`device_link_add()` will return
+``NULL`` and a ``WARNING`` will be logged.
+
+Notably this also prevents the addition of a device link from a parent
+device to a child.  However the converse is allowed, i.e. a device link
+from a child to a parent.  Since the driver core already guarantees
+correct suspend/resume and shutdown ordering between parent and child,
+such a device link only makes sense if a driver presence dependency is
+needed on top of that.  In this case driver authors should weigh
+carefully if a device link is at all the right tool for the purpose.
+A more suitable approach might be to simply use deferred probing or
+add a device flag causing the parent driver to be probed before the
+child one.
+
+State machine
+=============
+
+.. kernel-doc:: include/linux/device.h
+   :functions: device_link_state
+
+::
+
+                 .=============================.
+                 |                             |
+                 v                             |
+ DORMANT <=> AVAILABLE <=> CONSUMER_PROBE => ACTIVE
+    ^                                          |
+    |                                          |
+    '============ SUPPLIER_UNBIND <============'
+
+* The initial state of a device link is automatically determined by
+  :c:func:`device_link_add()` based on the driver presence on the supplier
+  and consumer.  If the link is created before any devices are probed, it
+  is set to ``DL_STATE_DORMANT``.
+
+* When a supplier device is bound to a driver, links to its consumers
+  progress to ``DL_STATE_AVAILABLE``.
+  (Call to :c:func:`device_links_driver_bound()` from
+  :c:func:`driver_bound()`.)
+
+* Before a consumer device is probed, presence of supplier drivers is
+  verified by checking the consumer device is not in the wait_for_suppliers
+  list and by checking that links to suppliers are in ``DL_STATE_AVAILABLE``
+  state.  The state of the links is updated to ``DL_STATE_CONSUMER_PROBE``.
+  (Call to :c:func:`device_links_check_suppliers()` from
+  :c:func:`really_probe()`.)
+  This prevents the supplier from unbinding.
+  (Call to :c:func:`wait_for_device_probe()` from
+  :c:func:`device_links_unbind_consumers()`.)
+
+* If the probe fails, links to suppliers revert back to ``DL_STATE_AVAILABLE``.
+  (Call to :c:func:`device_links_no_driver()` from :c:func:`really_probe()`.)
+
+* If the probe succeeds, links to suppliers progress to ``DL_STATE_ACTIVE``.
+  (Call to :c:func:`device_links_driver_bound()` from :c:func:`driver_bound()`.)
+
+* When the consumer's driver is later on removed, links to suppliers revert
+  back to ``DL_STATE_AVAILABLE``.
+  (Call to :c:func:`__device_links_no_driver()` from
+  :c:func:`device_links_driver_cleanup()`, which in turn is called from
+  :c:func:`__device_release_driver()`.)
+
+* Before a supplier's driver is removed, links to consumers that are not
+  bound to a driver are updated to ``DL_STATE_SUPPLIER_UNBIND``.
+  (Call to :c:func:`device_links_busy()` from
+  :c:func:`__device_release_driver()`.)
+  This prevents the consumers from binding.
+  (Call to :c:func:`device_links_check_suppliers()` from
+  :c:func:`really_probe()`.)
+  Consumers that are bound are freed from their driver; consumers that are
+  probing are waited for until they are done.
+  (Call to :c:func:`device_links_unbind_consumers()` from
+  :c:func:`__device_release_driver()`.)
+  Once all links to consumers are in ``DL_STATE_SUPPLIER_UNBIND`` state,
+  the supplier driver is released and the links revert to ``DL_STATE_DORMANT``.
+  (Call to :c:func:`device_links_driver_cleanup()` from
+  :c:func:`__device_release_driver()`.)
+
+API
+===
+
+.. kernel-doc:: drivers/base/core.c
+   :functions: device_link_add device_link_del device_link_remove

Documentation/driver-api/dma-buf.rst

@@ -0,0 +1,168 @@
+Buffer Sharing and Synchronization
+==================================
+
+The dma-buf subsystem provides the framework for sharing buffers for
+hardware (DMA) access across multiple device drivers and subsystems, and
+for synchronizing asynchronous hardware access.
+
+This is used, for example, by drm "prime" multi-GPU support, but is of
+course not limited to GPU use cases.
+
+The three main components of this are: (1) dma-buf, representing a
+sg_table and exposed to userspace as a file descriptor to allow passing
+between devices, (2) fence, which provides a mechanism to signal when
+one device as finished access, and (3) reservation, which manages the
+shared or exclusive fence(s) associated with the buffer.
+
+Shared DMA Buffers
+------------------
+
+This document serves as a guide to device-driver writers on what is the dma-buf
+buffer sharing API, how to use it for exporting and using shared buffers.
+
+Any device driver which wishes to be a part of DMA buffer sharing, can do so as
+either the 'exporter' of buffers, or the 'user' or 'importer' of buffers.
+
+Say a driver A wants to use buffers created by driver B, then we call B as the
+exporter, and A as buffer-user/importer.
+
+The exporter
+
+ - implements and manages operations in :c:type:`struct dma_buf_ops
+   <dma_buf_ops>` for the buffer,
+ - allows other users to share the buffer by using dma_buf sharing APIs,
+ - manages the details of buffer allocation, wrapped int a :c:type:`struct
+   dma_buf <dma_buf>`,
+ - decides about the actual backing storage where this allocation happens,
+ - and takes care of any migration of scatterlist - for all (shared) users of
+   this buffer.
+
+The buffer-user
+
+ - is one of (many) sharing users of the buffer.
+ - doesn't need to worry about how the buffer is allocated, or where.
+ - and needs a mechanism to get access to the scatterlist that makes up this
+   buffer in memory, mapped into its own address space, so it can access the
+   same area of memory. This interface is provided by :c:type:`struct
+   dma_buf_attachment <dma_buf_attachment>`.
+
+Any exporters or users of the dma-buf buffer sharing framework must have a
+'select DMA_SHARED_BUFFER' in their respective Kconfigs.
+
+Userspace Interface Notes
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Mostly a DMA buffer file descriptor is simply an opaque object for userspace,
+and hence the generic interface exposed is very minimal. There's a few things to
+consider though:
+
+- Since kernel 3.12 the dma-buf FD supports the llseek system call, but only
+  with offset=0 and whence=SEEK_END|SEEK_SET. SEEK_SET is supported to allow
+  the usual size discover pattern size = SEEK_END(0); SEEK_SET(0). Every other
+  llseek operation will report -EINVAL.
+
+  If llseek on dma-buf FDs isn't support the kernel will report -ESPIPE for all
+  cases. Userspace can use this to detect support for discovering the dma-buf
+  size using llseek.
+
+- In order to avoid fd leaks on exec, the FD_CLOEXEC flag must be set
+  on the file descriptor.  This is not just a resource leak, but a
+  potential security hole.  It could give the newly exec'd application
+  access to buffers, via the leaked fd, to which it should otherwise
+  not be permitted access.
+
+  The problem with doing this via a separate fcntl() call, versus doing it
+  atomically when the fd is created, is that this is inherently racy in a
+  multi-threaded app[3].  The issue is made worse when it is library code
+  opening/creating the file descriptor, as the application may not even be
+  aware of the fd's.
+
+  To avoid this problem, userspace must have a way to request O_CLOEXEC
+  flag be set when the dma-buf fd is created.  So any API provided by
+  the exporting driver to create a dmabuf fd must provide a way to let
+  userspace control setting of O_CLOEXEC flag passed in to dma_buf_fd().
+
+- Memory mapping the contents of the DMA buffer is also supported. See the
+  discussion below on `CPU Access to DMA Buffer Objects`_ for the full details.
+
+- The DMA buffer FD is also pollable, see `Fence Poll Support`_ below for
+  details.
+
+Basic Operation and Device DMA Access
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/dma-buf/dma-buf.c
+   :doc: dma buf device access
+
+CPU Access to DMA Buffer Objects
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/dma-buf/dma-buf.c
+   :doc: cpu access
+
+Fence Poll Support
+~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/dma-buf/dma-buf.c
+   :doc: fence polling
+
+Kernel Functions and Structures Reference
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/dma-buf/dma-buf.c
+   :export:
+
+.. kernel-doc:: include/linux/dma-buf.h
+   :internal:
+
+Reservation Objects
+-------------------
+
+.. kernel-doc:: drivers/dma-buf/reservation.c
+   :doc: Reservation Object Overview
+
+.. kernel-doc:: drivers/dma-buf/reservation.c
+   :export:
+
+.. kernel-doc:: include/linux/reservation.h
+   :internal:
+
+DMA Fences
+----------
+
+.. kernel-doc:: drivers/dma-buf/dma-fence.c
+   :doc: DMA fences overview
+
+DMA Fences Functions Reference
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/dma-buf/dma-fence.c
+   :export:
+
+.. kernel-doc:: include/linux/dma-fence.h
+   :internal:
+
+Seqno Hardware Fences
+~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: include/linux/seqno-fence.h
+   :internal:
+
+DMA Fence Array
+~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/dma-buf/dma-fence-array.c
+   :export:
+
+.. kernel-doc:: include/linux/dma-fence-array.h
+   :internal:
+
+DMA Fence uABI/Sync File
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/dma-buf/sync_file.c
+   :export:
+
+.. kernel-doc:: include/linux/sync_file.h
+   :internal:
+

Documentation/driver-api/dmaengine/client.rst

@@ -0,0 +1,275 @@
+====================
+DMA Engine API Guide
+====================
+
+Vinod Koul <vinod dot koul at intel.com>
+
+.. note:: For DMA Engine usage in async_tx please see:
+          ``Documentation/crypto/async-tx-api.txt``
+
+
+Below is a guide to device driver writers on how to use the Slave-DMA API of the
+DMA Engine. This is applicable only for slave DMA usage only.
+
+DMA usage
+=========
+
+The slave DMA usage consists of following steps:
+
+- Allocate a DMA slave channel
+
+- Set slave and controller specific parameters
+
+- Get a descriptor for transaction
+
+- Submit the transaction
+
+- Issue pending requests and wait for callback notification
+
+The details of these operations are:
+
+1. Allocate a DMA slave channel
+
+   Channel allocation is slightly different in the slave DMA context,
+   client drivers typically need a channel from a particular DMA
+   controller only and even in some cases a specific channel is desired.
+   To request a channel dma_request_chan() API is used.
+
+   Interface:
+
+   .. code-block:: c
+
+      struct dma_chan *dma_request_chan(struct device *dev, const char *name);
+
+   Which will find and return the ``name`` DMA channel associated with the 'dev'
+   device. The association is done via DT, ACPI or board file based
+   dma_slave_map matching table.
+
+   A channel allocated via this interface is exclusive to the caller,
+   until dma_release_channel() is called.
+
+2. Set slave and controller specific parameters
+
+   Next step is always to pass some specific information to the DMA
+   driver. Most of the generic information which a slave DMA can use
+   is in struct dma_slave_config. This allows the clients to specify
+   DMA direction, DMA addresses, bus widths, DMA burst lengths etc
+   for the peripheral.
+
+   If some DMA controllers have more parameters to be sent then they
+   should try to embed struct dma_slave_config in their controller
+   specific structure. That gives flexibility to client to pass more
+   parameters, if required.
+
+   Interface:
+
+   .. code-block:: c
+
+      int dmaengine_slave_config(struct dma_chan *chan,
+			struct dma_slave_config *config)
+
+   Please see the dma_slave_config structure definition in dmaengine.h
+   for a detailed explanation of the struct members. Please note
+   that the 'direction' member will be going away as it duplicates the
+   direction given in the prepare call.
+
+3. Get a descriptor for transaction
+
+  For slave usage the various modes of slave transfers supported by the
+  DMA-engine are:
+
+  - slave_sg: DMA a list of scatter gather buffers from/to a peripheral
+
+  - dma_cyclic: Perform a cyclic DMA operation from/to a peripheral till the
+    operation is explicitly stopped.
+
+  - interleaved_dma: This is common to Slave as well as M2M clients. For slave
+    address of devices' fifo could be already known to the driver.
+    Various types of operations could be expressed by setting
+    appropriate values to the 'dma_interleaved_template' members.
+
+  A non-NULL return of this transfer API represents a "descriptor" for
+  the given transaction.
+
+  Interface:
+
+  .. code-block:: c
+
+     struct dma_async_tx_descriptor *dmaengine_prep_slave_sg(
+		struct dma_chan *chan, struct scatterlist *sgl,
+		unsigned int sg_len, enum dma_data_direction direction,
+		unsigned long flags);
+
+     struct dma_async_tx_descriptor *dmaengine_prep_dma_cyclic(
+		struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len,
+		size_t period_len, enum dma_data_direction direction);
+
+     struct dma_async_tx_descriptor *dmaengine_prep_interleaved_dma(
+		struct dma_chan *chan, struct dma_interleaved_template *xt,
+		unsigned long flags);
+
+  The peripheral driver is expected to have mapped the scatterlist for
+  the DMA operation prior to calling dmaengine_prep_slave_sg(), and must
+  keep the scatterlist mapped until the DMA operation has completed.
+  The scatterlist must be mapped using the DMA struct device.
+  If a mapping needs to be synchronized later, dma_sync_*_for_*() must be
+  called using the DMA struct device, too.
+  So, normal setup should look like this:
+
+  .. code-block:: c
+
+     nr_sg = dma_map_sg(chan->device->dev, sgl, sg_len);
+	if (nr_sg == 0)
+		/* error */
+
+	desc = dmaengine_prep_slave_sg(chan, sgl, nr_sg, direction, flags);
+
+  Once a descriptor has been obtained, the callback information can be
+  added and the descriptor must then be submitted. Some DMA engine
+  drivers may hold a spinlock between a successful preparation and
+  submission so it is important that these two operations are closely
+  paired.
+
+  .. note::
+
+     Although the async_tx API specifies that completion callback
+     routines cannot submit any new operations, this is not the
+     case for slave/cyclic DMA.
+
+     For slave DMA, the subsequent transaction may not be available
+     for submission prior to callback function being invoked, so
+     slave DMA callbacks are permitted to prepare and submit a new
+     transaction.
+
+     For cyclic DMA, a callback function may wish to terminate the
+     DMA via dmaengine_terminate_async().
+
+     Therefore, it is important that DMA engine drivers drop any
+     locks before calling the callback function which may cause a
+     deadlock.
+
+     Note that callbacks will always be invoked from the DMA
+     engines tasklet, never from interrupt context.
+
+4. Submit the transaction
+
+   Once the descriptor has been prepared and the callback information
+   added, it must be placed on the DMA engine drivers pending queue.
+
+   Interface:
+
+   .. code-block:: c
+
+      dma_cookie_t dmaengine_submit(struct dma_async_tx_descriptor *desc)
+
+   This returns a cookie can be used to check the progress of DMA engine
+   activity via other DMA engine calls not covered in this document.
+
+   dmaengine_submit() will not start the DMA operation, it merely adds
+   it to the pending queue. For this, see step 5, dma_async_issue_pending.
+
+5. Issue pending DMA requests and wait for callback notification
+
+   The transactions in the pending queue can be activated by calling the
+   issue_pending API. If channel is idle then the first transaction in
+   queue is started and subsequent ones queued up.
+
+   On completion of each DMA operation, the next in queue is started and
+   a tasklet triggered. The tasklet will then call the client driver
+   completion callback routine for notification, if set.
+
+   Interface:
+
+   .. code-block:: c
+
+      void dma_async_issue_pending(struct dma_chan *chan);
+
+Further APIs:
+-------------
+
+1. Terminate APIs
+
+   .. code-block:: c
+
+      int dmaengine_terminate_sync(struct dma_chan *chan)
+      int dmaengine_terminate_async(struct dma_chan *chan)
+      int dmaengine_terminate_all(struct dma_chan *chan) /* DEPRECATED */
+
+   This causes all activity for the DMA channel to be stopped, and may
+   discard data in the DMA FIFO which hasn't been fully transferred.
+   No callback functions will be called for any incomplete transfers.
+
+   Two variants of this function are available.
+
+   dmaengine_terminate_async() might not wait until the DMA has been fully
+   stopped or until any running complete callbacks have finished. But it is
+   possible to call dmaengine_terminate_async() from atomic context or from
+   within a complete callback. dmaengine_synchronize() must be called before it
+   is safe to free the memory accessed by the DMA transfer or free resources
+   accessed from within the complete callback.
+
+   dmaengine_terminate_sync() will wait for the transfer and any running
+   complete callbacks to finish before it returns. But the function must not be
+   called from atomic context or from within a complete callback.
+
+   dmaengine_terminate_all() is deprecated and should not be used in new code.
+
+2. Pause API
+
+   .. code-block:: c
+
+      int dmaengine_pause(struct dma_chan *chan)
+
+   This pauses activity on the DMA channel without data loss.
+
+3. Resume API
+
+   .. code-block:: c
+
+       int dmaengine_resume(struct dma_chan *chan)
+
+   Resume a previously paused DMA channel. It is invalid to resume a
+   channel which is not currently paused.
+
+4. Check Txn complete
+
+   .. code-block:: c
+
+      enum dma_status dma_async_is_tx_complete(struct dma_chan *chan,
+		dma_cookie_t cookie, dma_cookie_t *last, dma_cookie_t *used)
+
+   This can be used to check the status of the channel. Please see
+   the documentation in include/linux/dmaengine.h for a more complete
+   description of this API.
+
+   This can be used in conjunction with dma_async_is_complete() and
+   the cookie returned from dmaengine_submit() to check for
+   completion of a specific DMA transaction.
+
+   .. note::
+
+      Not all DMA engine drivers can return reliable information for
+      a running DMA channel. It is recommended that DMA engine users
+      pause or stop (via dmaengine_terminate_all()) the channel before
+      using this API.
+
+5. Synchronize termination API
+
+   .. code-block:: c
+
+      void dmaengine_synchronize(struct dma_chan *chan)
+
+   Synchronize the termination of the DMA channel to the current context.
+
+   This function should be used after dmaengine_terminate_async() to synchronize
+   the termination of the DMA channel to the current context. The function will
+   wait for the transfer and any running complete callbacks to finish before it
+   returns.
+
+   If dmaengine_terminate_async() is used to stop the DMA channel this function
+   must be called before it is safe to free memory accessed by previously
+   submitted descriptors or to free any resources accessed within the complete
+   callback of previously submitted descriptors.
+
+   The behavior of this function is undefined if dma_async_issue_pending() has
+   been called between dmaengine_terminate_async() and this function.

Documentation/driver-api/dmaengine/dmatest.rst

@@ -0,0 +1,114 @@
+==============
+DMA Test Guide
+==============
+
+Andy Shevchenko <andriy.shevchenko@linux.intel.com>
+
+This small document introduces how to test DMA drivers using dmatest module.
+
+.. note::
+  The test suite works only on the channels that have at least one
+  capability of the following: DMA_MEMCPY (memory-to-memory), DMA_MEMSET
+  (const-to-memory or memory-to-memory, when emulated), DMA_XOR, DMA_PQ.
+
+Part 1 - How to build the test module
+=====================================
+
+The menuconfig contains an option that could be found by following path:
+
+	Device Drivers -> DMA Engine support -> DMA Test client
+
+In the configuration file the option called CONFIG_DMATEST. The dmatest could
+be built as module or inside kernel. Let's consider those cases.
+
+Part 2 - When dmatest is built as a module
+==========================================
+
+Example of usage::
+
+    % modprobe dmatest channel=dma0chan0 timeout=2000 iterations=1 run=1
+
+...or::
+
+    % modprobe dmatest
+    % echo dma0chan0 > /sys/module/dmatest/parameters/channel
+    % echo 2000 > /sys/module/dmatest/parameters/timeout
+    % echo 1 > /sys/module/dmatest/parameters/iterations
+    % echo 1 > /sys/module/dmatest/parameters/run
+
+...or on the kernel command line::
+
+    dmatest.channel=dma0chan0 dmatest.timeout=2000 dmatest.iterations=1 dmatest.run=1
+
+.. hint::
+  available channel list could be extracted by running the following command::
+
+    % ls -1 /sys/class/dma/
+
+Once started a message like "dmatest: Started 1 threads using dma0chan0" is
+emitted. After that only test failure messages are reported until the test
+stops.
+
+Note that running a new test will not stop any in progress test.
+
+The following command returns the state of the test. ::
+
+    % cat /sys/module/dmatest/parameters/run
+
+To wait for test completion userpace can poll 'run' until it is false, or use
+the wait parameter. Specifying 'wait=1' when loading the module causes module
+initialization to pause until a test run has completed, while reading
+/sys/module/dmatest/parameters/wait waits for any running test to complete
+before returning. For example, the following scripts wait for 42 tests
+to complete before exiting. Note that if 'iterations' is set to 'infinite' then
+waiting is disabled.
+
+Example::
+
+    % modprobe dmatest run=1 iterations=42 wait=1
+    % modprobe -r dmatest
+
+...or::
+
+    % modprobe dmatest run=1 iterations=42
+    % cat /sys/module/dmatest/parameters/wait
+    % modprobe -r dmatest
+
+Part 3 - When built-in in the kernel
+====================================
+
+The module parameters that is supplied to the kernel command line will be used
+for the first performed test. After user gets a control, the test could be
+re-run with the same or different parameters. For the details see the above
+section `Part 2 - When dmatest is built as a module`_.
+
+In both cases the module parameters are used as the actual values for the test
+case. You always could check them at run-time by running ::
+
+    % grep -H . /sys/module/dmatest/parameters/*
+
+Part 4 - Gathering the test results
+===================================
+
+Test results are printed to the kernel log buffer with the format::
+
+    "dmatest: result <channel>: <test id>: '<error msg>' with src_off=<val> dst_off=<val> len=<val> (<err code>)"
+
+Example of output::
+
+    % dmesg | tail -n 1
+    dmatest: result dma0chan0-copy0: #1: No errors with src_off=0x7bf dst_off=0x8ad len=0x3fea (0)
+
+The message format is unified across the different types of errors. A
+number in the parentheses represents additional information, e.g. error
+code, error counter, or status. A test thread also emits a summary line at
+completion listing the number of tests executed, number that failed, and a
+result code.
+
+Example::
+
+    % dmesg | tail -n 1
+    dmatest: dma0chan0-copy0: summary 1 test, 0 failures 1000 iops 100000 KB/s (0)
+
+The details of a data miscompare error are also emitted, but do not follow the
+above format.

Documentation/driver-api/dmaengine/index.rst

@@ -0,0 +1,55 @@
+=======================
+DMAEngine documentation
+=======================
+
+DMAEngine documentation provides documents for various aspects of DMAEngine
+framework.
+
+DMAEngine documentation
+-----------------------
+
+This book helps with DMAengine internal APIs and guide for DMAEngine device
+driver writers.
+
+.. toctree::
+   :maxdepth: 1
+
+   provider
+
+DMAEngine client documentation
+------------------------------
+
+This book is a guide to device driver writers on how to use the Slave-DMA
+API of the DMAEngine. This is applicable only for slave DMA usage only.
+
+.. toctree::
+   :maxdepth: 1
+
+   client
+
+DMA Test documentation
+----------------------
+
+This book introduces how to test DMA drivers using dmatest module.
+
+.. toctree::
+   :maxdepth: 1
+
+   dmatest
+
+PXA DMA documentation
+----------------------
+
+This book adds some notes about PXA DMA
+
+.. toctree::
+   :maxdepth: 1
+
+   pxa_dma
+
+.. only::  subproject
+
+   Indices
+   =======
+
+   * :ref:`genindex`

Documentation/driver-api/dmaengine/provider.rst

@@ -0,0 +1,504 @@
+==================================
+DMAengine controller documentation
+==================================
+
+Hardware Introduction
+=====================
+
+Most of the Slave DMA controllers have the same general principles of
+operations.
+
+They have a given number of channels to use for the DMA transfers, and
+a given number of requests lines.
+
+Requests and channels are pretty much orthogonal. Channels can be used
+to serve several to any requests. To simplify, channels are the
+entities that will be doing the copy, and requests what endpoints are
+involved.
+
+The request lines actually correspond to physical lines going from the
+DMA-eligible devices to the controller itself. Whenever the device
+will want to start a transfer, it will assert a DMA request (DRQ) by
+asserting that request line.
+
+A very simple DMA controller would only take into account a single
+parameter: the transfer size. At each clock cycle, it would transfer a
+byte of data from one buffer to another, until the transfer size has
+been reached.
+
+That wouldn't work well in the real world, since slave devices might
+require a specific number of bits to be transferred in a single
+cycle. For example, we may want to transfer as much data as the
+physical bus allows to maximize performances when doing a simple
+memory copy operation, but our audio device could have a narrower FIFO
+that requires data to be written exactly 16 or 24 bits at a time. This
+is why most if not all of the DMA controllers can adjust this, using a
+parameter called the transfer width.
+
+Moreover, some DMA controllers, whenever the RAM is used as a source
+or destination, can group the reads or writes in memory into a buffer,
+so instead of having a lot of small memory accesses, which is not
+really efficient, you'll get several bigger transfers. This is done
+using a parameter called the burst size, that defines how many single
+reads/writes it's allowed to do without the controller splitting the
+transfer into smaller sub-transfers.
+
+Our theoretical DMA controller would then only be able to do transfers
+that involve a single contiguous block of data. However, some of the
+transfers we usually have are not, and want to copy data from
+non-contiguous buffers to a contiguous buffer, which is called
+scatter-gather.
+
+DMAEngine, at least for mem2dev transfers, require support for
+scatter-gather. So we're left with two cases here: either we have a
+quite simple DMA controller that doesn't support it, and we'll have to
+implement it in software, or we have a more advanced DMA controller,
+that implements in hardware scatter-gather.
+
+The latter are usually programmed using a collection of chunks to
+transfer, and whenever the transfer is started, the controller will go
+over that collection, doing whatever we programmed there.
+
+This collection is usually either a table or a linked list. You will
+then push either the address of the table and its number of elements,
+or the first item of the list to one channel of the DMA controller,
+and whenever a DRQ will be asserted, it will go through the collection
+to know where to fetch the data from.
+
+Either way, the format of this collection is completely dependent on
+your hardware. Each DMA controller will require a different structure,
+but all of them will require, for every chunk, at least the source and
+destination addresses, whether it should increment these addresses or
+not and the three parameters we saw earlier: the burst size, the
+transfer width and the transfer size.
+
+The one last thing is that usually, slave devices won't issue DRQ by
+default, and you have to enable this in your slave device driver first
+whenever you're willing to use DMA.
+
+These were just the general memory-to-memory (also called mem2mem) or
+memory-to-device (mem2dev) kind of transfers. Most devices often
+support other kind of transfers or memory operations that dmaengine
+support and will be detailed later in this document.
+
+DMA Support in Linux
+====================
+
+Historically, DMA controller drivers have been implemented using the
+async TX API, to offload operations such as memory copy, XOR,
+cryptography, etc., basically any memory to memory operation.
+
+Over time, the need for memory to device transfers arose, and
+dmaengine was extended. Nowadays, the async TX API is written as a
+layer on top of dmaengine, and acts as a client. Still, dmaengine
+accommodates that API in some cases, and made some design choices to
+ensure that it stayed compatible.
+
+For more information on the Async TX API, please look the relevant
+documentation file in Documentation/crypto/async-tx-api.txt.
+
+DMAEngine APIs
+==============
+
+``struct dma_device`` Initialization
+------------------------------------
+
+Just like any other kernel framework, the whole DMAEngine registration
+relies on the driver filling a structure and registering against the
+framework. In our case, that structure is dma_device.
+
+The first thing you need to do in your driver is to allocate this
+structure. Any of the usual memory allocators will do, but you'll also
+need to initialize a few fields in there:
+
+- ``channels``: should be initialized as a list using the
+  INIT_LIST_HEAD macro for example
+
+- ``src_addr_widths``:
+  should contain a bitmask of the supported source transfer width
+
+- ``dst_addr_widths``:
+  should contain a bitmask of the supported destination transfer width
+
+- ``directions``:
+  should contain a bitmask of the supported slave directions
+  (i.e. excluding mem2mem transfers)
+
+- ``residue_granularity``:
+  granularity of the transfer residue reported to dma_set_residue.
+  This can be either:
+
+  - Descriptor:
+    your device doesn't support any kind of residue
+    reporting. The framework will only know that a particular
+    transaction descriptor is done.
+
+  - Segment:
+    your device is able to report which chunks have been transferred
+
+  - Burst:
+    your device is able to report which burst have been transferred
+
+- ``dev``: should hold the pointer to the ``struct device`` associated
+  to your current driver instance.
+
+Supported transaction types
+---------------------------
+
+The next thing you need is to set which transaction types your device
+(and driver) supports.
+
+Our ``dma_device structure`` has a field called cap_mask that holds the
+various types of transaction supported, and you need to modify this
+mask using the dma_cap_set function, with various flags depending on
+transaction types you support as an argument.
+
+All those capabilities are defined in the ``dma_transaction_type enum``,
+in ``include/linux/dmaengine.h``
+
+Currently, the types available are:
+
+- DMA_MEMCPY
+
+  - The device is able to do memory to memory copies
+
+- DMA_XOR
+
+  - The device is able to perform XOR operations on memory areas
+
+  - Used to accelerate XOR intensive tasks, such as RAID5
+
+- DMA_XOR_VAL
+
+  - The device is able to perform parity check using the XOR
+    algorithm against a memory buffer.
+
+- DMA_PQ
+
+  - The device is able to perform RAID6 P+Q computations, P being a
+    simple XOR, and Q being a Reed-Solomon algorithm.
+
+- DMA_PQ_VAL
+
+  - The device is able to perform parity check using RAID6 P+Q
+    algorithm against a memory buffer.
+
+- DMA_INTERRUPT
+
+  - The device is able to trigger a dummy transfer that will
+    generate periodic interrupts
+
+  - Used by the client drivers to register a callback that will be
+    called on a regular basis through the DMA controller interrupt
+
+- DMA_PRIVATE
+
+  - The devices only supports slave transfers, and as such isn't
+    available for async transfers.
+
+- DMA_ASYNC_TX
+
+  - Must not be set by the device, and will be set by the framework
+    if needed
+
+  - TODO: What is it about?
+
+- DMA_SLAVE
+
+  - The device can handle device to memory transfers, including
+    scatter-gather transfers.
+
+  - While in the mem2mem case we were having two distinct types to
+    deal with a single chunk to copy or a collection of them, here,
+    we just have a single transaction type that is supposed to
+    handle both.
+
+  - If you want to transfer a single contiguous memory buffer,
+    simply build a scatter list with only one item.
+
+- DMA_CYCLIC
+
+  - The device can handle cyclic transfers.
+
+  - A cyclic transfer is a transfer where the chunk collection will
+    loop over itself, with the last item pointing to the first.
+
+  - It's usually used for audio transfers, where you want to operate
+    on a single ring buffer that you will fill with your audio data.
+
+- DMA_INTERLEAVE
+
+  - The device supports interleaved transfer.
+
+  - These transfers can transfer data from a non-contiguous buffer
+    to a non-contiguous buffer, opposed to DMA_SLAVE that can
+    transfer data from a non-contiguous data set to a continuous
+    destination buffer.
+
+  - It's usually used for 2d content transfers, in which case you
+    want to transfer a portion of uncompressed data directly to the
+    display to print it
+
+These various types will also affect how the source and destination
+addresses change over time.
+
+Addresses pointing to RAM are typically incremented (or decremented)
+after each transfer. In case of a ring buffer, they may loop
+(DMA_CYCLIC). Addresses pointing to a device's register (e.g. a FIFO)
+are typically fixed.
+
+Device operations
+-----------------
+
+Our dma_device structure also requires a few function pointers in
+order to implement the actual logic, now that we described what
+operations we were able to perform.
+
+The functions that we have to fill in there, and hence have to
+implement, obviously depend on the transaction types you reported as
+supported.
+
+- ``device_alloc_chan_resources``
+
+- ``device_free_chan_resources``
+
+  - These functions will be called whenever a driver will call
+    ``dma_request_channel`` or ``dma_release_channel`` for the first/last
+    time on the channel associated to that driver.
+
+  - They are in charge of allocating/freeing all the needed
+    resources in order for that channel to be useful for your driver.
+
+  - These functions can sleep.
+
+- ``device_prep_dma_*``
+
+  - These functions are matching the capabilities you registered
+    previously.
+
+  - These functions all take the buffer or the scatterlist relevant
+    for the transfer being prepared, and should create a hardware
+    descriptor or a list of hardware descriptors from it
+
+  - These functions can be called from an interrupt context
+
+  - Any allocation you might do should be using the GFP_NOWAIT
+    flag, in order not to potentially sleep, but without depleting
+    the emergency pool either.
+
+  - Drivers should try to pre-allocate any memory they might need
+    during the transfer setup at probe time to avoid putting to
+    much pressure on the nowait allocator.
+
+  - It should return a unique instance of the
+    ``dma_async_tx_descriptor structure``, that further represents this
+    particular transfer.
+
+  - This structure can be initialized using the function
+    ``dma_async_tx_descriptor_init``.
+
+  - You'll also need to set two fields in this structure:
+
+    - flags:
+      TODO: Can it be modified by the driver itself, or
+      should it be always the flags passed in the arguments
+
+    - tx_submit: A pointer to a function you have to implement,
+      that is supposed to push the current transaction descriptor to a
+      pending queue, waiting for issue_pending to be called.
+
+  - In this structure the function pointer callback_result can be
+    initialized in order for the submitter to be notified that a
+    transaction has completed. In the earlier code the function pointer
+    callback has been used. However it does not provide any status to the
+    transaction and will be deprecated. The result structure defined as
+    ``dmaengine_result`` that is passed in to callback_result
+    has two fields:
+
+    - result: This provides the transfer result defined by
+      ``dmaengine_tx_result``. Either success or some error condition.
+
+    - residue: Provides the residue bytes of the transfer for those that
+      support residue.
+
+- ``device_issue_pending``
+
+  - Takes the first transaction descriptor in the pending queue,
+    and starts the transfer. Whenever that transfer is done, it
+    should move to the next transaction in the list.
+
+  - This function can be called in an interrupt context
+
+- ``device_tx_status``
+
+  - Should report the bytes left to go over on the given channel
+
+  - Should only care about the transaction descriptor passed as
+    argument, not the currently active one on a given channel
+
+  - The tx_state argument might be NULL
+
+  - Should use dma_set_residue to report it
+
+  - In the case of a cyclic transfer, it should only take into
+    account the current period.
+
+  - This function can be called in an interrupt context.
+
+- device_config
+
+  - Reconfigures the channel with the configuration given as argument
+
+  - This command should NOT perform synchronously, or on any
+    currently queued transfers, but only on subsequent ones
+
+  - In this case, the function will receive a ``dma_slave_config``
+    structure pointer as an argument, that will detail which
+    configuration to use.
+
+  - Even though that structure contains a direction field, this
+    field is deprecated in favor of the direction argument given to
+    the prep_* functions
+
+  - This call is mandatory for slave operations only. This should NOT be
+    set or expected to be set for memcpy operations.
+    If a driver support both, it should use this call for slave
+    operations only and not for memcpy ones.
+
+- device_pause
+
+  - Pauses a transfer on the channel
+
+  - This command should operate synchronously on the channel,
+    pausing right away the work of the given channel
+
+- device_resume
+
+  - Resumes a transfer on the channel
+
+  - This command should operate synchronously on the channel,
+    resuming right away the work of the given channel
+
+- device_terminate_all
+
+  - Aborts all the pending and ongoing transfers on the channel
+
+  - For aborted transfers the complete callback should not be called
+
+  - Can be called from atomic context or from within a complete
+    callback of a descriptor. Must not sleep. Drivers must be able
+    to handle this correctly.
+
+  - Termination may be asynchronous. The driver does not have to
+    wait until the currently active transfer has completely stopped.
+    See device_synchronize.
+
+- device_synchronize
+
+  - Must synchronize the termination of a channel to the current
+    context.
+
+  - Must make sure that memory for previously submitted
+    descriptors is no longer accessed by the DMA controller.
+
+  - Must make sure that all complete callbacks for previously
+    submitted descriptors have finished running and none are
+    scheduled to run.
+
+  - May sleep.
+
+
+Misc notes
+==========
+
+(stuff that should be documented, but don't really know
+where to put them)
+
+``dma_run_dependencies``
+
+- Should be called at the end of an async TX transfer, and can be
+  ignored in the slave transfers case.
+
+- Makes sure that dependent operations are run before marking it
+  as complete.
+
+dma_cookie_t
+
+- it's a DMA transaction ID that will increment over time.
+
+- Not really relevant any more since the introduction of ``virt-dma``
+  that abstracts it away.
+
+DMA_CTRL_ACK
+
+- If clear, the descriptor cannot be reused by provider until the
+  client acknowledges receipt, i.e. has has a chance to establish any
+  dependency chains
+
+- This can be acked by invoking async_tx_ack()
+
+- If set, does not mean descriptor can be reused
+
+DMA_CTRL_REUSE
+
+- If set, the descriptor can be reused after being completed. It should
+  not be freed by provider if this flag is set.
+
+- The descriptor should be prepared for reuse by invoking
+  ``dmaengine_desc_set_reuse()`` which will set DMA_CTRL_REUSE.
+
+- ``dmaengine_desc_set_reuse()`` will succeed only when channel support
+  reusable descriptor as exhibited by capabilities
+
+- As a consequence, if a device driver wants to skip the
+  ``dma_map_sg()`` and ``dma_unmap_sg()`` in between 2 transfers,
+  because the DMA'd data wasn't used, it can resubmit the transfer right after
+  its completion.
+
+- Descriptor can be freed in few ways
+
+  - Clearing DMA_CTRL_REUSE by invoking
+    ``dmaengine_desc_clear_reuse()`` and submitting for last txn
+
+  - Explicitly invoking ``dmaengine_desc_free()``, this can succeed only
+    when DMA_CTRL_REUSE is already set
+
+  - Terminating the channel
+
+- DMA_PREP_CMD
+
+  - If set, the client driver tells DMA controller that passed data in DMA
+    API is command data.
+
+  - Interpretation of command data is DMA controller specific. It can be
+    used for issuing commands to other peripherals/register reads/register
+    writes for which the descriptor should be in different format from
+    normal data descriptors.
+
+General Design Notes
+====================
+
+Most of the DMAEngine drivers you'll see are based on a similar design
+that handles the end of transfer interrupts in the handler, but defer
+most work to a tasklet, including the start of a new transfer whenever
+the previous transfer ended.
+
+This is a rather inefficient design though, because the inter-transfer
+latency will be not only the interrupt latency, but also the
+scheduling latency of the tasklet, which will leave the channel idle
+in between, which will slow down the global transfer rate.
+
+You should avoid this kind of practice, and instead of electing a new
+transfer in your tasklet, move that part to the interrupt handler in
+order to have a shorter idle window (that we can't really avoid
+anyway).
+
+Glossary
+========
+
+- Burst: A number of consecutive read or write operations that
+  can be queued to buffers before being flushed to memory.
+
+- Chunk: A contiguous collection of bursts
+
+- Transfer: A collection of chunks (be it contiguous or not)

Documentation/driver-api/dmaengine/pxa_dma.rst

@@ -0,0 +1,190 @@
+==============================
+PXA/MMP - DMA Slave controller
+==============================
+
+Constraints
+===========
+
+a) Transfers hot queuing
+A driver submitting a transfer and issuing it should be granted the transfer
+is queued even on a running DMA channel.
+This implies that the queuing doesn't wait for the previous transfer end,
+and that the descriptor chaining is not only done in the irq/tasklet code
+triggered by the end of the transfer.
+A transfer which is submitted and issued on a phy doesn't wait for a phy to
+stop and restart, but is submitted on a "running channel". The other
+drivers, especially mmp_pdma waited for the phy to stop before relaunching
+a new transfer.
+
+b) All transfers having asked for confirmation should be signaled
+Any issued transfer with DMA_PREP_INTERRUPT should trigger a callback call.
+This implies that even if an irq/tasklet is triggered by end of tx1, but
+at the time of irq/dma tx2 is already finished, tx1->complete() and
+tx2->complete() should be called.
+
+c) Channel running state
+A driver should be able to query if a channel is running or not. For the
+multimedia case, such as video capture, if a transfer is submitted and then
+a check of the DMA channel reports a "stopped channel", the transfer should
+not be issued until the next "start of frame interrupt", hence the need to
+know if a channel is in running or stopped state.
+
+d) Bandwidth guarantee
+The PXA architecture has 4 levels of DMAs priorities : high, normal, low.
+The high priorities get twice as much bandwidth as the normal, which get twice
+as much as the low priorities.
+A driver should be able to request a priority, especially the real-time
+ones such as pxa_camera with (big) throughputs.
+
+Design
+======
+a) Virtual channels
+Same concept as in sa11x0 driver, ie. a driver was assigned a "virtual
+channel" linked to the requestor line, and the physical DMA channel is
+assigned on the fly when the transfer is issued.
+
+b) Transfer anatomy for a scatter-gather transfer
+
+::
+
+   +------------+-----+---------------+----------------+-----------------+
+   | desc-sg[0] | ... | desc-sg[last] | status updater | finisher/linker |
+   +------------+-----+---------------+----------------+-----------------+
+
+This structure is pointed by dma->sg_cpu.
+The descriptors are used as follows :
+
+    - desc-sg[i]: i-th descriptor, transferring the i-th sg
+      element to the video buffer scatter gather
+
+    - status updater
+      Transfers a single u32 to a well known dma coherent memory to leave
+      a trace that this transfer is done. The "well known" is unique per
+      physical channel, meaning that a read of this value will tell which
+      is the last finished transfer at that point in time.
+
+    - finisher: has ddadr=DADDR_STOP, dcmd=ENDIRQEN
+
+    - linker: has ddadr= desc-sg[0] of next transfer, dcmd=0
+
+c) Transfers hot-chaining
+Suppose the running chain is:
+
+::
+
+   Buffer 1              Buffer 2
+   +---------+----+---+  +----+----+----+---+
+   | d0 | .. | dN | l |  | d0 | .. | dN | f |
+   +---------+----+-|-+  ^----+----+----+---+
+                    |    |
+                    +----+
+
+After a call to dmaengine_submit(b3), the chain will look like:
+
+::
+
+   Buffer 1              Buffer 2              Buffer 3
+   +---------+----+---+  +----+----+----+---+  +----+----+----+---+
+   | d0 | .. | dN | l |  | d0 | .. | dN | l |  | d0 | .. | dN | f |
+   +---------+----+-|-+  ^----+----+----+-|-+  ^----+----+----+---+
+                    |    |                |    |
+                    +----+                +----+
+                                         new_link
+
+If while new_link was created the DMA channel stopped, it is _not_
+restarted. Hot-chaining doesn't break the assumption that
+dma_async_issue_pending() is to be used to ensure the transfer is actually started.
+
+One exception to this rule :
+
+- if Buffer1 and Buffer2 had all their addresses 8 bytes aligned
+
+- and if Buffer3 has at least one address not 4 bytes aligned
+
+- then hot-chaining cannot happen, as the channel must be stopped, the
+  "align bit" must be set, and the channel restarted As a consequence,
+  such a transfer tx_submit() will be queued on the submitted queue, and
+  this specific case if the DMA is already running in aligned mode.
+
+d) Transfers completion updater
+Each time a transfer is completed on a channel, an interrupt might be
+generated or not, up to the client's request. But in each case, the last
+descriptor of a transfer, the "status updater", will write the latest
+transfer being completed into the physical channel's completion mark.
+
+This will speed up residue calculation, for large transfers such as video
+buffers which hold around 6k descriptors or more. This also allows without
+any lock to find out what is the latest completed transfer in a running
+DMA chain.
+
+e) Transfers completion, irq and tasklet
+When a transfer flagged as "DMA_PREP_INTERRUPT" is finished, the dma irq
+is raised. Upon this interrupt, a tasklet is scheduled for the physical
+channel.
+
+The tasklet is responsible for :
+
+- reading the physical channel last updater mark
+
+- calling all the transfer callbacks of finished transfers, based on
+  that mark, and each transfer flags.
+
+If a transfer is completed while this handling is done, a dma irq will
+be raised, and the tasklet will be scheduled once again, having a new
+updater mark.
+
+f) Residue
+Residue granularity will be descriptor based. The issued but not completed
+transfers will be scanned for all of their descriptors against the
+currently running descriptor.
+
+g) Most complicated case of driver's tx queues
+The most tricky situation is when :
+
+ - there are not "acked" transfers (tx0)
+
+ - a driver submitted an aligned tx1, not chained
+
+ - a driver submitted an aligned tx2 => tx2 is cold chained to tx1
+
+ - a driver issued tx1+tx2 => channel is running in aligned mode
+
+ - a driver submitted an aligned tx3 => tx3 is hot-chained
+
+ - a driver submitted an unaligned tx4 => tx4 is put in submitted queue,
+   not chained
+
+ - a driver issued tx4 => tx4 is put in issued queue, not chained
+
+ - a driver submitted an aligned tx5 => tx5 is put in submitted queue, not
+   chained
+
+ - a driver submitted an aligned tx6 => tx6 is put in submitted queue,
+   cold chained to tx5
+
+ This translates into (after tx4 is issued) :
+
+ - issued queue
+
+ ::
+
+      +-----+ +-----+ +-----+ +-----+
+      | tx1 | | tx2 | | tx3 | | tx4 |
+      +---|-+ ^---|-+ ^-----+ +-----+
+          |   |   |   |
+          +---+   +---+
+        - submitted queue
+      +-----+ +-----+
+      | tx5 | | tx6 |
+      +---|-+ ^-----+
+          |   |
+          +---+
+
+- completed queue : empty
+
+- allocated queue : tx0
+
+It should be noted that after tx3 is completed, the channel is stopped, and
+restarted in "unaligned mode" to handle tx4.
+
+Author: Robert Jarzmik <robert.jarzmik@free.fr>

Documentation/driver-api/edac.rst

@@ -0,0 +1,178 @@
+Error Detection And Correction (EDAC) Devices
+=============================================
+
+Main Concepts used at the EDAC subsystem
+----------------------------------------
+
+There are several things to be aware of that aren't at all obvious, like
+*sockets, *socket sets*, *banks*, *rows*, *chip-select rows*, *channels*,
+etc...
+
+These are some of the many terms that are thrown about that don't always
+mean what people think they mean (Inconceivable!).  In the interest of
+creating a common ground for discussion, terms and their definitions
+will be established.
+
+* Memory devices
+
+The individual DRAM chips on a memory stick.  These devices commonly
+output 4 and 8 bits each (x4, x8). Grouping several of these in parallel
+provides the number of bits that the memory controller expects:
+typically 72 bits, in order to provide 64 bits + 8 bits of ECC data.
+
+* Memory Stick
+
+A printed circuit board that aggregates multiple memory devices in
+parallel.  In general, this is the Field Replaceable Unit (FRU) which
+gets replaced, in the case of excessive errors. Most often it is also
+called DIMM (Dual Inline Memory Module).
+
+* Memory Socket
+
+A physical connector on the motherboard that accepts a single memory
+stick. Also called as "slot" on several datasheets.
+
+* Channel
+
+A memory controller channel, responsible to communicate with a group of
+DIMMs. Each channel has its own independent control (command) and data
+bus, and can be used independently or grouped with other channels.
+
+* Branch
+
+It is typically the highest hierarchy on a Fully-Buffered DIMM memory
+controller. Typically, it contains two channels. Two channels at the
+same branch can be used in single mode or in lockstep mode. When
+lockstep is enabled, the cacheline is doubled, but it generally brings
+some performance penalty. Also, it is generally not possible to point to
+just one memory stick when an error occurs, as the error correction code
+is calculated using two DIMMs instead of one. Due to that, it is capable
+of correcting more errors than on single mode.
+
+* Single-channel
+
+The data accessed by the memory controller is contained into one dimm
+only. E. g. if the data is 64 bits-wide, the data flows to the CPU using
+one 64 bits parallel access. Typically used with SDR, DDR, DDR2 and DDR3
+memories. FB-DIMM and RAMBUS use a different concept for channel, so
+this concept doesn't apply there.
+
+* Double-channel
+
+The data size accessed by the memory controller is interlaced into two
+dimms, accessed at the same time. E. g. if the DIMM is 64 bits-wide (72
+bits with ECC), the data flows to the CPU using a 128 bits parallel
+access.
+
+* Chip-select row
+
+This is the name of the DRAM signal used to select the DRAM ranks to be
+accessed. Common chip-select rows for single channel are 64 bits, for
+dual channel 128 bits. It may not be visible by the memory controller,
+as some DIMM types have a memory buffer that can hide direct access to
+it from the Memory Controller.
+
+* Single-Ranked stick
+
+A Single-ranked stick has 1 chip-select row of memory. Motherboards
+commonly drive two chip-select pins to a memory stick. A single-ranked
+stick, will occupy only one of those rows. The other will be unused.
+
+.. _doubleranked:
+
+* Double-Ranked stick
+
+A double-ranked stick has two chip-select rows which access different
+sets of memory devices.  The two rows cannot be accessed concurrently.
+
+* Double-sided stick
+
+**DEPRECATED TERM**, see :ref:`Double-Ranked stick <doubleranked>`.
+
+A double-sided stick has two chip-select rows which access different sets
+of memory devices. The two rows cannot be accessed concurrently.
+"Double-sided" is irrespective of the memory devices being mounted on
+both sides of the memory stick.
+
+* Socket set
+
+All of the memory sticks that are required for a single memory access or
+all of the memory sticks spanned by a chip-select row.  A single socket
+set has two chip-select rows and if double-sided sticks are used these
+will occupy those chip-select rows.
+
+* Bank
+
+This term is avoided because it is unclear when needing to distinguish
+between chip-select rows and socket sets.
+
+
+Memory Controllers
+------------------
+
+Most of the EDAC core is focused on doing Memory Controller error detection.
+The :c:func:`edac_mc_alloc`. It uses internally the struct ``mem_ctl_info``
+to describe the memory controllers, with is an opaque struct for the EDAC
+drivers. Only the EDAC core is allowed to touch it.
+
+.. kernel-doc:: include/linux/edac.h
+
+.. kernel-doc:: drivers/edac/edac_mc.h
+
+PCI Controllers
+---------------
+
+The EDAC subsystem provides a mechanism to handle PCI controllers by calling
+the :c:func:`edac_pci_alloc_ctl_info`. It will use the struct
+:c:type:`edac_pci_ctl_info` to describe the PCI controllers.
+
+.. kernel-doc:: drivers/edac/edac_pci.h
+
+EDAC Blocks
+-----------
+
+The EDAC subsystem also provides a generic mechanism to report errors on
+other parts of the hardware via :c:func:`edac_device_alloc_ctl_info` function.
+
+The structures :c:type:`edac_dev_sysfs_block_attribute`,
+:c:type:`edac_device_block`, :c:type:`edac_device_instance` and
+:c:type:`edac_device_ctl_info` provide a generic or abstract 'edac_device'
+representation at sysfs.
+
+This set of structures and the code that implements the APIs for the same, provide for registering EDAC type devices which are NOT standard memory or
+PCI, like:
+
+- CPU caches (L1 and L2)
+- DMA engines
+- Core CPU switches
+- Fabric switch units
+- PCIe interface controllers
+- other EDAC/ECC type devices that can be monitored for
+  errors, etc.
+
+It allows for a 2 level set of hierarchy.
+
+For example, a cache could be composed of L1, L2 and L3 levels of cache.
+Each CPU core would have its own L1 cache, while sharing L2 and maybe L3
+caches. On such case, those can be represented via the following sysfs
+nodes::
+
+	/sys/devices/system/edac/..
+
+	pci/		<existing pci directory (if available)>
+	mc/		<existing memory device directory>
+	cpu/cpu0/..	<L1 and L2 block directory>
+		/L1-cache/ce_count
+			 /ue_count
+		/L2-cache/ce_count
+			 /ue_count
+	cpu/cpu1/..	<L1 and L2 block directory>
+		/L1-cache/ce_count
+			 /ue_count
+		/L2-cache/ce_count
+			 /ue_count
+	...
+
+	the L1 and L2 directories would be "edac_device_block's"
+
+.. kernel-doc:: drivers/edac/edac_device.h

Documentation/driver-api/firmware/built-in-fw.rst

@@ -0,0 +1,33 @@
+=================
+Built-in firmware
+=================
+
+Firmware can be built-in to the kernel, this means building the firmware
+into vmlinux directly, to enable avoiding having to look for firmware from
+the filesystem. Instead, firmware can be looked for inside the kernel
+directly. You can enable built-in firmware using the kernel configuration
+options:
+
+  * CONFIG_EXTRA_FIRMWARE
+  * CONFIG_EXTRA_FIRMWARE_DIR
+
+There are a few reasons why you might want to consider building your firmware
+into the kernel with CONFIG_EXTRA_FIRMWARE:
+
+* Speed
+* Firmware is needed for accessing the boot device, and the user doesn't
+  want to stuff the firmware into the boot initramfs.
+
+Even if you have these needs there are a few reasons why you may not be
+able to make use of built-in firmware:
+
+* Legalese - firmware is non-GPL compatible
+* Some firmware may be optional
+* Firmware upgrades are possible, therefore a new firmware would implicate
+  a complete kernel rebuild.
+* Some firmware files may be really large in size. The remote-proc subsystem
+  is an example subsystem which deals with these sorts of firmware
+* The firmware may need to be scraped out from some device specific location
+  dynamically, an example is calibration data for for some WiFi chipsets. This
+  calibration data can be unique per sold device.
+

Documentation/driver-api/firmware/core.rst

@@ -0,0 +1,16 @@
+==========================
+Firmware API core features
+==========================
+
+The firmware API has a rich set of core features available. This section
+documents these features.
+
+.. toctree::
+
+   fw_search_path
+   built-in-fw
+   firmware_cache
+   direct-fs-lookup
+   fallback-mechanisms
+   lookup-order
+

Documentation/driver-api/firmware/direct-fs-lookup.rst

@@ -0,0 +1,30 @@
+========================
+Direct filesystem lookup
+========================
+
+Direct filesystem lookup is the most common form of firmware lookup performed
+by the kernel. The kernel looks for the firmware directly on the root
+filesystem in the paths documented in the section 'Firmware search paths'.
+The filesystem lookup is implemented in fw_get_filesystem_firmware(), it
+uses common core kernel file loader facility kernel_read_file_from_path().
+The max path allowed is PATH_MAX -- currently this is 4096 characters.
+
+It is recommended you keep /lib/firmware paths on your root filesystem,
+avoid having a separate partition for them in order to avoid possible
+races with lookups and avoid uses of the custom fallback mechanisms
+documented below.
+
+Firmware and initramfs
+----------------------
+
+Drivers which are built-in to the kernel should have the firmware integrated
+also as part of the initramfs used to boot the kernel given that otherwise
+a race is possible with loading the driver and the real rootfs not yet being
+available. Stuffing the firmware into initramfs resolves this race issue,
+however note that using initrd does not suffice to address the same race.
+
+There are circumstances that justify not wanting to include firmware into
+initramfs, such as dealing with large firmware firmware files for the
+remote-proc subsystem. For such cases using a userspace fallback mechanism
+is currently the only viable solution as only userspace can know for sure
+when the real rootfs is ready and mounted.

Documentation/driver-api/firmware/fallback-mechanisms.rst

@@ -0,0 +1,204 @@
+===================
+Fallback mechanisms
+===================
+
+A fallback mechanism is supported to allow to overcome failures to do a direct
+filesystem lookup on the root filesystem or when the firmware simply cannot be
+installed for practical reasons on the root filesystem. The kernel
+configuration options related to supporting the firmware fallback mechanism are:
+
+  * CONFIG_FW_LOADER_USER_HELPER: enables building the firmware fallback
+    mechanism. Most distributions enable this option today. If enabled but
+    CONFIG_FW_LOADER_USER_HELPER_FALLBACK is disabled, only the custom fallback
+    mechanism is available and for the request_firmware_nowait() call.
+  * CONFIG_FW_LOADER_USER_HELPER_FALLBACK: force enables each request to
+    enable the kobject uevent fallback mechanism on all firmware API calls
+    except request_firmware_direct(). Most distributions disable this option
+    today. The call request_firmware_nowait() allows for one alternative
+    fallback mechanism: if this kconfig option is enabled and your second
+    argument to request_firmware_nowait(), uevent, is set to false you are
+    informing the kernel that you have a custom fallback mechanism and it will
+    manually load the firmware. Read below for more details.
+
+Note that this means when having this configuration:
+
+CONFIG_FW_LOADER_USER_HELPER=y
+CONFIG_FW_LOADER_USER_HELPER_FALLBACK=n
+
+the kobject uevent fallback mechanism will never take effect even
+for request_firmware_nowait() when uevent is set to true.
+
+Justifying the firmware fallback mechanism
+==========================================
+
+Direct filesystem lookups may fail for a variety of reasons. Known reasons for
+this are worth itemizing and documenting as it justifies the need for the
+fallback mechanism:
+
+* Race against access with the root filesystem upon bootup.
+
+* Races upon resume from suspend. This is resolved by the firmware cache, but
+  the firmware cache is only supported if you use uevents, and its not
+  supported for request_firmware_into_buf().
+
+* Firmware is not accessible through typical means:
+        * It cannot be installed into the root filesystem
+        * The firmware provides very unique device specific data tailored for
+          the unit gathered with local information. An example is calibration
+          data for WiFi chipsets for mobile devices. This calibration data is
+          not common to all units, but tailored per unit.  Such information may
+          be installed on a separate flash partition other than where the root
+          filesystem is provided.
+
+Types of fallback mechanisms
+============================
+
+There are really two fallback mechanisms available using one shared sysfs
+interface as a loading facility:
+
+* Kobject uevent fallback mechanism
+* Custom fallback mechanism
+
+First lets document the shared sysfs loading facility.
+
+Firmware sysfs loading facility
+===============================
+
+In order to help device drivers upload firmware using a fallback mechanism
+the firmware infrastructure creates a sysfs interface to enable userspace
+to load and indicate when firmware is ready. The sysfs directory is created
+via fw_create_instance(). This call creates a new struct device named after
+the firmware requested, and establishes it in the device hierarchy by
+associating the device used to make the request as the device's parent.
+The sysfs directory's file attributes are defined and controlled through
+the new device's class (firmware_class) and group (fw_dev_attr_groups).
+This is actually where the original firmware_class module name came from,
+given that originally the only firmware loading mechanism available was the
+mechanism we now use as a fallback mechanism, which registers a struct class
+firmware_class. Because the attributes exposed are part of the module name, the
+module name firmware_class cannot be renamed in the future, to ensure backward
+compatibility with old userspace.
+
+To load firmware using the sysfs interface we expose a loading indicator,
+and a file upload firmware into:
+
+  * /sys/$DEVPATH/loading
+  * /sys/$DEVPATH/data
+
+To upload firmware you will echo 1 onto the loading file to indicate
+you are loading firmware. You then write the firmware into the data file,
+and you notify the kernel the firmware is ready by echo'ing 0 onto
+the loading file.
+
+The firmware device used to help load firmware using sysfs is only created if
+direct firmware loading fails and if the fallback mechanism is enabled for your
+firmware request, this is set up with :c:func:`firmware_fallback_sysfs`. It is
+important to re-iterate that no device is created if a direct filesystem lookup
+succeeded.
+
+Using::
+
+        echo 1 > /sys/$DEVPATH/loading
+
+Will clean any previous partial load at once and make the firmware API
+return an error. When loading firmware the firmware_class grows a buffer
+for the firmware in PAGE_SIZE increments to hold the image as it comes in.
+
+firmware_data_read() and firmware_loading_show() are just provided for the
+test_firmware driver for testing, they are not called in normal use or
+expected to be used regularly by userspace.
+
+firmware_fallback_sysfs
+-----------------------
+.. kernel-doc:: drivers/base/firmware_loader/fallback.c
+   :functions: firmware_fallback_sysfs
+
+Firmware kobject uevent fallback mechanism
+==========================================
+
+Since a device is created for the sysfs interface to help load firmware as a
+fallback mechanism userspace can be informed of the addition of the device by
+relying on kobject uevents. The addition of the device into the device
+hierarchy means the fallback mechanism for firmware loading has been initiated.
+For details of implementation refer to fw_load_sysfs_fallback(), in particular
+on the use of dev_set_uevent_suppress() and kobject_uevent().
+
+The kernel's kobject uevent mechanism is implemented in lib/kobject_uevent.c,
+it issues uevents to userspace. As a supplement to kobject uevents Linux
+distributions could also enable CONFIG_UEVENT_HELPER_PATH, which makes use of
+core kernel's usermode helper (UMH) functionality to call out to a userspace
+helper for kobject uevents. In practice though no standard distribution has
+ever used the CONFIG_UEVENT_HELPER_PATH. If CONFIG_UEVENT_HELPER_PATH is
+enabled this binary would be called each time kobject_uevent_env() gets called
+in the kernel for each kobject uevent triggered.
+
+Different implementations have been supported in userspace to take advantage of
+this fallback mechanism. When firmware loading was only possible using the
+sysfs mechanism the userspace component "hotplug" provided the functionality of
+monitoring for kobject events. Historically this was superseded be systemd's
+udev, however firmware loading support was removed from udev as of systemd
+commit be2ea723b1d0 ("udev: remove userspace firmware loading support")
+as of v217 on August, 2014. This means most Linux distributions today are
+not using or taking advantage of the firmware fallback mechanism provided
+by kobject uevents. This is specially exacerbated due to the fact that most
+distributions today disable CONFIG_FW_LOADER_USER_HELPER_FALLBACK.
+
+Refer to do_firmware_uevent() for details of the kobject event variables
+setup. The variables currently passed to userspace with a "kobject add"
+event are:
+
+* FIRMWARE=firmware name
+* TIMEOUT=timeout value
+* ASYNC=whether or not the API request was asynchronous
+
+By default DEVPATH is set by the internal kernel kobject infrastructure.
+Below is an example simple kobject uevent script::
+
+        # Both $DEVPATH and $FIRMWARE are already provided in the environment.
+        MY_FW_DIR=/lib/firmware/
+        echo 1 > /sys/$DEVPATH/loading
+        cat $MY_FW_DIR/$FIRMWARE > /sys/$DEVPATH/data
+        echo 0 > /sys/$DEVPATH/loading
+
+Firmware custom fallback mechanism
+==================================
+
+Users of the request_firmware_nowait() call have yet another option available
+at their disposal: rely on the sysfs fallback mechanism but request that no
+kobject uevents be issued to userspace. The original logic behind this
+was that utilities other than udev might be required to lookup firmware
+in non-traditional paths -- paths outside of the listing documented in the
+section 'Direct filesystem lookup'. This option is not available to any of
+the other API calls as uevents are always forced for them.
+
+Since uevents are only meaningful if the fallback mechanism is enabled
+in your kernel it would seem odd to enable uevents with kernels that do not
+have the fallback mechanism enabled in their kernels. Unfortunately we also
+rely on the uevent flag which can be disabled by request_firmware_nowait() to
+also setup the firmware cache for firmware requests. As documented above,
+the firmware cache is only set up if uevent is enabled for an API call.
+Although this can disable the firmware cache for request_firmware_nowait()
+calls, users of this API should not use it for the purposes of disabling
+the cache as that was not the original purpose of the flag. Not setting
+the uevent flag means you want to opt-in for the firmware fallback mechanism
+but you want to suppress kobject uevents, as you have a custom solution which
+will monitor for your device addition into the device hierarchy somehow and
+load firmware for you through a custom path.
+
+Firmware fallback timeout
+=========================
+
+The firmware fallback mechanism has a timeout. If firmware is not loaded
+onto the sysfs interface by the timeout value an error is sent to the
+driver. By default the timeout is set to 60 seconds if uevents are
+desirable, otherwise MAX_JIFFY_OFFSET is used (max timeout possible).
+The logic behind using MAX_JIFFY_OFFSET for non-uevents is that a custom
+solution will have as much time as it needs to load firmware.
+
+You can customize the firmware timeout by echo'ing your desired timeout into
+the following file:
+
+* /sys/class/firmware/timeout
+
+If you echo 0 into it means MAX_JIFFY_OFFSET will be used. The data type
+for the timeout is an int.

Documentation/driver-api/firmware/firmware_cache.rst

@@ -0,0 +1,51 @@
+==============
+Firmware cache
+==============
+
+When Linux resumes from suspend some device drivers require firmware lookups to
+re-initialize devices. During resume there may be a period of time during which
+firmware lookups are not possible, during this short period of time firmware
+requests will fail. Time is of essence though, and delaying drivers to wait for
+the root filesystem for firmware delays user experience with device
+functionality. In order to support these requirements the firmware
+infrastructure implements a firmware cache for device drivers for most API
+calls, automatically behind the scenes.
+
+The firmware cache makes using certain firmware API calls safe during a device
+driver's suspend and resume callback.  Users of these API calls needn't cache
+the firmware by themselves for dealing with firmware loss during system resume.
+
+The firmware cache works by requesting for firmware prior to suspend and
+caching it in memory. Upon resume device drivers using the firmware API will
+have access to the firmware immediately, without having to wait for the root
+filesystem to mount or dealing with possible race issues with lookups as the
+root filesystem mounts.
+
+Some implementation details about the firmware cache setup:
+
+* The firmware cache is setup by adding a devres entry for each device that
+  uses all synchronous call except :c:func:`request_firmware_into_buf`.
+
+* If an asynchronous call is used the firmware cache is only set up for a
+  device if if the second argument (uevent) to request_firmware_nowait() is
+  true. When uevent is true it requests that a kobject uevent be sent to
+  userspace for the firmware request through the sysfs fallback mechanism
+  if the firmware file is not found.
+
+* If the firmware cache is determined to be needed as per the above two
+  criteria the firmware cache is setup by adding a devres entry for the
+  device making the firmware request.
+
+* The firmware devres entry is maintained throughout the lifetime of the
+  device. This means that even if you release_firmware() the firmware cache
+  will still be used on resume from suspend.
+
+* The timeout for the fallback mechanism is temporarily reduced to 10 seconds
+  as the firmware cache is set up during suspend, the timeout is set back to
+  the old value you had configured after the cache is set up.
+
+* Upon suspend any pending non-uevent firmware requests are killed to avoid
+  stalling the kernel, this is done with kill_requests_without_uevent(). Kernel
+  calls requiring the non-uevent therefore need to implement their own firmware
+  cache mechanism but must not use the firmware API on suspend.
+

Documentation/driver-api/firmware/fw_search_path.rst

@@ -0,0 +1,26 @@
+=====================
+Firmware search paths
+=====================
+
+The following search paths are used to look for firmware on your
+root filesystem.
+
+* fw_path_para - module parameter - default is empty so this is ignored
+* /lib/firmware/updates/UTS_RELEASE/
+* /lib/firmware/updates/
+* /lib/firmware/UTS_RELEASE/
+* /lib/firmware/
+
+The module parameter ''path'' can be passed to the firmware_class module
+to activate the first optional custom fw_path_para. The custom path can
+only be up to 256 characters long. The kernel parameter passed would be:
+
+* 'firmware_class.path=$CUSTOMIZED_PATH'
+
+There is an alternative to customize the path at run time after bootup, you
+can use the file:
+
+* /sys/module/firmware_class/parameters/path
+
+You would echo into it your custom path and firmware requested will be
+searched for there first.

Documentation/driver-api/firmware/index.rst

@@ -0,0 +1,17 @@
+==================
+Linux Firmware API
+==================
+
+.. toctree::
+
+   introduction
+   core
+   request_firmware
+   other_interfaces
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`

Documentation/driver-api/firmware/introduction.rst

@@ -0,0 +1,27 @@
+============
+Introduction
+============
+
+The firmware API enables kernel code to request files required
+for functionality from userspace, the uses vary:
+
+* Microcode for CPU errata
+* Device driver firmware, required to be loaded onto device
+  microcontrollers
+* Device driver information data (calibration data, EEPROM overrides),
+  some of which can be completely optional.
+
+Types of firmware requests
+==========================
+
+There are two types of calls:
+
+* Synchronous
+* Asynchronous
+
+Which one you use vary depending on your requirements, the rule of thumb
+however is you should strive to use the asynchronous APIs unless you also
+are already using asynchronous initialization mechanisms which will not
+stall or delay boot. Even if loading firmware does not take a lot of time
+processing firmware might, and this can still delay boot or initialization,
+as such mechanisms such as asynchronous probe can help supplement drivers.

Documentation/driver-api/firmware/lookup-order.rst

@@ -0,0 +1,18 @@
+=====================
+Firmware lookup order
+=====================
+
+Different functionality is available to enable firmware to be found.
+Below is chronological order of how firmware will be looked for once
+a driver issues a firmware API call.
+
+* The ''Built-in firmware'' is checked first, if the firmware is present we
+  return it immediately
+* The ''Firmware cache'' is looked at next. If the firmware is found we
+  return it immediately
+* The ''Direct filesystem lookup'' is performed next, if found we
+  return it immediately
+* If no firmware has been found and the fallback mechanism was enabled
+  the sysfs interface is created. After this either a kobject uevent
+  is issued or the custom firmware loading is relied upon for firmware
+  loading up to the timeout value.

Documentation/driver-api/firmware/other_interfaces.rst

@@ -0,0 +1,15 @@
+Other Firmware Interfaces
+=========================
+
+DMI Interfaces
+--------------
+
+.. kernel-doc:: drivers/firmware/dmi_scan.c
+   :export:
+
+EDD Interfaces
+--------------
+
+.. kernel-doc:: drivers/firmware/edd.c
+   :internal:
+

Documentation/driver-api/firmware/request_firmware.rst

@@ -0,0 +1,75 @@
+====================
+request_firmware API
+====================
+
+You would typically load firmware and then load it into your device somehow.
+The typical firmware work flow is reflected below::
+
+	 if(request_firmware(&fw_entry, $FIRMWARE, device) == 0)
+                copy_fw_to_device(fw_entry->data, fw_entry->size);
+	 release_firmware(fw_entry);
+
+Synchronous firmware requests
+=============================
+
+Synchronous firmware requests will wait until the firmware is found or until
+an error is returned.
+
+request_firmware
+----------------
+.. kernel-doc:: drivers/base/firmware_loader/main.c
+   :functions: request_firmware
+
+firmware_request_nowarn
+-----------------------
+.. kernel-doc:: drivers/base/firmware_loader/main.c
+   :functions: firmware_request_nowarn
+
+request_firmware_direct
+-----------------------
+.. kernel-doc:: drivers/base/firmware_loader/main.c
+   :functions: request_firmware_direct
+
+request_firmware_into_buf
+-------------------------
+.. kernel-doc:: drivers/base/firmware_loader/main.c
+   :functions: request_firmware_into_buf
+
+Asynchronous firmware requests
+==============================
+
+Asynchronous firmware requests allow driver code to not have to wait
+until the firmware or an error is returned. Function callbacks are
+provided so that when the firmware or an error is found the driver is
+informed through the callback. request_firmware_nowait() cannot be called
+in atomic contexts.
+
+request_firmware_nowait
+-----------------------
+.. kernel-doc:: drivers/base/firmware_loader/main.c
+   :functions: request_firmware_nowait
+
+Special optimizations on reboot
+===============================
+
+Some devices have an optimization in place to enable the firmware to be
+retained during system reboot. When such optimizations are used the driver
+author must ensure the firmware is still available on resume from suspend,
+this can be done with firmware_request_cache() instead of requesting for the
+firmware to be loaded.
+
+firmware_request_cache()
+------------------------
+.. kernel-doc:: drivers/base/firmware_loader/main.c
+   :functions: firmware_request_cache
+
+request firmware API expected driver use
+========================================
+
+Once an API call returns you process the firmware and then release the
+firmware. For example if you used request_firmware() and it returns,
+the driver has the firmware image accessible in fw_entry->{data,size}.
+If something went wrong request_firmware() returns non-zero and fw_entry
+is set to NULL. Once your driver is done with processing the firmware it
+can call call release_firmware(fw_entry) to release the firmware image
+and any related resource.

Documentation/driver-api/fpga/fpga-bridge.rst

@@ -0,0 +1,49 @@
+FPGA Bridge
+===========
+
+API to implement a new FPGA bridge
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: include/linux/fpga/fpga-bridge.h
+   :functions: fpga_bridge
+
+.. kernel-doc:: include/linux/fpga/fpga-bridge.h
+   :functions: fpga_bridge_ops
+
+.. kernel-doc:: drivers/fpga/fpga-bridge.c
+   :functions: fpga_bridge_create
+
+.. kernel-doc:: drivers/fpga/fpga-bridge.c
+   :functions: fpga_bridge_free
+
+.. kernel-doc:: drivers/fpga/fpga-bridge.c
+   :functions: fpga_bridge_register
+
+.. kernel-doc:: drivers/fpga/fpga-bridge.c
+   :functions: fpga_bridge_unregister
+
+API to control an FPGA bridge
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+You probably won't need these directly.  FPGA regions should handle this.
+
+.. kernel-doc:: drivers/fpga/fpga-bridge.c
+   :functions: of_fpga_bridge_get
+
+.. kernel-doc:: drivers/fpga/fpga-bridge.c
+   :functions: fpga_bridge_get
+
+.. kernel-doc:: drivers/fpga/fpga-bridge.c
+   :functions: fpga_bridge_put
+
+.. kernel-doc:: drivers/fpga/fpga-bridge.c
+   :functions: fpga_bridge_get_to_list
+
+.. kernel-doc:: drivers/fpga/fpga-bridge.c
+   :functions: of_fpga_bridge_get_to_list
+
+.. kernel-doc:: drivers/fpga/fpga-bridge.c
+   :functions: fpga_bridge_enable
+
+.. kernel-doc:: drivers/fpga/fpga-bridge.c
+   :functions: fpga_bridge_disable

Documentation/driver-api/fpga/fpga-mgr.rst

@@ -0,0 +1,225 @@
+FPGA Manager
+============
+
+Overview
+--------
+
+The FPGA manager core exports a set of functions for programming an FPGA with
+an image.  The API is manufacturer agnostic.  All manufacturer specifics are
+hidden away in a low level driver which registers a set of ops with the core.
+The FPGA image data itself is very manufacturer specific, but for our purposes
+it's just binary data.  The FPGA manager core won't parse it.
+
+The FPGA image to be programmed can be in a scatter gather list, a single
+contiguous buffer, or a firmware file.  Because allocating contiguous kernel
+memory for the buffer should be avoided, users are encouraged to use a scatter
+gather list instead if possible.
+
+The particulars for programming the image are presented in a structure (struct
+fpga_image_info).  This struct contains parameters such as pointers to the
+FPGA image as well as image-specific particulars such as whether the image was
+built for full or partial reconfiguration.
+
+How to support a new FPGA device
+--------------------------------
+
+To add another FPGA manager, write a driver that implements a set of ops.  The
+probe function calls fpga_mgr_register(), such as::
+
+	static const struct fpga_manager_ops socfpga_fpga_ops = {
+		.write_init = socfpga_fpga_ops_configure_init,
+		.write = socfpga_fpga_ops_configure_write,
+		.write_complete = socfpga_fpga_ops_configure_complete,
+		.state = socfpga_fpga_ops_state,
+	};
+
+	static int socfpga_fpga_probe(struct platform_device *pdev)
+	{
+		struct device *dev = &pdev->dev;
+		struct socfpga_fpga_priv *priv;
+		struct fpga_manager *mgr;
+		int ret;
+
+		priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+		if (!priv)
+			return -ENOMEM;
+
+		/*
+		 * do ioremaps, get interrupts, etc. and save
+		 * them in priv
+		 */
+
+		mgr = fpga_mgr_create(dev, "Altera SOCFPGA FPGA Manager",
+				      &socfpga_fpga_ops, priv);
+		if (!mgr)
+			return -ENOMEM;
+
+		platform_set_drvdata(pdev, mgr);
+
+		ret = fpga_mgr_register(mgr);
+		if (ret)
+			fpga_mgr_free(mgr);
+
+		return ret;
+	}
+
+	static int socfpga_fpga_remove(struct platform_device *pdev)
+	{
+		struct fpga_manager *mgr = platform_get_drvdata(pdev);
+
+		fpga_mgr_unregister(mgr);
+
+		return 0;
+	}
+
+
+The ops will implement whatever device specific register writes are needed to
+do the programming sequence for this particular FPGA.  These ops return 0 for
+success or negative error codes otherwise.
+
+The programming sequence is::
+ 1. .write_init
+ 2. .write or .write_sg (may be called once or multiple times)
+ 3. .write_complete
+
+The .write_init function will prepare the FPGA to receive the image data.  The
+buffer passed into .write_init will be at most .initial_header_size bytes long;
+if the whole bitstream is not immediately available then the core code will
+buffer up at least this much before starting.
+
+The .write function writes a buffer to the FPGA. The buffer may be contain the
+whole FPGA image or may be a smaller chunk of an FPGA image.  In the latter
+case, this function is called multiple times for successive chunks. This interface
+is suitable for drivers which use PIO.
+
+The .write_sg version behaves the same as .write except the input is a sg_table
+scatter list. This interface is suitable for drivers which use DMA.
+
+The .write_complete function is called after all the image has been written
+to put the FPGA into operating mode.
+
+The ops include a .state function which will determine the state the FPGA is in
+and return a code of type enum fpga_mgr_states.  It doesn't result in a change
+in state.
+
+How to write an image buffer to a supported FPGA
+------------------------------------------------
+
+Some sample code::
+
+	#include <linux/fpga/fpga-mgr.h>
+
+	struct fpga_manager *mgr;
+	struct fpga_image_info *info;
+	int ret;
+
+	/*
+	 * Get a reference to FPGA manager.  The manager is not locked, so you can
+	 * hold onto this reference without it preventing programming.
+	 *
+	 * This example uses the device node of the manager.  Alternatively, use
+	 * fpga_mgr_get(dev) instead if you have the device.
+	 */
+	mgr = of_fpga_mgr_get(mgr_node);
+
+	/* struct with information about the FPGA image to program. */
+	info = fpga_image_info_alloc(dev);
+
+	/* flags indicates whether to do full or partial reconfiguration */
+	info->flags = FPGA_MGR_PARTIAL_RECONFIG;
+
+	/*
+	 * At this point, indicate where the image is. This is pseudo-code; you're
+	 * going to use one of these three.
+	 */
+	if (image is in a scatter gather table) {
+
+		info->sgt = [your scatter gather table]
+
+	} else if (image is in a buffer) {
+
+		info->buf = [your image buffer]
+		info->count = [image buffer size]
+
+	} else if (image is in a firmware file) {
+
+		info->firmware_name = devm_kstrdup(dev, firmware_name, GFP_KERNEL);
+
+	}
+
+	/* Get exclusive control of FPGA manager */
+	ret = fpga_mgr_lock(mgr);
+
+	/* Load the buffer to the FPGA */
+	ret = fpga_mgr_buf_load(mgr, &info, buf, count);
+
+	/* Release the FPGA manager */
+	fpga_mgr_unlock(mgr);
+	fpga_mgr_put(mgr);
+
+	/* Deallocate the image info if you're done with it */
+	fpga_image_info_free(info);
+
+API for implementing a new FPGA Manager driver
+----------------------------------------------
+
+.. kernel-doc:: include/linux/fpga/fpga-mgr.h
+   :functions: fpga_manager
+
+.. kernel-doc:: include/linux/fpga/fpga-mgr.h
+   :functions: fpga_manager_ops
+
+.. kernel-doc:: drivers/fpga/fpga-mgr.c
+   :functions: fpga_mgr_create
+
+.. kernel-doc:: drivers/fpga/fpga-mgr.c
+   :functions: fpga_mgr_free
+
+.. kernel-doc:: drivers/fpga/fpga-mgr.c
+   :functions: fpga_mgr_register
+
+.. kernel-doc:: drivers/fpga/fpga-mgr.c
+   :functions: fpga_mgr_unregister
+
+API for programming an FPGA
+---------------------------
+
+FPGA Manager flags
+
+.. kernel-doc:: include/linux/fpga/fpga-mgr.h
+   :doc: FPGA Manager flags
+
+.. kernel-doc:: include/linux/fpga/fpga-mgr.h
+   :functions: fpga_image_info
+
+.. kernel-doc:: include/linux/fpga/fpga-mgr.h
+   :functions: fpga_mgr_states
+
+.. kernel-doc:: drivers/fpga/fpga-mgr.c
+   :functions: fpga_image_info_alloc
+
+.. kernel-doc:: drivers/fpga/fpga-mgr.c
+   :functions: fpga_image_info_free
+
+.. kernel-doc:: drivers/fpga/fpga-mgr.c
+   :functions: of_fpga_mgr_get
+
+.. kernel-doc:: drivers/fpga/fpga-mgr.c
+   :functions: fpga_mgr_get
+
+.. kernel-doc:: drivers/fpga/fpga-mgr.c
+   :functions: fpga_mgr_put
+
+.. kernel-doc:: drivers/fpga/fpga-mgr.c
+   :functions: fpga_mgr_lock
+
+.. kernel-doc:: drivers/fpga/fpga-mgr.c
+   :functions: fpga_mgr_unlock
+
+.. kernel-doc:: include/linux/fpga/fpga-mgr.h
+   :functions: fpga_mgr_states
+
+Note - use :c:func:`fpga_region_program_fpga()` instead of :c:func:`fpga_mgr_load()`
+
+.. kernel-doc:: drivers/fpga/fpga-mgr.c
+   :functions: fpga_mgr_load

Documentation/driver-api/fpga/fpga-region.rst

@@ -0,0 +1,102 @@
+FPGA Region
+===========
+
+Overview
+--------
+
+This document is meant to be a brief overview of the FPGA region API usage.  A
+more conceptual look at regions can be found in the Device Tree binding
+document [#f1]_.
+
+For the purposes of this API document, let's just say that a region associates
+an FPGA Manager and a bridge (or bridges) with a reprogrammable region of an
+FPGA or the whole FPGA.  The API provides a way to register a region and to
+program a region.
+
+Currently the only layer above fpga-region.c in the kernel is the Device Tree
+support (of-fpga-region.c) described in [#f1]_.  The DT support layer uses regions
+to program the FPGA and then DT to handle enumeration.  The common region code
+is intended to be used by other schemes that have other ways of accomplishing
+enumeration after programming.
+
+An fpga-region can be set up to know the following things:
+
+ * which FPGA manager to use to do the programming
+
+ * which bridges to disable before programming and enable afterwards.
+
+Additional info needed to program the FPGA image is passed in the struct
+fpga_image_info including:
+
+ * pointers to the image as either a scatter-gather buffer, a contiguous
+   buffer, or the name of firmware file
+
+ * flags indicating specifics such as whether the image is for partial
+   reconfiguration.
+
+How to program an FPGA using a region
+-------------------------------------
+
+First, allocate the info struct::
+
+	info = fpga_image_info_alloc(dev);
+	if (!info)
+		return -ENOMEM;
+
+Set flags as needed, i.e.::
+
+	info->flags |= FPGA_MGR_PARTIAL_RECONFIG;
+
+Point to your FPGA image, such as::
+
+	info->sgt = &sgt;
+
+Add info to region and do the programming::
+
+	region->info = info;
+	ret = fpga_region_program_fpga(region);
+
+:c:func:`fpga_region_program_fpga()` operates on info passed in the
+fpga_image_info (region->info).  This function will attempt to:
+
+ * lock the region's mutex
+ * lock the region's FPGA manager
+ * build a list of FPGA bridges if a method has been specified to do so
+ * disable the bridges
+ * program the FPGA
+ * re-enable the bridges
+ * release the locks
+
+Then you will want to enumerate whatever hardware has appeared in the FPGA.
+
+How to add a new FPGA region
+----------------------------
+
+An example of usage can be seen in the probe function of [#f2]_.
+
+.. [#f1] ../devicetree/bindings/fpga/fpga-region.txt
+.. [#f2] ../../drivers/fpga/of-fpga-region.c
+
+API to program an FPGA
+----------------------
+
+.. kernel-doc:: drivers/fpga/fpga-region.c
+   :functions: fpga_region_program_fpga
+
+API to add a new FPGA region
+----------------------------
+
+.. kernel-doc:: include/linux/fpga/fpga-region.h
+   :functions: fpga_region
+
+.. kernel-doc:: drivers/fpga/fpga-region.c
+   :functions: fpga_region_create
+
+.. kernel-doc:: drivers/fpga/fpga-region.c
+   :functions: fpga_region_free
+
+.. kernel-doc:: drivers/fpga/fpga-region.c
+   :functions: fpga_region_register
+
+.. kernel-doc:: drivers/fpga/fpga-region.c
+   :functions: fpga_region_unregister

Documentation/driver-api/fpga/index.rst

@@ -0,0 +1,13 @@
+==============
+FPGA Subsystem
+==============
+
+:Author: Alan Tull
+
+.. toctree::
+   :maxdepth: 2
+
+   intro
+   fpga-mgr
+   fpga-bridge
+   fpga-region

Documentation/driver-api/fpga/intro.rst

@@ -0,0 +1,54 @@
+Introduction
+============
+
+The FPGA subsystem supports reprogramming FPGAs dynamically under
+Linux.  Some of the core intentions of the FPGA subsystems are:
+
+* The FPGA subsystem is vendor agnostic.
+
+* The FPGA subsystem separates upper layers (userspace interfaces and
+  enumeration) from lower layers that know how to program a specific
+  FPGA.
+
+* Code should not be shared between upper and lower layers.  This
+  should go without saying.  If that seems necessary, there's probably
+  framework functionality that can be added that will benefit
+  other users.  Write the linux-fpga mailing list and maintainers and
+  seek out a solution that expands the framework for broad reuse.
+
+* Generally, when adding code, think of the future.  Plan for reuse.
+
+The framework in the kernel is divided into:
+
+FPGA Manager
+------------
+
+If you are adding a new FPGA or a new method of programming an FPGA,
+this is the subsystem for you.  Low level FPGA manager drivers contain
+the knowledge of how to program a specific device.  This subsystem
+includes the framework in fpga-mgr.c and the low level drivers that
+are registered with it.
+
+FPGA Bridge
+-----------
+
+FPGA Bridges prevent spurious signals from going out of an FPGA or a
+region of an FPGA during programming.  They are disabled before
+programming begins and re-enabled afterwards.  An FPGA bridge may be
+actual hard hardware that gates a bus to a CPU or a soft ("freeze")
+bridge in FPGA fabric that surrounds a partial reconfiguration region
+of an FPGA.  This subsystem includes fpga-bridge.c and the low level
+drivers that are registered with it.
+
+FPGA Region
+-----------
+
+If you are adding a new interface to the FPGA framework, add it on top
+of an FPGA region to allow the most reuse of your interface.
+
+The FPGA Region framework (fpga-region.c) associates managers and
+bridges as reconfigurable regions.  A region may refer to the whole
+FPGA in full reconfiguration or to a partial reconfiguration region.
+
+The Device Tree FPGA Region support (of-fpga-region.c) handles
+reprogramming FPGAs when device tree overlays are applied.

Documentation/driver-api/frame-buffer.rst

@@ -0,0 +1,62 @@
+Frame Buffer Library
+====================
+
+The frame buffer drivers depend heavily on four data structures. These
+structures are declared in include/linux/fb.h. They are fb_info,
+fb_var_screeninfo, fb_fix_screeninfo and fb_monospecs. The last
+three can be made available to and from userland.
+
+fb_info defines the current state of a particular video card. Inside
+fb_info, there exists a fb_ops structure which is a collection of
+needed functions to make fbdev and fbcon work. fb_info is only visible
+to the kernel.
+
+fb_var_screeninfo is used to describe the features of a video card
+that are user defined. With fb_var_screeninfo, things such as depth
+and the resolution may be defined.
+
+The next structure is fb_fix_screeninfo. This defines the properties
+of a card that are created when a mode is set and can't be changed
+otherwise. A good example of this is the start of the frame buffer
+memory. This "locks" the address of the frame buffer memory, so that it
+cannot be changed or moved.
+
+The last structure is fb_monospecs. In the old API, there was little
+importance for fb_monospecs. This allowed for forbidden things such as
+setting a mode of 800x600 on a fix frequency monitor. With the new API,
+fb_monospecs prevents such things, and if used correctly, can prevent a
+monitor from being cooked. fb_monospecs will not be useful until
+kernels 2.5.x.
+
+Frame Buffer Memory
+-------------------
+
+.. kernel-doc:: drivers/video/fbdev/core/fbmem.c
+   :export:
+
+Frame Buffer Colormap
+---------------------
+
+.. kernel-doc:: drivers/video/fbdev/core/fbcmap.c
+   :export:
+
+Frame Buffer Video Mode Database
+--------------------------------
+
+.. kernel-doc:: drivers/video/fbdev/core/modedb.c
+   :internal:
+
+.. kernel-doc:: drivers/video/fbdev/core/modedb.c
+   :export:
+
+Frame Buffer Macintosh Video Mode Database
+------------------------------------------
+
+.. kernel-doc:: drivers/video/fbdev/macmodes.c
+   :export:
+
+Frame Buffer Fonts
+------------------
+
+Refer to the file lib/fonts/fonts.c for more information.
+

Documentation/driver-api/gpio/board.rst

@@ -0,0 +1,195 @@
+=============
+GPIO Mappings
+=============
+
+This document explains how GPIOs can be assigned to given devices and functions.
+
+Note that it only applies to the new descriptor-based interface. For a
+description of the deprecated integer-based GPIO interface please refer to
+gpio-legacy.txt (actually, there is no real mapping possible with the old
+interface; you just fetch an integer from somewhere and request the
+corresponding GPIO).
+
+All platforms can enable the GPIO library, but if the platform strictly
+requires GPIO functionality to be present, it needs to select GPIOLIB from its
+Kconfig. Then, how GPIOs are mapped depends on what the platform uses to
+describe its hardware layout. Currently, mappings can be defined through device
+tree, ACPI, and platform data.
+
+Device Tree
+-----------
+GPIOs can easily be mapped to devices and functions in the device tree. The
+exact way to do it depends on the GPIO controller providing the GPIOs, see the
+device tree bindings for your controller.
+
+GPIOs mappings are defined in the consumer device's node, in a property named
+<function>-gpios, where <function> is the function the driver will request
+through gpiod_get(). For example::
+
+	foo_device {
+		compatible = "acme,foo";
+		...
+		led-gpios = <&gpio 15 GPIO_ACTIVE_HIGH>, /* red */
+			    <&gpio 16 GPIO_ACTIVE_HIGH>, /* green */
+			    <&gpio 17 GPIO_ACTIVE_HIGH>; /* blue */
+
+		power-gpios = <&gpio 1 GPIO_ACTIVE_LOW>;
+	};
+
+Properties named <function>-gpio are also considered valid and old bindings use
+it but are only supported for compatibility reasons and should not be used for
+newer bindings since it has been deprecated.
+
+This property will make GPIOs 15, 16 and 17 available to the driver under the
+"led" function, and GPIO 1 as the "power" GPIO::
+
+	struct gpio_desc *red, *green, *blue, *power;
+
+	red = gpiod_get_index(dev, "led", 0, GPIOD_OUT_HIGH);
+	green = gpiod_get_index(dev, "led", 1, GPIOD_OUT_HIGH);
+	blue = gpiod_get_index(dev, "led", 2, GPIOD_OUT_HIGH);
+
+	power = gpiod_get(dev, "power", GPIOD_OUT_HIGH);
+
+The led GPIOs will be active high, while the power GPIO will be active low (i.e.
+gpiod_is_active_low(power) will be true).
+
+The second parameter of the gpiod_get() functions, the con_id string, has to be
+the <function>-prefix of the GPIO suffixes ("gpios" or "gpio", automatically
+looked up by the gpiod functions internally) used in the device tree. With above
+"led-gpios" example, use the prefix without the "-" as con_id parameter: "led".
+
+Internally, the GPIO subsystem prefixes the GPIO suffix ("gpios" or "gpio")
+with the string passed in con_id to get the resulting string
+(``snprintf(... "%s-%s", con_id, gpio_suffixes[]``).
+
+ACPI
+----
+ACPI also supports function names for GPIOs in a similar fashion to DT.
+The above DT example can be converted to an equivalent ACPI description
+with the help of _DSD (Device Specific Data), introduced in ACPI 5.1::
+
+	Device (FOO) {
+		Name (_CRS, ResourceTemplate () {
+			GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
+				"\\_SB.GPI0") {15} // red
+			GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
+				"\\_SB.GPI0") {16} // green
+			GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
+				"\\_SB.GPI0") {17} // blue
+			GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
+				"\\_SB.GPI0") {1} // power
+		})
+
+		Name (_DSD, Package () {
+			ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+			Package () {
+				Package () {
+					"led-gpios",
+					Package () {
+						^FOO, 0, 0, 1,
+						^FOO, 1, 0, 1,
+						^FOO, 2, 0, 1,
+					}
+				},
+				Package () {
+					"power-gpios",
+					Package () {^FOO, 3, 0, 0},
+				},
+			}
+		})
+	}
+
+For more information about the ACPI GPIO bindings see
+Documentation/acpi/gpio-properties.txt.
+
+Platform Data
+-------------
+Finally, GPIOs can be bound to devices and functions using platform data. Board
+files that desire to do so need to include the following header::
+
+	#include <linux/gpio/machine.h>
+
+GPIOs are mapped by the means of tables of lookups, containing instances of the
+gpiod_lookup structure. Two macros are defined to help declaring such mappings::
+
+	GPIO_LOOKUP(chip_label, chip_hwnum, con_id, flags)
+	GPIO_LOOKUP_IDX(chip_label, chip_hwnum, con_id, idx, flags)
+
+where
+
+  - chip_label is the label of the gpiod_chip instance providing the GPIO
+  - chip_hwnum is the hardware number of the GPIO within the chip
+  - con_id is the name of the GPIO function from the device point of view. It
+	can be NULL, in which case it will match any function.
+  - idx is the index of the GPIO within the function.
+  - flags is defined to specify the following properties:
+	* GPIO_ACTIVE_HIGH	- GPIO line is active high
+	* GPIO_ACTIVE_LOW	- GPIO line is active low
+	* GPIO_OPEN_DRAIN	- GPIO line is set up as open drain
+	* GPIO_OPEN_SOURCE	- GPIO line is set up as open source
+	* GPIO_PERSISTENT	- GPIO line is persistent during
+				  suspend/resume and maintains its value
+	* GPIO_TRANSITORY	- GPIO line is transitory and may loose its
+				  electrical state during suspend/resume
+
+In the future, these flags might be extended to support more properties.
+
+Note that GPIO_LOOKUP() is just a shortcut to GPIO_LOOKUP_IDX() where idx = 0.
+
+A lookup table can then be defined as follows, with an empty entry defining its
+end. The 'dev_id' field of the table is the identifier of the device that will
+make use of these GPIOs. It can be NULL, in which case it will be matched for
+calls to gpiod_get() with a NULL device.
+
+.. code-block:: c
+
+        struct gpiod_lookup_table gpios_table = {
+                .dev_id = "foo.0",
+                .table = {
+                        GPIO_LOOKUP_IDX("gpio.0", 15, "led", 0, GPIO_ACTIVE_HIGH),
+                        GPIO_LOOKUP_IDX("gpio.0", 16, "led", 1, GPIO_ACTIVE_HIGH),
+                        GPIO_LOOKUP_IDX("gpio.0", 17, "led", 2, GPIO_ACTIVE_HIGH),
+                        GPIO_LOOKUP("gpio.0", 1, "power", GPIO_ACTIVE_LOW),
+                        { },
+                },
+        };
+
+And the table can be added by the board code as follows::
+
+	gpiod_add_lookup_table(&gpios_table);
+
+The driver controlling "foo.0" will then be able to obtain its GPIOs as follows::
+
+	struct gpio_desc *red, *green, *blue, *power;
+
+	red = gpiod_get_index(dev, "led", 0, GPIOD_OUT_HIGH);
+	green = gpiod_get_index(dev, "led", 1, GPIOD_OUT_HIGH);
+	blue = gpiod_get_index(dev, "led", 2, GPIOD_OUT_HIGH);
+
+	power = gpiod_get(dev, "power", GPIOD_OUT_HIGH);
+
+Since the "led" GPIOs are mapped as active-high, this example will switch their
+signals to 1, i.e. enabling the LEDs. And for the "power" GPIO, which is mapped
+as active-low, its actual signal will be 0 after this code. Contrary to the
+legacy integer GPIO interface, the active-low property is handled during
+mapping and is thus transparent to GPIO consumers.
+
+A set of functions such as gpiod_set_value() is available to work with
+the new descriptor-oriented interface.
+
+Boards using platform data can also hog GPIO lines by defining GPIO hog tables.
+
+.. code-block:: c
+
+        struct gpiod_hog gpio_hog_table[] = {
+                GPIO_HOG("gpio.0", 10, "foo", GPIO_ACTIVE_LOW, GPIOD_OUT_HIGH),
+                { }
+        };
+
+And the table can be added to the board code as follows::
+
+        gpiod_add_hogs(gpio_hog_table);
+
+The line will be hogged as soon as the gpiochip is created or - in case the
+chip was created earlier - when the hog table is registered.

Documentation/driver-api/gpio/consumer.rst

@@ -0,0 +1,439 @@
+==================================
+GPIO Descriptor Consumer Interface
+==================================
+
+This document describes the consumer interface of the GPIO framework. Note that
+it describes the new descriptor-based interface. For a description of the
+deprecated integer-based GPIO interface please refer to gpio-legacy.txt.
+
+
+Guidelines for GPIOs consumers
+==============================
+
+Drivers that can't work without standard GPIO calls should have Kconfig entries
+that depend on GPIOLIB or select GPIOLIB. The functions that allow a driver to
+obtain and use GPIOs are available by including the following file:
+
+	#include <linux/gpio/consumer.h>
+
+There are static inline stubs for all functions in the header file in the case
+where GPIOLIB is disabled. When these stubs are called they will emit
+warnings. These stubs are used for two use cases:
+
+- Simple compile coverage with e.g. COMPILE_TEST - it does not matter that
+  the current platform does not enable or select GPIOLIB because we are not
+  going to execute the system anyway.
+
+- Truly optional GPIOLIB support - where the driver does not really make use
+  of the GPIOs on certain compile-time configurations for certain systems, but
+  will use it under other compile-time configurations. In this case the
+  consumer must make sure not to call into these functions, or the user will
+  be met with console warnings that may be perceived as intimidating.
+
+All the functions that work with the descriptor-based GPIO interface are
+prefixed with ``gpiod_``. The ``gpio_`` prefix is used for the legacy
+interface. No other function in the kernel should use these prefixes. The use
+of the legacy functions is strongly discouraged, new code should use
+<linux/gpio/consumer.h> and descriptors exclusively.
+
+
+Obtaining and Disposing GPIOs
+=============================
+
+With the descriptor-based interface, GPIOs are identified with an opaque,
+non-forgeable handler that must be obtained through a call to one of the
+gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the
+device that will use the GPIO and the function the requested GPIO is supposed to
+fulfill::
+
+	struct gpio_desc *gpiod_get(struct device *dev, const char *con_id,
+				    enum gpiod_flags flags)
+
+If a function is implemented by using several GPIOs together (e.g. a simple LED
+device that displays digits), an additional index argument can be specified::
+
+	struct gpio_desc *gpiod_get_index(struct device *dev,
+					  const char *con_id, unsigned int idx,
+					  enum gpiod_flags flags)
+
+For a more detailed description of the con_id parameter in the DeviceTree case
+see Documentation/driver-api/gpio/board.rst
+
+The flags parameter is used to optionally specify a direction and initial value
+for the GPIO. Values can be:
+
+* GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set
+  later with one of the dedicated functions.
+* GPIOD_IN to initialize the GPIO as input.
+* GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0.
+* GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1.
+* GPIOD_OUT_LOW_OPEN_DRAIN same as GPIOD_OUT_LOW but also enforce the line
+  to be electrically used with open drain.
+* GPIOD_OUT_HIGH_OPEN_DRAIN same as GPIOD_OUT_HIGH but also enforce the line
+  to be electrically used with open drain.
+
+The two last flags are used for use cases where open drain is mandatory, such
+as I2C: if the line is not already configured as open drain in the mappings
+(see board.txt), then open drain will be enforced anyway and a warning will be
+printed that the board configuration needs to be updated to match the use case.
+
+Both functions return either a valid GPIO descriptor, or an error code checkable
+with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
+if and only if no GPIO has been assigned to the device/function/index triplet,
+other error codes are used for cases where a GPIO has been assigned but an error
+occurred while trying to acquire it. This is useful to discriminate between mere
+errors and an absence of GPIO for optional GPIO parameters. For the common
+pattern where a GPIO is optional, the gpiod_get_optional() and
+gpiod_get_index_optional() functions can be used. These functions return NULL
+instead of -ENOENT if no GPIO has been assigned to the requested function::
+
+	struct gpio_desc *gpiod_get_optional(struct device *dev,
+					     const char *con_id,
+					     enum gpiod_flags flags)
+
+	struct gpio_desc *gpiod_get_index_optional(struct device *dev,
+						   const char *con_id,
+						   unsigned int index,
+						   enum gpiod_flags flags)
+
+Note that gpio_get*_optional() functions (and their managed variants), unlike
+the rest of gpiolib API, also return NULL when gpiolib support is disabled.
+This is helpful to driver authors, since they do not need to special case
+-ENOSYS return codes.  System integrators should however be careful to enable
+gpiolib on systems that need it.
+
+For a function using multiple GPIOs all of those can be obtained with one call::
+
+	struct gpio_descs *gpiod_get_array(struct device *dev,
+					   const char *con_id,
+					   enum gpiod_flags flags)
+
+This function returns a struct gpio_descs which contains an array of
+descriptors::
+
+	struct gpio_descs {
+		unsigned int ndescs;
+		struct gpio_desc *desc[];
+	}
+
+The following function returns NULL instead of -ENOENT if no GPIOs have been
+assigned to the requested function::
+
+	struct gpio_descs *gpiod_get_array_optional(struct device *dev,
+						    const char *con_id,
+						    enum gpiod_flags flags)
+
+Device-managed variants of these functions are also defined::
+
+	struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id,
+					 enum gpiod_flags flags)
+
+	struct gpio_desc *devm_gpiod_get_index(struct device *dev,
+					       const char *con_id,
+					       unsigned int idx,
+					       enum gpiod_flags flags)
+
+	struct gpio_desc *devm_gpiod_get_optional(struct device *dev,
+						  const char *con_id,
+						  enum gpiod_flags flags)
+
+	struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev,
+							const char *con_id,
+							unsigned int index,
+							enum gpiod_flags flags)
+
+	struct gpio_descs *devm_gpiod_get_array(struct device *dev,
+						const char *con_id,
+						enum gpiod_flags flags)
+
+	struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev,
+							 const char *con_id,
+							 enum gpiod_flags flags)
+
+A GPIO descriptor can be disposed of using the gpiod_put() function::
+
+	void gpiod_put(struct gpio_desc *desc)
+
+For an array of GPIOs this function can be used::
+
+	void gpiod_put_array(struct gpio_descs *descs)
+
+It is strictly forbidden to use a descriptor after calling these functions.
+It is also not allowed to individually release descriptors (using gpiod_put())
+from an array acquired with gpiod_get_array().
+
+The device-managed variants are, unsurprisingly::
+
+	void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
+
+	void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs)
+
+
+Using GPIOs
+===========
+
+Setting Direction
+-----------------
+The first thing a driver must do with a GPIO is setting its direction. If no
+direction-setting flags have been given to gpiod_get*(), this is done by
+invoking one of the gpiod_direction_*() functions::
+
+	int gpiod_direction_input(struct gpio_desc *desc)
+	int gpiod_direction_output(struct gpio_desc *desc, int value)
+
+The return value is zero for success, else a negative errno. It should be
+checked, since the get/set calls don't return errors and since misconfiguration
+is possible. You should normally issue these calls from a task context. However,
+for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
+of early board setup.
+
+For output GPIOs, the value provided becomes the initial output value. This
+helps avoid signal glitching during system startup.
+
+A driver can also query the current direction of a GPIO::
+
+	int gpiod_get_direction(const struct gpio_desc *desc)
+
+This function returns 0 for output, 1 for input, or an error code in case of error.
+
+Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
+without setting its direction first is illegal and will result in undefined
+behavior!**
+
+
+Spinlock-Safe GPIO Access
+-------------------------
+Most GPIO controllers can be accessed with memory read/write instructions. Those
+don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
+handlers and similar contexts.
+
+Use the following calls to access GPIOs from an atomic context::
+
+	int gpiod_get_value(const struct gpio_desc *desc);
+	void gpiod_set_value(struct gpio_desc *desc, int value);
+
+The values are boolean, zero for low, nonzero for high. When reading the value
+of an output pin, the value returned should be what's seen on the pin. That
+won't always match the specified output value, because of issues including
+open-drain signaling and output latencies.
+
+The get/set calls do not return errors because "invalid GPIO" should have been
+reported earlier from gpiod_direction_*(). However, note that not all platforms
+can read the value of output pins; those that can't should always return zero.
+Also, using these calls for GPIOs that can't safely be accessed without sleeping
+(see below) is an error.
+
+
+GPIO Access That May Sleep
+--------------------------
+Some GPIO controllers must be accessed using message based buses like I2C or
+SPI. Commands to read or write those GPIO values require waiting to get to the
+head of a queue to transmit a command and get its response. This requires
+sleeping, which can't be done from inside IRQ handlers.
+
+Platforms that support this type of GPIO distinguish them from other GPIOs by
+returning nonzero from this call::
+
+	int gpiod_cansleep(const struct gpio_desc *desc)
+
+To access such GPIOs, a different set of accessors is defined::
+
+	int gpiod_get_value_cansleep(const struct gpio_desc *desc)
+	void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
+
+Accessing such GPIOs requires a context which may sleep, for example a threaded
+IRQ handler, and those accessors must be used instead of spinlock-safe
+accessors without the cansleep() name suffix.
+
+Other than the fact that these accessors might sleep, and will work on GPIOs
+that can't be accessed from hardIRQ handlers, these calls act the same as the
+spinlock-safe calls.
+
+
+The active low and open drain semantics
+---------------------------------------
+As a consumer should not have to care about the physical line level, all of the
+gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
+the *logical* value. With this they take the active low property into account.
+This means that they check whether the GPIO is configured to be active low,
+and if so, they manipulate the passed value before the physical line level is
+driven.
+
+The same is applicable for open drain or open source output lines: those do not
+actively drive their output high (open drain) or low (open source), they just
+switch their output to a high impedance value. The consumer should not need to
+care. (For details read about open drain in driver.txt.)
+
+With this, all the gpiod_set_(array)_value_xxx() functions interpret the
+parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line
+level will be driven accordingly.
+
+As an example, if the active low property for a dedicated GPIO is set, and the
+gpiod_set_(array)_value_xxx() passes "asserted" ("1"), the physical line level
+will be driven low.
+
+To summarize::
+
+  Function (example)                 line property          physical line
+  gpiod_set_raw_value(desc, 0);      don't care             low
+  gpiod_set_raw_value(desc, 1);      don't care             high
+  gpiod_set_value(desc, 0);          default (active high)  low
+  gpiod_set_value(desc, 1);          default (active high)  high
+  gpiod_set_value(desc, 0);          active low             high
+  gpiod_set_value(desc, 1);          active low             low
+  gpiod_set_value(desc, 0);          default (active high)  low
+  gpiod_set_value(desc, 1);          default (active high)  high
+  gpiod_set_value(desc, 0);          open drain             low
+  gpiod_set_value(desc, 1);          open drain             high impedance
+  gpiod_set_value(desc, 0);          open source            high impedance
+  gpiod_set_value(desc, 1);          open source            high
+
+It is possible to override these semantics using the set_raw/get_raw functions
+but it should be avoided as much as possible, especially by system-agnostic drivers
+which should not need to care about the actual physical line level and worry about
+the logical value instead.
+
+
+Accessing raw GPIO values
+-------------------------
+Consumers exist that need to manage the logical state of a GPIO line, i.e. the value
+their device will actually receive, no matter what lies between it and the GPIO
+line.
+
+The following set of calls ignore the active-low or open drain property of a GPIO and
+work on the raw line value::
+
+	int gpiod_get_raw_value(const struct gpio_desc *desc)
+	void gpiod_set_raw_value(struct gpio_desc *desc, int value)
+	int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc)
+	void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value)
+	int gpiod_direction_output_raw(struct gpio_desc *desc, int value)
+
+The active low state of a GPIO can also be queried using the following call::
+
+	int gpiod_is_active_low(const struct gpio_desc *desc)
+
+Note that these functions should only be used with great moderation; a driver
+should not have to care about the physical line level or open drain semantics.
+
+
+Access multiple GPIOs with a single function call
+-------------------------------------------------
+The following functions get or set the values of an array of GPIOs::
+
+	int gpiod_get_array_value(unsigned int array_size,
+				  struct gpio_desc **desc_array,
+				  int *value_array);
+	int gpiod_get_raw_array_value(unsigned int array_size,
+				      struct gpio_desc **desc_array,
+				      int *value_array);
+	int gpiod_get_array_value_cansleep(unsigned int array_size,
+					   struct gpio_desc **desc_array,
+					   int *value_array);
+	int gpiod_get_raw_array_value_cansleep(unsigned int array_size,
+					   struct gpio_desc **desc_array,
+					   int *value_array);
+
+	void gpiod_set_array_value(unsigned int array_size,
+				   struct gpio_desc **desc_array,
+				   int *value_array)
+	void gpiod_set_raw_array_value(unsigned int array_size,
+				       struct gpio_desc **desc_array,
+				       int *value_array)
+	void gpiod_set_array_value_cansleep(unsigned int array_size,
+					    struct gpio_desc **desc_array,
+					    int *value_array)
+	void gpiod_set_raw_array_value_cansleep(unsigned int array_size,
+						struct gpio_desc **desc_array,
+						int *value_array)
+
+The array can be an arbitrary set of GPIOs. The functions will try to access
+GPIOs belonging to the same bank or chip simultaneously if supported by the
+corresponding chip driver. In that case a significantly improved performance
+can be expected. If simultaneous access is not possible the GPIOs will be
+accessed sequentially.
+
+The functions take three arguments:
+	* array_size	- the number of array elements
+	* desc_array	- an array of GPIO descriptors
+	* value_array	- an array to store the GPIOs' values (get) or
+			  an array of values to assign to the GPIOs (set)
+
+The descriptor array can be obtained using the gpiod_get_array() function
+or one of its variants. If the group of descriptors returned by that function
+matches the desired group of GPIOs, those GPIOs can be accessed by simply using
+the struct gpio_descs returned by gpiod_get_array()::
+
+	struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
+	gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
+			      my_gpio_values);
+
+It is also possible to access a completely arbitrary array of descriptors. The
+descriptors may be obtained using any combination of gpiod_get() and
+gpiod_get_array(). Afterwards the array of descriptors has to be setup
+manually before it can be passed to one of the above functions.
+
+Note that for optimal performance GPIOs belonging to the same chip should be
+contiguous within the array of descriptors.
+
+The return value of gpiod_get_array_value() and its variants is 0 on success
+or negative on error. Note the difference to gpiod_get_value(), which returns
+0 or 1 on success to convey the GPIO value. With the array functions, the GPIO
+values are stored in value_array rather than passed back as return value.
+
+
+GPIOs mapped to IRQs
+--------------------
+GPIO lines can quite often be used as IRQs. You can get the IRQ number
+corresponding to a given GPIO using the following call::
+
+	int gpiod_to_irq(const struct gpio_desc *desc)
+
+It will return an IRQ number, or a negative errno code if the mapping can't be
+done (most likely because that particular GPIO cannot be used as IRQ). It is an
+unchecked error to use a GPIO that wasn't set up as an input using
+gpiod_direction_input(), or to use an IRQ number that didn't originally come
+from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep.
+
+Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
+free_irq(). They will often be stored into IRQ resources for platform devices,
+by the board-specific initialization code. Note that IRQ trigger options are
+part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
+capabilities.
+
+
+GPIOs and ACPI
+==============
+
+On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
+the _CRS configuration objects of devices.  Those resources do not provide
+connection IDs (names) for GPIOs, so it is necessary to use an additional
+mechanism for this purpose.
+
+Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
+which, among other things, may be used to provide connection IDs for specific
+GPIOs described by the GpioIo()/GpioInt() resources in _CRS.  If that is the
+case, it will be handled by the GPIO subsystem automatically.  However, if the
+_DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
+connection IDs need to be provided by device drivers.
+
+For details refer to Documentation/acpi/gpio-properties.txt
+
+
+Interacting With the Legacy GPIO Subsystem
+==========================================
+Many kernel subsystems still handle GPIOs using the legacy integer-based
+interface. Although it is strongly encouraged to upgrade them to the safer
+descriptor-based API, the following two functions allow you to convert a GPIO
+descriptor into the GPIO integer namespace and vice-versa::
+
+	int desc_to_gpio(const struct gpio_desc *desc)
+	struct gpio_desc *gpio_to_desc(unsigned gpio)
+
+The GPIO number returned by desc_to_gpio() can be safely used as long as the
+GPIO descriptor has not been freed. All the same, a GPIO number passed to
+gpio_to_desc() must have been properly acquired, and usage of the returned GPIO
+descriptor is only possible after the GPIO number has been released.
+
+Freeing a GPIO obtained by one API with the other API is forbidden and an
+unchecked error.

Documentation/driver-api/gpio/driver.rst

@@ -0,0 +1,429 @@
+================================
+GPIO Descriptor Driver Interface
+================================
+
+This document serves as a guide for GPIO chip drivers writers. Note that it
+describes the new descriptor-based interface. For a description of the
+deprecated integer-based GPIO interface please refer to gpio-legacy.txt.
+
+Each GPIO controller driver needs to include the following header, which defines
+the structures used to define a GPIO driver:
+
+	#include <linux/gpio/driver.h>
+
+
+Internal Representation of GPIOs
+================================
+
+Inside a GPIO driver, individual GPIOs are identified by their hardware number,
+which is a unique number between 0 and n, n being the number of GPIOs managed by
+the chip. This number is purely internal: the hardware number of a particular
+GPIO descriptor is never made visible outside of the driver.
+
+On top of this internal number, each GPIO also need to have a global number in
+the integer GPIO namespace so that it can be used with the legacy GPIO
+interface. Each chip must thus have a "base" number (which can be automatically
+assigned), and for each GPIO the global number will be (base + hardware number).
+Although the integer representation is considered deprecated, it still has many
+users and thus needs to be maintained.
+
+So for example one platform could use numbers 32-159 for GPIOs, with a
+controller defining 128 GPIOs at a "base" of 32 ; while another platform uses
+numbers 0..63 with one set of GPIO controllers, 64-79 with another type of GPIO
+controller, and on one particular board 80-95 with an FPGA. The numbers need not
+be contiguous; either of those platforms could also use numbers 2000-2063 to
+identify GPIOs in a bank of I2C GPIO expanders.
+
+
+Controller Drivers: gpio_chip
+=============================
+
+In the gpiolib framework each GPIO controller is packaged as a "struct
+gpio_chip" (see linux/gpio/driver.h for its complete definition) with members
+common to each controller of that type:
+
+ - methods to establish GPIO line direction
+ - methods used to access GPIO line values
+ - method to set electrical configuration for a given GPIO line
+ - method to return the IRQ number associated to a given GPIO line
+ - flag saying whether calls to its methods may sleep
+ - optional line names array to identify lines
+ - optional debugfs dump method (showing extra state like pullup config)
+ - optional base number (will be automatically assigned if omitted)
+ - optional label for diagnostics and GPIO chip mapping using platform data
+
+The code implementing a gpio_chip should support multiple instances of the
+controller, possibly using the driver model. That code will configure each
+gpio_chip and issue ``gpiochip_add[_data]()`` or ``devm_gpiochip_add_data()``.
+Removing a GPIO controller should be rare; use ``[devm_]gpiochip_remove()``
+when it is unavoidable.
+
+Often a gpio_chip is part of an instance-specific structure with states not
+exposed by the GPIO interfaces, such as addressing, power management, and more.
+Chips such as audio codecs will have complex non-GPIO states.
+
+Any debugfs dump method should normally ignore signals which haven't been
+requested as GPIOs. They can use gpiochip_is_requested(), which returns either
+NULL or the label associated with that GPIO when it was requested.
+
+RT_FULL: the GPIO driver should not use spinlock_t or any sleepable APIs
+(like PM runtime) in its gpio_chip implementation (.get/.set and direction
+control callbacks) if it is expected to call GPIO APIs from atomic context
+on -RT (inside hard IRQ handlers and similar contexts). Normally this should
+not be required.
+
+
+GPIO electrical configuration
+-----------------------------
+
+GPIOs can be configured for several electrical modes of operation by using the
+.set_config() callback. Currently this API supports setting debouncing and
+single-ended modes (open drain/open source). These settings are described
+below.
+
+The .set_config() callback uses the same enumerators and configuration
+semantics as the generic pin control drivers. This is not a coincidence: it is
+possible to assign the .set_config() to the function gpiochip_generic_config()
+which will result in pinctrl_gpio_set_config() being called and eventually
+ending up in the pin control back-end "behind" the GPIO controller, usually
+closer to the actual pins. This way the pin controller can manage the below
+listed GPIO configurations.
+
+If a pin controller back-end is used, the GPIO controller or hardware
+description needs to provide "GPIO ranges" mapping the GPIO line offsets to pin
+numbers on the pin controller so they can properly cross-reference each other.
+
+
+GPIOs with debounce support
+---------------------------
+
+Debouncing is a configuration set to a pin indicating that it is connected to
+a mechanical switch or button, or similar that may bounce. Bouncing means the
+line is pulled high/low quickly at very short intervals for mechanical
+reasons. This can result in the value being unstable or irqs fireing repeatedly
+unless the line is debounced.
+
+Debouncing in practice involves setting up a timer when something happens on
+the line, wait a little while and then sample the line again, so see if it
+still has the same value (low or high). This could also be repeated by a clever
+state machine, waiting for a line to become stable. In either case, it sets
+a certain number of milliseconds for debouncing, or just "on/off" if that time
+is not configurable.
+
+
+GPIOs with open drain/source support
+------------------------------------
+
+Open drain (CMOS) or open collector (TTL) means the line is not actively driven
+high: instead you provide the drain/collector as output, so when the transistor
+is not open, it will present a high-impedance (tristate) to the external rail::
+
+
+   CMOS CONFIGURATION      TTL CONFIGURATION
+
+            ||--- out              +--- out
+     in ----||                   |/
+            ||--+         in ----|
+                |                |\
+               GND	           GND
+
+This configuration is normally used as a way to achieve one of two things:
+
+- Level-shifting: to reach a logical level higher than that of the silicon
+  where the output resides.
+
+- inverse wire-OR on an I/O line, for example a GPIO line, making it possible
+  for any driving stage on the line to drive it low even if any other output
+  to the same line is simultaneously driving it high. A special case of this
+  is driving the SCL and SCA lines of an I2C bus, which is by definition a
+  wire-OR bus.
+
+Both usecases require that the line be equipped with a pull-up resistor. This
+resistor will make the line tend to high level unless one of the transistors on
+the rail actively pulls it down.
+
+The level on the line will go as high as the VDD on the pull-up resistor, which
+may be higher than the level supported by the transistor, achieving a
+level-shift to the higher VDD.
+
+Integrated electronics often have an output driver stage in the form of a CMOS
+"totem-pole" with one N-MOS and one P-MOS transistor where one of them drives
+the line high and one of them drives the line low. This is called a push-pull
+output. The "totem-pole" looks like so::
+
+                     VDD
+                      |
+            OD    ||--+
+         +--/ ---o||     P-MOS-FET
+         |        ||--+
+    IN --+            +----- out
+         |        ||--+
+         +--/ ----||     N-MOS-FET
+            OS    ||--+
+                      |
+                     GND
+
+The desired output signal (e.g. coming directly from some GPIO output register)
+arrives at IN. The switches named "OD" and "OS" are normally closed, creating
+a push-pull circuit.
+
+Consider the little "switches" named "OD" and "OS" that enable/disable the
+P-MOS or N-MOS transistor right after the split of the input. As you can see,
+either transistor will go totally numb if this switch is open. The totem-pole
+is then halved and give high impedance instead of actively driving the line
+high or low respectively. That is usually how software-controlled open
+drain/source works.
+
+Some GPIO hardware come in open drain / open source configuration. Some are
+hard-wired lines that will only support open drain or open source no matter
+what: there is only one transistor there. Some are software-configurable:
+by flipping a bit in a register the output can be configured as open drain
+or open source, in practice by flicking open the switches labeled "OD" and "OS"
+in the drawing above.
+
+By disabling the P-MOS transistor, the output can be driven between GND and
+high impedance (open drain), and by disabling the N-MOS transistor, the output
+can be driven between VDD and high impedance (open source). In the first case,
+a pull-up resistor is needed on the outgoing rail to complete the circuit, and
+in the second case, a pull-down resistor is needed on the rail.
+
+Hardware that supports open drain or open source or both, can implement a
+special callback in the gpio_chip: .set_config() that takes a generic
+pinconf packed value telling whether to configure the line as open drain,
+open source or push-pull. This will happen in response to the
+GPIO_OPEN_DRAIN or GPIO_OPEN_SOURCE flag set in the machine file, or coming
+from other hardware descriptions.
+
+If this state can not be configured in hardware, i.e. if the GPIO hardware does
+not support open drain/open source in hardware, the GPIO library will instead
+use a trick: when a line is set as output, if the line is flagged as open
+drain, and the IN output value is low, it will be driven low as usual. But
+if the IN output value is set to high, it will instead *NOT* be driven high,
+instead it will be switched to input, as input mode is high impedance, thus
+achieveing an "open drain emulation" of sorts: electrically the behaviour will
+be identical, with the exception of possible hardware glitches when switching
+the mode of the line.
+
+For open source configuration the same principle is used, just that instead
+of actively driving the line low, it is set to input.
+
+
+GPIO drivers providing IRQs
+---------------------------
+It is custom that GPIO drivers (GPIO chips) are also providing interrupts,
+most often cascaded off a parent interrupt controller, and in some special
+cases the GPIO logic is melded with a SoC's primary interrupt controller.
+
+The IRQ portions of the GPIO block are implemented using an irqchip, using
+the header <linux/irq.h>. So basically such a driver is utilizing two sub-
+systems simultaneously: gpio and irq.
+
+RT_FULL: a realtime compliant GPIO driver should not use spinlock_t or any
+sleepable APIs (like PM runtime) as part of its irq_chip implementation.
+
+* spinlock_t should be replaced with raw_spinlock_t [1].
+* If sleepable APIs have to be used, these can be done from the .irq_bus_lock()
+  and .irq_bus_unlock() callbacks, as these are the only slowpath callbacks
+  on an irqchip. Create the callbacks if needed [2].
+
+GPIO irqchips usually fall in one of two categories:
+
+* CHAINED GPIO irqchips: these are usually the type that is embedded on
+  an SoC. This means that there is a fast IRQ flow handler for the GPIOs that
+  gets called in a chain from the parent IRQ handler, most typically the
+  system interrupt controller. This means that the GPIO irqchip handler will
+  be called immediately from the parent irqchip, while holding the IRQs
+  disabled. The GPIO irqchip will then end up calling something like this
+  sequence in its interrupt handler::
+
+    static irqreturn_t foo_gpio_irq(int irq, void *data)
+        chained_irq_enter(...);
+        generic_handle_irq(...);
+        chained_irq_exit(...);
+
+  Chained GPIO irqchips typically can NOT set the .can_sleep flag on
+  struct gpio_chip, as everything happens directly in the callbacks: no
+  slow bus traffic like I2C can be used.
+
+  RT_FULL: Note, chained IRQ handlers will not be forced threaded on -RT.
+  As result, spinlock_t or any sleepable APIs (like PM runtime) can't be used
+  in chained IRQ handler.
+  If required (and if it can't be converted to the nested threaded GPIO irqchip)
+  a chained IRQ handler can be converted to generic irq handler and this way
+  it will be a threaded IRQ handler on -RT and a hard IRQ handler on non-RT
+  (for example, see [3]).
+  Know W/A: The generic_handle_irq() is expected to be called with IRQ disabled,
+  so the IRQ core will complain if it is called from an IRQ handler which is
+  forced to a thread. The "fake?" raw lock can be used to W/A this problem::
+
+	raw_spinlock_t wa_lock;
+	static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank)
+		unsigned long wa_lock_flags;
+		raw_spin_lock_irqsave(&bank->wa_lock, wa_lock_flags);
+		generic_handle_irq(irq_find_mapping(bank->chip.irq.domain, bit));
+		raw_spin_unlock_irqrestore(&bank->wa_lock, wa_lock_flags);
+
+* GENERIC CHAINED GPIO irqchips: these are the same as "CHAINED GPIO irqchips",
+  but chained IRQ handlers are not used. Instead GPIO IRQs dispatching is
+  performed by generic IRQ handler which is configured using request_irq().
+  The GPIO irqchip will then end up calling something like this sequence in
+  its interrupt handler::
+
+    static irqreturn_t gpio_rcar_irq_handler(int irq, void *dev_id)
+        for each detected GPIO IRQ
+            generic_handle_irq(...);
+
+  RT_FULL: Such kind of handlers will be forced threaded on -RT, as result IRQ
+  core will complain that generic_handle_irq() is called with IRQ enabled and
+  the same W/A as for "CHAINED GPIO irqchips" can be applied.
+
+* NESTED THREADED GPIO irqchips: these are off-chip GPIO expanders and any
+  other GPIO irqchip residing on the other side of a sleeping bus. Of course
+  such drivers that need slow bus traffic to read out IRQ status and similar,
+  traffic which may in turn incur other IRQs to happen, cannot be handled
+  in a quick IRQ handler with IRQs disabled. Instead they need to spawn a
+  thread and then mask the parent IRQ line until the interrupt is handled
+  by the driver. The hallmark of this driver is to call something like
+  this in its interrupt handler::
+
+    static irqreturn_t foo_gpio_irq(int irq, void *data)
+        ...
+        handle_nested_irq(irq);
+
+  The hallmark of threaded GPIO irqchips is that they set the .can_sleep
+  flag on struct gpio_chip to true, indicating that this chip may sleep
+  when accessing the GPIOs.
+
+To help out in handling the set-up and management of GPIO irqchips and the
+associated irqdomain and resource allocation callbacks, the gpiolib has
+some helpers that can be enabled by selecting the GPIOLIB_IRQCHIP Kconfig
+symbol:
+
+* gpiochip_irqchip_add(): adds a chained irqchip to a gpiochip. It will pass
+  the struct gpio_chip* for the chip to all IRQ callbacks, so the callbacks
+  need to embed the gpio_chip in its state container and obtain a pointer
+  to the container using container_of().
+  (See Documentation/driver-model/design-patterns.txt)
+
+* gpiochip_irqchip_add_nested(): adds a nested irqchip to a gpiochip.
+  Apart from that it works exactly like the chained irqchip.
+
+* gpiochip_set_chained_irqchip(): sets up a chained irq handler for a
+  gpio_chip from a parent IRQ and passes the struct gpio_chip* as handler
+  data. (Notice handler data, since the irqchip data is likely used by the
+  parent irqchip!).
+
+* gpiochip_set_nested_irqchip(): sets up a nested irq handler for a
+  gpio_chip from a parent IRQ. As the parent IRQ has usually been
+  explicitly requested by the driver, this does very little more than
+  mark all the child IRQs as having the other IRQ as parent.
+
+If there is a need to exclude certain GPIOs from the IRQ domain, you can
+set .irq.need_valid_mask of the gpiochip before gpiochip_add_data() is
+called. This allocates an .irq.valid_mask with as many bits set as there
+are GPIOs in the chip. Drivers can exclude GPIOs by clearing bits from this
+mask. The mask must be filled in before gpiochip_irqchip_add() or
+gpiochip_irqchip_add_nested() is called.
+
+To use the helpers please keep the following in mind:
+
+- Make sure to assign all relevant members of the struct gpio_chip so that
+  the irqchip can initialize. E.g. .dev and .can_sleep shall be set up
+  properly.
+
+- Nominally set all handlers to handle_bad_irq() in the setup call and pass
+  handle_bad_irq() as flow handler parameter in gpiochip_irqchip_add() if it is
+  expected for GPIO driver that irqchip .set_type() callback have to be called
+  before using/enabling GPIO IRQ. Then set the handler to handle_level_irq()
+  and/or handle_edge_irq() in the irqchip .set_type() callback depending on
+  what your controller supports.
+
+It is legal for any IRQ consumer to request an IRQ from any irqchip no matter
+if that is a combined GPIO+IRQ driver. The basic premise is that gpio_chip and
+irq_chip are orthogonal, and offering their services independent of each
+other.
+
+gpiod_to_irq() is just a convenience function to figure out the IRQ for a
+certain GPIO line and should not be relied upon to have been called before
+the IRQ is used.
+
+So always prepare the hardware and make it ready for action in respective
+callbacks from the GPIO and irqchip APIs. Do not rely on gpiod_to_irq() having
+been called first.
+
+This orthogonality leads to ambiguities that we need to solve: if there is
+competition inside the subsystem which side is using the resource (a certain
+GPIO line and register for example) it needs to deny certain operations and
+keep track of usage inside of the gpiolib subsystem. This is why the API
+below exists.
+
+
+Locking IRQ usage
+-----------------
+Input GPIOs can be used as IRQ signals. When this happens, a driver is requested
+to mark the GPIO as being used as an IRQ::
+
+	int gpiochip_lock_as_irq(struct gpio_chip *chip, unsigned int offset)
+
+This will prevent the use of non-irq related GPIO APIs until the GPIO IRQ lock
+is released::
+
+	void gpiochip_unlock_as_irq(struct gpio_chip *chip, unsigned int offset)
+
+When implementing an irqchip inside a GPIO driver, these two functions should
+typically be called in the .startup() and .shutdown() callbacks from the
+irqchip.
+
+When using the gpiolib irqchip helpers, these callback are automatically
+assigned.
+
+Real-Time compliance for GPIO IRQ chips
+---------------------------------------
+
+Any provider of irqchips needs to be carefully tailored to support Real Time
+preemption. It is desirable that all irqchips in the GPIO subsystem keep this
+in mind and do the proper testing to assure they are real time-enabled.
+So, pay attention on above " RT_FULL:" notes, please.
+The following is a checklist to follow when preparing a driver for real
+time-compliance:
+
+- ensure spinlock_t is not used as part irq_chip implementation;
+- ensure that sleepable APIs are not used as part irq_chip implementation.
+  If sleepable APIs have to be used, these can be done from the .irq_bus_lock()
+  and .irq_bus_unlock() callbacks;
+- Chained GPIO irqchips: ensure spinlock_t or any sleepable APIs are not used
+  from chained IRQ handler;
+- Generic chained GPIO irqchips: take care about generic_handle_irq() calls and
+  apply corresponding W/A;
+- Chained GPIO irqchips: get rid of chained IRQ handler and use generic irq
+  handler if possible :)
+- regmap_mmio: Sry, but you are in trouble :( if MMIO regmap is used as for
+  GPIO IRQ chip implementation;
+- Test your driver with the appropriate in-kernel real time test cases for both
+  level and edge IRQs.
+
+
+Requesting self-owned GPIO pins
+-------------------------------
+
+Sometimes it is useful to allow a GPIO chip driver to request its own GPIO
+descriptors through the gpiolib API. Using gpio_request() for this purpose
+does not help since it pins the module to the kernel forever (it calls
+try_module_get()). A GPIO driver can use the following functions instead
+to request and free descriptors without being pinned to the kernel forever::
+
+	struct gpio_desc *gpiochip_request_own_desc(struct gpio_desc *desc,
+						    const char *label)
+
+	void gpiochip_free_own_desc(struct gpio_desc *desc)
+
+Descriptors requested with gpiochip_request_own_desc() must be released with
+gpiochip_free_own_desc().
+
+These functions must be used with care since they do not affect module use
+count. Do not use the functions to request gpio descriptors not owned by the
+calling driver.
+
+* [1] http://www.spinics.net/lists/linux-omap/msg120425.html
+* [2] https://lkml.org/lkml/2015/9/25/494
+* [3] https://lkml.org/lkml/2015/9/25/495

Documentation/driver-api/gpio/drivers-on-gpio.rst

@@ -0,0 +1,101 @@
+============================
+Subsystem drivers using GPIO
+============================
+
+Note that standard kernel drivers exist for common GPIO tasks and will provide
+the right in-kernel and userspace APIs/ABIs for the job, and that these
+drivers can quite easily interconnect with other kernel subsystems using
+hardware descriptions such as device tree or ACPI:
+
+- leds-gpio: drivers/leds/leds-gpio.c will handle LEDs connected to  GPIO
+  lines, giving you the LED sysfs interface
+
+- ledtrig-gpio: drivers/leds/trigger/ledtrig-gpio.c will provide a LED trigger,
+  i.e. a LED will turn on/off in response to a GPIO line going high or low
+  (and that LED may in turn use the leds-gpio as per above).
+
+- gpio-keys: drivers/input/keyboard/gpio_keys.c is used when your GPIO line
+  can generate interrupts in response to a key press. Also supports debounce.
+
+- gpio-keys-polled: drivers/input/keyboard/gpio_keys_polled.c is used when your
+  GPIO line cannot generate interrupts, so it needs to be periodically polled
+  by a timer.
+
+- gpio_mouse: drivers/input/mouse/gpio_mouse.c is used to provide a mouse with
+  up to three buttons by simply using GPIOs and no mouse port. You can cut the
+  mouse cable and connect the wires to GPIO lines or solder a mouse connector
+  to the lines for a more permanent solution of this type.
+
+- gpio-beeper: drivers/input/misc/gpio-beeper.c is used to provide a beep from
+  an external speaker connected to a GPIO line.
+
+- extcon-gpio: drivers/extcon/extcon-gpio.c is used when you need to read an
+  external connector status, such as a headset line for an audio driver or an
+  HDMI connector. It will provide a better userspace sysfs interface than GPIO.
+
+- restart-gpio: drivers/power/reset/gpio-restart.c is used to restart/reboot
+  the system by pulling a GPIO line and will register a restart handler so
+  userspace can issue the right system call to restart the system.
+
+- poweroff-gpio: drivers/power/reset/gpio-poweroff.c is used to power the
+  system down by pulling a GPIO line and will register a pm_power_off()
+  callback so that userspace can issue the right system call to power down the
+  system.
+
+- gpio-gate-clock: drivers/clk/clk-gpio.c is used to control a gated clock
+  (off/on) that uses a GPIO, and integrated with the clock subsystem.
+
+- i2c-gpio: drivers/i2c/busses/i2c-gpio.c is used to drive an I2C bus
+  (two wires, SDA and SCL lines) by hammering (bitbang) two GPIO lines. It will
+  appear as any other I2C bus to the system and makes it possible to connect
+  drivers for the I2C devices on the bus like any other I2C bus driver.
+
+- spi_gpio: drivers/spi/spi-gpio.c is used to drive an SPI bus (variable number
+  of wires, at least SCK and optionally MISO, MOSI and chip select lines) using
+  GPIO hammering (bitbang). It will appear as any other SPI bus on the system
+  and makes it possible to connect drivers for SPI devices on the bus like
+  any other SPI bus driver. For example any MMC/SD card can then be connected
+  to this SPI by using the mmc_spi host from the MMC/SD card subsystem.
+
+- w1-gpio: drivers/w1/masters/w1-gpio.c is used to drive a one-wire bus using
+  a GPIO line, integrating with the W1 subsystem and handling devices on
+  the bus like any other W1 device.
+
+- gpio-fan: drivers/hwmon/gpio-fan.c is used to control a fan for cooling the
+  system, connected to a GPIO line (and optionally a GPIO alarm line),
+  presenting all the right in-kernel and sysfs interfaces to make your system
+  not overheat.
+
+- gpio-regulator: drivers/regulator/gpio-regulator.c is used to control a
+  regulator providing a certain voltage by pulling a GPIO line, integrating
+  with the regulator subsystem and giving you all the right interfaces.
+
+- gpio-wdt: drivers/watchdog/gpio_wdt.c is used to provide a watchdog timer
+  that will periodically "ping" a hardware connected to a GPIO line by toggling
+  it from 1-to-0-to-1. If that hardware does not receive its "ping"
+  periodically, it will reset the system.
+
+- gpio-nand: drivers/mtd/nand/raw/gpio.c is used to connect a NAND flash chip
+  to a set of simple GPIO lines: RDY, NCE, ALE, CLE, NWP. It interacts with the
+  NAND flash MTD subsystem and provides chip access and partition parsing like
+  any other NAND driving hardware.
+
+- ps2-gpio: drivers/input/serio/ps2-gpio.c is used to drive a PS/2 (IBM) serio
+  bus, data and clock line, by bit banging two GPIO lines. It will appear as
+  any other serio bus to the system and makes it possible to connect drivers
+  for e.g. keyboards and other PS/2 protocol based devices.
+
+- cec-gpio: drivers/media/platform/cec-gpio/ is used to interact with a CEC
+  Consumer Electronics Control bus using only GPIO. It is used to communicate
+  with devices on the HDMI bus.
+
+Apart from this there are special GPIO drivers in subsystems like MMC/SD to
+read card detect and write protect GPIO lines, and in the TTY serial subsystem
+to emulate MCTRL (modem control) signals CTS/RTS by using two GPIO lines. The
+MTD NOR flash has add-ons for extra GPIO lines too, though the address bus is
+usually connected directly to the flash.
+
+Use those instead of talking directly to the GPIOs using sysfs; they integrate
+with kernel frameworks better than your userspace code could. Needless to say,
+just using the appropriate kernel drivers will simplify and speed up your
+embedded hacking in particular by providing ready-made components.

Documentation/driver-api/gpio/index.rst

@@ -0,0 +1,48 @@
+===================================
+General Purpose Input/Output (GPIO)
+===================================
+
+Contents:
+
+.. toctree::
+   :maxdepth: 2
+
+   intro
+   driver
+   consumer
+   board
+   drivers-on-gpio
+   legacy
+
+Core
+====
+
+.. kernel-doc:: include/linux/gpio/driver.h
+   :internal:
+
+.. kernel-doc:: drivers/gpio/gpiolib.c
+   :export:
+
+ACPI support
+============
+
+.. kernel-doc:: drivers/gpio/gpiolib-acpi.c
+   :export:
+
+Device tree support
+===================
+
+.. kernel-doc:: drivers/gpio/gpiolib-of.c
+   :export:
+
+Device-managed API
+==================
+
+.. kernel-doc:: drivers/gpio/devres.c
+   :export:
+
+sysfs helpers
+=============
+
+.. kernel-doc:: drivers/gpio/gpiolib-sysfs.c
+   :export:

Documentation/driver-api/gpio/intro.rst

@@ -0,0 +1,124 @@
+============
+Introduction
+============
+
+
+GPIO Interfaces
+===============
+
+The documents in this directory give detailed instructions on how to access
+GPIOs in drivers, and how to write a driver for a device that provides GPIOs
+itself.
+
+Due to the history of GPIO interfaces in the kernel, there are two different
+ways to obtain and use GPIOs:
+
+  - The descriptor-based interface is the preferred way to manipulate GPIOs,
+    and is described by all the files in this directory excepted gpio-legacy.txt.
+  - The legacy integer-based interface which is considered deprecated (but still
+    usable for compatibility reasons) is documented in gpio-legacy.txt.
+
+The remainder of this document applies to the new descriptor-based interface.
+gpio-legacy.txt contains the same information applied to the legacy
+integer-based interface.
+
+
+What is a GPIO?
+===============
+
+A "General Purpose Input/Output" (GPIO) is a flexible software-controlled
+digital signal. They are provided from many kinds of chip, and are familiar
+to Linux developers working with embedded and custom hardware. Each GPIO
+represents a bit connected to a particular pin, or "ball" on Ball Grid Array
+(BGA) packages. Board schematics show which external hardware connects to
+which GPIOs. Drivers can be written generically, so that board setup code
+passes such pin configuration data to drivers.
+
+System-on-Chip (SOC) processors heavily rely on GPIOs. In some cases, every
+non-dedicated pin can be configured as a GPIO; and most chips have at least
+several dozen of them. Programmable logic devices (like FPGAs) can easily
+provide GPIOs; multifunction chips like power managers, and audio codecs
+often have a few such pins to help with pin scarcity on SOCs; and there are
+also "GPIO Expander" chips that connect using the I2C or SPI serial buses.
+Most PC southbridges have a few dozen GPIO-capable pins (with only the BIOS
+firmware knowing how they're used).
+
+The exact capabilities of GPIOs vary between systems. Common options:
+
+  - Output values are writable (high=1, low=0). Some chips also have
+    options about how that value is driven, so that for example only one
+    value might be driven, supporting "wire-OR" and similar schemes for the
+    other value (notably, "open drain" signaling).
+
+  - Input values are likewise readable (1, 0). Some chips support readback
+    of pins configured as "output", which is very useful in such "wire-OR"
+    cases (to support bidirectional signaling). GPIO controllers may have
+    input de-glitch/debounce logic, sometimes with software controls.
+
+  - Inputs can often be used as IRQ signals, often edge triggered but
+    sometimes level triggered. Such IRQs may be configurable as system
+    wakeup events, to wake the system from a low power state.
+
+  - Usually a GPIO will be configurable as either input or output, as needed
+    by different product boards; single direction ones exist too.
+
+  - Most GPIOs can be accessed while holding spinlocks, but those accessed
+    through a serial bus normally can't. Some systems support both types.
+
+On a given board each GPIO is used for one specific purpose like monitoring
+MMC/SD card insertion/removal, detecting card write-protect status, driving
+a LED, configuring a transceiver, bit-banging a serial bus, poking a hardware
+watchdog, sensing a switch, and so on.
+
+
+Common GPIO Properties
+======================
+
+These properties are met through all the other documents of the GPIO interface
+and it is useful to understand them, especially if you need to define GPIO
+mappings.
+
+Active-High and Active-Low
+--------------------------
+It is natural to assume that a GPIO is "active" when its output signal is 1
+("high"), and inactive when it is 0 ("low"). However in practice the signal of a
+GPIO may be inverted before is reaches its destination, or a device could decide
+to have different conventions about what "active" means. Such decisions should
+be transparent to device drivers, therefore it is possible to define a GPIO as
+being either active-high ("1" means "active", the default) or active-low ("0"
+means "active") so that drivers only need to worry about the logical signal and
+not about what happens at the line level.
+
+Open Drain and Open Source
+--------------------------
+Sometimes shared signals need to use "open drain" (where only the low signal
+level is actually driven), or "open source" (where only the high signal level is
+driven) signaling. That term applies to CMOS transistors; "open collector" is
+used for TTL. A pullup or pulldown resistor causes the high or low signal level.
+This is sometimes called a "wire-AND"; or more practically, from the negative
+logic (low=true) perspective this is a "wire-OR".
+
+One common example of an open drain signal is a shared active-low IRQ line.
+Also, bidirectional data bus signals sometimes use open drain signals.
+
+Some GPIO controllers directly support open drain and open source outputs; many
+don't. When you need open drain signaling but your hardware doesn't directly
+support it, there's a common idiom you can use to emulate it with any GPIO pin
+that can be used as either an input or an output:
+
+ LOW:	gpiod_direction_output(gpio, 0) ... this drives the signal and overrides
+	the pullup.
+
+ HIGH:	gpiod_direction_input(gpio) ... this turns off the output, so the pullup
+	(or some other device) controls the signal.
+
+The same logic can be applied to emulate open source signaling, by driving the
+high signal and configuring the GPIO as input for low. This open drain/open
+source emulation can be handled transparently by the GPIO framework.
+
+If you are "driving" the signal high but gpiod_get_value(gpio) reports a low
+value (after the appropriate rise time passes), you know some other component is
+driving the shared signal low. That's not necessarily an error. As one common
+example, that's how I2C clocks are stretched:  a slave that needs a slower clock
+delays the rising edge of SCK, and the I2C master adjusts its signaling rate
+accordingly.

Documentation/driver-api/gpio/legacy.rst

@@ -0,0 +1,770 @@
+======================
+Legacy GPIO Interfaces
+======================
+
+This provides an overview of GPIO access conventions on Linux.
+
+These calls use the gpio_* naming prefix.  No other calls should use that
+prefix, or the related __gpio_* prefix.
+
+
+What is a GPIO?
+===============
+A "General Purpose Input/Output" (GPIO) is a flexible software-controlled
+digital signal.  They are provided from many kinds of chip, and are familiar
+to Linux developers working with embedded and custom hardware.  Each GPIO
+represents a bit connected to a particular pin, or "ball" on Ball Grid Array
+(BGA) packages.  Board schematics show which external hardware connects to
+which GPIOs.  Drivers can be written generically, so that board setup code
+passes such pin configuration data to drivers.
+
+System-on-Chip (SOC) processors heavily rely on GPIOs.  In some cases, every
+non-dedicated pin can be configured as a GPIO; and most chips have at least
+several dozen of them.  Programmable logic devices (like FPGAs) can easily
+provide GPIOs; multifunction chips like power managers, and audio codecs
+often have a few such pins to help with pin scarcity on SOCs; and there are
+also "GPIO Expander" chips that connect using the I2C or SPI serial busses.
+Most PC southbridges have a few dozen GPIO-capable pins (with only the BIOS
+firmware knowing how they're used).
+
+The exact capabilities of GPIOs vary between systems.  Common options:
+
+  - Output values are writable (high=1, low=0).  Some chips also have
+    options about how that value is driven, so that for example only one
+    value might be driven ... supporting "wire-OR" and similar schemes
+    for the other value (notably, "open drain" signaling).
+
+  - Input values are likewise readable (1, 0).  Some chips support readback
+    of pins configured as "output", which is very useful in such "wire-OR"
+    cases (to support bidirectional signaling).  GPIO controllers may have
+    input de-glitch/debounce logic, sometimes with software controls.
+
+  - Inputs can often be used as IRQ signals, often edge triggered but
+    sometimes level triggered.  Such IRQs may be configurable as system
+    wakeup events, to wake the system from a low power state.
+
+  - Usually a GPIO will be configurable as either input or output, as needed
+    by different product boards; single direction ones exist too.
+
+  - Most GPIOs can be accessed while holding spinlocks, but those accessed
+    through a serial bus normally can't.  Some systems support both types.
+
+On a given board each GPIO is used for one specific purpose like monitoring
+MMC/SD card insertion/removal, detecting card writeprotect status, driving
+a LED, configuring a transceiver, bitbanging a serial bus, poking a hardware
+watchdog, sensing a switch, and so on.
+
+
+GPIO conventions
+================
+Note that this is called a "convention" because you don't need to do it this
+way, and it's no crime if you don't.  There **are** cases where portability
+is not the main issue; GPIOs are often used for the kind of board-specific
+glue logic that may even change between board revisions, and can't ever be
+used on a board that's wired differently.  Only least-common-denominator
+functionality can be very portable.  Other features are platform-specific,
+and that can be critical for glue logic.
+
+Plus, this doesn't require any implementation framework, just an interface.
+One platform might implement it as simple inline functions accessing chip
+registers; another might implement it by delegating through abstractions
+used for several very different kinds of GPIO controller.  (There is some
+optional code supporting such an implementation strategy, described later
+in this document, but drivers acting as clients to the GPIO interface must
+not care how it's implemented.)
+
+That said, if the convention is supported on their platform, drivers should
+use it when possible.  Platforms must select GPIOLIB if GPIO functionality
+is strictly required.  Drivers that can't work without
+standard GPIO calls should have Kconfig entries which depend on GPIOLIB.  The
+GPIO calls are available, either as "real code" or as optimized-away stubs,
+when drivers use the include file:
+
+	#include <linux/gpio.h>
+
+If you stick to this convention then it'll be easier for other developers to
+see what your code is doing, and help maintain it.
+
+Note that these operations include I/O barriers on platforms which need to
+use them; drivers don't need to add them explicitly.
+
+
+Identifying GPIOs
+-----------------
+GPIOs are identified by unsigned integers in the range 0..MAX_INT.  That
+reserves "negative" numbers for other purposes like marking signals as
+"not available on this board", or indicating faults.  Code that doesn't
+touch the underlying hardware treats these integers as opaque cookies.
+
+Platforms define how they use those integers, and usually #define symbols
+for the GPIO lines so that board-specific setup code directly corresponds
+to the relevant schematics.  In contrast, drivers should only use GPIO
+numbers passed to them from that setup code, using platform_data to hold
+board-specific pin configuration data (along with other board specific
+data they need).  That avoids portability problems.
+
+So for example one platform uses numbers 32-159 for GPIOs; while another
+uses numbers 0..63 with one set of GPIO controllers, 64-79 with another
+type of GPIO controller, and on one particular board 80-95 with an FPGA.
+The numbers need not be contiguous; either of those platforms could also
+use numbers 2000-2063 to identify GPIOs in a bank of I2C GPIO expanders.
+
+If you want to initialize a structure with an invalid GPIO number, use
+some negative number (perhaps "-EINVAL"); that will never be valid.  To
+test if such number from such a structure could reference a GPIO, you
+may use this predicate:
+
+	int gpio_is_valid(int number);
+
+A number that's not valid will be rejected by calls which may request
+or free GPIOs (see below).  Other numbers may also be rejected; for
+example, a number might be valid but temporarily unused on a given board.
+
+Whether a platform supports multiple GPIO controllers is a platform-specific
+implementation issue, as are whether that support can leave "holes" in the space
+of GPIO numbers, and whether new controllers can be added at runtime.  Such issues
+can affect things including whether adjacent GPIO numbers are both valid.
+
+Using GPIOs
+-----------
+The first thing a system should do with a GPIO is allocate it, using
+the gpio_request() call; see later.
+
+One of the next things to do with a GPIO, often in board setup code when
+setting up a platform_device using the GPIO, is mark its direction::
+
+	/* set as input or output, returning 0 or negative errno */
+	int gpio_direction_input(unsigned gpio);
+	int gpio_direction_output(unsigned gpio, int value);
+
+The return value is zero for success, else a negative errno.  It should
+be checked, since the get/set calls don't have error returns and since
+misconfiguration is possible.  You should normally issue these calls from
+a task context.  However, for spinlock-safe GPIOs it's OK to use them
+before tasking is enabled, as part of early board setup.
+
+For output GPIOs, the value provided becomes the initial output value.
+This helps avoid signal glitching during system startup.
+
+For compatibility with legacy interfaces to GPIOs, setting the direction
+of a GPIO implicitly requests that GPIO (see below) if it has not been
+requested already.  That compatibility is being removed from the optional
+gpiolib framework.
+
+Setting the direction can fail if the GPIO number is invalid, or when
+that particular GPIO can't be used in that mode.  It's generally a bad
+idea to rely on boot firmware to have set the direction correctly, since
+it probably wasn't validated to do more than boot Linux.  (Similarly,
+that board setup code probably needs to multiplex that pin as a GPIO,
+and configure pullups/pulldowns appropriately.)
+
+
+Spinlock-Safe GPIO access
+-------------------------
+Most GPIO controllers can be accessed with memory read/write instructions.
+Those don't need to sleep, and can safely be done from inside hard
+(nonthreaded) IRQ handlers and similar contexts.
+
+Use the following calls to access such GPIOs,
+for which gpio_cansleep() will always return false (see below)::
+
+	/* GPIO INPUT:  return zero or nonzero */
+	int gpio_get_value(unsigned gpio);
+
+	/* GPIO OUTPUT */
+	void gpio_set_value(unsigned gpio, int value);
+
+The values are boolean, zero for low, nonzero for high.  When reading the
+value of an output pin, the value returned should be what's seen on the
+pin ... that won't always match the specified output value, because of
+issues including open-drain signaling and output latencies.
+
+The get/set calls have no error returns because "invalid GPIO" should have
+been reported earlier from gpio_direction_*().  However, note that not all
+platforms can read the value of output pins; those that can't should always
+return zero.  Also, using these calls for GPIOs that can't safely be accessed
+without sleeping (see below) is an error.
+
+Platform-specific implementations are encouraged to optimize the two
+calls to access the GPIO value in cases where the GPIO number (and for
+output, value) are constant.  It's normal for them to need only a couple
+of instructions in such cases (reading or writing a hardware register),
+and not to need spinlocks.  Such optimized calls can make bitbanging
+applications a lot more efficient (in both space and time) than spending
+dozens of instructions on subroutine calls.
+
+
+GPIO access that may sleep
+--------------------------
+Some GPIO controllers must be accessed using message based busses like I2C
+or SPI.  Commands to read or write those GPIO values require waiting to
+get to the head of a queue to transmit a command and get its response.
+This requires sleeping, which can't be done from inside IRQ handlers.
+
+Platforms that support this type of GPIO distinguish them from other GPIOs
+by returning nonzero from this call (which requires a valid GPIO number,
+which should have been previously allocated with gpio_request)::
+
+	int gpio_cansleep(unsigned gpio);
+
+To access such GPIOs, a different set of accessors is defined::
+
+	/* GPIO INPUT:  return zero or nonzero, might sleep */
+	int gpio_get_value_cansleep(unsigned gpio);
+
+	/* GPIO OUTPUT, might sleep */
+	void gpio_set_value_cansleep(unsigned gpio, int value);
+
+
+Accessing such GPIOs requires a context which may sleep,  for example
+a threaded IRQ handler, and those accessors must be used instead of
+spinlock-safe accessors without the cansleep() name suffix.
+
+Other than the fact that these accessors might sleep, and will work
+on GPIOs that can't be accessed from hardIRQ handlers, these calls act
+the same as the spinlock-safe calls.
+
+**IN ADDITION** calls to setup and configure such GPIOs must be made
+from contexts which may sleep, since they may need to access the GPIO
+controller chip too  (These setup calls are usually made from board
+setup or driver probe/teardown code, so this is an easy constraint.)::
+
+                gpio_direction_input()
+                gpio_direction_output()
+                gpio_request()
+
+        ## 	gpio_request_one()
+        ##	gpio_request_array()
+        ## 	gpio_free_array()
+
+                gpio_free()
+                gpio_set_debounce()
+
+
+
+Claiming and Releasing GPIOs
+----------------------------
+To help catch system configuration errors, two calls are defined::
+
+	/* request GPIO, returning 0 or negative errno.
+	 * non-null labels may be useful for diagnostics.
+	 */
+	int gpio_request(unsigned gpio, const char *label);
+
+	/* release previously-claimed GPIO */
+	void gpio_free(unsigned gpio);
+
+Passing invalid GPIO numbers to gpio_request() will fail, as will requesting
+GPIOs that have already been claimed with that call.  The return value of
+gpio_request() must be checked.  You should normally issue these calls from
+a task context.  However, for spinlock-safe GPIOs it's OK to request GPIOs
+before tasking is enabled, as part of early board setup.
+
+These calls serve two basic purposes.  One is marking the signals which
+are actually in use as GPIOs, for better diagnostics; systems may have
+several hundred potential GPIOs, but often only a dozen are used on any
+given board.  Another is to catch conflicts, identifying errors when
+(a) two or more drivers wrongly think they have exclusive use of that
+signal, or (b) something wrongly believes it's safe to remove drivers
+needed to manage a signal that's in active use.  That is, requesting a
+GPIO can serve as a kind of lock.
+
+Some platforms may also use knowledge about what GPIOs are active for
+power management, such as by powering down unused chip sectors and, more
+easily, gating off unused clocks.
+
+For GPIOs that use pins known to the pinctrl subsystem, that subsystem should
+be informed of their use; a gpiolib driver's .request() operation may call
+pinctrl_gpio_request(), and a gpiolib driver's .free() operation may call
+pinctrl_gpio_free(). The pinctrl subsystem allows a pinctrl_gpio_request()
+to succeed concurrently with a pin or pingroup being "owned" by a device for
+pin multiplexing.
+
+Any programming of pin multiplexing hardware that is needed to route the
+GPIO signal to the appropriate pin should occur within a GPIO driver's
+.direction_input() or .direction_output() operations, and occur after any
+setup of an output GPIO's value. This allows a glitch-free migration from a
+pin's special function to GPIO. This is sometimes required when using a GPIO
+to implement a workaround on signals typically driven by a non-GPIO HW block.
+
+Some platforms allow some or all GPIO signals to be routed to different pins.
+Similarly, other aspects of the GPIO or pin may need to be configured, such as
+pullup/pulldown. Platform software should arrange that any such details are
+configured prior to gpio_request() being called for those GPIOs, e.g. using
+the pinctrl subsystem's mapping table, so that GPIO users need not be aware
+of these details.
+
+Also note that it's your responsibility to have stopped using a GPIO
+before you free it.
+
+Considering in most cases GPIOs are actually configured right after they
+are claimed, three additional calls are defined::
+
+	/* request a single GPIO, with initial configuration specified by
+	 * 'flags', identical to gpio_request() wrt other arguments and
+	 * return value
+	 */
+	int gpio_request_one(unsigned gpio, unsigned long flags, const char *label);
+
+	/* request multiple GPIOs in a single call
+	 */
+	int gpio_request_array(struct gpio *array, size_t num);
+
+	/* release multiple GPIOs in a single call
+	 */
+	void gpio_free_array(struct gpio *array, size_t num);
+
+where 'flags' is currently defined to specify the following properties:
+
+	* GPIOF_DIR_IN		- to configure direction as input
+	* GPIOF_DIR_OUT		- to configure direction as output
+
+	* GPIOF_INIT_LOW	- as output, set initial level to LOW
+	* GPIOF_INIT_HIGH	- as output, set initial level to HIGH
+	* GPIOF_OPEN_DRAIN	- gpio pin is open drain type.
+	* GPIOF_OPEN_SOURCE	- gpio pin is open source type.
+
+	* GPIOF_EXPORT_DIR_FIXED	- export gpio to sysfs, keep direction
+	* GPIOF_EXPORT_DIR_CHANGEABLE	- also export, allow changing direction
+
+since GPIOF_INIT_* are only valid when configured as output, so group valid
+combinations as:
+
+	* GPIOF_IN		- configure as input
+	* GPIOF_OUT_INIT_LOW	- configured as output, initial level LOW
+	* GPIOF_OUT_INIT_HIGH	- configured as output, initial level HIGH
+
+When setting the flag as GPIOF_OPEN_DRAIN then it will assume that pins is
+open drain type. Such pins will not be driven to 1 in output mode. It is
+require to connect pull-up on such pins. By enabling this flag, gpio lib will
+make the direction to input when it is asked to set value of 1 in output mode
+to make the pin HIGH. The pin is make to LOW by driving value 0 in output mode.
+
+When setting the flag as GPIOF_OPEN_SOURCE then it will assume that pins is
+open source type. Such pins will not be driven to 0 in output mode. It is
+require to connect pull-down on such pin. By enabling this flag, gpio lib will
+make the direction to input when it is asked to set value of 0 in output mode
+to make the pin LOW. The pin is make to HIGH by driving value 1 in output mode.
+
+In the future, these flags can be extended to support more properties.
+
+Further more, to ease the claim/release of multiple GPIOs, 'struct gpio' is
+introduced to encapsulate all three fields as::
+
+	struct gpio {
+		unsigned	gpio;
+		unsigned long	flags;
+		const char	*label;
+	};
+
+A typical example of usage::
+
+	static struct gpio leds_gpios[] = {
+		{ 32, GPIOF_OUT_INIT_HIGH, "Power LED" }, /* default to ON */
+		{ 33, GPIOF_OUT_INIT_LOW,  "Green LED" }, /* default to OFF */
+		{ 34, GPIOF_OUT_INIT_LOW,  "Red LED"   }, /* default to OFF */
+		{ 35, GPIOF_OUT_INIT_LOW,  "Blue LED"  }, /* default to OFF */
+		{ ... },
+	};
+
+	err = gpio_request_one(31, GPIOF_IN, "Reset Button");
+	if (err)
+		...
+
+	err = gpio_request_array(leds_gpios, ARRAY_SIZE(leds_gpios));
+	if (err)
+		...
+
+	gpio_free_array(leds_gpios, ARRAY_SIZE(leds_gpios));
+
+
+GPIOs mapped to IRQs
+--------------------
+GPIO numbers are unsigned integers; so are IRQ numbers.  These make up
+two logically distinct namespaces (GPIO 0 need not use IRQ 0).  You can
+map between them using calls like::
+
+	/* map GPIO numbers to IRQ numbers */
+	int gpio_to_irq(unsigned gpio);
+
+	/* map IRQ numbers to GPIO numbers (avoid using this) */
+	int irq_to_gpio(unsigned irq);
+
+Those return either the corresponding number in the other namespace, or
+else a negative errno code if the mapping can't be done.  (For example,
+some GPIOs can't be used as IRQs.)  It is an unchecked error to use a GPIO
+number that wasn't set up as an input using gpio_direction_input(), or
+to use an IRQ number that didn't originally come from gpio_to_irq().
+
+These two mapping calls are expected to cost on the order of a single
+addition or subtraction.  They're not allowed to sleep.
+
+Non-error values returned from gpio_to_irq() can be passed to request_irq()
+or free_irq().  They will often be stored into IRQ resources for platform
+devices, by the board-specific initialization code.  Note that IRQ trigger
+options are part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are
+system wakeup capabilities.
+
+Non-error values returned from irq_to_gpio() would most commonly be used
+with gpio_get_value(), for example to initialize or update driver state
+when the IRQ is edge-triggered.  Note that some platforms don't support
+this reverse mapping, so you should avoid using it.
+
+
+Emulating Open Drain Signals
+----------------------------
+Sometimes shared signals need to use "open drain" signaling, where only the
+low signal level is actually driven.  (That term applies to CMOS transistors;
+"open collector" is used for TTL.)  A pullup resistor causes the high signal
+level.  This is sometimes called a "wire-AND"; or more practically, from the
+negative logic (low=true) perspective this is a "wire-OR".
+
+One common example of an open drain signal is a shared active-low IRQ line.
+Also, bidirectional data bus signals sometimes use open drain signals.
+
+Some GPIO controllers directly support open drain outputs; many don't.  When
+you need open drain signaling but your hardware doesn't directly support it,
+there's a common idiom you can use to emulate it with any GPIO pin that can
+be used as either an input or an output:
+
+ LOW:	gpio_direction_output(gpio, 0) ... this drives the signal
+	and overrides the pullup.
+
+ HIGH:	gpio_direction_input(gpio) ... this turns off the output,
+	so the pullup (or some other device) controls the signal.
+
+If you are "driving" the signal high but gpio_get_value(gpio) reports a low
+value (after the appropriate rise time passes), you know some other component
+is driving the shared signal low.  That's not necessarily an error.  As one
+common example, that's how I2C clocks are stretched:  a slave that needs a
+slower clock delays the rising edge of SCK, and the I2C master adjusts its
+signaling rate accordingly.
+
+
+GPIO controllers and the pinctrl subsystem
+------------------------------------------
+
+A GPIO controller on a SOC might be tightly coupled with the pinctrl
+subsystem, in the sense that the pins can be used by other functions
+together with an optional gpio feature. We have already covered the
+case where e.g. a GPIO controller need to reserve a pin or set the
+direction of a pin by calling any of::
+
+  pinctrl_gpio_request()
+  pinctrl_gpio_free()
+  pinctrl_gpio_direction_input()
+  pinctrl_gpio_direction_output()
+
+But how does the pin control subsystem cross-correlate the GPIO
+numbers (which are a global business) to a certain pin on a certain
+pin controller?
+
+This is done by registering "ranges" of pins, which are essentially
+cross-reference tables. These are described in
+Documentation/driver-api/pinctl.rst
+
+While the pin allocation is totally managed by the pinctrl subsystem,
+gpio (under gpiolib) is still maintained by gpio drivers. It may happen
+that different pin ranges in a SoC is managed by different gpio drivers.
+
+This makes it logical to let gpio drivers announce their pin ranges to
+the pin ctrl subsystem before it will call 'pinctrl_gpio_request' in order
+to request the corresponding pin to be prepared by the pinctrl subsystem
+before any gpio usage.
+
+For this, the gpio controller can register its pin range with pinctrl
+subsystem. There are two ways of doing it currently: with or without DT.
+
+For with DT support refer to Documentation/devicetree/bindings/gpio/gpio.txt.
+
+For non-DT support, user can call gpiochip_add_pin_range() with appropriate
+parameters to register a range of gpio pins with a pinctrl driver. For this
+exact name string of pinctrl device has to be passed as one of the
+argument to this routine.
+
+
+What do these conventions omit?
+===============================
+One of the biggest things these conventions omit is pin multiplexing, since
+this is highly chip-specific and nonportable.  One platform might not need
+explicit multiplexing; another might have just two options for use of any
+given pin; another might have eight options per pin; another might be able
+to route a given GPIO to any one of several pins.  (Yes, those examples all
+come from systems that run Linux today.)
+
+Related to multiplexing is configuration and enabling of the pullups or
+pulldowns integrated on some platforms.  Not all platforms support them,
+or support them in the same way; and any given board might use external
+pullups (or pulldowns) so that the on-chip ones should not be used.
+(When a circuit needs 5 kOhm, on-chip 100 kOhm resistors won't do.)
+Likewise drive strength (2 mA vs 20 mA) and voltage (1.8V vs 3.3V) is a
+platform-specific issue, as are models like (not) having a one-to-one
+correspondence between configurable pins and GPIOs.
+
+There are other system-specific mechanisms that are not specified here,
+like the aforementioned options for input de-glitching and wire-OR output.
+Hardware may support reading or writing GPIOs in gangs, but that's usually
+configuration dependent:  for GPIOs sharing the same bank.  (GPIOs are
+commonly grouped in banks of 16 or 32, with a given SOC having several such
+banks.)  Some systems can trigger IRQs from output GPIOs, or read values
+from pins not managed as GPIOs.  Code relying on such mechanisms will
+necessarily be nonportable.
+
+Dynamic definition of GPIOs is not currently standard; for example, as
+a side effect of configuring an add-on board with some GPIO expanders.
+
+
+GPIO implementor's framework (OPTIONAL)
+=======================================
+As noted earlier, there is an optional implementation framework making it
+easier for platforms to support different kinds of GPIO controller using
+the same programming interface.  This framework is called "gpiolib".
+
+As a debugging aid, if debugfs is available a /sys/kernel/debug/gpio file
+will be found there.  That will list all the controllers registered through
+this framework, and the state of the GPIOs currently in use.
+
+
+Controller Drivers: gpio_chip
+-----------------------------
+In this framework each GPIO controller is packaged as a "struct gpio_chip"
+with information common to each controller of that type:
+
+ - methods to establish GPIO direction
+ - methods used to access GPIO values
+ - flag saying whether calls to its methods may sleep
+ - optional debugfs dump method (showing extra state like pullup config)
+ - label for diagnostics
+
+There is also per-instance data, which may come from device.platform_data:
+the number of its first GPIO, and how many GPIOs it exposes.
+
+The code implementing a gpio_chip should support multiple instances of the
+controller, possibly using the driver model.  That code will configure each
+gpio_chip and issue gpiochip_add().  Removing a GPIO controller should be
+rare; use gpiochip_remove() when it is unavoidable.
+
+Most often a gpio_chip is part of an instance-specific structure with state
+not exposed by the GPIO interfaces, such as addressing, power management,
+and more.  Chips such as codecs will have complex non-GPIO state.
+
+Any debugfs dump method should normally ignore signals which haven't been
+requested as GPIOs.  They can use gpiochip_is_requested(), which returns
+either NULL or the label associated with that GPIO when it was requested.
+
+
+Platform Support
+----------------
+To force-enable this framework, a platform's Kconfig will "select" GPIOLIB,
+else it is up to the user to configure support for GPIO.
+
+It may also provide a custom value for ARCH_NR_GPIOS, so that it better
+reflects the number of GPIOs in actual use on that platform, without
+wasting static table space.  (It should count both built-in/SoC GPIOs and
+also ones on GPIO expanders.
+
+If neither of these options are selected, the platform does not support
+GPIOs through GPIO-lib and the code cannot be enabled by the user.
+
+Trivial implementations of those functions can directly use framework
+code, which always dispatches through the gpio_chip::
+
+  #define gpio_get_value	__gpio_get_value
+  #define gpio_set_value	__gpio_set_value
+  #define gpio_cansleep		__gpio_cansleep
+
+Fancier implementations could instead define those as inline functions with
+logic optimizing access to specific SOC-based GPIOs.  For example, if the
+referenced GPIO is the constant "12", getting or setting its value could
+cost as little as two or three instructions, never sleeping.  When such an
+optimization is not possible those calls must delegate to the framework
+code, costing at least a few dozen instructions.  For bitbanged I/O, such
+instruction savings can be significant.
+
+For SOCs, platform-specific code defines and registers gpio_chip instances
+for each bank of on-chip GPIOs.  Those GPIOs should be numbered/labeled to
+match chip vendor documentation, and directly match board schematics.  They
+may well start at zero and go up to a platform-specific limit.  Such GPIOs
+are normally integrated into platform initialization to make them always be
+available, from arch_initcall() or earlier; they can often serve as IRQs.
+
+
+Board Support
+-------------
+For external GPIO controllers -- such as I2C or SPI expanders, ASICs, multi
+function devices, FPGAs or CPLDs -- most often board-specific code handles
+registering controller devices and ensures that their drivers know what GPIO
+numbers to use with gpiochip_add().  Their numbers often start right after
+platform-specific GPIOs.
+
+For example, board setup code could create structures identifying the range
+of GPIOs that chip will expose, and passes them to each GPIO expander chip
+using platform_data.  Then the chip driver's probe() routine could pass that
+data to gpiochip_add().
+
+Initialization order can be important.  For example, when a device relies on
+an I2C-based GPIO, its probe() routine should only be called after that GPIO
+becomes available.  That may mean the device should not be registered until
+calls for that GPIO can work.  One way to address such dependencies is for
+such gpio_chip controllers to provide setup() and teardown() callbacks to
+board specific code; those board specific callbacks would register devices
+once all the necessary resources are available, and remove them later when
+the GPIO controller device becomes unavailable.
+
+
+Sysfs Interface for Userspace (OPTIONAL)
+========================================
+Platforms which use the "gpiolib" implementors framework may choose to
+configure a sysfs user interface to GPIOs.  This is different from the
+debugfs interface, since it provides control over GPIO direction and
+value instead of just showing a gpio state summary.  Plus, it could be
+present on production systems without debugging support.
+
+Given appropriate hardware documentation for the system, userspace could
+know for example that GPIO #23 controls the write protect line used to
+protect boot loader segments in flash memory.  System upgrade procedures
+may need to temporarily remove that protection, first importing a GPIO,
+then changing its output state, then updating the code before re-enabling
+the write protection.  In normal use, GPIO #23 would never be touched,
+and the kernel would have no need to know about it.
+
+Again depending on appropriate hardware documentation, on some systems
+userspace GPIO can be used to determine system configuration data that
+standard kernels won't know about.  And for some tasks, simple userspace
+GPIO drivers could be all that the system really needs.
+
+Note that standard kernel drivers exist for common "LEDs and Buttons"
+GPIO tasks:  "leds-gpio" and "gpio_keys", respectively.  Use those
+instead of talking directly to the GPIOs; they integrate with kernel
+frameworks better than your userspace code could.
+
+
+Paths in Sysfs
+--------------
+There are three kinds of entry in /sys/class/gpio:
+
+   -	Control interfaces used to get userspace control over GPIOs;
+
+   -	GPIOs themselves; and
+
+   -	GPIO controllers ("gpio_chip" instances).
+
+That's in addition to standard files including the "device" symlink.
+
+The control interfaces are write-only:
+
+    /sys/class/gpio/
+
+    	"export" ... Userspace may ask the kernel to export control of
+		a GPIO to userspace by writing its number to this file.
+
+		Example:  "echo 19 > export" will create a "gpio19" node
+		for GPIO #19, if that's not requested by kernel code.
+
+    	"unexport" ... Reverses the effect of exporting to userspace.
+
+		Example:  "echo 19 > unexport" will remove a "gpio19"
+		node exported using the "export" file.
+
+GPIO signals have paths like /sys/class/gpio/gpio42/ (for GPIO #42)
+and have the following read/write attributes:
+
+    /sys/class/gpio/gpioN/
+
+	"direction" ... reads as either "in" or "out".  This value may
+		normally be written.  Writing as "out" defaults to
+		initializing the value as low.  To ensure glitch free
+		operation, values "low" and "high" may be written to
+		configure the GPIO as an output with that initial value.
+
+		Note that this attribute *will not exist* if the kernel
+		doesn't support changing the direction of a GPIO, or
+		it was exported by kernel code that didn't explicitly
+		allow userspace to reconfigure this GPIO's direction.
+
+	"value" ... reads as either 0 (low) or 1 (high).  If the GPIO
+		is configured as an output, this value may be written;
+		any nonzero value is treated as high.
+
+		If the pin can be configured as interrupt-generating interrupt
+		and if it has been configured to generate interrupts (see the
+		description of "edge"), you can poll(2) on that file and
+		poll(2) will return whenever the interrupt was triggered. If
+		you use poll(2), set the events POLLPRI and POLLERR. If you
+		use select(2), set the file descriptor in exceptfds. After
+		poll(2) returns, either lseek(2) to the beginning of the sysfs
+		file and read the new value or close the file and re-open it
+		to read the value.
+
+	"edge" ... reads as either "none", "rising", "falling", or
+		"both". Write these strings to select the signal edge(s)
+		that will make poll(2) on the "value" file return.
+
+		This file exists only if the pin can be configured as an
+		interrupt generating input pin.
+
+	"active_low" ... reads as either 0 (false) or 1 (true).  Write
+		any nonzero value to invert the value attribute both
+		for reading and writing.  Existing and subsequent
+		poll(2) support configuration via the edge attribute
+		for "rising" and "falling" edges will follow this
+		setting.
+
+GPIO controllers have paths like /sys/class/gpio/gpiochip42/ (for the
+controller implementing GPIOs starting at #42) and have the following
+read-only attributes:
+
+    /sys/class/gpio/gpiochipN/
+
+    	"base" ... same as N, the first GPIO managed by this chip
+
+    	"label" ... provided for diagnostics (not always unique)
+
+    	"ngpio" ... how many GPIOs this manges (N to N + ngpio - 1)
+
+Board documentation should in most cases cover what GPIOs are used for
+what purposes.  However, those numbers are not always stable; GPIOs on
+a daughtercard might be different depending on the base board being used,
+or other cards in the stack.  In such cases, you may need to use the
+gpiochip nodes (possibly in conjunction with schematics) to determine
+the correct GPIO number to use for a given signal.
+
+
+Exporting from Kernel code
+--------------------------
+Kernel code can explicitly manage exports of GPIOs which have already been
+requested using gpio_request()::
+
+	/* export the GPIO to userspace */
+	int gpio_export(unsigned gpio, bool direction_may_change);
+
+	/* reverse gpio_export() */
+	void gpio_unexport();
+
+	/* create a sysfs link to an exported GPIO node */
+	int gpio_export_link(struct device *dev, const char *name,
+		unsigned gpio)
+
+After a kernel driver requests a GPIO, it may only be made available in
+the sysfs interface by gpio_export().  The driver can control whether the
+signal direction may change.  This helps drivers prevent userspace code
+from accidentally clobbering important system state.
+
+This explicit exporting can help with debugging (by making some kinds
+of experiments easier), or can provide an always-there interface that's
+suitable for documenting as part of a board support package.
+
+After the GPIO has been exported, gpio_export_link() allows creating
+symlinks from elsewhere in sysfs to the GPIO sysfs node.  Drivers can
+use this to provide the interface under their own device in sysfs with
+a descriptive name.
+
+
+API Reference
+=============
+
+The functions listed in this section are deprecated. The GPIO descriptor based
+API should be used in new code.
+
+.. kernel-doc:: drivers/gpio/gpiolib-legacy.c
+   :export:

Documentation/driver-api/hsi.rst

@@ -0,0 +1,88 @@
+High Speed Synchronous Serial Interface (HSI)
+=============================================
+
+Introduction
+---------------
+
+High Speed Syncronous Interface (HSI) is a fullduplex, low latency protocol,
+that is optimized for die-level interconnect between an Application Processor
+and a Baseband chipset. It has been specified by the MIPI alliance in 2003 and
+implemented by multiple vendors since then.
+
+The HSI interface supports full duplex communication over multiple channels
+(typically 8) and is capable of reaching speeds up to 200 Mbit/s.
+
+The serial protocol uses two signals, DATA and FLAG as combined data and clock
+signals and an additional READY signal for flow control. An additional WAKE
+signal can be used to wakeup the chips from standby modes. The signals are
+commonly prefixed by AC for signals going from the application die to the
+cellular die and CA for signals going the other way around.
+
+::
+
+    +------------+                                 +---------------+
+    |  Cellular  |                                 |  Application  |
+    |    Die     |                                 |      Die      |
+    |            | - - - - - - CAWAKE - - - - - - >|               |
+    |           T|------------ CADATA ------------>|R              |
+    |           X|------------ CAFLAG ------------>|X              |
+    |            |<----------- ACREADY ------------|               |
+    |            |                                 |               |
+    |            |                                 |               |
+    |            |< - - - - -  ACWAKE - - - - - - -|               |
+    |           R|<----------- ACDATA -------------|T              |
+    |           X|<----------- ACFLAG -------------|X              |
+    |            |------------ CAREADY ----------->|               |
+    |            |                                 |               |
+    |            |                                 |               |
+    +------------+                                 +---------------+
+
+HSI Subsystem in Linux
+-------------------------
+
+In the Linux kernel the hsi subsystem is supposed to be used for HSI devices.
+The hsi subsystem contains drivers for hsi controllers including support for
+multi-port controllers and provides a generic API for using the HSI ports.
+
+It also contains HSI client drivers, which make use of the generic API to
+implement a protocol used on the HSI interface. These client drivers can
+use an arbitrary number of channels.
+
+hsi-char Device
+------------------
+
+Each port automatically registers a generic client driver called hsi_char,
+which provides a charecter device for userspace representing the HSI port.
+It can be used to communicate via HSI from userspace. Userspace may
+configure the hsi_char device using the following ioctl commands:
+
+HSC_RESET
+ flush the HSI port
+
+HSC_SET_PM
+ enable or disable the client.
+
+HSC_SEND_BREAK
+ send break
+
+HSC_SET_RX
+ set RX configuration
+
+HSC_GET_RX
+ get RX configuration
+
+HSC_SET_TX
+ set TX configuration
+
+HSC_GET_TX
+ get TX configuration
+
+The kernel HSI API
+------------------
+
+.. kernel-doc:: include/linux/hsi/hsi.h
+   :internal:
+
+.. kernel-doc:: drivers/hsi/hsi_core.c
+   :export:
+

Documentation/driver-api/i2c.rst

@@ -0,0 +1,48 @@
+I\ :sup:`2`\ C and SMBus Subsystem
+==================================
+
+I\ :sup:`2`\ C (or without fancy typography, "I2C") is an acronym for
+the "Inter-IC" bus, a simple bus protocol which is widely used where low
+data rate communications suffice. Since it's also a licensed trademark,
+some vendors use another name (such as "Two-Wire Interface", TWI) for
+the same bus. I2C only needs two signals (SCL for clock, SDA for data),
+conserving board real estate and minimizing signal quality issues. Most
+I2C devices use seven bit addresses, and bus speeds of up to 400 kHz;
+there's a high speed extension (3.4 MHz) that's not yet found wide use.
+I2C is a multi-master bus; open drain signaling is used to arbitrate
+between masters, as well as to handshake and to synchronize clocks from
+slower clients.
+
+The Linux I2C programming interfaces support the master side of bus
+interactions and the slave side. The programming interface is
+structured around two kinds of driver, and two kinds of device. An I2C
+"Adapter Driver" abstracts the controller hardware; it binds to a
+physical device (perhaps a PCI device or platform_device) and exposes a
+:c:type:`struct i2c_adapter <i2c_adapter>` representing each
+I2C bus segment it manages. On each I2C bus segment will be I2C devices
+represented by a :c:type:`struct i2c_client <i2c_client>`.
+Those devices will be bound to a :c:type:`struct i2c_driver
+<i2c_driver>`, which should follow the standard Linux driver model. There
+are functions to perform various I2C protocol operations; at this writing
+all such functions are usable only from task context.
+
+The System Management Bus (SMBus) is a sibling protocol. Most SMBus
+systems are also I2C conformant. The electrical constraints are tighter
+for SMBus, and it standardizes particular protocol messages and idioms.
+Controllers that support I2C can also support most SMBus operations, but
+SMBus controllers don't support all the protocol options that an I2C
+controller will. There are functions to perform various SMBus protocol
+operations, either using I2C primitives or by issuing SMBus commands to
+i2c_adapter devices which don't support those I2C operations.
+
+.. kernel-doc:: include/linux/i2c.h
+   :internal:
+
+.. kernel-doc:: drivers/i2c/i2c-boardinfo.c
+   :functions: i2c_register_board_info
+
+.. kernel-doc:: drivers/i2c/i2c-core-base.c
+   :export:
+
+.. kernel-doc:: drivers/i2c/i2c-core-smbus.c
+   :export:

Documentation/driver-api/iio/buffers.rst

@@ -0,0 +1,125 @@
+=======
+Buffers
+=======
+
+* struct :c:type:`iio_buffer` — general buffer structure
+* :c:func:`iio_validate_scan_mask_onehot` — Validates that exactly one channel
+  is selected
+* :c:func:`iio_buffer_get` — Grab a reference to the buffer
+* :c:func:`iio_buffer_put` — Release the reference to the buffer
+
+The Industrial I/O core offers a way for continuous data capture based on a
+trigger source. Multiple data channels can be read at once from
+:file:`/dev/iio:device{X}` character device node, thus reducing the CPU load.
+
+IIO buffer sysfs interface
+==========================
+An IIO buffer has an associated attributes directory under
+:file:`/sys/bus/iio/iio:device{X}/buffer/*`. Here are some of the existing
+attributes:
+
+* :file:`length`, the total number of data samples (capacity) that can be
+  stored by the buffer.
+* :file:`enable`, activate buffer capture.
+
+IIO buffer setup
+================
+
+The meta information associated with a channel reading placed in a buffer is
+called a scan element . The important bits configuring scan elements are
+exposed to userspace applications via the
+:file:`/sys/bus/iio/iio:device{X}/scan_elements/*` directory. This file contains
+attributes of the following form:
+
+* :file:`enable`, used for enabling a channel. If and only if its attribute
+  is non *zero*, then a triggered capture will contain data samples for this
+  channel.
+* :file:`type`, description of the scan element data storage within the buffer
+  and hence the form in which it is read from user space.
+  Format is [be|le]:[s|u]bits/storagebitsXrepeat[>>shift] .
+  * *be* or *le*, specifies big or little endian.
+  * *s* or *u*, specifies if signed (2's complement) or unsigned.
+  * *bits*, is the number of valid data bits.
+  * *storagebits*, is the number of bits (after padding) that it occupies in the
+  buffer.
+  * *shift*, if specified, is the shift that needs to be applied prior to
+  masking out unused bits.
+  * *repeat*, specifies the number of bits/storagebits repetitions. When the
+  repeat element is 0 or 1, then the repeat value is omitted.
+
+For example, a driver for a 3-axis accelerometer with 12 bit resolution where
+data is stored in two 8-bits registers as follows::
+
+        7   6   5   4   3   2   1   0
+      +---+---+---+---+---+---+---+---+
+      |D3 |D2 |D1 |D0 | X | X | X | X | (LOW byte, address 0x06)
+      +---+---+---+---+---+---+---+---+
+
+        7   6   5   4   3   2   1   0
+      +---+---+---+---+---+---+---+---+
+      |D11|D10|D9 |D8 |D7 |D6 |D5 |D4 | (HIGH byte, address 0x07)
+      +---+---+---+---+---+---+---+---+
+
+will have the following scan element type for each axis::
+
+      $ cat /sys/bus/iio/devices/iio:device0/scan_elements/in_accel_y_type
+      le:s12/16>>4
+
+A user space application will interpret data samples read from the buffer as
+two byte little endian signed data, that needs a 4 bits right shift before
+masking out the 12 valid bits of data.
+
+For implementing buffer support a driver should initialize the following
+fields in iio_chan_spec definition::
+
+   struct iio_chan_spec {
+   /* other members */
+           int scan_index
+           struct {
+                   char sign;
+                   u8 realbits;
+                   u8 storagebits;
+                   u8 shift;
+                   u8 repeat;
+                   enum iio_endian endianness;
+                  } scan_type;
+          };
+
+The driver implementing the accelerometer described above will have the
+following channel definition::
+
+   struct struct iio_chan_spec accel_channels[] = {
+           {
+                   .type = IIO_ACCEL,
+		   .modified = 1,
+		   .channel2 = IIO_MOD_X,
+		   /* other stuff here */
+		   .scan_index = 0,
+		   .scan_type = {
+		           .sign = 's',
+			   .realbits = 12,
+			   .storagebits = 16,
+			   .shift = 4,
+			   .endianness = IIO_LE,
+		   },
+           }
+           /* similar for Y (with channel2 = IIO_MOD_Y, scan_index = 1)
+            * and Z (with channel2 = IIO_MOD_Z, scan_index = 2) axis
+            */
+    }
+
+Here **scan_index** defines the order in which the enabled channels are placed
+inside the buffer. Channels with a lower **scan_index** will be placed before
+channels with a higher index. Each channel needs to have a unique
+**scan_index**.
+
+Setting **scan_index** to -1 can be used to indicate that the specific channel
+does not support buffered capture. In this case no entries will be created for
+the channel in the scan_elements directory.
+
+More details
+============
+.. kernel-doc:: include/linux/iio/buffer.h
+.. kernel-doc:: drivers/iio/industrialio-buffer.c
+   :export:
+

Documentation/driver-api/iio/core.rst

@@ -0,0 +1,182 @@
+=============
+Core elements
+=============
+
+The Industrial I/O core offers a unified framework for writing drivers for
+many different types of embedded sensors. a standard interface to user space
+applications manipulating sensors. The implementation can be found under
+:file:`drivers/iio/industrialio-*`
+
+Industrial I/O Devices
+----------------------
+
+* struct :c:type:`iio_dev` - industrial I/O device
+* :c:func:`iio_device_alloc()` - alocate an :c:type:`iio_dev` from a driver
+* :c:func:`iio_device_free()` - free an :c:type:`iio_dev` from a driver
+* :c:func:`iio_device_register()` - register a device with the IIO subsystem
+* :c:func:`iio_device_unregister()` - unregister a device from the IIO
+  subsystem
+
+An IIO device usually corresponds to a single hardware sensor and it
+provides all the information needed by a driver handling a device.
+Let's first have a look at the functionality embedded in an IIO device
+then we will show how a device driver makes use of an IIO device.
+
+There are two ways for a user space application to interact with an IIO driver.
+
+1. :file:`/sys/bus/iio/iio:device{X}/`, this represents a hardware sensor
+   and groups together the data channels of the same chip.
+2. :file:`/dev/iio:device{X}`, character device node interface used for
+   buffered data transfer and for events information retrieval.
+
+A typical IIO driver will register itself as an :doc:`I2C <../i2c>` or
+:doc:`SPI <../spi>` driver and will create two routines, probe and remove.
+
+At probe:
+
+1. Call :c:func:`iio_device_alloc()`, which allocates memory for an IIO device.
+2. Initialize IIO device fields with driver specific information (e.g.
+   device name, device channels).
+3. Call :c:func:`iio_device_register()`, this registers the device with the
+   IIO core. After this call the device is ready to accept requests from user
+   space applications.
+
+At remove, we free the resources allocated in probe in reverse order:
+
+1. :c:func:`iio_device_unregister()`, unregister the device from the IIO core.
+2. :c:func:`iio_device_free()`, free the memory allocated for the IIO device.
+
+IIO device sysfs interface
+==========================
+
+Attributes are sysfs files used to expose chip info and also allowing
+applications to set various configuration parameters. For device with
+index X, attributes can be found under /sys/bus/iio/iio:deviceX/ directory.
+Common attributes are:
+
+* :file:`name`, description of the physical chip.
+* :file:`dev`, shows the major:minor pair associated with
+  :file:`/dev/iio:deviceX` node.
+* :file:`sampling_frequency_available`, available discrete set of sampling
+  frequency values for device.
+* Available standard attributes for IIO devices are described in the
+  :file:`Documentation/ABI/testing/sysfs-bus-iio` file in the Linux kernel
+  sources.
+
+IIO device channels
+===================
+
+struct :c:type:`iio_chan_spec` - specification of a single channel
+
+An IIO device channel is a representation of a data channel. An IIO device can
+have one or multiple channels. For example:
+
+* a thermometer sensor has one channel representing the temperature measurement.
+* a light sensor with two channels indicating the measurements in the visible
+  and infrared spectrum.
+* an accelerometer can have up to 3 channels representing acceleration on X, Y
+  and Z axes.
+
+An IIO channel is described by the struct :c:type:`iio_chan_spec`.
+A thermometer driver for the temperature sensor in the example above would
+have to describe its channel as follows::
+
+   static const struct iio_chan_spec temp_channel[] = {
+        {
+            .type = IIO_TEMP,
+            .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
+        },
+   };
+
+Channel sysfs attributes exposed to userspace are specified in the form of
+bitmasks. Depending on their shared info, attributes can be set in one of the
+following masks:
+
+* **info_mask_separate**, attributes will be specific to
+  this channel
+* **info_mask_shared_by_type**, attributes are shared by all channels of the
+  same type
+* **info_mask_shared_by_dir**, attributes are shared by all channels of the same
+  direction
+* **info_mask_shared_by_all**, attributes are shared by all channels
+
+When there are multiple data channels per channel type we have two ways to
+distinguish between them:
+
+* set **.modified** field of :c:type:`iio_chan_spec` to 1. Modifiers are
+  specified using **.channel2** field of the same :c:type:`iio_chan_spec`
+  structure and are used to indicate a physically unique characteristic of the
+  channel such as its direction or spectral response. For example, a light
+  sensor can have two channels, one for infrared light and one for both
+  infrared and visible light.
+* set **.indexed** field of :c:type:`iio_chan_spec` to 1. In this case the
+  channel is simply another instance with an index specified by the **.channel**
+  field.
+
+Here is how we can make use of the channel's modifiers::
+
+   static const struct iio_chan_spec light_channels[] = {
+           {
+                   .type = IIO_INTENSITY,
+                   .modified = 1,
+                   .channel2 = IIO_MOD_LIGHT_IR,
+                   .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+                   .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ),
+           },
+           {
+                   .type = IIO_INTENSITY,
+                   .modified = 1,
+                   .channel2 = IIO_MOD_LIGHT_BOTH,
+                   .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+                   .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ),
+           },
+           {
+                   .type = IIO_LIGHT,
+                   .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
+                   .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ),
+           },
+      }
+
+This channel's definition will generate two separate sysfs files for raw data
+retrieval:
+
+* :file:`/sys/bus/iio/iio:device{X}/in_intensity_ir_raw`
+* :file:`/sys/bus/iio/iio:device{X}/in_intensity_both_raw`
+
+one file for processed data:
+
+* :file:`/sys/bus/iio/iio:device{X}/in_illuminance_input`
+
+and one shared sysfs file for sampling frequency:
+
+* :file:`/sys/bus/iio/iio:device{X}/sampling_frequency`.
+
+Here is how we can make use of the channel's indexing::
+
+   static const struct iio_chan_spec light_channels[] = {
+           {
+                   .type = IIO_VOLTAGE,
+		   .indexed = 1,
+		   .channel = 0,
+		   .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+	   },
+           {
+	           .type = IIO_VOLTAGE,
+                   .indexed = 1,
+                   .channel = 1,
+                   .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+           },
+   }
+
+This will generate two separate attributes files for raw data retrieval:
+
+* :file:`/sys/bus/iio/devices/iio:device{X}/in_voltage0_raw`, representing
+  voltage measurement for channel 0.
+* :file:`/sys/bus/iio/devices/iio:device{X}/in_voltage1_raw`, representing
+  voltage measurement for channel 1.
+
+More details
+============
+.. kernel-doc:: include/linux/iio/iio.h
+.. kernel-doc:: drivers/iio/industrialio-core.c
+   :export:

Documentation/driver-api/iio/hw-consumer.rst

@@ -0,0 +1,51 @@
+===========
+HW consumer
+===========
+An IIO device can be directly connected to another device in hardware. in this
+case the buffers between IIO provider and IIO consumer are handled by hardware.
+The Industrial I/O HW consumer offers a way to bond these IIO devices without
+software buffer for data. The implementation can be found under
+:file:`drivers/iio/buffer/hw-consumer.c`
+
+
+* struct :c:type:`iio_hw_consumer` — Hardware consumer structure
+* :c:func:`iio_hw_consumer_alloc` — Allocate IIO hardware consumer
+* :c:func:`iio_hw_consumer_free` — Free IIO hardware consumer
+* :c:func:`iio_hw_consumer_enable` — Enable IIO hardware consumer
+* :c:func:`iio_hw_consumer_disable` — Disable IIO hardware consumer
+
+
+HW consumer setup
+=================
+
+As standard IIO device the implementation is based on IIO provider/consumer.
+A typical IIO HW consumer setup looks like this::
+
+	static struct iio_hw_consumer *hwc;
+
+	static const struct iio_info adc_info = {
+		.read_raw = adc_read_raw,
+	};
+
+	static int adc_read_raw(struct iio_dev *indio_dev,
+				struct iio_chan_spec const *chan, int *val,
+				int *val2, long mask)
+	{
+		ret = iio_hw_consumer_enable(hwc);
+
+		/* Acquire data */
+
+		ret = iio_hw_consumer_disable(hwc);
+	}
+
+	static int adc_probe(struct platform_device *pdev)
+	{
+		hwc = devm_iio_hw_consumer_alloc(&iio->dev);
+	}
+
+More details
+============
+.. kernel-doc:: include/linux/iio/hw-consumer.h
+.. kernel-doc:: drivers/iio/buffer/industrialio-hw-consumer.c
+   :export:
+

Documentation/driver-api/iio/index.rst

@@ -0,0 +1,18 @@
+.. include:: <isonum.txt>
+
+Industrial I/O
+==============
+
+**Copyright** |copy| 2015 Intel Corporation
+
+Contents:
+
+.. toctree::
+   :maxdepth: 2
+
+   intro
+   core
+   buffers
+   triggers
+   triggered-buffers
+   hw-consumer

Documentation/driver-api/iio/intro.rst

@@ -0,0 +1,33 @@
+.. include:: <isonum.txt>
+
+============
+Introduction
+============
+
+The main purpose of the Industrial I/O subsystem (IIO) is to provide support
+for devices that in some sense perform either
+analog-to-digital conversion (ADC) or digital-to-analog conversion (DAC)
+or both. The aim is to fill the gap between the somewhat similar hwmon and
+:doc:`input <../input>` subsystems. Hwmon is directed at low sample rate
+sensors used to monitor and control the system itself, like fan speed control
+or temperature measurement. :doc:`Input <../input>` is, as its name suggests,
+focused on human interaction input devices (keyboard, mouse, touchscreen).
+In some cases there is considerable overlap between these and IIO.
+
+Devices that fall into this category include:
+
+* analog to digital converters (ADCs)
+* accelerometers
+* capacitance to digital converters (CDCs)
+* digital to analog converters (DACs)
+* gyroscopes
+* inertial measurement units (IMUs)
+* color and light sensors
+* magnetometers
+* pressure sensors
+* proximity sensors
+* temperature sensors
+
+Usually these sensors are connected via :doc:`SPI <../spi>` or
+:doc:`I2C <../i2c>`. A common use case of the sensors devices is to have
+combined functionality (e.g. light plus proximity sensor).

Documentation/driver-api/iio/triggered-buffers.rst

@@ -0,0 +1,69 @@
+=================
+Triggered Buffers
+=================
+
+Now that we know what buffers and triggers are let's see how they work together.
+
+IIO triggered buffer setup
+==========================
+
+* :c:func:`iio_triggered_buffer_setup` — Setup triggered buffer and pollfunc
+* :c:func:`iio_triggered_buffer_cleanup` — Free resources allocated by
+  :c:func:`iio_triggered_buffer_setup`
+* struct :c:type:`iio_buffer_setup_ops` — buffer setup related callbacks
+
+A typical triggered buffer setup looks like this::
+
+    const struct iio_buffer_setup_ops sensor_buffer_setup_ops = {
+      .preenable    = sensor_buffer_preenable,
+      .postenable   = sensor_buffer_postenable,
+      .postdisable  = sensor_buffer_postdisable,
+      .predisable   = sensor_buffer_predisable,
+    };
+
+    irqreturn_t sensor_iio_pollfunc(int irq, void *p)
+    {
+        pf->timestamp = iio_get_time_ns((struct indio_dev *)p);
+        return IRQ_WAKE_THREAD;
+    }
+
+    irqreturn_t sensor_trigger_handler(int irq, void *p)
+    {
+        u16 buf[8];
+        int i = 0;
+
+        /* read data for each active channel */
+        for_each_set_bit(bit, active_scan_mask, masklength)
+            buf[i++] = sensor_get_data(bit)
+
+        iio_push_to_buffers_with_timestamp(indio_dev, buf, timestamp);
+
+        iio_trigger_notify_done(trigger);
+        return IRQ_HANDLED;
+    }
+
+    /* setup triggered buffer, usually in probe function */
+    iio_triggered_buffer_setup(indio_dev, sensor_iio_polfunc,
+                               sensor_trigger_handler,
+                               sensor_buffer_setup_ops);
+
+The important things to notice here are:
+
+* :c:type:`iio_buffer_setup_ops`, the buffer setup functions to be called at
+  predefined points in the buffer configuration sequence (e.g. before enable,
+  after disable). If not specified, the IIO core uses the default
+  iio_triggered_buffer_setup_ops.
+* **sensor_iio_pollfunc**, the function that will be used as top half of poll
+  function. It should do as little processing as possible, because it runs in
+  interrupt context. The most common operation is recording of the current
+  timestamp and for this reason one can use the IIO core defined
+  :c:func:`iio_pollfunc_store_time` function.
+* **sensor_trigger_handler**, the function that will be used as bottom half of
+  the poll function. This runs in the context of a kernel thread and all the
+  processing takes place here. It usually reads data from the device and
+  stores it in the internal buffer together with the timestamp recorded in the
+  top half.
+
+More details
+============
+.. kernel-doc:: drivers/iio/buffer/industrialio-triggered-buffer.c

Documentation/driver-api/iio/triggers.rst

@@ -0,0 +1,80 @@
+========
+Triggers
+========
+
+* struct :c:type:`iio_trigger` — industrial I/O trigger device
+* :c:func:`devm_iio_trigger_alloc` — Resource-managed iio_trigger_alloc
+* :c:func:`devm_iio_trigger_free` — Resource-managed iio_trigger_free
+* :c:func:`devm_iio_trigger_register` — Resource-managed iio_trigger_register
+* :c:func:`devm_iio_trigger_unregister` — Resource-managed
+  iio_trigger_unregister
+* :c:func:`iio_trigger_validate_own_device` — Check if a trigger and IIO
+  device belong to the same device
+
+In many situations it is useful for a driver to be able to capture data based
+on some external event (trigger) as opposed to periodically polling for data.
+An IIO trigger can be provided by a device driver that also has an IIO device
+based on hardware generated events (e.g. data ready or threshold exceeded) or
+provided by a separate driver from an independent interrupt source (e.g. GPIO
+line connected to some external system, timer interrupt or user space writing
+a specific file in sysfs). A trigger may initiate data capture for a number of
+sensors and also it may be completely unrelated to the sensor itself.
+
+IIO trigger sysfs interface
+===========================
+
+There are two locations in sysfs related to triggers:
+
+* :file:`/sys/bus/iio/devices/trigger{Y}/*`, this file is created once an
+  IIO trigger is registered with the IIO core and corresponds to trigger
+  with index Y.
+  Because triggers can be very different depending on type there are few
+  standard attributes that we can describe here:
+
+  * :file:`name`, trigger name that can be later used for association with a
+    device.
+  * :file:`sampling_frequency`, some timer based triggers use this attribute to
+    specify the frequency for trigger calls.
+
+* :file:`/sys/bus/iio/devices/iio:device{X}/trigger/*`, this directory is
+  created once the device supports a triggered buffer. We can associate a
+  trigger with our  device by writing the trigger's name in the
+  :file:`current_trigger` file.
+
+IIO trigger setup
+=================
+
+Let's see a simple example of how to setup a trigger to be used by a driver::
+
+      struct iio_trigger_ops trigger_ops = {
+          .set_trigger_state = sample_trigger_state,
+          .validate_device = sample_validate_device,
+      }
+
+      struct iio_trigger *trig;
+
+      /* first, allocate memory for our trigger */
+      trig = iio_trigger_alloc(dev, "trig-%s-%d", name, idx);
+
+      /* setup trigger operations field */
+      trig->ops = &trigger_ops;
+
+      /* now register the trigger with the IIO core */
+      iio_trigger_register(trig);
+
+IIO trigger ops
+===============
+
+* struct :c:type:`iio_trigger_ops` — operations structure for an iio_trigger.
+
+Notice that a trigger has a set of operations attached:
+
+* :file:`set_trigger_state`, switch the trigger on/off on demand.
+* :file:`validate_device`, function to validate the device when the current
+  trigger gets changed.
+
+More details
+============
+.. kernel-doc:: include/linux/iio/trigger.h
+.. kernel-doc:: drivers/iio/industrialio-trigger.c
+   :export:

Documentation/driver-api/index.rst

@@ -0,0 +1,62 @@
+========================================
+The Linux driver implementer's API guide
+========================================
+
+The kernel offers a wide variety of interfaces to support the development
+of device drivers.  This document is an only somewhat organized collection
+of some of those interfaces — it will hopefully get better over time!  The
+available subsections can be seen below.
+
+.. class:: toc-title
+
+	   Table of contents
+
+.. toctree::
+   :maxdepth: 2
+
+   basics
+   infrastructure
+   pm/index
+   clk
+   device-io
+   device_connection
+   dma-buf
+   device_link
+   message-based
+   sound
+   frame-buffer
+   regulator
+   iio/index
+   input
+   usb/index
+   pci
+   spi
+   i2c
+   hsi
+   edac
+   scsi
+   libata
+   target
+   mtdnand
+   miscellaneous
+   w1
+   rapidio
+   s390-drivers
+   vme
+   80211/index
+   uio-howto
+   firmware/index
+   pinctl
+   gpio/index
+   misc_devices
+   dmaengine/index
+   slimbus
+   soundwire/index
+   fpga/index
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`

Documentation/driver-api/infrastructure.rst

@@ -0,0 +1,84 @@
+Device drivers infrastructure
+=============================
+
+The Basic Device Driver-Model Structures
+----------------------------------------
+
+.. kernel-doc:: include/linux/device.h
+   :internal:
+
+Device Drivers Base
+-------------------
+
+.. kernel-doc:: drivers/base/init.c
+   :internal:
+
+.. kernel-doc:: drivers/base/driver.c
+   :export:
+
+.. kernel-doc:: drivers/base/core.c
+   :export:
+
+.. kernel-doc:: drivers/base/syscore.c
+   :export:
+
+.. kernel-doc:: drivers/base/class.c
+   :export:
+
+.. kernel-doc:: drivers/base/node.c
+   :internal:
+
+.. kernel-doc:: drivers/base/firmware_loader/main.c
+   :export:
+
+.. kernel-doc:: drivers/base/transport_class.c
+   :export:
+
+.. kernel-doc:: drivers/base/dd.c
+   :export:
+
+.. kernel-doc:: include/linux/platform_device.h
+   :internal:
+
+.. kernel-doc:: drivers/base/platform.c
+   :export:
+
+.. kernel-doc:: drivers/base/bus.c
+   :export:
+
+Device Drivers DMA Management
+-----------------------------
+
+.. kernel-doc:: kernel/dma/coherent.c
+   :export:
+
+.. kernel-doc:: kernel/dma/mapping.c
+   :export:
+
+Device drivers PnP support
+--------------------------
+
+.. kernel-doc:: drivers/pnp/core.c
+   :internal:
+
+.. kernel-doc:: drivers/pnp/card.c
+   :export:
+
+.. kernel-doc:: drivers/pnp/driver.c
+   :internal:
+
+.. kernel-doc:: drivers/pnp/manager.c
+   :export:
+
+.. kernel-doc:: drivers/pnp/support.c
+   :export:
+
+Userspace IO devices
+--------------------
+
+.. kernel-doc:: drivers/uio/uio.c
+   :export:
+
+.. kernel-doc:: include/linux/uio_driver.h
+   :internal:
+

Documentation/driver-api/input.rst

@@ -0,0 +1,51 @@
+Input Subsystem
+===============
+
+Input core
+----------
+
+.. kernel-doc:: include/linux/input.h
+   :internal:
+
+.. kernel-doc:: drivers/input/input.c
+   :export:
+
+.. kernel-doc:: drivers/input/ff-core.c
+   :export:
+
+.. kernel-doc:: drivers/input/ff-memless.c
+   :export:
+
+Multitouch Library
+------------------
+
+.. kernel-doc:: include/linux/input/mt.h
+   :internal:
+
+.. kernel-doc:: drivers/input/input-mt.c
+   :export:
+
+Polled input devices
+--------------------
+
+.. kernel-doc:: include/linux/input-polldev.h
+   :internal:
+
+.. kernel-doc:: drivers/input/input-polldev.c
+   :export:
+
+Matrix keyboards/keypads
+------------------------
+
+.. kernel-doc:: include/linux/input/matrix_keypad.h
+   :internal:
+
+Sparse keymap support
+---------------------
+
+.. kernel-doc:: include/linux/input/sparse-keymap.h
+   :internal:
+
+.. kernel-doc:: drivers/input/sparse-keymap.c
+   :export:
+

Documentation/driver-api/message-based.rst

@@ -0,0 +1,12 @@
+Message-based devices
+=====================
+
+Fusion message devices
+----------------------
+
+.. kernel-doc:: drivers/message/fusion/mptbase.c
+   :export:
+
+.. kernel-doc:: drivers/message/fusion/mptscsih.c
+   :export:
+

Documentation/driver-api/misc_devices.rst

@@ -0,0 +1,5 @@
+Miscellaneous Devices
+=====================
+
+.. kernel-doc:: drivers/char/misc.c
+   :export:

Documentation/driver-api/miscellaneous.rst

@@ -0,0 +1,49 @@
+Parallel Port Devices
+=====================
+
+.. kernel-doc:: include/linux/parport.h
+   :internal:
+
+.. kernel-doc:: drivers/parport/ieee1284.c
+   :export:
+
+.. kernel-doc:: drivers/parport/share.c
+   :export:
+
+.. kernel-doc:: drivers/parport/daisy.c
+   :internal:
+
+16x50 UART Driver
+=================
+
+.. kernel-doc:: drivers/tty/serial/serial_core.c
+   :export:
+
+.. kernel-doc:: drivers/tty/serial/8250/8250_core.c
+   :export:
+
+Pulse-Width Modulation (PWM)
+============================
+
+Pulse-width modulation is a modulation technique primarily used to
+control power supplied to electrical devices.
+
+The PWM framework provides an abstraction for providers and consumers of
+PWM signals. A controller that provides one or more PWM signals is
+registered as :c:type:`struct pwm_chip <pwm_chip>`. Providers
+are expected to embed this structure in a driver-specific structure.
+This structure contains fields that describe a particular chip.
+
+A chip exposes one or more PWM signal sources, each of which exposed as
+a :c:type:`struct pwm_device <pwm_device>`. Operations can be
+performed on PWM devices to control the period, duty cycle, polarity and
+active state of the signal.
+
+Note that PWM devices are exclusive resources: they can always only be
+used by one consumer at a time.
+
+.. kernel-doc:: include/linux/pwm.h
+   :internal:
+
+.. kernel-doc:: drivers/pwm/core.c
+   :export:

Documentation/driver-api/pci.rst

@@ -0,0 +1,47 @@
+PCI Support Library
+-------------------
+
+.. kernel-doc:: drivers/pci/pci.c
+   :export:
+
+.. kernel-doc:: drivers/pci/pci-driver.c
+   :export:
+
+.. kernel-doc:: drivers/pci/remove.c
+   :export:
+
+.. kernel-doc:: drivers/pci/search.c
+   :export:
+
+.. kernel-doc:: drivers/pci/msi.c
+   :export:
+
+.. kernel-doc:: drivers/pci/bus.c
+   :export:
+
+.. kernel-doc:: drivers/pci/access.c
+   :export:
+
+.. kernel-doc:: drivers/pci/irq.c
+   :export:
+
+.. kernel-doc:: drivers/pci/probe.c
+   :export:
+
+.. kernel-doc:: drivers/pci/slot.c
+   :export:
+
+.. kernel-doc:: drivers/pci/rom.c
+   :export:
+
+.. kernel-doc:: drivers/pci/iov.c
+   :export:
+
+.. kernel-doc:: drivers/pci/pci-sysfs.c
+   :internal:
+
+PCI Hotplug Support Library
+---------------------------
+
+.. kernel-doc:: drivers/pci/hotplug/pci_hotplug_core.c
+   :export:

Documentation/driver-api/pm/conf.py

@@ -0,0 +1,10 @@
+# -*- coding: utf-8; mode: python -*-
+
+project = "Device Power Management"
+
+tags.add("subproject")
+
+latex_documents = [
+    ('index', 'pm.tex', project,
+     'The kernel development community', 'manual'),
+]

Documentation/driver-api/pm/devices.rst

@@ -0,0 +1,827 @@
+.. |struct dev_pm_ops| replace:: :c:type:`struct dev_pm_ops <dev_pm_ops>`
+.. |struct dev_pm_domain| replace:: :c:type:`struct dev_pm_domain <dev_pm_domain>`
+.. |struct bus_type| replace:: :c:type:`struct bus_type <bus_type>`
+.. |struct device_type| replace:: :c:type:`struct device_type <device_type>`
+.. |struct class| replace:: :c:type:`struct class <class>`
+.. |struct wakeup_source| replace:: :c:type:`struct wakeup_source <wakeup_source>`
+.. |struct device| replace:: :c:type:`struct device <device>`
+
+==============================
+Device Power Management Basics
+==============================
+
+::
+
+ Copyright (c) 2010-2011 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc.
+ Copyright (c) 2010 Alan Stern <stern@rowland.harvard.edu>
+ Copyright (c) 2016 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+
+Most of the code in Linux is device drivers, so most of the Linux power
+management (PM) code is also driver-specific.  Most drivers will do very
+little; others, especially for platforms with small batteries (like cell
+phones), will do a lot.
+
+This writeup gives an overview of how drivers interact with system-wide
+power management goals, emphasizing the models and interfaces that are
+shared by everything that hooks up to the driver model core.  Read it as
+background for the domain-specific work you'd do with any specific driver.
+
+
+Two Models for Device Power Management
+======================================
+
+Drivers will use one or both of these models to put devices into low-power
+states:
+
+    System Sleep model:
+
+	Drivers can enter low-power states as part of entering system-wide
+	low-power states like "suspend" (also known as "suspend-to-RAM"), or
+	(mostly for systems with disks) "hibernation" (also known as
+	"suspend-to-disk").
+
+	This is something that device, bus, and class drivers collaborate on
+	by implementing various role-specific suspend and resume methods to
+	cleanly power down hardware and software subsystems, then reactivate
+	them without loss of data.
+
+	Some drivers can manage hardware wakeup events, which make the system
+	leave the low-power state.  This feature may be enabled or disabled
+	using the relevant :file:`/sys/devices/.../power/wakeup` file (for
+	Ethernet drivers the ioctl interface used by ethtool may also be used
+	for this purpose); enabling it may cost some power usage, but let the
+	whole system enter low-power states more often.
+
+    Runtime Power Management model:
+
+	Devices may also be put into low-power states while the system is
+	running, independently of other power management activity in principle.
+	However, devices are not generally independent of each other (for
+	example, a parent device cannot be suspended unless all of its child
+	devices have been suspended).  Moreover, depending on the bus type the
+	device is on, it may be necessary to carry out some bus-specific
+	operations on the device for this purpose.  Devices put into low power
+	states at run time may require special handling during system-wide power
+	transitions (suspend or hibernation).
+
+	For these reasons not only the device driver itself, but also the
+	appropriate subsystem (bus type, device type or device class) driver and
+	the PM core are involved in runtime power management.  As in the system
+	sleep power management case, they need to collaborate by implementing
+	various role-specific suspend and resume methods, so that the hardware
+	is cleanly powered down and reactivated without data or service loss.
+
+There's not a lot to be said about those low-power states except that they are
+very system-specific, and often device-specific.  Also, that if enough devices
+have been put into low-power states (at runtime), the effect may be very similar
+to entering some system-wide low-power state (system sleep) ... and that
+synergies exist, so that several drivers using runtime PM might put the system
+into a state where even deeper power saving options are available.
+
+Most suspended devices will have quiesced all I/O: no more DMA or IRQs (except
+for wakeup events), no more data read or written, and requests from upstream
+drivers are no longer accepted.  A given bus or platform may have different
+requirements though.
+
+Examples of hardware wakeup events include an alarm from a real time clock,
+network wake-on-LAN packets, keyboard or mouse activity, and media insertion
+or removal (for PCMCIA, MMC/SD, USB, and so on).
+
+Interfaces for Entering System Sleep States
+===========================================
+
+There are programming interfaces provided for subsystems (bus type, device type,
+device class) and device drivers to allow them to participate in the power
+management of devices they are concerned with.  These interfaces cover both
+system sleep and runtime power management.
+
+
+Device Power Management Operations
+----------------------------------
+
+Device power management operations, at the subsystem level as well as at the
+device driver level, are implemented by defining and populating objects of type
+|struct dev_pm_ops| defined in :file:`include/linux/pm.h`.  The roles of the
+methods included in it will be explained in what follows.  For now, it should be
+sufficient to remember that the last three methods are specific to runtime power
+management while the remaining ones are used during system-wide power
+transitions.
+
+There also is a deprecated "old" or "legacy" interface for power management
+operations available at least for some subsystems.  This approach does not use
+|struct dev_pm_ops| objects and it is suitable only for implementing system
+sleep power management methods in a limited way.  Therefore it is not described
+in this document, so please refer directly to the source code for more
+information about it.
+
+
+Subsystem-Level Methods
+-----------------------
+
+The core methods to suspend and resume devices reside in
+|struct dev_pm_ops| pointed to by the :c:member:`ops` member of
+|struct dev_pm_domain|, or by the :c:member:`pm` member of |struct bus_type|,
+|struct device_type| and |struct class|.  They are mostly of interest to the
+people writing infrastructure for platforms and buses, like PCI or USB, or
+device type and device class drivers.  They also are relevant to the writers of
+device drivers whose subsystems (PM domains, device types, device classes and
+bus types) don't provide all power management methods.
+
+Bus drivers implement these methods as appropriate for the hardware and the
+drivers using it; PCI works differently from USB, and so on.  Not many people
+write subsystem-level drivers; most driver code is a "device driver" that builds
+on top of bus-specific framework code.
+
+For more information on these driver calls, see the description later;
+they are called in phases for every device, respecting the parent-child
+sequencing in the driver model tree.
+
+
+:file:`/sys/devices/.../power/wakeup` files
+-------------------------------------------
+
+All device objects in the driver model contain fields that control the handling
+of system wakeup events (hardware signals that can force the system out of a
+sleep state).  These fields are initialized by bus or device driver code using
+:c:func:`device_set_wakeup_capable()` and :c:func:`device_set_wakeup_enable()`,
+defined in :file:`include/linux/pm_wakeup.h`.
+
+The :c:member:`power.can_wakeup` flag just records whether the device (and its
+driver) can physically support wakeup events.  The
+:c:func:`device_set_wakeup_capable()` routine affects this flag.  The
+:c:member:`power.wakeup` field is a pointer to an object of type
+|struct wakeup_source| used for controlling whether or not the device should use
+its system wakeup mechanism and for notifying the PM core of system wakeup
+events signaled by the device.  This object is only present for wakeup-capable
+devices (i.e. devices whose :c:member:`can_wakeup` flags are set) and is created
+(or removed) by :c:func:`device_set_wakeup_capable()`.
+
+Whether or not a device is capable of issuing wakeup events is a hardware
+matter, and the kernel is responsible for keeping track of it.  By contrast,
+whether or not a wakeup-capable device should issue wakeup events is a policy
+decision, and it is managed by user space through a sysfs attribute: the
+:file:`power/wakeup` file.  User space can write the "enabled" or "disabled"
+strings to it to indicate whether or not, respectively, the device is supposed
+to signal system wakeup.  This file is only present if the
+:c:member:`power.wakeup` object exists for the given device and is created (or
+removed) along with that object, by :c:func:`device_set_wakeup_capable()`.
+Reads from the file will return the corresponding string.
+
+The initial value in the :file:`power/wakeup` file is "disabled" for the
+majority of devices; the major exceptions are power buttons, keyboards, and
+Ethernet adapters whose WoL (wake-on-LAN) feature has been set up with ethtool.
+It should also default to "enabled" for devices that don't generate wakeup
+requests on their own but merely forward wakeup requests from one bus to another
+(like PCI Express ports).
+
+The :c:func:`device_may_wakeup()` routine returns true only if the
+:c:member:`power.wakeup` object exists and the corresponding :file:`power/wakeup`
+file contains the "enabled" string.  This information is used by subsystems,
+like the PCI bus type code, to see whether or not to enable the devices' wakeup
+mechanisms.  If device wakeup mechanisms are enabled or disabled directly by
+drivers, they also should use :c:func:`device_may_wakeup()` to decide what to do
+during a system sleep transition.  Device drivers, however, are not expected to
+call :c:func:`device_set_wakeup_enable()` directly in any case.
+
+It ought to be noted that system wakeup is conceptually different from "remote
+wakeup" used by runtime power management, although it may be supported by the
+same physical mechanism.  Remote wakeup is a feature allowing devices in
+low-power states to trigger specific interrupts to signal conditions in which
+they should be put into the full-power state.  Those interrupts may or may not
+be used to signal system wakeup events, depending on the hardware design.  On
+some systems it is impossible to trigger them from system sleep states.  In any
+case, remote wakeup should always be enabled for runtime power management for
+all devices and drivers that support it.
+
+
+:file:`/sys/devices/.../power/control` files
+--------------------------------------------
+
+Each device in the driver model has a flag to control whether it is subject to
+runtime power management.  This flag, :c:member:`runtime_auto`, is initialized
+by the bus type (or generally subsystem) code using :c:func:`pm_runtime_allow()`
+or :c:func:`pm_runtime_forbid()`; the default is to allow runtime power
+management.
+
+The setting can be adjusted by user space by writing either "on" or "auto" to
+the device's :file:`power/control` sysfs file.  Writing "auto" calls
+:c:func:`pm_runtime_allow()`, setting the flag and allowing the device to be
+runtime power-managed by its driver.  Writing "on" calls
+:c:func:`pm_runtime_forbid()`, clearing the flag, returning the device to full
+power if it was in a low-power state, and preventing the
+device from being runtime power-managed.  User space can check the current value
+of the :c:member:`runtime_auto` flag by reading that file.
+
+The device's :c:member:`runtime_auto` flag has no effect on the handling of
+system-wide power transitions.  In particular, the device can (and in the
+majority of cases should and will) be put into a low-power state during a
+system-wide transition to a sleep state even though its :c:member:`runtime_auto`
+flag is clear.
+
+For more information about the runtime power management framework, refer to
+:file:`Documentation/power/runtime_pm.txt`.
+
+
+Calling Drivers to Enter and Leave System Sleep States
+======================================================
+
+When the system goes into a sleep state, each device's driver is asked to
+suspend the device by putting it into a state compatible with the target
+system state.  That's usually some version of "off", but the details are
+system-specific.  Also, wakeup-enabled devices will usually stay partly
+functional in order to wake the system.
+
+When the system leaves that low-power state, the device's driver is asked to
+resume it by returning it to full power.  The suspend and resume operations
+always go together, and both are multi-phase operations.
+
+For simple drivers, suspend might quiesce the device using class code
+and then turn its hardware as "off" as possible during suspend_noirq.  The
+matching resume calls would then completely reinitialize the hardware
+before reactivating its class I/O queues.
+
+More power-aware drivers might prepare the devices for triggering system wakeup
+events.
+
+
+Call Sequence Guarantees
+------------------------
+
+To ensure that bridges and similar links needing to talk to a device are
+available when the device is suspended or resumed, the device hierarchy is
+walked in a bottom-up order to suspend devices.  A top-down order is
+used to resume those devices.
+
+The ordering of the device hierarchy is defined by the order in which devices
+get registered:  a child can never be registered, probed or resumed before
+its parent; and can't be removed or suspended after that parent.
+
+The policy is that the device hierarchy should match hardware bus topology.
+[Or at least the control bus, for devices which use multiple busses.]
+In particular, this means that a device registration may fail if the parent of
+the device is suspending (i.e. has been chosen by the PM core as the next
+device to suspend) or has already suspended, as well as after all of the other
+devices have been suspended.  Device drivers must be prepared to cope with such
+situations.
+
+
+System Power Management Phases
+------------------------------
+
+Suspending or resuming the system is done in several phases.  Different phases
+are used for suspend-to-idle, shallow (standby), and deep ("suspend-to-RAM")
+sleep states and the hibernation state ("suspend-to-disk").  Each phase involves
+executing callbacks for every device before the next phase begins.  Not all
+buses or classes support all these callbacks and not all drivers use all the
+callbacks.  The various phases always run after tasks have been frozen and
+before they are unfrozen.  Furthermore, the ``*_noirq`` phases run at a time
+when IRQ handlers have been disabled (except for those marked with the
+IRQF_NO_SUSPEND flag).
+
+All phases use PM domain, bus, type, class or driver callbacks (that is, methods
+defined in ``dev->pm_domain->ops``, ``dev->bus->pm``, ``dev->type->pm``,
+``dev->class->pm`` or ``dev->driver->pm``).  These callbacks are regarded by the
+PM core as mutually exclusive.  Moreover, PM domain callbacks always take
+precedence over all of the other callbacks and, for example, type callbacks take
+precedence over bus, class and driver callbacks.  To be precise, the following
+rules are used to determine which callback to execute in the given phase:
+
+    1.	If ``dev->pm_domain`` is present, the PM core will choose the callback
+	provided by ``dev->pm_domain->ops`` for execution.
+
+    2.	Otherwise, if both ``dev->type`` and ``dev->type->pm`` are present, the
+	callback provided by ``dev->type->pm`` will be chosen for execution.
+
+    3.	Otherwise, if both ``dev->class`` and ``dev->class->pm`` are present,
+	the callback provided by ``dev->class->pm`` will be chosen for
+	execution.
+
+    4.	Otherwise, if both ``dev->bus`` and ``dev->bus->pm`` are present, the
+	callback provided by ``dev->bus->pm`` will be chosen for execution.
+
+This allows PM domains and device types to override callbacks provided by bus
+types or device classes if necessary.
+
+The PM domain, type, class and bus callbacks may in turn invoke device- or
+driver-specific methods stored in ``dev->driver->pm``, but they don't have to do
+that.
+
+If the subsystem callback chosen for execution is not present, the PM core will
+execute the corresponding method from the ``dev->driver->pm`` set instead if
+there is one.
+
+
+Entering System Suspend
+-----------------------
+
+When the system goes into the freeze, standby or memory sleep state,
+the phases are: ``prepare``, ``suspend``, ``suspend_late``, ``suspend_noirq``.
+
+    1.	The ``prepare`` phase is meant to prevent races by preventing new
+	devices from being registered; the PM core would never know that all the
+	children of a device had been suspended if new children could be
+	registered at will.  [By contrast, from the PM core's perspective,
+	devices may be unregistered at any time.]  Unlike the other
+	suspend-related phases, during the ``prepare`` phase the device
+	hierarchy is traversed top-down.
+
+	After the ``->prepare`` callback method returns, no new children may be
+	registered below the device.  The method may also prepare the device or
+	driver in some way for the upcoming system power transition, but it
+	should not put the device into a low-power state.  Moreover, if the
+	device supports runtime power management, the ``->prepare`` callback
+	method must not update its state in case it is necessary to resume it
+	from runtime suspend later on.
+
+	For devices supporting runtime power management, the return value of the
+	prepare callback can be used to indicate to the PM core that it may
+	safely leave the device in runtime suspend (if runtime-suspended
+	already), provided that all of the device's descendants are also left in
+	runtime suspend.  Namely, if the prepare callback returns a positive
+	number and that happens for all of the descendants of the device too,
+	and all of them (including the device itself) are runtime-suspended, the
+	PM core will skip the ``suspend``, ``suspend_late`` and
+	``suspend_noirq`` phases as well as all of the corresponding phases of
+	the subsequent device resume for all of these devices.	In that case,
+	the ``->complete`` callback will be invoked directly after the
+	``->prepare`` callback and is entirely responsible for putting the
+	device into a consistent state as appropriate.
+
+	Note that this direct-complete procedure applies even if the device is
+	disabled for runtime PM; only the runtime-PM status matters.  It follows
+	that if a device has system-sleep callbacks but does not support runtime
+	PM, then its prepare callback must never return a positive value.  This
+	is because all such devices are initially set to runtime-suspended with
+	runtime PM disabled.
+
+	This feature also can be controlled by device drivers by using the
+	``DPM_FLAG_NEVER_SKIP`` and ``DPM_FLAG_SMART_PREPARE`` driver power
+	management flags.  [Typically, they are set at the time the driver is
+	probed against the device in question by passing them to the
+	:c:func:`dev_pm_set_driver_flags` helper function.]  If the first of
+	these flags is set, the PM core will not apply the direct-complete
+	procedure described above to the given device and, consequenty, to any
+	of its ancestors.  The second flag, when set, informs the middle layer
+	code (bus types, device types, PM domains, classes) that it should take
+	the return value of the ``->prepare`` callback provided by the driver
+	into account and it may only return a positive value from its own
+	``->prepare`` callback if the driver's one also has returned a positive
+	value.
+
+    2.	The ``->suspend`` methods should quiesce the device to stop it from
+	performing I/O.  They also may save the device registers and put it into
+	the appropriate low-power state, depending on the bus type the device is
+	on, and they may enable wakeup events.
+
+	However, for devices supporting runtime power management, the
+	``->suspend`` methods provided by subsystems (bus types and PM domains
+	in particular) must follow an additional rule regarding what can be done
+	to the devices before their drivers' ``->suspend`` methods are called.
+	Namely, they can only resume the devices from runtime suspend by
+	calling :c:func:`pm_runtime_resume` for them, if that is necessary, and
+	they must not update the state of the devices in any other way at that
+	time (in case the drivers need to resume the devices from runtime
+	suspend in their ``->suspend`` methods).
+
+    3.	For a number of devices it is convenient to split suspend into the
+	"quiesce device" and "save device state" phases, in which cases
+	``suspend_late`` is meant to do the latter.  It is always executed after
+	runtime power management has been disabled for the device in question.
+
+    4.	The ``suspend_noirq`` phase occurs after IRQ handlers have been disabled,
+	which means that the driver's interrupt handler will not be called while
+	the callback method is running.  The ``->suspend_noirq`` methods should
+	save the values of the device's registers that weren't saved previously
+	and finally put the device into the appropriate low-power state.
+
+	The majority of subsystems and device drivers need not implement this
+	callback.  However, bus types allowing devices to share interrupt
+	vectors, like PCI, generally need it; otherwise a driver might encounter
+	an error during the suspend phase by fielding a shared interrupt
+	generated by some other device after its own device had been set to low
+	power.
+
+At the end of these phases, drivers should have stopped all I/O transactions
+(DMA, IRQs), saved enough state that they can re-initialize or restore previous
+state (as needed by the hardware), and placed the device into a low-power state.
+On many platforms they will gate off one or more clock sources; sometimes they
+will also switch off power supplies or reduce voltages.  [Drivers supporting
+runtime PM may already have performed some or all of these steps.]
+
+If :c:func:`device_may_wakeup(dev)` returns ``true``, the device should be
+prepared for generating hardware wakeup signals to trigger a system wakeup event
+when the system is in the sleep state.  For example, :c:func:`enable_irq_wake()`
+might identify GPIO signals hooked up to a switch or other external hardware,
+and :c:func:`pci_enable_wake()` does something similar for the PCI PME signal.
+
+If any of these callbacks returns an error, the system won't enter the desired
+low-power state.  Instead, the PM core will unwind its actions by resuming all
+the devices that were suspended.
+
+
+Leaving System Suspend
+----------------------
+
+When resuming from freeze, standby or memory sleep, the phases are:
+``resume_noirq``, ``resume_early``, ``resume``, ``complete``.
+
+    1.	The ``->resume_noirq`` callback methods should perform any actions
+	needed before the driver's interrupt handlers are invoked.  This
+	generally means undoing the actions of the ``suspend_noirq`` phase.  If
+	the bus type permits devices to share interrupt vectors, like PCI, the
+	method should bring the device and its driver into a state in which the
+	driver can recognize if the device is the source of incoming interrupts,
+	if any, and handle them correctly.
+
+	For example, the PCI bus type's ``->pm.resume_noirq()`` puts the device
+	into the full-power state (D0 in the PCI terminology) and restores the
+	standard configuration registers of the device.  Then it calls the
+	device driver's ``->pm.resume_noirq()`` method to perform device-specific
+	actions.
+
+    2.	The ``->resume_early`` methods should prepare devices for the execution
+	of the resume methods.  This generally involves undoing the actions of
+	the preceding ``suspend_late`` phase.
+
+    3.	The ``->resume`` methods should bring the device back to its operating
+	state, so that it can perform normal I/O.  This generally involves
+	undoing the actions of the ``suspend`` phase.
+
+    4.	The ``complete`` phase should undo the actions of the ``prepare`` phase.
+        For this reason, unlike the other resume-related phases, during the
+        ``complete`` phase the device hierarchy is traversed bottom-up.
+
+	Note, however, that new children may be registered below the device as
+	soon as the ``->resume`` callbacks occur; it's not necessary to wait
+	until the ``complete`` phase with that.
+
+	Moreover, if the preceding ``->prepare`` callback returned a positive
+	number, the device may have been left in runtime suspend throughout the
+	whole system suspend and resume (the ``suspend``, ``suspend_late``,
+	``suspend_noirq`` phases of system suspend and the ``resume_noirq``,
+	``resume_early``, ``resume`` phases of system resume may have been
+	skipped for it).  In that case, the ``->complete`` callback is entirely
+	responsible for putting the device into a consistent state after system
+	suspend if necessary.  [For example, it may need to queue up a runtime
+	resume request for the device for this purpose.]  To check if that is
+	the case, the ``->complete`` callback can consult the device's
+	``power.direct_complete`` flag.  Namely, if that flag is set when the
+	``->complete`` callback is being run, it has been called directly after
+	the preceding ``->prepare`` and special actions may be required
+	to make the device work correctly afterward.
+
+At the end of these phases, drivers should be as functional as they were before
+suspending: I/O can be performed using DMA and IRQs, and the relevant clocks are
+gated on.
+
+However, the details here may again be platform-specific.  For example,
+some systems support multiple "run" states, and the mode in effect at
+the end of resume might not be the one which preceded suspension.
+That means availability of certain clocks or power supplies changed,
+which could easily affect how a driver works.
+
+Drivers need to be able to handle hardware which has been reset since all of the
+suspend methods were called, for example by complete reinitialization.
+This may be the hardest part, and the one most protected by NDA'd documents
+and chip errata.  It's simplest if the hardware state hasn't changed since
+the suspend was carried out, but that can only be guaranteed if the target
+system sleep entered was suspend-to-idle.  For the other system sleep states
+that may not be the case (and usually isn't for ACPI-defined system sleep
+states, like S3).
+
+Drivers must also be prepared to notice that the device has been removed
+while the system was powered down, whenever that's physically possible.
+PCMCIA, MMC, USB, Firewire, SCSI, and even IDE are common examples of busses
+where common Linux platforms will see such removal.  Details of how drivers
+will notice and handle such removals are currently bus-specific, and often
+involve a separate thread.
+
+These callbacks may return an error value, but the PM core will ignore such
+errors since there's nothing it can do about them other than printing them in
+the system log.
+
+
+Entering Hibernation
+--------------------
+
+Hibernating the system is more complicated than putting it into sleep states,
+because it involves creating and saving a system image.  Therefore there are
+more phases for hibernation, with a different set of callbacks.  These phases
+always run after tasks have been frozen and enough memory has been freed.
+
+The general procedure for hibernation is to quiesce all devices ("freeze"),
+create an image of the system memory while everything is stable, reactivate all
+devices ("thaw"), write the image to permanent storage, and finally shut down
+the system ("power off").  The phases used to accomplish this are: ``prepare``,
+``freeze``, ``freeze_late``, ``freeze_noirq``, ``thaw_noirq``, ``thaw_early``,
+``thaw``, ``complete``, ``prepare``, ``poweroff``, ``poweroff_late``,
+``poweroff_noirq``.
+
+    1.	The ``prepare`` phase is discussed in the "Entering System Suspend"
+	section above.
+
+    2.	The ``->freeze`` methods should quiesce the device so that it doesn't
+	generate IRQs or DMA, and they may need to save the values of device
+	registers.  However the device does not have to be put in a low-power
+	state, and to save time it's best not to do so.  Also, the device should
+	not be prepared to generate wakeup events.
+
+    3.	The ``freeze_late`` phase is analogous to the ``suspend_late`` phase
+	described earlier, except that the device should not be put into a
+	low-power state and should not be allowed to generate wakeup events.
+
+    4.	The ``freeze_noirq`` phase is analogous to the ``suspend_noirq`` phase
+	discussed earlier, except again that the device should not be put into
+	a low-power state and should not be allowed to generate wakeup events.
+
+At this point the system image is created.  All devices should be inactive and
+the contents of memory should remain undisturbed while this happens, so that the
+image forms an atomic snapshot of the system state.
+
+    5.	The ``thaw_noirq`` phase is analogous to the ``resume_noirq`` phase
+	discussed earlier.  The main difference is that its methods can assume
+	the device is in the same state as at the end of the ``freeze_noirq``
+	phase.
+
+    6.	The ``thaw_early`` phase is analogous to the ``resume_early`` phase
+	described above.  Its methods should undo the actions of the preceding
+	``freeze_late``, if necessary.
+
+    7.	The ``thaw`` phase is analogous to the ``resume`` phase discussed
+	earlier.  Its methods should bring the device back to an operating
+	state, so that it can be used for saving the image if necessary.
+
+    8.	The ``complete`` phase is discussed in the "Leaving System Suspend"
+	section above.
+
+At this point the system image is saved, and the devices then need to be
+prepared for the upcoming system shutdown.  This is much like suspending them
+before putting the system into the suspend-to-idle, shallow or deep sleep state,
+and the phases are similar.
+
+    9.	The ``prepare`` phase is discussed above.
+
+    10.	The ``poweroff`` phase is analogous to the ``suspend`` phase.
+
+    11.	The ``poweroff_late`` phase is analogous to the ``suspend_late`` phase.
+
+    12.	The ``poweroff_noirq`` phase is analogous to the ``suspend_noirq`` phase.
+
+The ``->poweroff``, ``->poweroff_late`` and ``->poweroff_noirq`` callbacks
+should do essentially the same things as the ``->suspend``, ``->suspend_late``
+and ``->suspend_noirq`` callbacks, respectively.  The only notable difference is
+that they need not store the device register values, because the registers
+should already have been stored during the ``freeze``, ``freeze_late`` or
+``freeze_noirq`` phases.
+
+
+Leaving Hibernation
+-------------------
+
+Resuming from hibernation is, again, more complicated than resuming from a sleep
+state in which the contents of main memory are preserved, because it requires
+a system image to be loaded into memory and the pre-hibernation memory contents
+to be restored before control can be passed back to the image kernel.
+
+Although in principle the image might be loaded into memory and the
+pre-hibernation memory contents restored by the boot loader, in practice this
+can't be done because boot loaders aren't smart enough and there is no
+established protocol for passing the necessary information.  So instead, the
+boot loader loads a fresh instance of the kernel, called "the restore kernel",
+into memory and passes control to it in the usual way.  Then the restore kernel
+reads the system image, restores the pre-hibernation memory contents, and passes
+control to the image kernel.  Thus two different kernel instances are involved
+in resuming from hibernation.  In fact, the restore kernel may be completely
+different from the image kernel: a different configuration and even a different
+version.  This has important consequences for device drivers and their
+subsystems.
+
+To be able to load the system image into memory, the restore kernel needs to
+include at least a subset of device drivers allowing it to access the storage
+medium containing the image, although it doesn't need to include all of the
+drivers present in the image kernel.  After the image has been loaded, the
+devices managed by the boot kernel need to be prepared for passing control back
+to the image kernel.  This is very similar to the initial steps involved in
+creating a system image, and it is accomplished in the same way, using
+``prepare``, ``freeze``, and ``freeze_noirq`` phases.  However, the devices
+affected by these phases are only those having drivers in the restore kernel;
+other devices will still be in whatever state the boot loader left them.
+
+Should the restoration of the pre-hibernation memory contents fail, the restore
+kernel would go through the "thawing" procedure described above, using the
+``thaw_noirq``, ``thaw_early``, ``thaw``, and ``complete`` phases, and then
+continue running normally.  This happens only rarely.  Most often the
+pre-hibernation memory contents are restored successfully and control is passed
+to the image kernel, which then becomes responsible for bringing the system back
+to the working state.
+
+To achieve this, the image kernel must restore the devices' pre-hibernation
+functionality.  The operation is much like waking up from a sleep state (with
+the memory contents preserved), although it involves different phases:
+``restore_noirq``, ``restore_early``, ``restore``, ``complete``.
+
+    1.	The ``restore_noirq`` phase is analogous to the ``resume_noirq`` phase.
+
+    2.	The ``restore_early`` phase is analogous to the ``resume_early`` phase.
+
+    3.	The ``restore`` phase is analogous to the ``resume`` phase.
+
+    4.	The ``complete`` phase is discussed above.
+
+The main difference from ``resume[_early|_noirq]`` is that
+``restore[_early|_noirq]`` must assume the device has been accessed and
+reconfigured by the boot loader or the restore kernel.  Consequently, the state
+of the device may be different from the state remembered from the ``freeze``,
+``freeze_late`` and ``freeze_noirq`` phases.  The device may even need to be
+reset and completely re-initialized.  In many cases this difference doesn't
+matter, so the ``->resume[_early|_noirq]`` and ``->restore[_early|_norq]``
+method pointers can be set to the same routines.  Nevertheless, different
+callback pointers are used in case there is a situation where it actually does
+matter.
+
+
+Power Management Notifiers
+==========================
+
+There are some operations that cannot be carried out by the power management
+callbacks discussed above, because the callbacks occur too late or too early.
+To handle these cases, subsystems and device drivers may register power
+management notifiers that are called before tasks are frozen and after they have
+been thawed.  Generally speaking, the PM notifiers are suitable for performing
+actions that either require user space to be available, or at least won't
+interfere with user space.
+
+For details refer to :doc:`notifiers`.
+
+
+Device Low-Power (suspend) States
+=================================
+
+Device low-power states aren't standard.  One device might only handle
+"on" and "off", while another might support a dozen different versions of
+"on" (how many engines are active?), plus a state that gets back to "on"
+faster than from a full "off".
+
+Some buses define rules about what different suspend states mean.  PCI
+gives one example: after the suspend sequence completes, a non-legacy
+PCI device may not perform DMA or issue IRQs, and any wakeup events it
+issues would be issued through the PME# bus signal.  Plus, there are
+several PCI-standard device states, some of which are optional.
+
+In contrast, integrated system-on-chip processors often use IRQs as the
+wakeup event sources (so drivers would call :c:func:`enable_irq_wake`) and
+might be able to treat DMA completion as a wakeup event (sometimes DMA can stay
+active too, it'd only be the CPU and some peripherals that sleep).
+
+Some details here may be platform-specific.  Systems may have devices that
+can be fully active in certain sleep states, such as an LCD display that's
+refreshed using DMA while most of the system is sleeping lightly ... and
+its frame buffer might even be updated by a DSP or other non-Linux CPU while
+the Linux control processor stays idle.
+
+Moreover, the specific actions taken may depend on the target system state.
+One target system state might allow a given device to be very operational;
+another might require a hard shut down with re-initialization on resume.
+And two different target systems might use the same device in different
+ways; the aforementioned LCD might be active in one product's "standby",
+but a different product using the same SOC might work differently.
+
+
+Device Power Management Domains
+===============================
+
+Sometimes devices share reference clocks or other power resources.  In those
+cases it generally is not possible to put devices into low-power states
+individually.  Instead, a set of devices sharing a power resource can be put
+into a low-power state together at the same time by turning off the shared
+power resource.  Of course, they also need to be put into the full-power state
+together, by turning the shared power resource on.  A set of devices with this
+property is often referred to as a power domain. A power domain may also be
+nested inside another power domain. The nested domain is referred to as the
+sub-domain of the parent domain.
+
+Support for power domains is provided through the :c:member:`pm_domain` field of
+|struct device|.  This field is a pointer to an object of type
+|struct dev_pm_domain|, defined in :file:`include/linux/pm.h`, providing a set
+of power management callbacks analogous to the subsystem-level and device driver
+callbacks that are executed for the given device during all power transitions,
+instead of the respective subsystem-level callbacks.  Specifically, if a
+device's :c:member:`pm_domain` pointer is not NULL, the ``->suspend()`` callback
+from the object pointed to by it will be executed instead of its subsystem's
+(e.g. bus type's) ``->suspend()`` callback and analogously for all of the
+remaining callbacks.  In other words, power management domain callbacks, if
+defined for the given device, always take precedence over the callbacks provided
+by the device's subsystem (e.g. bus type).
+
+The support for device power management domains is only relevant to platforms
+needing to use the same device driver power management callbacks in many
+different power domain configurations and wanting to avoid incorporating the
+support for power domains into subsystem-level callbacks, for example by
+modifying the platform bus type.  Other platforms need not implement it or take
+it into account in any way.
+
+Devices may be defined as IRQ-safe which indicates to the PM core that their
+runtime PM callbacks may be invoked with disabled interrupts (see
+:file:`Documentation/power/runtime_pm.txt` for more information).  If an
+IRQ-safe device belongs to a PM domain, the runtime PM of the domain will be
+disallowed, unless the domain itself is defined as IRQ-safe. However, it
+makes sense to define a PM domain as IRQ-safe only if all the devices in it
+are IRQ-safe. Moreover, if an IRQ-safe domain has a parent domain, the runtime
+PM of the parent is only allowed if the parent itself is IRQ-safe too with the
+additional restriction that all child domains of an IRQ-safe parent must also
+be IRQ-safe.
+
+
+Runtime Power Management
+========================
+
+Many devices are able to dynamically power down while the system is still
+running. This feature is useful for devices that are not being used, and
+can offer significant power savings on a running system.  These devices
+often support a range of runtime power states, which might use names such
+as "off", "sleep", "idle", "active", and so on.  Those states will in some
+cases (like PCI) be partially constrained by the bus the device uses, and will
+usually include hardware states that are also used in system sleep states.
+
+A system-wide power transition can be started while some devices are in low
+power states due to runtime power management.  The system sleep PM callbacks
+should recognize such situations and react to them appropriately, but the
+necessary actions are subsystem-specific.
+
+In some cases the decision may be made at the subsystem level while in other
+cases the device driver may be left to decide.  In some cases it may be
+desirable to leave a suspended device in that state during a system-wide power
+transition, but in other cases the device must be put back into the full-power
+state temporarily, for example so that its system wakeup capability can be
+disabled.  This all depends on the hardware and the design of the subsystem and
+device driver in question.
+
+If it is necessary to resume a device from runtime suspend during a system-wide
+transition into a sleep state, that can be done by calling
+:c:func:`pm_runtime_resume` for it from the ``->suspend`` callback (or its
+couterpart for transitions related to hibernation) of either the device's driver
+or a subsystem responsible for it (for example, a bus type or a PM domain).
+That is guaranteed to work by the requirement that subsystems must not change
+the state of devices (possibly except for resuming them from runtime suspend)
+from their ``->prepare`` and ``->suspend`` callbacks (or equivalent) *before*
+invoking device drivers' ``->suspend`` callbacks (or equivalent).
+
+Some bus types and PM domains have a policy to resume all devices from runtime
+suspend upfront in their ``->suspend`` callbacks, but that may not be really
+necessary if the driver of the device can cope with runtime-suspended devices.
+The driver can indicate that by setting ``DPM_FLAG_SMART_SUSPEND`` in
+:c:member:`power.driver_flags` at the probe time, by passing it to the
+:c:func:`dev_pm_set_driver_flags` helper.  That also may cause middle-layer code
+(bus types, PM domains etc.) to skip the ``->suspend_late`` and
+``->suspend_noirq`` callbacks provided by the driver if the device remains in
+runtime suspend at the beginning of the ``suspend_late`` phase of system-wide
+suspend (or in the ``poweroff_late`` phase of hibernation), when runtime PM
+has been disabled for it, under the assumption that its state should not change
+after that point until the system-wide transition is over (the PM core itself
+does that for devices whose "noirq", "late" and "early" system-wide PM callbacks
+are executed directly by it).  If that happens, the driver's system-wide resume
+callbacks, if present, may still be invoked during the subsequent system-wide
+resume transition and the device's runtime power management status may be set
+to "active" before enabling runtime PM for it, so the driver must be prepared to
+cope with the invocation of its system-wide resume callbacks back-to-back with
+its ``->runtime_suspend`` one (without the intervening ``->runtime_resume`` and
+so on) and the final state of the device must reflect the "active" runtime PM
+status in that case.
+
+During system-wide resume from a sleep state it's easiest to put devices into
+the full-power state, as explained in :file:`Documentation/power/runtime_pm.txt`.
+[Refer to that document for more information regarding this particular issue as
+well as for information on the device runtime power management framework in
+general.]
+
+However, it often is desirable to leave devices in suspend after system
+transitions to the working state, especially if those devices had been in
+runtime suspend before the preceding system-wide suspend (or analogous)
+transition.  Device drivers can use the ``DPM_FLAG_LEAVE_SUSPENDED`` flag to
+indicate to the PM core (and middle-layer code) that they prefer the specific
+devices handled by them to be left suspended and they have no problems with
+skipping their system-wide resume callbacks for this reason.  Whether or not the
+devices will actually be left in suspend may depend on their state before the
+given system suspend-resume cycle and on the type of the system transition under
+way.  In particular, devices are not left suspended if that transition is a
+restore from hibernation, as device states are not guaranteed to be reflected
+by the information stored in the hibernation image in that case.
+
+The middle-layer code involved in the handling of the device is expected to
+indicate to the PM core if the device may be left in suspend by setting its
+:c:member:`power.may_skip_resume` status bit which is checked by the PM core
+during the "noirq" phase of the preceding system-wide suspend (or analogous)
+transition.  The middle layer is then responsible for handling the device as
+appropriate in its "noirq" resume callback, which is executed regardless of
+whether or not the device is left suspended, but the other resume callbacks
+(except for ``->complete``) will be skipped automatically by the PM core if the
+device really can be left in suspend.
+
+For devices whose "noirq", "late" and "early" driver callbacks are invoked
+directly by the PM core, all of the system-wide resume callbacks are skipped if
+``DPM_FLAG_LEAVE_SUSPENDED`` is set and the device is in runtime suspend during
+the ``suspend_noirq`` (or analogous) phase or the transition under way is a
+proper system suspend (rather than anything related to hibernation) and the
+device's wakeup settings are suitable for runtime PM (that is, it cannot
+generate wakeup signals at all or it is allowed to wake up the system from
+sleep).

Documentation/driver-api/pm/index.rst

@@ -0,0 +1,16 @@
+=======================
+Device Power Management
+=======================
+
+.. toctree::
+
+   devices
+   notifiers
+   types
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`

Documentation/driver-api/pm/notifiers.rst

@@ -0,0 +1,70 @@
+=============================
+Suspend/Hibernation Notifiers
+=============================
+
+::
+
+ Copyright (c) 2016 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+
+There are some operations that subsystems or drivers may want to carry out
+before hibernation/suspend or after restore/resume, but they require the system
+to be fully functional, so the drivers' and subsystems' ``->suspend()`` and
+``->resume()`` or even ``->prepare()`` and ``->complete()`` callbacks are not
+suitable for this purpose.
+
+For example, device drivers may want to upload firmware to their devices after
+resume/restore, but they cannot do it by calling :c:func:`request_firmware()`
+from their ``->resume()`` or ``->complete()`` callback routines (user land
+processes are frozen at these points).  The solution may be to load the firmware
+into memory before processes are frozen and upload it from there in the
+``->resume()`` routine.  A suspend/hibernation notifier may be used for that.
+
+Subsystems or drivers having such needs can register suspend notifiers that
+will be called upon the following events by the PM core:
+
+``PM_HIBERNATION_PREPARE``
+	The system is going to hibernate, tasks will be frozen immediately. This
+	is different from ``PM_SUSPEND_PREPARE`` below,	because in this case
+	additional work is done between the notifiers and the invocation of PM
+	callbacks for the "freeze" transition.
+
+``PM_POST_HIBERNATION``
+	The system memory state has been restored from a hibernation image or an
+	error occurred during hibernation.  Device restore callbacks have been
+	executed and tasks have been thawed.
+
+``PM_RESTORE_PREPARE``
+	The system is going to restore a hibernation image.  If all goes well,
+	the restored image kernel will issue a ``PM_POST_HIBERNATION``
+	notification.
+
+``PM_POST_RESTORE``
+	An error occurred during restore from hibernation.  Device restore
+	callbacks have been executed and tasks have been thawed.
+
+``PM_SUSPEND_PREPARE``
+	The system is preparing for suspend.
+
+``PM_POST_SUSPEND``
+	The system has just resumed or an error occurred during suspend.  Device
+	resume callbacks have been executed and tasks have been thawed.
+
+It is generally assumed that whatever the notifiers do for
+``PM_HIBERNATION_PREPARE``, should be undone for ``PM_POST_HIBERNATION``.
+Analogously, operations carried out for ``PM_SUSPEND_PREPARE`` should be
+reversed for ``PM_POST_SUSPEND``.
+
+Moreover, if one of the notifiers fails for the ``PM_HIBERNATION_PREPARE`` or
+``PM_SUSPEND_PREPARE`` event, the notifiers that have already succeeded for that
+event will be called for ``PM_POST_HIBERNATION`` or ``PM_POST_SUSPEND``,
+respectively.
+
+The hibernation and suspend notifiers are called with :c:data:`pm_mutex` held.
+They are defined in the usual way, but their last argument is meaningless (it is
+always NULL).
+
+To register and/or unregister a suspend notifier use
+:c:func:`register_pm_notifier()` and :c:func:`unregister_pm_notifier()`,
+respectively (both defined in :file:`include/linux/suspend.h`).  If you don't
+need to unregister the notifier, you can also use the :c:func:`pm_notifier()`
+macro defined in :file:`include/linux/suspend.h`.

Documentation/driver-api/pm/types.rst

@@ -0,0 +1,5 @@
+==================================
+Device Power Management Data Types
+==================================
+
+.. kernel-doc:: include/linux/pm.h

Documentation/driver-api/rapidio.rst

@@ -0,0 +1,107 @@
+=======================
+RapidIO Subsystem Guide
+=======================
+
+:Author: Matt Porter
+
+Introduction
+============
+
+RapidIO is a high speed switched fabric interconnect with features aimed
+at the embedded market. RapidIO provides support for memory-mapped I/O
+as well as message-based transactions over the switched fabric network.
+RapidIO has a standardized discovery mechanism not unlike the PCI bus
+standard that allows simple detection of devices in a network.
+
+This documentation is provided for developers intending to support
+RapidIO on new architectures, write new drivers, or to understand the
+subsystem internals.
+
+Known Bugs and Limitations
+==========================
+
+Bugs
+----
+
+None. ;)
+
+Limitations
+-----------
+
+1. Access/management of RapidIO memory regions is not supported
+
+2. Multiple host enumeration is not supported
+
+RapidIO driver interface
+========================
+
+Drivers are provided a set of calls in order to interface with the
+subsystem to gather info on devices, request/map memory region
+resources, and manage mailboxes/doorbells.
+
+Functions
+---------
+
+.. kernel-doc:: include/linux/rio_drv.h
+   :internal:
+
+.. kernel-doc:: drivers/rapidio/rio-driver.c
+   :export:
+
+.. kernel-doc:: drivers/rapidio/rio.c
+   :export:
+
+Internals
+=========
+
+This chapter contains the autogenerated documentation of the RapidIO
+subsystem.
+
+Structures
+----------
+
+.. kernel-doc:: include/linux/rio.h
+   :internal:
+
+Enumeration and Discovery
+-------------------------
+
+.. kernel-doc:: drivers/rapidio/rio-scan.c
+   :internal:
+
+Driver functionality
+--------------------
+
+.. kernel-doc:: drivers/rapidio/rio.c
+   :internal:
+
+.. kernel-doc:: drivers/rapidio/rio-access.c
+   :internal:
+
+Device model support
+--------------------
+
+.. kernel-doc:: drivers/rapidio/rio-driver.c
+   :internal:
+
+PPC32 support
+-------------
+
+.. kernel-doc:: arch/powerpc/sysdev/fsl_rio.c
+   :internal:
+
+Credits
+=======
+
+The following people have contributed to the RapidIO subsystem directly
+or indirectly:
+
+1. Matt Porter\ mporter@kernel.crashing.org
+
+2. Randy Vinson\ rvinson@mvista.com
+
+3. Dan Malek\ dan@embeddedalley.com
+
+The following people have contributed to this document:
+
+1. Matt Porter\ mporter@kernel.crashing.org

Documentation/driver-api/regulator.rst

@@ -0,0 +1,170 @@
+.. Copyright 2007-2008 Wolfson Microelectronics
+
+..   This documentation is free software; you can redistribute
+..   it and/or modify it under the terms of the GNU General Public
+..   License version 2 as published by the Free Software Foundation.
+
+=================================
+Voltage and current regulator API
+=================================
+
+:Author: Liam Girdwood
+:Author: Mark Brown
+
+Introduction
+============
+
+This framework is designed to provide a standard kernel interface to
+control voltage and current regulators.
+
+The intention is to allow systems to dynamically control regulator power
+output in order to save power and prolong battery life. This applies to
+both voltage regulators (where voltage output is controllable) and
+current sinks (where current limit is controllable).
+
+Note that additional (and currently more complete) documentation is
+available in the Linux kernel source under
+``Documentation/power/regulator``.
+
+Glossary
+--------
+
+The regulator API uses a number of terms which may not be familiar:
+
+Regulator
+
+    Electronic device that supplies power to other devices. Most regulators
+    can enable and disable their output and some can also control their
+    output voltage or current.
+
+Consumer
+
+    Electronic device which consumes power provided by a regulator. These
+    may either be static, requiring only a fixed supply, or dynamic,
+    requiring active management of the regulator at runtime.
+
+Power Domain
+
+    The electronic circuit supplied by a given regulator, including the
+    regulator and all consumer devices. The configuration of the regulator
+    is shared between all the components in the circuit.
+
+Power Management Integrated Circuit (PMIC)
+
+    An IC which contains numerous regulators and often also other
+    subsystems. In an embedded system the primary PMIC is often equivalent
+    to a combination of the PSU and southbridge in a desktop system.
+
+Consumer driver interface
+=========================
+
+This offers a similar API to the kernel clock framework. Consumer
+drivers use `get <#API-regulator-get>`__ and
+`put <#API-regulator-put>`__ operations to acquire and release
+regulators. Functions are provided to `enable <#API-regulator-enable>`__
+and `disable <#API-regulator-disable>`__ the regulator and to get and
+set the runtime parameters of the regulator.
+
+When requesting regulators consumers use symbolic names for their
+supplies, such as "Vcc", which are mapped into actual regulator devices
+by the machine interface.
+
+A stub version of this API is provided when the regulator framework is
+not in use in order to minimise the need to use ifdefs.
+
+Enabling and disabling
+----------------------
+
+The regulator API provides reference counted enabling and disabling of
+regulators. Consumer devices use the :c:func:`regulator_enable()` and
+:c:func:`regulator_disable()` functions to enable and disable
+regulators. Calls to the two functions must be balanced.
+
+Note that since multiple consumers may be using a regulator and machine
+constraints may not allow the regulator to be disabled there is no
+guarantee that calling :c:func:`regulator_disable()` will actually
+cause the supply provided by the regulator to be disabled. Consumer
+drivers should assume that the regulator may be enabled at all times.
+
+Configuration
+-------------
+
+Some consumer devices may need to be able to dynamically configure their
+supplies. For example, MMC drivers may need to select the correct
+operating voltage for their cards. This may be done while the regulator
+is enabled or disabled.
+
+The :c:func:`regulator_set_voltage()` and
+:c:func:`regulator_set_current_limit()` functions provide the primary
+interface for this. Both take ranges of voltages and currents, supporting
+drivers that do not require a specific value (eg, CPU frequency scaling
+normally permits the CPU to use a wider range of supply voltages at lower
+frequencies but does not require that the supply voltage be lowered). Where
+an exact value is required both minimum and maximum values should be
+identical.
+
+Callbacks
+---------
+
+Callbacks may also be registered for events such as regulation failures.
+
+Regulator driver interface
+==========================
+
+Drivers for regulator chips register the regulators with the regulator
+core, providing operations structures to the core. A notifier interface
+allows error conditions to be reported to the core.
+
+Registration should be triggered by explicit setup done by the platform,
+supplying a struct :c:type:`regulator_init_data` for the regulator
+containing constraint and supply information.
+
+Machine interface
+=================
+
+This interface provides a way to define how regulators are connected to
+consumers on a given system and what the valid operating parameters are
+for the system.
+
+Supplies
+--------
+
+Regulator supplies are specified using struct
+:c:type:`regulator_consumer_supply`. This is done at driver registration
+time as part of the machine constraints.
+
+Constraints
+-----------
+
+As well as defining the connections the machine interface also provides
+constraints defining the operations that clients are allowed to perform
+and the parameters that may be set. This is required since generally
+regulator devices will offer more flexibility than it is safe to use on
+a given system, for example supporting higher supply voltages than the
+consumers are rated for.
+
+This is done at driver registration time` by providing a
+struct :c:type:`regulation_constraints`.
+
+The constraints may also specify an initial configuration for the
+regulator in the constraints, which is particularly useful for use with
+static consumers.
+
+API reference
+=============
+
+Due to limitations of the kernel documentation framework and the
+existing layout of the source code the entire regulator API is
+documented here.
+
+.. kernel-doc:: include/linux/regulator/consumer.h
+   :internal:
+
+.. kernel-doc:: include/linux/regulator/machine.h
+   :internal:
+
+.. kernel-doc:: include/linux/regulator/driver.h
+   :internal:
+
+.. kernel-doc:: drivers/regulator/core.c
+   :export:

Documentation/driver-api/s390-drivers.rst

@@ -0,0 +1,135 @@
+===================================
+Writing s390 channel device drivers
+===================================
+
+:Author: Cornelia Huck
+
+Introduction
+============
+
+This document describes the interfaces available for device drivers that
+drive s390 based channel attached I/O devices. This includes interfaces
+for interaction with the hardware and interfaces for interacting with
+the common driver core. Those interfaces are provided by the s390 common
+I/O layer.
+
+The document assumes a familarity with the technical terms associated
+with the s390 channel I/O architecture. For a description of this
+architecture, please refer to the "z/Architecture: Principles of
+Operation", IBM publication no. SA22-7832.
+
+While most I/O devices on a s390 system are typically driven through the
+channel I/O mechanism described here, there are various other methods
+(like the diag interface). These are out of the scope of this document.
+
+The s390 common I/O layer also provides access to some devices that are
+not strictly considered I/O devices. They are considered here as well,
+although they are not the focus of this document.
+
+Some additional information can also be found in the kernel source under
+Documentation/s390/driver-model.txt.
+
+The css bus
+===========
+
+The css bus contains the subchannels available on the system. They fall
+into several categories:
+
+* Standard I/O subchannels, for use by the system. They have a child
+  device on the ccw bus and are described below.
+* I/O subchannels bound to the vfio-ccw driver. See
+  Documentation/s390/vfio-ccw.txt.
+* Message subchannels. No Linux driver currently exists.
+* CHSC subchannels (at most one). The chsc subchannel driver can be used
+  to send asynchronous chsc commands.
+* eADM subchannels. Used for talking to storage class memory.
+
+The ccw bus
+===========
+
+The ccw bus typically contains the majority of devices available to a
+s390 system. Named after the channel command word (ccw), the basic
+command structure used to address its devices, the ccw bus contains
+so-called channel attached devices. They are addressed via I/O
+subchannels, visible on the css bus. A device driver for
+channel-attached devices, however, will never interact with the
+subchannel directly, but only via the I/O device on the ccw bus, the ccw
+device.
+
+I/O functions for channel-attached devices
+------------------------------------------
+
+Some hardware structures have been translated into C structures for use
+by the common I/O layer and device drivers. For more information on the
+hardware structures represented here, please consult the Principles of
+Operation.
+
+.. kernel-doc:: arch/s390/include/asm/cio.h
+   :internal:
+
+ccw devices
+-----------
+
+Devices that want to initiate channel I/O need to attach to the ccw bus.
+Interaction with the driver core is done via the common I/O layer, which
+provides the abstractions of ccw devices and ccw device drivers.
+
+The functions that initiate or terminate channel I/O all act upon a ccw
+device structure. Device drivers must not bypass those functions or
+strange side effects may happen.
+
+.. kernel-doc:: arch/s390/include/asm/ccwdev.h
+   :internal:
+
+.. kernel-doc:: drivers/s390/cio/device.c
+   :export:
+
+.. kernel-doc:: drivers/s390/cio/device_ops.c
+   :export:
+
+The channel-measurement facility
+--------------------------------
+
+The channel-measurement facility provides a means to collect measurement
+data which is made available by the channel subsystem for each channel
+attached device.
+
+.. kernel-doc:: arch/s390/include/uapi/asm/cmb.h
+   :internal:
+
+.. kernel-doc:: drivers/s390/cio/cmf.c
+   :export:
+
+The ccwgroup bus
+================
+
+The ccwgroup bus only contains artificial devices, created by the user.
+Many networking devices (e.g. qeth) are in fact composed of several ccw
+devices (like read, write and data channel for qeth). The ccwgroup bus
+provides a mechanism to create a meta-device which contains those ccw
+devices as slave devices and can be associated with the netdevice.
+
+ccw group devices
+-----------------
+
+.. kernel-doc:: arch/s390/include/asm/ccwgroup.h
+   :internal:
+
+.. kernel-doc:: drivers/s390/cio/ccwgroup.c
+   :export:
+
+Generic interfaces
+==================
+
+The following section contains interfaces in use not only by drivers
+dealing with ccw devices, but drivers for various other s390 hardware
+as well.
+
+Adapter interrupts
+------------------
+
+The common I/O layer provides helper functions for dealing with adapter
+interrupts and interrupt vectors.
+
+.. kernel-doc:: drivers/s390/cio/airq.c
+   :export:

Documentation/driver-api/scsi.rst

@@ -0,0 +1,338 @@
+=====================
+SCSI Interfaces Guide
+=====================
+
+:Author: James Bottomley
+:Author: Rob Landley
+
+Introduction
+============
+
+Protocol vs bus
+---------------
+
+Once upon a time, the Small Computer Systems Interface defined both a
+parallel I/O bus and a data protocol to connect a wide variety of
+peripherals (disk drives, tape drives, modems, printers, scanners,
+optical drives, test equipment, and medical devices) to a host computer.
+
+Although the old parallel (fast/wide/ultra) SCSI bus has largely fallen
+out of use, the SCSI command set is more widely used than ever to
+communicate with devices over a number of different busses.
+
+The `SCSI protocol <http://www.t10.org/scsi-3.htm>`__ is a big-endian
+peer-to-peer packet based protocol. SCSI commands are 6, 10, 12, or 16
+bytes long, often followed by an associated data payload.
+
+SCSI commands can be transported over just about any kind of bus, and
+are the default protocol for storage devices attached to USB, SATA, SAS,
+Fibre Channel, FireWire, and ATAPI devices. SCSI packets are also
+commonly exchanged over Infiniband,
+`I2O <http://i2o.shadowconnect.com/faq.php>`__, TCP/IP
+(`iSCSI <https://en.wikipedia.org/wiki/ISCSI>`__), even `Parallel
+ports <http://cyberelk.net/tim/parport/parscsi.html>`__.
+
+Design of the Linux SCSI subsystem
+----------------------------------
+
+The SCSI subsystem uses a three layer design, with upper, mid, and low
+layers. Every operation involving the SCSI subsystem (such as reading a
+sector from a disk) uses one driver at each of the 3 levels: one upper
+layer driver, one lower layer driver, and the SCSI midlayer.
+
+The SCSI upper layer provides the interface between userspace and the
+kernel, in the form of block and char device nodes for I/O and ioctl().
+The SCSI lower layer contains drivers for specific hardware devices.
+
+In between is the SCSI mid-layer, analogous to a network routing layer
+such as the IPv4 stack. The SCSI mid-layer routes a packet based data
+protocol between the upper layer's /dev nodes and the corresponding
+devices in the lower layer. It manages command queues, provides error
+handling and power management functions, and responds to ioctl()
+requests.
+
+SCSI upper layer
+================
+
+The upper layer supports the user-kernel interface by providing device
+nodes.
+
+sd (SCSI Disk)
+--------------
+
+sd (sd_mod.o)
+
+sr (SCSI CD-ROM)
+----------------
+
+sr (sr_mod.o)
+
+st (SCSI Tape)
+--------------
+
+st (st.o)
+
+sg (SCSI Generic)
+-----------------
+
+sg (sg.o)
+
+ch (SCSI Media Changer)
+-----------------------
+
+ch (ch.c)
+
+SCSI mid layer
+==============
+
+SCSI midlayer implementation
+----------------------------
+
+include/scsi/scsi_device.h
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: include/scsi/scsi_device.h
+   :internal:
+
+drivers/scsi/scsi.c
+~~~~~~~~~~~~~~~~~~~
+
+Main file for the SCSI midlayer.
+
+.. kernel-doc:: drivers/scsi/scsi.c
+   :export:
+
+drivers/scsi/scsicam.c
+~~~~~~~~~~~~~~~~~~~~~~
+
+`SCSI Common Access
+Method <http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf>`__ support
+functions, for use with HDIO_GETGEO, etc.
+
+.. kernel-doc:: drivers/scsi/scsicam.c
+   :export:
+
+drivers/scsi/scsi_error.c
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Common SCSI error/timeout handling routines.
+
+.. kernel-doc:: drivers/scsi/scsi_error.c
+   :export:
+
+drivers/scsi/scsi_devinfo.c
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Manage scsi_dev_info_list, which tracks blacklisted and whitelisted
+devices.
+
+.. kernel-doc:: drivers/scsi/scsi_devinfo.c
+   :internal:
+
+drivers/scsi/scsi_ioctl.c
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Handle ioctl() calls for SCSI devices.
+
+.. kernel-doc:: drivers/scsi/scsi_ioctl.c
+   :export:
+
+drivers/scsi/scsi_lib.c
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+SCSI queuing library.
+
+.. kernel-doc:: drivers/scsi/scsi_lib.c
+   :export:
+
+drivers/scsi/scsi_lib_dma.c
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+SCSI library functions depending on DMA (map and unmap scatter-gather
+lists).
+
+.. kernel-doc:: drivers/scsi/scsi_lib_dma.c
+   :export:
+
+drivers/scsi/scsi_proc.c
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The functions in this file provide an interface between the PROC file
+system and the SCSI device drivers It is mainly used for debugging,
+statistics and to pass information directly to the lowlevel driver. I.E.
+plumbing to manage /proc/scsi/\*
+
+.. kernel-doc:: drivers/scsi/scsi_proc.c
+   :internal:
+
+drivers/scsi/scsi_netlink.c
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Infrastructure to provide async events from transports to userspace via
+netlink, using a single NETLINK_SCSITRANSPORT protocol for all
+transports. See `the original patch
+submission <http://marc.info/?l=linux-scsi&m=115507374832500&w=2>`__ for
+more details.
+
+.. kernel-doc:: drivers/scsi/scsi_netlink.c
+   :internal:
+
+drivers/scsi/scsi_scan.c
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Scan a host to determine which (if any) devices are attached. The
+general scanning/probing algorithm is as follows, exceptions are made to
+it depending on device specific flags, compilation options, and global
+variable (boot or module load time) settings. A specific LUN is scanned
+via an INQUIRY command; if the LUN has a device attached, a scsi_device
+is allocated and setup for it. For every id of every channel on the
+given host, start by scanning LUN 0. Skip hosts that don't respond at
+all to a scan of LUN 0. Otherwise, if LUN 0 has a device attached,
+allocate and setup a scsi_device for it. If target is SCSI-3 or up,
+issue a REPORT LUN, and scan all of the LUNs returned by the REPORT LUN;
+else, sequentially scan LUNs up until some maximum is reached, or a LUN
+is seen that cannot have a device attached to it.
+
+.. kernel-doc:: drivers/scsi/scsi_scan.c
+   :internal:
+
+drivers/scsi/scsi_sysctl.c
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Set up the sysctl entry: "/dev/scsi/logging_level"
+(DEV_SCSI_LOGGING_LEVEL) which sets/returns scsi_logging_level.
+
+drivers/scsi/scsi_sysfs.c
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+SCSI sysfs interface routines.
+
+.. kernel-doc:: drivers/scsi/scsi_sysfs.c
+   :export:
+
+drivers/scsi/hosts.c
+~~~~~~~~~~~~~~~~~~~~
+
+mid to lowlevel SCSI driver interface
+
+.. kernel-doc:: drivers/scsi/hosts.c
+   :export:
+
+drivers/scsi/scsi_common.c
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+general support functions
+
+.. kernel-doc:: drivers/scsi/scsi_common.c
+   :export:
+
+Transport classes
+-----------------
+
+Transport classes are service libraries for drivers in the SCSI lower
+layer, which expose transport attributes in sysfs.
+
+Fibre Channel transport
+~~~~~~~~~~~~~~~~~~~~~~~
+
+The file drivers/scsi/scsi_transport_fc.c defines transport attributes
+for Fibre Channel.
+
+.. kernel-doc:: drivers/scsi/scsi_transport_fc.c
+   :export:
+
+iSCSI transport class
+~~~~~~~~~~~~~~~~~~~~~
+
+The file drivers/scsi/scsi_transport_iscsi.c defines transport
+attributes for the iSCSI class, which sends SCSI packets over TCP/IP
+connections.
+
+.. kernel-doc:: drivers/scsi/scsi_transport_iscsi.c
+   :export:
+
+Serial Attached SCSI (SAS) transport class
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The file drivers/scsi/scsi_transport_sas.c defines transport
+attributes for Serial Attached SCSI, a variant of SATA aimed at large
+high-end systems.
+
+The SAS transport class contains common code to deal with SAS HBAs, an
+aproximated representation of SAS topologies in the driver model, and
+various sysfs attributes to expose these topologies and management
+interfaces to userspace.
+
+In addition to the basic SCSI core objects this transport class
+introduces two additional intermediate objects: The SAS PHY as
+represented by struct sas_phy defines an "outgoing" PHY on a SAS HBA or
+Expander, and the SAS remote PHY represented by struct sas_rphy defines
+an "incoming" PHY on a SAS Expander or end device. Note that this is
+purely a software concept, the underlying hardware for a PHY and a
+remote PHY is the exactly the same.
+
+There is no concept of a SAS port in this code, users can see what PHYs
+form a wide port based on the port_identifier attribute, which is the
+same for all PHYs in a port.
+
+.. kernel-doc:: drivers/scsi/scsi_transport_sas.c
+   :export:
+
+SATA transport class
+~~~~~~~~~~~~~~~~~~~~
+
+The SATA transport is handled by libata, which has its own book of
+documentation in this directory.
+
+Parallel SCSI (SPI) transport class
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The file drivers/scsi/scsi_transport_spi.c defines transport
+attributes for traditional (fast/wide/ultra) SCSI busses.
+
+.. kernel-doc:: drivers/scsi/scsi_transport_spi.c
+   :export:
+
+SCSI RDMA (SRP) transport class
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The file drivers/scsi/scsi_transport_srp.c defines transport
+attributes for SCSI over Remote Direct Memory Access.
+
+.. kernel-doc:: drivers/scsi/scsi_transport_srp.c
+   :export:
+
+SCSI lower layer
+================
+
+Host Bus Adapter transport types
+--------------------------------
+
+Many modern device controllers use the SCSI command set as a protocol to
+communicate with their devices through many different types of physical
+connections.
+
+In SCSI language a bus capable of carrying SCSI commands is called a
+"transport", and a controller connecting to such a bus is called a "host
+bus adapter" (HBA).
+
+Debug transport
+~~~~~~~~~~~~~~~
+
+The file drivers/scsi/scsi_debug.c simulates a host adapter with a
+variable number of disks (or disk like devices) attached, sharing a
+common amount of RAM. Does a lot of checking to make sure that we are
+not getting blocks mixed up, and panics the kernel if anything out of
+the ordinary is seen.
+
+To be more realistic, the simulated devices have the transport
+attributes of SAS disks.
+
+For documentation see http://sg.danny.cz/sg/sdebug26.html
+
+todo
+~~~~
+
+Parallel (fast/wide/ultra) SCSI, USB, SATA, SAS, Fibre Channel,
+FireWire, ATAPI devices, Infiniband, I2O, Parallel ports,
+netlink...

Documentation/driver-api/slimbus.rst

@@ -0,0 +1,132 @@
+============================
+Linux kernel SLIMbus support
+============================
+
+Overview
+========
+
+What is SLIMbus?
+----------------
+SLIMbus (Serial Low Power Interchip Media Bus) is a specification developed by
+MIPI (Mobile Industry Processor Interface) alliance. The bus uses master/slave
+configuration, and is a 2-wire multi-drop implementation (clock, and data).
+
+Currently, SLIMbus is used to interface between application processors of SoCs
+(System-on-Chip) and peripheral components (typically codec). SLIMbus uses
+Time-Division-Multiplexing to accommodate multiple data channels, and
+a control channel.
+
+The control channel is used for various control functions such as bus
+management, configuration and status updates. These messages can be unicast (e.g.
+reading/writing device specific values), or multicast (e.g. data channel
+reconfiguration sequence is a broadcast message announced to all devices)
+
+A data channel is used for data-transfer between 2 SLIMbus devices. Data
+channel uses dedicated ports on the device.
+
+Hardware description:
+---------------------
+SLIMbus specification has different types of device classifications based on
+their capabilities.
+A manager device is responsible for enumeration, configuration, and dynamic
+channel allocation. Every bus has 1 active manager.
+
+A generic device is a device providing application functionality (e.g. codec).
+
+Framer device is responsible for clocking the bus, and transmitting frame-sync
+and framing information on the bus.
+
+Each SLIMbus component has an interface device for monitoring physical layer.
+
+Typically each SoC contains SLIMbus component having 1 manager, 1 framer device,
+1 generic device (for data channel support), and 1 interface device.
+External peripheral SLIMbus component usually has 1 generic device (for
+functionality/data channel support), and an associated interface device.
+The generic device's registers are mapped as 'value elements' so that they can
+be written/read using SLIMbus control channel exchanging control/status type of
+information.
+In case there are multiple framer devices on the same bus, manager device is
+responsible to select the active-framer for clocking the bus.
+
+Per specification, SLIMbus uses "clock gears" to do power management based on
+current frequency and bandwidth requirements. There are 10 clock gears and each
+gear changes the SLIMbus frequency to be twice its previous gear.
+
+Each device has a 6-byte enumeration-address and the manager assigns every
+device with a 1-byte logical address after the devices report presence on the
+bus.
+
+Software description:
+---------------------
+There are 2 types of SLIMbus drivers:
+
+slim_controller represents a 'controller' for SLIMbus. This driver should
+implement duties needed by the SoC (manager device, associated
+interface device for monitoring the layers and reporting errors, default
+framer device).
+
+slim_device represents the 'generic device/component' for SLIMbus, and a
+slim_driver should implement driver for that slim_device.
+
+Device notifications to the driver:
+-----------------------------------
+Since SLIMbus devices have mechanisms for reporting their presence, the
+framework allows drivers to bind when corresponding devices report their
+presence on the bus.
+However, it is possible that the driver needs to be probed
+first so that it can enable corresponding SLIMbus device (e.g. power it up and/or
+take it out of reset). To support that behavior, the framework allows drivers
+to probe first as well  (e.g. using standard DeviceTree compatibility field).
+This creates the necessity for the driver to know when the device is functional
+(i.e. reported present). device_up callback is used for that reason when the
+device reports present and is assigned a logical address by the controller.
+
+Similarly, SLIMbus devices 'report absent' when they go down. A 'device_down'
+callback notifies the driver when the device reports absent and its logical
+address assignment is invalidated by the controller.
+
+Another notification "boot_device" is used to notify the slim_driver when
+controller resets the bus. This notification allows the driver to take necessary
+steps to boot the device so that it's functional after the bus has been reset.
+
+Driver and Controller APIs:
+---------------------------
+.. kernel-doc:: include/linux/slimbus.h
+   :internal:
+
+.. kernel-doc:: drivers/slimbus/slimbus.h
+   :internal:
+
+.. kernel-doc:: drivers/slimbus/core.c
+   :export:
+
+Clock-pause:
+------------
+SLIMbus mandates that a reconfiguration sequence (known as clock-pause) be
+broadcast to all active devices on the bus before the bus can enter low-power
+mode. Controller uses this sequence when it decides to enter low-power mode so
+that corresponding clocks and/or power-rails can be turned off to save power.
+Clock-pause is exited by waking up framer device (if controller driver initiates
+exiting low power mode), or by toggling the data line (if a slave device wants
+to initiate it).
+
+Clock-pause APIs:
+~~~~~~~~~~~~~~~~~
+.. kernel-doc:: drivers/slimbus/sched.c
+   :export:
+
+Messaging:
+----------
+The framework supports regmap and read/write apis to exchange control-information
+with a SLIMbus device. APIs can be synchronous or asynchronous.
+The header file <linux/slimbus.h> has more documentation about messaging APIs.
+
+Messaging APIs:
+~~~~~~~~~~~~~~~
+.. kernel-doc:: drivers/slimbus/messaging.c
+   :export:
+
+Streaming APIs:
+~~~~~~~~~~~~~~~
+.. kernel-doc:: drivers/slimbus/stream.c
+   :export:

Documentation/driver-api/sound.rst

@@ -0,0 +1,54 @@
+Sound Devices
+=============
+
+.. kernel-doc:: include/sound/core.h
+   :internal:
+
+.. kernel-doc:: sound/sound_core.c
+   :export:
+
+.. kernel-doc:: include/sound/pcm.h
+   :internal:
+
+.. kernel-doc:: sound/core/pcm.c
+   :export:
+
+.. kernel-doc:: sound/core/device.c
+   :export:
+
+.. kernel-doc:: sound/core/info.c
+   :export:
+
+.. kernel-doc:: sound/core/rawmidi.c
+   :export:
+
+.. kernel-doc:: sound/core/sound.c
+   :export:
+
+.. kernel-doc:: sound/core/memory.c
+   :export:
+
+.. kernel-doc:: sound/core/pcm_memory.c
+   :export:
+
+.. kernel-doc:: sound/core/init.c
+   :export:
+
+.. kernel-doc:: sound/core/isadma.c
+   :export:
+
+.. kernel-doc:: sound/core/control.c
+   :export:
+
+.. kernel-doc:: sound/core/pcm_lib.c
+   :export:
+
+.. kernel-doc:: sound/core/hwdep.c
+   :export:
+
+.. kernel-doc:: sound/core/pcm_native.c
+   :export:
+
+.. kernel-doc:: sound/core/memalloc.c
+   :export:
+

Documentation/driver-api/soundwire/error_handling.rst

@@ -0,0 +1,65 @@
+========================
+SoundWire Error Handling
+========================
+
+The SoundWire PHY was designed with care and errors on the bus are going to
+be very unlikely, and if they happen it should be limited to single bit
+errors. Examples of this design can be found in the synchronization
+mechanism (sync loss after two errors) and short CRCs used for the Bulk
+Register Access.
+
+The errors can be detected with multiple mechanisms:
+
+1. Bus clash or parity errors: This mechanism relies on low-level detectors
+   that are independent of the payload and usages, and they cover both control
+   and audio data. The current implementation only logs such errors.
+   Improvements could be invalidating an entire programming sequence and
+   restarting from a known position. In the case of such errors outside of a
+   control/command sequence, there is no concealment or recovery for audio
+   data enabled by the SoundWire protocol, the location of the error will also
+   impact its audibility (most-significant bits will be more impacted in PCM),
+   and after a number of such errors are detected the bus might be reset. Note
+   that bus clashes due to programming errors (two streams using the same bit
+   slots) or electrical issues during the transmit/receive transition cannot
+   be distinguished, although a recurring bus clash when audio is enabled is a
+   indication of a bus allocation issue. The interrupt mechanism can also help
+   identify Slaves which detected a Bus Clash or a Parity Error, but they may
+   not be responsible for the errors so resetting them individually is not a
+   viable recovery strategy.
+
+2. Command status: Each command is associated with a status, which only
+   covers transmission of the data between devices. The ACK status indicates
+   that the command was received and will be executed by the end of the
+   current frame. A NAK indicates that the command was in error and will not
+   be applied. In case of a bad programming (command sent to non-existent
+   Slave or to a non-implemented register) or electrical issue, no response
+   signals the command was ignored. Some Master implementations allow for a
+   command to be retransmitted several times.  If the retransmission fails,
+   backtracking and restarting the entire programming sequence might be a
+   solution. Alternatively some implementations might directly issue a bus
+   reset and re-enumerate all devices.
+
+3. Timeouts: In a number of cases such as ChannelPrepare or
+   ClockStopPrepare, the bus driver is supposed to poll a register field until
+   it transitions to a NotFinished value of zero. The MIPI SoundWire spec 1.1
+   does not define timeouts but the MIPI SoundWire DisCo document adds
+   recommendation on timeouts. If such configurations do not complete, the
+   driver will return a -ETIMEOUT. Such timeouts are symptoms of a faulty
+   Slave device and are likely impossible to recover from.
+
+Errors during global reconfiguration sequences are extremely difficult to
+handle:
+
+1. BankSwitch: An error during the last command issuing a BankSwitch is
+   difficult to backtrack from. Retransmitting the Bank Switch command may be
+   possible in a single segment setup, but this can lead to synchronization
+   problems when enabling multiple bus segments (a command with side effects
+   such as frame reconfiguration would be handled at different times). A global
+   hard-reset might be the best solution.
+
+Note that SoundWire does not provide a mechanism to detect illegal values
+written in valid registers. In a number of cases the standard even mentions
+that the Slave might behave in implementation-defined ways. The bus
+implementation does not provide a recovery mechanism for such errors, Slave
+or Master driver implementers are responsible for writing valid values in
+valid registers and implement additional range checking if needed.

Documentation/driver-api/soundwire/index.rst

@@ -0,0 +1,18 @@
+=======================
+SoundWire Documentation
+=======================
+
+.. toctree::
+   :maxdepth: 1
+
+   summary
+   stream
+   error_handling
+   locking
+
+.. only::  subproject
+
+   Indices
+   =======
+
+   * :ref:`genindex`

Documentation/driver-api/soundwire/locking.rst

@@ -0,0 +1,106 @@
+=================
+SoundWire Locking
+=================
+
+This document explains locking mechanism of the SoundWire Bus. Bus uses
+following locks in order to avoid race conditions in Bus operations on
+shared resources.
+
+  - Bus lock
+
+  - Message lock
+
+Bus lock
+========
+
+SoundWire Bus lock is a mutex and is part of Bus data structure
+(sdw_bus) which is used for every Bus instance. This lock is used to
+serialize each of the following operations(s) within SoundWire Bus instance.
+
+  - Addition and removal of Slave(s), changing Slave status.
+
+  - Prepare, Enable, Disable and De-prepare stream operations.
+
+  - Access of Stream data structure.
+
+Message lock
+============
+
+SoundWire message transfer lock. This mutex is part of
+Bus data structure (sdw_bus). This lock is used to serialize the message
+transfers (read/write) within a SoundWire Bus instance.
+
+Below examples show how locks are acquired.
+
+Example 1
+---------
+
+Message transfer.
+
+  1. For every message transfer
+
+     a. Acquire Message lock.
+
+     b. Transfer message (Read/Write) to Slave1 or broadcast message on
+        Bus in case of bank switch.
+
+     c. Release Message lock ::
+
+	+----------+                    +---------+
+	|          |                    |         |
+	|   Bus    |                    | Master  |
+	|          |                    | Driver  |
+	|          |                    |         |
+	+----+-----+                    +----+----+
+	     |                               |
+	     |     bus->ops->xfer_msg()      |
+	     <-------------------------------+   a. Acquire Message lock
+	     |                               |   b. Transfer message
+	     |                               |
+	     +------------------------------->   c. Release Message lock
+	     |    return success/error       |   d. Return success/error
+	     |                               |
+	     +                               +
+
+Example 2
+---------
+
+Prepare operation.
+
+  1. Acquire lock for Bus instance associated with Master 1.
+
+  2. For every message transfer in Prepare operation
+
+     a. Acquire Message lock.
+
+     b. Transfer message (Read/Write) to Slave1 or broadcast message on
+        Bus in case of bank switch.
+
+     c. Release Message lock.
+
+  3. Release lock for Bus instance associated with Master 1 ::
+
+	+----------+                    +---------+
+	|          |                    |         |
+	|   Bus    |                    | Master  |
+	|          |                    | Driver  |
+	|          |                    |         |
+	+----+-----+                    +----+----+
+	     |                               |
+	     |    sdw_prepare_stream()       |
+	     <-------------------------------+   1. Acquire bus lock
+	     |                               |   2. Perform stream prepare
+	     |                               |
+	     |                               |
+	     |     bus->ops->xfer_msg()      |
+	     <-------------------------------+   a. Acquire Message lock
+	     |                               |   b. Transfer message
+	     |                               |
+	     +------------------------------->   c. Release Message lock
+	     |    return success/error       |   d. Return success/error
+	     |                               |
+	     |                               |
+	     |    return success/error       |   3. Release bus lock
+	     +------------------------------->   4. Return success/error
+	     |                               |
+	     +                               +

Documentation/driver-api/soundwire/stream.rst

@@ -0,0 +1,372 @@
+=========================
+Audio Stream in SoundWire
+=========================
+
+An audio stream is a logical or virtual connection created between
+
+  (1) System memory buffer(s) and Codec(s)
+
+  (2) DSP memory buffer(s) and Codec(s)
+
+  (3) FIFO(s) and Codec(s)
+
+  (4) Codec(s) and Codec(s)
+
+which is typically driven by a DMA(s) channel through the data link. An
+audio stream contains one or more channels of data. All channels within
+stream must have same sample rate and same sample size.
+
+Assume a stream with two channels (Left & Right) is opened using SoundWire
+interface. Below are some ways a stream can be represented in SoundWire.
+
+Stream Sample in memory (System memory, DSP memory or FIFOs) ::
+
+	-------------------------
+	| L | R | L | R | L | R |
+	-------------------------
+
+Example 1: Stereo Stream with L and R channels is rendered from Master to
+Slave. Both Master and Slave is using single port. ::
+
+	+---------------+                    Clock Signal  +---------------+
+	|    Master     +----------------------------------+     Slave     |
+	|   Interface   |                                  |   Interface   |
+	|               |                                  |       1       |
+	|               |                     Data Signal  |               |
+	|    L  +  R    +----------------------------------+    L  +  R    |
+	|     (Data)    |     Data Direction               |     (Data)    |
+	+---------------+  +----------------------->       +---------------+
+
+
+Example 2: Stereo Stream with L and R channels is captured from Slave to
+Master. Both Master and Slave is using single port. ::
+
+
+	+---------------+                    Clock Signal  +---------------+
+	|    Master     +----------------------------------+     Slave     |
+	|   Interface   |                                  |   Interface   |
+	|               |                                  |       1       |
+	|               |                     Data Signal  |               |
+	|    L  +  R    +----------------------------------+    L  +  R    |
+	|     (Data)    |     Data Direction               |     (Data)    |
+	+---------------+  <-----------------------+       +---------------+
+
+
+Example 3: Stereo Stream with L and R channels is rendered by Master. Each
+of the L and R channel is received by two different Slaves. Master and both
+Slaves are using single port. ::
+
+	+---------------+                    Clock Signal  +---------------+
+	|    Master     +---------+------------------------+     Slave     |
+	|   Interface   |         |                        |   Interface   |
+	|               |         |                        |       1       |
+	|               |         |           Data Signal  |               |
+	|    L  +  R    +---+------------------------------+       L       |
+	|     (Data)    |   |     |    Data Direction      |     (Data)    |
+	+---------------+   |     |   +------------->      +---------------+
+	                    |     |
+	                    |     |
+	                    |     |                        +---------------+
+	                    |     +----------------------> |     Slave     |
+	                    |                              |   Interface   |
+	                    |                              |       2       |
+	                    |                              |               |
+	                    +----------------------------> |       R       |
+	                                                   |     (Data)    |
+	                                                   +---------------+
+
+
+Example 4: Stereo Stream with L and R channel is rendered by two different
+Ports of the Master and is received by only single Port of the Slave
+interface. ::
+
+	+--------------------+
+	|                    |
+	|     +--------------+                             +----------------+
+	|     |             ||                             |                |
+	|     |  Data Port  ||  L Channel                  |                |
+	|     |      1      |------------+                 |                |
+	|     |  L Channel  ||           |                 +-----+----+     |
+	|     |   (Data)    ||           |   L + R Channel ||    Data |     |
+	| Master  +----------+           | +---+---------> ||    Port |     |
+	| Interface          |           |                 ||     1   |     |
+	|     +--------------+           |                 ||         |     |
+	|     |             ||           |                 +----------+     |
+	|     |  Data Port  |------------+                 |                |
+	|     |      2      ||  R Channel                  |     Slave      |
+	|     |  R Channel  ||                             |   Interface    |
+	|     |   (Data)    ||                             |       1        |
+	|     +--------------+         Clock Signal        |     L  +  R    |
+	|                    +---------------------------> |      (Data)    |
+	+--------------------+                             |                |
+							   +----------------+
+
+SoundWire Stream Management flow
+================================
+
+Stream definitions
+------------------
+
+  (1) Current stream: This is classified as the stream on which operation has
+      to be performed like prepare, enable, disable, de-prepare etc.
+
+  (2) Active stream: This is classified as the stream which is already active
+      on Bus other than current stream. There can be multiple active streams
+      on the Bus.
+
+SoundWire Bus manages stream operations for each stream getting
+rendered/captured on the SoundWire Bus. This section explains Bus operations
+done for each of the stream allocated/released on Bus. Following are the
+stream states maintained by the Bus for each of the audio stream.
+
+
+SoundWire stream states
+-----------------------
+
+Below shows the SoundWire stream states and state transition diagram. ::
+
+	+-----------+     +------------+     +----------+     +----------+
+	| ALLOCATED +---->| CONFIGURED +---->| PREPARED +---->| ENABLED  |
+	|   STATE   |     |    STATE   |     |  STATE   |     |  STATE   |
+	+-----------+     +------------+     +----------+     +----+-----+
+	                                                           ^
+	                                                           |
+	                                                           |
+	                                                           v
+	         +----------+           +------------+        +----+-----+
+	         | RELEASED |<----------+ DEPREPARED |<-------+ DISABLED |
+	         |  STATE   |           |   STATE    |        |  STATE   |
+	         +----------+           +------------+        +----------+
+
+NOTE: State transition between prepare and deprepare is supported in Spec
+but not in the software (subsystem)
+
+NOTE2: Stream state transition checks need to be handled by caller
+framework, for example ALSA/ASoC. No checks for stream transition exist in
+SoundWire subsystem.
+
+Stream State Operations
+-----------------------
+
+Below section explains the operations done by the Bus on Master(s) and
+Slave(s) as part of stream state transitions.
+
+SDW_STREAM_ALLOCATED
+~~~~~~~~~~~~~~~~~~~~
+
+Allocation state for stream. This is the entry state
+of the stream. Operations performed before entering in this state:
+
+  (1) A stream runtime is allocated for the stream. This stream
+      runtime is used as a reference for all the operations performed
+      on the stream.
+
+  (2) The resources required for holding stream runtime information are
+      allocated and initialized. This holds all stream related information
+      such as stream type (PCM/PDM) and parameters, Master and Slave
+      interface associated with the stream, stream state etc.
+
+After all above operations are successful, stream state is set to
+``SDW_STREAM_ALLOCATED``.
+
+Bus implements below API for allocate a stream which needs to be called once
+per stream. From ASoC DPCM framework, this stream state maybe linked to
+.startup() operation.
+
+  .. code-block:: c
+  int sdw_alloc_stream(char * stream_name);
+
+
+SDW_STREAM_CONFIGURED
+~~~~~~~~~~~~~~~~~~~~~
+
+Configuration state of stream. Operations performed before entering in
+this state:
+
+  (1) The resources allocated for stream information in SDW_STREAM_ALLOCATED
+      state are updated here. This includes stream parameters, Master(s)
+      and Slave(s) runtime information associated with current stream.
+
+  (2) All the Master(s) and Slave(s) associated with current stream provide
+      the port information to Bus which includes port numbers allocated by
+      Master(s) and Slave(s) for current stream and their channel mask.
+
+After all above operations are successful, stream state is set to
+``SDW_STREAM_CONFIGURED``.
+
+Bus implements below APIs for CONFIG state which needs to be called by
+the respective Master(s) and Slave(s) associated with stream. These APIs can
+only be invoked once by respective Master(s) and Slave(s). From ASoC DPCM
+framework, this stream state is linked to .hw_params() operation.
+
+  .. code-block:: c
+  int sdw_stream_add_master(struct sdw_bus * bus,
+		struct sdw_stream_config * stream_config,
+		struct sdw_ports_config * ports_config,
+		struct sdw_stream_runtime * stream);
+
+  int sdw_stream_add_slave(struct sdw_slave * slave,
+		struct sdw_stream_config * stream_config,
+		struct sdw_ports_config * ports_config,
+		struct sdw_stream_runtime * stream);
+
+
+SDW_STREAM_PREPARED
+~~~~~~~~~~~~~~~~~~~
+
+Prepare state of stream. Operations performed before entering in this state:
+
+  (1) Bus parameters such as bandwidth, frame shape, clock frequency,
+      are computed based on current stream as well as already active
+      stream(s) on Bus. Re-computation is required to accommodate current
+      stream on the Bus.
+
+  (2) Transport and port parameters of all Master(s) and Slave(s) port(s) are
+      computed for the current as well as already active stream based on frame
+      shape and clock frequency computed in step 1.
+
+  (3) Computed Bus and transport parameters are programmed in Master(s) and
+      Slave(s) registers. The banked registers programming is done on the
+      alternate bank (bank currently unused). Port(s) are enabled for the
+      already active stream(s) on the alternate bank (bank currently unused).
+      This is done in order to not disrupt already active stream(s).
+
+  (4) Once all the values are programmed, Bus initiates switch to alternate
+      bank where all new values programmed gets into effect.
+
+  (5) Ports of Master(s) and Slave(s) for current stream are prepared by
+      programming PrepareCtrl register.
+
+After all above operations are successful, stream state is set to
+``SDW_STREAM_PREPARED``.
+
+Bus implements below API for PREPARE state which needs to be called once per
+stream. From ASoC DPCM framework, this stream state is linked to
+.prepare() operation.
+
+  .. code-block:: c
+  int sdw_prepare_stream(struct sdw_stream_runtime * stream);
+
+
+SDW_STREAM_ENABLED
+~~~~~~~~~~~~~~~~~~
+
+Enable state of stream. The data port(s) are enabled upon entering this state.
+Operations performed before entering in this state:
+
+  (1) All the values computed in SDW_STREAM_PREPARED state are programmed
+      in alternate bank (bank currently unused). It includes programming of
+      already active stream(s) as well.
+
+  (2) All the Master(s) and Slave(s) port(s) for the current stream are
+      enabled on alternate bank (bank currently unused) by programming
+      ChannelEn register.
+
+  (3) Once all the values are programmed, Bus initiates switch to alternate
+      bank where all new values programmed gets into effect and port(s)
+      associated with current stream are enabled.
+
+After all above operations are successful, stream state is set to
+``SDW_STREAM_ENABLED``.
+
+Bus implements below API for ENABLE state which needs to be called once per
+stream. From ASoC DPCM framework, this stream state is linked to
+.trigger() start operation.
+
+  .. code-block:: c
+  int sdw_enable_stream(struct sdw_stream_runtime * stream);
+
+SDW_STREAM_DISABLED
+~~~~~~~~~~~~~~~~~~~
+
+Disable state of stream. The data port(s) are disabled upon exiting this state.
+Operations performed before entering in this state:
+
+  (1) All the Master(s) and Slave(s) port(s) for the current stream are
+      disabled on alternate bank (bank currently unused) by programming
+      ChannelEn register.
+
+  (2) All the current configuration of Bus and active stream(s) are programmed
+      into alternate bank (bank currently unused).
+
+  (3) Once all the values are programmed, Bus initiates switch to alternate
+      bank where all new values programmed gets into effect and port(s) associated
+      with current stream are disabled.
+
+After all above operations are successful, stream state is set to
+``SDW_STREAM_DISABLED``.
+
+Bus implements below API for DISABLED state which needs to be called once
+per stream. From ASoC DPCM framework, this stream state is linked to
+.trigger() stop operation.
+
+  .. code-block:: c
+  int sdw_disable_stream(struct sdw_stream_runtime * stream);
+
+
+SDW_STREAM_DEPREPARED
+~~~~~~~~~~~~~~~~~~~~~
+
+De-prepare state of stream. Operations performed before entering in this
+state:
+
+  (1) All the port(s) of Master(s) and Slave(s) for current stream are
+      de-prepared by programming PrepareCtrl register.
+
+  (2) The payload bandwidth of current stream is reduced from the total
+      bandwidth requirement of bus and new parameters calculated and
+      applied by performing bank switch etc.
+
+After all above operations are successful, stream state is set to
+``SDW_STREAM_DEPREPARED``.
+
+Bus implements below API for DEPREPARED state which needs to be called once
+per stream. From ASoC DPCM framework, this stream state is linked to
+.trigger() stop operation.
+
+  .. code-block:: c
+  int sdw_deprepare_stream(struct sdw_stream_runtime * stream);
+
+
+SDW_STREAM_RELEASED
+~~~~~~~~~~~~~~~~~~~
+
+Release state of stream. Operations performed before entering in this state:
+
+  (1) Release port resources for all Master(s) and Slave(s) port(s)
+      associated with current stream.
+
+  (2) Release Master(s) and Slave(s) runtime resources associated with
+      current stream.
+
+  (3) Release stream runtime resources associated with current stream.
+
+After all above operations are successful, stream state is set to
+``SDW_STREAM_RELEASED``.
+
+Bus implements below APIs for RELEASE state which needs to be called by
+all the Master(s) and Slave(s) associated with stream. From ASoC DPCM
+framework, this stream state is linked to .hw_free() operation.
+
+  .. code-block:: c
+  int sdw_stream_remove_master(struct sdw_bus * bus,
+		struct sdw_stream_runtime * stream);
+  int sdw_stream_remove_slave(struct sdw_slave * slave,
+		struct sdw_stream_runtime * stream);
+
+
+The .shutdown() ASoC DPCM operation calls below Bus API to release
+stream assigned as part of ALLOCATED state.
+
+In .shutdown() the data structure maintaining stream state are freed up.
+
+  .. code-block:: c
+  void sdw_release_stream(struct sdw_stream_runtime * stream);
+
+Not Supported
+=============
+
+1. A single port with multiple channels supported cannot be used between two
+streams or across stream. For example a port with 4 channels cannot be used
+to handle 2 independent stereo streams even though it's possible in theory
+in SoundWire.

Documentation/driver-api/soundwire/summary.rst

@@ -0,0 +1,207 @@
+===========================
+SoundWire Subsystem Summary
+===========================
+
+SoundWire is a new interface ratified in 2015 by the MIPI Alliance.
+SoundWire is used for transporting data typically related to audio
+functions. SoundWire interface is optimized to integrate audio devices in
+mobile or mobile inspired systems.
+
+SoundWire is a 2-pin multi-drop interface with data and clock line. It
+facilitates development of low cost, efficient, high performance systems.
+Broad level key features of SoundWire interface include:
+
+ (1) Transporting all of payload data channels, control information, and setup
+     commands over a single two-pin interface.
+
+ (2) Lower clock frequency, and hence lower power consumption, by use of DDR
+     (Dual Data Rate) data transmission.
+
+ (3) Clock scaling and optional multiple data lanes to give wide flexibility
+     in data rate to match system requirements.
+
+ (4) Device status monitoring, including interrupt-style alerts to the Master.
+
+The SoundWire protocol supports up to eleven Slave interfaces. All the
+interfaces share the common Bus containing data and clock line. Each of the
+Slaves can support up to 14 Data Ports. 13 Data Ports are dedicated to audio
+transport. Data Port0 is dedicated to transport of Bulk control information,
+each of the audio Data Ports (1..14) can support up to 8 Channels in
+transmit or receiving mode (typically fixed direction but configurable
+direction is enabled by the specification).  Bandwidth restrictions to
+~19.2..24.576Mbits/s don't however allow for 11*13*8 channels to be
+transmitted simultaneously.
+
+Below figure shows an example of connectivity between a SoundWire Master and
+two Slave devices. ::
+
+        +---------------+                                       +---------------+
+        |               |                       Clock Signal    |               |
+        |    Master     |-------+-------------------------------|    Slave      |
+        |   Interface   |       |               Data Signal     |  Interface 1  |
+        |               |-------|-------+-----------------------|               |
+        +---------------+       |       |                       +---------------+
+                                |       |
+                                |       |
+                                |       |
+                             +--+-------+--+
+                             |             |
+                             |   Slave     |
+                             | Interface 2 |
+                             |             |
+                             +-------------+
+
+
+Terminology
+===========
+
+The MIPI SoundWire specification uses the term 'device' to refer to a Master
+or Slave interface, which of course can be confusing. In this summary and
+code we use the term interface only to refer to the hardware. We follow the
+Linux device model by mapping each Slave interface connected on the bus as a
+device managed by a specific driver. The Linux SoundWire subsystem provides
+a framework to implement a SoundWire Slave driver with an API allowing
+3rd-party vendors to enable implementation-defined functionality while
+common setup/configuration tasks are handled by the bus.
+
+Bus:
+Implements SoundWire Linux Bus which handles the SoundWire protocol.
+Programs all the MIPI-defined Slave registers. Represents a SoundWire
+Master. Multiple instances of Bus may be present in a system.
+
+Slave:
+Registers as SoundWire Slave device (Linux Device). Multiple Slave devices
+can register to a Bus instance.
+
+Slave driver:
+Driver controlling the Slave device. MIPI-specified registers are controlled
+directly by the Bus (and transmitted through the Master driver/interface).
+Any implementation-defined Slave register is controlled by Slave driver. In
+practice, it is expected that the Slave driver relies on regmap and does not
+request direct register access.
+
+Programming interfaces (SoundWire Master interface Driver)
+==========================================================
+
+SoundWire Bus supports programming interfaces for the SoundWire Master
+implementation and SoundWire Slave devices. All the code uses the "sdw"
+prefix commonly used by SoC designers and 3rd party vendors.
+
+Each of the SoundWire Master interfaces needs to be registered to the Bus.
+Bus implements API to read standard Master MIPI properties and also provides
+callback in Master ops for Master driver to implement its own functions that
+provides capabilities information. DT support is not implemented at this
+time but should be trivial to add since capabilities are enabled with the
+``device_property_`` API.
+
+The Master interface along with the Master interface capabilities are
+registered based on board file, DT or ACPI.
+
+Following is the Bus API to register the SoundWire Bus:
+
+.. code-block:: c
+
+	int sdw_add_bus_master(struct sdw_bus *bus)
+	{
+		if (!bus->dev)
+			return -ENODEV;
+
+		mutex_init(&bus->lock);
+		INIT_LIST_HEAD(&bus->slaves);
+
+		/* Check ACPI for Slave devices */
+		sdw_acpi_find_slaves(bus);
+
+		/* Check DT for Slave devices */
+		sdw_of_find_slaves(bus);
+
+		return 0;
+	}
+
+This will initialize sdw_bus object for Master device. "sdw_master_ops" and
+"sdw_master_port_ops" callback functions are provided to the Bus.
+
+"sdw_master_ops" is used by Bus to control the Bus in the hardware specific
+way. It includes Bus control functions such as sending the SoundWire
+read/write messages on Bus, setting up clock frequency & Stream
+Synchronization Point (SSP). The "sdw_master_ops" structure abstracts the
+hardware details of the Master from the Bus.
+
+"sdw_master_port_ops" is used by Bus to setup the Port parameters of the
+Master interface Port. Master interface Port register map is not defined by
+MIPI specification, so Bus calls the "sdw_master_port_ops" callback
+function to do Port operations like "Port Prepare", "Port Transport params
+set", "Port enable and disable". The implementation of the Master driver can
+then perform hardware-specific configurations.
+
+Programming interfaces (SoundWire Slave Driver)
+===============================================
+
+The MIPI specification requires each Slave interface to expose a unique
+48-bit identifier, stored in 6 read-only dev_id registers. This dev_id
+identifier contains vendor and part information, as well as a field enabling
+to differentiate between identical components. An additional class field is
+currently unused. Slave driver is written for a specific vendor and part
+identifier, Bus enumerates the Slave device based on these two ids.
+Slave device and driver match is done based on these two ids . Probe
+of the Slave driver is called by Bus on successful match between device and
+driver id. A parent/child relationship is enforced between Master and Slave
+devices (the logical representation is aligned with the physical
+connectivity).
+
+The information on Master/Slave dependencies is stored in platform data,
+board-file, ACPI or DT. The MIPI Software specification defines additional
+link_id parameters for controllers that have multiple Master interfaces. The
+dev_id registers are only unique in the scope of a link, and the link_id
+unique in the scope of a controller. Both dev_id and link_id are not
+necessarily unique at the system level but the parent/child information is
+used to avoid ambiguity.
+
+.. code-block:: c
+
+	static const struct sdw_device_id slave_id[] = {
+	        SDW_SLAVE_ENTRY(0x025d, 0x700, 0),
+	        {},
+	};
+	MODULE_DEVICE_TABLE(sdw, slave_id);
+
+	static struct sdw_driver slave_sdw_driver = {
+	        .driver = {
+	                   .name = "slave_xxx",
+	                   .pm = &slave_runtime_pm,
+	                   },
+		.probe = slave_sdw_probe,
+		.remove = slave_sdw_remove,
+		.ops = &slave_slave_ops,
+		.id_table = slave_id,
+	};
+
+
+For capabilities, Bus implements API to read standard Slave MIPI properties
+and also provides callback in Slave ops for Slave driver to implement own
+function that provides capabilities information. Bus needs to know a set of
+Slave capabilities to program Slave registers and to control the Bus
+reconfigurations.
+
+Future enhancements to be done
+==============================
+
+ (1) Bulk Register Access (BRA) transfers.
+
+
+ (2) Multiple data lane support.
+
+Links
+=====
+
+SoundWire MIPI specification 1.1 is available at:
+https://members.mipi.org/wg/All-Members/document/70290
+
+SoundWire MIPI DisCo (Discovery and Configuration) specification is
+available at:
+https://www.mipi.org/specifications/mipi-disco-soundwire
+
+(publicly accessible with registration or directly accessible to MIPI
+members)
+
+MIPI Alliance Manufacturer ID Page: mid.mipi.org

Documentation/driver-api/spi.rst

@@ -0,0 +1,53 @@
+Serial Peripheral Interface (SPI)
+=================================
+
+SPI is the "Serial Peripheral Interface", widely used with embedded
+systems because it is a simple and efficient interface: basically a
+multiplexed shift register. Its three signal wires hold a clock (SCK,
+often in the range of 1-20 MHz), a "Master Out, Slave In" (MOSI) data
+line, and a "Master In, Slave Out" (MISO) data line. SPI is a full
+duplex protocol; for each bit shifted out the MOSI line (one per clock)
+another is shifted in on the MISO line. Those bits are assembled into
+words of various sizes on the way to and from system memory. An
+additional chipselect line is usually active-low (nCS); four signals are
+normally used for each peripheral, plus sometimes an interrupt.
+
+The SPI bus facilities listed here provide a generalized interface to
+declare SPI busses and devices, manage them according to the standard
+Linux driver model, and perform input/output operations. At this time,
+only "master" side interfaces are supported, where Linux talks to SPI
+peripherals and does not implement such a peripheral itself. (Interfaces
+to support implementing SPI slaves would necessarily look different.)
+
+The programming interface is structured around two kinds of driver, and
+two kinds of device. A "Controller Driver" abstracts the controller
+hardware, which may be as simple as a set of GPIO pins or as complex as
+a pair of FIFOs connected to dual DMA engines on the other side of the
+SPI shift register (maximizing throughput). Such drivers bridge between
+whatever bus they sit on (often the platform bus) and SPI, and expose
+the SPI side of their device as a :c:type:`struct spi_master
+<spi_master>`. SPI devices are children of that master,
+represented as a :c:type:`struct spi_device <spi_device>` and
+manufactured from :c:type:`struct spi_board_info
+<spi_board_info>` descriptors which are usually provided by
+board-specific initialization code. A :c:type:`struct spi_driver
+<spi_driver>` is called a "Protocol Driver", and is bound to a
+spi_device using normal driver model calls.
+
+The I/O model is a set of queued messages. Protocol drivers submit one
+or more :c:type:`struct spi_message <spi_message>` objects,
+which are processed and completed asynchronously. (There are synchronous
+wrappers, however.) Messages are built from one or more
+:c:type:`struct spi_transfer <spi_transfer>` objects, each of
+which wraps a full duplex SPI transfer. A variety of protocol tweaking
+options are needed, because different chips adopt very different
+policies for how they use the bits transferred with SPI.
+
+.. kernel-doc:: include/linux/spi/spi.h
+   :internal:
+
+.. kernel-doc:: drivers/spi/spi.c
+   :functions: spi_register_board_info
+
+.. kernel-doc:: drivers/spi/spi.c
+   :export:

Documentation/driver-api/target.rst

@@ -0,0 +1,64 @@
+=================================
+target and iSCSI Interfaces Guide
+=================================
+
+Introduction and Overview
+=========================
+
+TBD
+
+Target core device interfaces
+=============================
+
+.. kernel-doc:: drivers/target/target_core_device.c
+    :export:
+
+Target core transport interfaces
+================================
+
+.. kernel-doc:: drivers/target/target_core_transport.c
+    :export:
+
+Target-supported userspace I/O
+==============================
+
+.. kernel-doc:: drivers/target/target_core_user.c
+    :doc: Userspace I/O
+
+.. kernel-doc:: include/uapi/linux/target_core_user.h
+    :doc: Ring Design
+
+iSCSI helper functions
+======================
+
+.. kernel-doc:: drivers/scsi/libiscsi.c
+   :export:
+
+
+iSCSI boot information
+======================
+
+.. kernel-doc:: drivers/scsi/iscsi_boot_sysfs.c
+   :export:
+
+
+iSCSI transport class
+=====================
+
+The file drivers/scsi/scsi_transport_iscsi.c defines transport
+attributes for the iSCSI class, which sends SCSI packets over TCP/IP
+connections.
+
+.. kernel-doc:: drivers/scsi/scsi_transport_iscsi.c
+   :export:
+
+
+iSCSI TCP interfaces
+====================
+
+.. kernel-doc:: drivers/scsi/iscsi_tcp.c
+   :internal:
+
+.. kernel-doc:: drivers/scsi/libiscsi_tcp.c
+   :export:
+

Documentation/driver-api/uio-howto.rst

@@ -0,0 +1,723 @@
+=======================
+The Userspace I/O HOWTO
+=======================
+
+:Author: Hans-Jürgen Koch Linux developer, Linutronix
+:Date:   2006-12-11
+
+About this document
+===================
+
+Translations
+------------
+
+If you know of any translations for this document, or you are interested
+in translating it, please email me hjk@hansjkoch.de.
+
+Preface
+-------
+
+For many types of devices, creating a Linux kernel driver is overkill.
+All that is really needed is some way to handle an interrupt and provide
+access to the memory space of the device. The logic of controlling the
+device does not necessarily have to be within the kernel, as the device
+does not need to take advantage of any of other resources that the
+kernel provides. One such common class of devices that are like this are
+for industrial I/O cards.
+
+To address this situation, the userspace I/O system (UIO) was designed.
+For typical industrial I/O cards, only a very small kernel module is
+needed. The main part of the driver will run in user space. This
+simplifies development and reduces the risk of serious bugs within a
+kernel module.
+
+Please note that UIO is not an universal driver interface. Devices that
+are already handled well by other kernel subsystems (like networking or
+serial or USB) are no candidates for an UIO driver. Hardware that is
+ideally suited for an UIO driver fulfills all of the following:
+
+-  The device has memory that can be mapped. The device can be
+   controlled completely by writing to this memory.
+
+-  The device usually generates interrupts.
+
+-  The device does not fit into one of the standard kernel subsystems.
+
+Acknowledgments
+---------------
+
+I'd like to thank Thomas Gleixner and Benedikt Spranger of Linutronix,
+who have not only written most of the UIO code, but also helped greatly
+writing this HOWTO by giving me all kinds of background information.
+
+Feedback
+--------
+
+Find something wrong with this document? (Or perhaps something right?) I
+would love to hear from you. Please email me at hjk@hansjkoch.de.
+
+About UIO
+=========
+
+If you use UIO for your card's driver, here's what you get:
+
+-  only one small kernel module to write and maintain.
+
+-  develop the main part of your driver in user space, with all the
+   tools and libraries you're used to.
+
+-  bugs in your driver won't crash the kernel.
+
+-  updates of your driver can take place without recompiling the kernel.
+
+How UIO works
+-------------
+
+Each UIO device is accessed through a device file and several sysfs
+attribute files. The device file will be called ``/dev/uio0`` for the
+first device, and ``/dev/uio1``, ``/dev/uio2`` and so on for subsequent
+devices.
+
+``/dev/uioX`` is used to access the address space of the card. Just use
+:c:func:`mmap()` to access registers or RAM locations of your card.
+
+Interrupts are handled by reading from ``/dev/uioX``. A blocking
+:c:func:`read()` from ``/dev/uioX`` will return as soon as an
+interrupt occurs. You can also use :c:func:`select()` on
+``/dev/uioX`` to wait for an interrupt. The integer value read from
+``/dev/uioX`` represents the total interrupt count. You can use this
+number to figure out if you missed some interrupts.
+
+For some hardware that has more than one interrupt source internally,
+but not separate IRQ mask and status registers, there might be
+situations where userspace cannot determine what the interrupt source
+was if the kernel handler disables them by writing to the chip's IRQ
+register. In such a case, the kernel has to disable the IRQ completely
+to leave the chip's register untouched. Now the userspace part can
+determine the cause of the interrupt, but it cannot re-enable
+interrupts. Another cornercase is chips where re-enabling interrupts is
+a read-modify-write operation to a combined IRQ status/acknowledge
+register. This would be racy if a new interrupt occurred simultaneously.
+
+To address these problems, UIO also implements a write() function. It is
+normally not used and can be ignored for hardware that has only a single
+interrupt source or has separate IRQ mask and status registers. If you
+need it, however, a write to ``/dev/uioX`` will call the
+:c:func:`irqcontrol()` function implemented by the driver. You have
+to write a 32-bit value that is usually either 0 or 1 to disable or
+enable interrupts. If a driver does not implement
+:c:func:`irqcontrol()`, :c:func:`write()` will return with
+``-ENOSYS``.
+
+To handle interrupts properly, your custom kernel module can provide its
+own interrupt handler. It will automatically be called by the built-in
+handler.
+
+For cards that don't generate interrupts but need to be polled, there is
+the possibility to set up a timer that triggers the interrupt handler at
+configurable time intervals. This interrupt simulation is done by
+calling :c:func:`uio_event_notify()` from the timer's event
+handler.
+
+Each driver provides attributes that are used to read or write
+variables. These attributes are accessible through sysfs files. A custom
+kernel driver module can add its own attributes to the device owned by
+the uio driver, but not added to the UIO device itself at this time.
+This might change in the future if it would be found to be useful.
+
+The following standard attributes are provided by the UIO framework:
+
+-  ``name``: The name of your device. It is recommended to use the name
+   of your kernel module for this.
+
+-  ``version``: A version string defined by your driver. This allows the
+   user space part of your driver to deal with different versions of the
+   kernel module.
+
+-  ``event``: The total number of interrupts handled by the driver since
+   the last time the device node was read.
+
+These attributes appear under the ``/sys/class/uio/uioX`` directory.
+Please note that this directory might be a symlink, and not a real
+directory. Any userspace code that accesses it must be able to handle
+this.
+
+Each UIO device can make one or more memory regions available for memory
+mapping. This is necessary because some industrial I/O cards require
+access to more than one PCI memory region in a driver.
+
+Each mapping has its own directory in sysfs, the first mapping appears
+as ``/sys/class/uio/uioX/maps/map0/``. Subsequent mappings create
+directories ``map1/``, ``map2/``, and so on. These directories will only
+appear if the size of the mapping is not 0.
+
+Each ``mapX/`` directory contains four read-only files that show
+attributes of the memory:
+
+-  ``name``: A string identifier for this mapping. This is optional, the
+   string can be empty. Drivers can set this to make it easier for
+   userspace to find the correct mapping.
+
+-  ``addr``: The address of memory that can be mapped.
+
+-  ``size``: The size, in bytes, of the memory pointed to by addr.
+
+-  ``offset``: The offset, in bytes, that has to be added to the pointer
+   returned by :c:func:`mmap()` to get to the actual device memory.
+   This is important if the device's memory is not page aligned.
+   Remember that pointers returned by :c:func:`mmap()` are always
+   page aligned, so it is good style to always add this offset.
+
+From userspace, the different mappings are distinguished by adjusting
+the ``offset`` parameter of the :c:func:`mmap()` call. To map the
+memory of mapping N, you have to use N times the page size as your
+offset::
+
+    offset = N * getpagesize();
+
+Sometimes there is hardware with memory-like regions that can not be
+mapped with the technique described here, but there are still ways to
+access them from userspace. The most common example are x86 ioports. On
+x86 systems, userspace can access these ioports using
+:c:func:`ioperm()`, :c:func:`iopl()`, :c:func:`inb()`,
+:c:func:`outb()`, and similar functions.
+
+Since these ioport regions can not be mapped, they will not appear under
+``/sys/class/uio/uioX/maps/`` like the normal memory described above.
+Without information about the port regions a hardware has to offer, it
+becomes difficult for the userspace part of the driver to find out which
+ports belong to which UIO device.
+
+To address this situation, the new directory
+``/sys/class/uio/uioX/portio/`` was added. It only exists if the driver
+wants to pass information about one or more port regions to userspace.
+If that is the case, subdirectories named ``port0``, ``port1``, and so
+on, will appear underneath ``/sys/class/uio/uioX/portio/``.
+
+Each ``portX/`` directory contains four read-only files that show name,
+start, size, and type of the port region:
+
+-  ``name``: A string identifier for this port region. The string is
+   optional and can be empty. Drivers can set it to make it easier for
+   userspace to find a certain port region.
+
+-  ``start``: The first port of this region.
+
+-  ``size``: The number of ports in this region.
+
+-  ``porttype``: A string describing the type of port.
+
+Writing your own kernel module
+==============================
+
+Please have a look at ``uio_cif.c`` as an example. The following
+paragraphs explain the different sections of this file.
+
+struct uio_info
+---------------
+
+This structure tells the framework the details of your driver, Some of
+the members are required, others are optional.
+
+-  ``const char *name``: Required. The name of your driver as it will
+   appear in sysfs. I recommend using the name of your module for this.
+
+-  ``const char *version``: Required. This string appears in
+   ``/sys/class/uio/uioX/version``.
+
+-  ``struct uio_mem mem[ MAX_UIO_MAPS ]``: Required if you have memory
+   that can be mapped with :c:func:`mmap()`. For each mapping you
+   need to fill one of the ``uio_mem`` structures. See the description
+   below for details.
+
+-  ``struct uio_port port[ MAX_UIO_PORTS_REGIONS ]``: Required if you
+   want to pass information about ioports to userspace. For each port
+   region you need to fill one of the ``uio_port`` structures. See the
+   description below for details.
+
+-  ``long irq``: Required. If your hardware generates an interrupt, it's
+   your modules task to determine the irq number during initialization.
+   If you don't have a hardware generated interrupt but want to trigger
+   the interrupt handler in some other way, set ``irq`` to
+   ``UIO_IRQ_CUSTOM``. If you had no interrupt at all, you could set
+   ``irq`` to ``UIO_IRQ_NONE``, though this rarely makes sense.
+
+-  ``unsigned long irq_flags``: Required if you've set ``irq`` to a
+   hardware interrupt number. The flags given here will be used in the
+   call to :c:func:`request_irq()`.
+
+-  ``int (*mmap)(struct uio_info *info, struct vm_area_struct *vma)``:
+   Optional. If you need a special :c:func:`mmap()`
+   function, you can set it here. If this pointer is not NULL, your
+   :c:func:`mmap()` will be called instead of the built-in one.
+
+-  ``int (*open)(struct uio_info *info, struct inode *inode)``:
+   Optional. You might want to have your own :c:func:`open()`,
+   e.g. to enable interrupts only when your device is actually used.
+
+-  ``int (*release)(struct uio_info *info, struct inode *inode)``:
+   Optional. If you define your own :c:func:`open()`, you will
+   probably also want a custom :c:func:`release()` function.
+
+-  ``int (*irqcontrol)(struct uio_info *info, s32 irq_on)``:
+   Optional. If you need to be able to enable or disable interrupts
+   from userspace by writing to ``/dev/uioX``, you can implement this
+   function. The parameter ``irq_on`` will be 0 to disable interrupts
+   and 1 to enable them.
+
+Usually, your device will have one or more memory regions that can be
+mapped to user space. For each region, you have to set up a
+``struct uio_mem`` in the ``mem[]`` array. Here's a description of the
+fields of ``struct uio_mem``:
+
+-  ``const char *name``: Optional. Set this to help identify the memory
+   region, it will show up in the corresponding sysfs node.
+
+-  ``int memtype``: Required if the mapping is used. Set this to
+   ``UIO_MEM_PHYS`` if you you have physical memory on your card to be
+   mapped. Use ``UIO_MEM_LOGICAL`` for logical memory (e.g. allocated
+   with :c:func:`kmalloc()`). There's also ``UIO_MEM_VIRTUAL`` for
+   virtual memory.
+
+-  ``phys_addr_t addr``: Required if the mapping is used. Fill in the
+   address of your memory block. This address is the one that appears in
+   sysfs.
+
+-  ``resource_size_t size``: Fill in the size of the memory block that
+   ``addr`` points to. If ``size`` is zero, the mapping is considered
+   unused. Note that you *must* initialize ``size`` with zero for all
+   unused mappings.
+
+-  ``void *internal_addr``: If you have to access this memory region
+   from within your kernel module, you will want to map it internally by
+   using something like :c:func:`ioremap()`. Addresses returned by
+   this function cannot be mapped to user space, so you must not store
+   it in ``addr``. Use ``internal_addr`` instead to remember such an
+   address.
+
+Please do not touch the ``map`` element of ``struct uio_mem``! It is
+used by the UIO framework to set up sysfs files for this mapping. Simply
+leave it alone.
+
+Sometimes, your device can have one or more port regions which can not
+be mapped to userspace. But if there are other possibilities for
+userspace to access these ports, it makes sense to make information
+about the ports available in sysfs. For each region, you have to set up
+a ``struct uio_port`` in the ``port[]`` array. Here's a description of
+the fields of ``struct uio_port``:
+
+-  ``char *porttype``: Required. Set this to one of the predefined
+   constants. Use ``UIO_PORT_X86`` for the ioports found in x86
+   architectures.
+
+-  ``unsigned long start``: Required if the port region is used. Fill in
+   the number of the first port of this region.
+
+-  ``unsigned long size``: Fill in the number of ports in this region.
+   If ``size`` is zero, the region is considered unused. Note that you
+   *must* initialize ``size`` with zero for all unused regions.
+
+Please do not touch the ``portio`` element of ``struct uio_port``! It is
+used internally by the UIO framework to set up sysfs files for this
+region. Simply leave it alone.
+
+Adding an interrupt handler
+---------------------------
+
+What you need to do in your interrupt handler depends on your hardware
+and on how you want to handle it. You should try to keep the amount of
+code in your kernel interrupt handler low. If your hardware requires no
+action that you *have* to perform after each interrupt, then your
+handler can be empty.
+
+If, on the other hand, your hardware *needs* some action to be performed
+after each interrupt, then you *must* do it in your kernel module. Note
+that you cannot rely on the userspace part of your driver. Your
+userspace program can terminate at any time, possibly leaving your
+hardware in a state where proper interrupt handling is still required.
+
+There might also be applications where you want to read data from your
+hardware at each interrupt and buffer it in a piece of kernel memory
+you've allocated for that purpose. With this technique you could avoid
+loss of data if your userspace program misses an interrupt.
+
+A note on shared interrupts: Your driver should support interrupt
+sharing whenever this is possible. It is possible if and only if your
+driver can detect whether your hardware has triggered the interrupt or
+not. This is usually done by looking at an interrupt status register. If
+your driver sees that the IRQ bit is actually set, it will perform its
+actions, and the handler returns IRQ_HANDLED. If the driver detects
+that it was not your hardware that caused the interrupt, it will do
+nothing and return IRQ_NONE, allowing the kernel to call the next
+possible interrupt handler.
+
+If you decide not to support shared interrupts, your card won't work in
+computers with no free interrupts. As this frequently happens on the PC
+platform, you can save yourself a lot of trouble by supporting interrupt
+sharing.
+
+Using uio_pdrv for platform devices
+-----------------------------------
+
+In many cases, UIO drivers for platform devices can be handled in a
+generic way. In the same place where you define your
+``struct platform_device``, you simply also implement your interrupt
+handler and fill your ``struct uio_info``. A pointer to this
+``struct uio_info`` is then used as ``platform_data`` for your platform
+device.
+
+You also need to set up an array of ``struct resource`` containing
+addresses and sizes of your memory mappings. This information is passed
+to the driver using the ``.resource`` and ``.num_resources`` elements of
+``struct platform_device``.
+
+You now have to set the ``.name`` element of ``struct platform_device``
+to ``"uio_pdrv"`` to use the generic UIO platform device driver. This
+driver will fill the ``mem[]`` array according to the resources given,
+and register the device.
+
+The advantage of this approach is that you only have to edit a file you
+need to edit anyway. You do not have to create an extra driver.
+
+Using uio_pdrv_genirq for platform devices
+------------------------------------------
+
+Especially in embedded devices, you frequently find chips where the irq
+pin is tied to its own dedicated interrupt line. In such cases, where
+you can be really sure the interrupt is not shared, we can take the
+concept of ``uio_pdrv`` one step further and use a generic interrupt
+handler. That's what ``uio_pdrv_genirq`` does.
+
+The setup for this driver is the same as described above for
+``uio_pdrv``, except that you do not implement an interrupt handler. The
+``.handler`` element of ``struct uio_info`` must remain ``NULL``. The
+``.irq_flags`` element must not contain ``IRQF_SHARED``.
+
+You will set the ``.name`` element of ``struct platform_device`` to
+``"uio_pdrv_genirq"`` to use this driver.
+
+The generic interrupt handler of ``uio_pdrv_genirq`` will simply disable
+the interrupt line using :c:func:`disable_irq_nosync()`. After
+doing its work, userspace can reenable the interrupt by writing
+0x00000001 to the UIO device file. The driver already implements an
+:c:func:`irq_control()` to make this possible, you must not
+implement your own.
+
+Using ``uio_pdrv_genirq`` not only saves a few lines of interrupt
+handler code. You also do not need to know anything about the chip's
+internal registers to create the kernel part of the driver. All you need
+to know is the irq number of the pin the chip is connected to.
+
+Using uio_dmem_genirq for platform devices
+------------------------------------------
+
+In addition to statically allocated memory ranges, they may also be a
+desire to use dynamically allocated regions in a user space driver. In
+particular, being able to access memory made available through the
+dma-mapping API, may be particularly useful. The ``uio_dmem_genirq``
+driver provides a way to accomplish this.
+
+This driver is used in a similar manner to the ``"uio_pdrv_genirq"``
+driver with respect to interrupt configuration and handling.
+
+Set the ``.name`` element of ``struct platform_device`` to
+``"uio_dmem_genirq"`` to use this driver.
+
+When using this driver, fill in the ``.platform_data`` element of
+``struct platform_device``, which is of type
+``struct uio_dmem_genirq_pdata`` and which contains the following
+elements:
+
+-  ``struct uio_info uioinfo``: The same structure used as the
+   ``uio_pdrv_genirq`` platform data
+
+-  ``unsigned int *dynamic_region_sizes``: Pointer to list of sizes of
+   dynamic memory regions to be mapped into user space.
+
+-  ``unsigned int num_dynamic_regions``: Number of elements in
+   ``dynamic_region_sizes`` array.
+
+The dynamic regions defined in the platform data will be appended to the
+`` mem[] `` array after the platform device resources, which implies
+that the total number of static and dynamic memory regions cannot exceed
+``MAX_UIO_MAPS``.
+
+The dynamic memory regions will be allocated when the UIO device file,
+``/dev/uioX`` is opened. Similar to static memory resources, the memory
+region information for dynamic regions is then visible via sysfs at
+``/sys/class/uio/uioX/maps/mapY/*``. The dynamic memory regions will be
+freed when the UIO device file is closed. When no processes are holding
+the device file open, the address returned to userspace is ~0.
+
+Writing a driver in userspace
+=============================
+
+Once you have a working kernel module for your hardware, you can write
+the userspace part of your driver. You don't need any special libraries,
+your driver can be written in any reasonable language, you can use
+floating point numbers and so on. In short, you can use all the tools
+and libraries you'd normally use for writing a userspace application.
+
+Getting information about your UIO device
+-----------------------------------------
+
+Information about all UIO devices is available in sysfs. The first thing
+you should do in your driver is check ``name`` and ``version`` to make
+sure your talking to the right device and that its kernel driver has the
+version you expect.
+
+You should also make sure that the memory mapping you need exists and
+has the size you expect.
+
+There is a tool called ``lsuio`` that lists UIO devices and their
+attributes. It is available here:
+
+http://www.osadl.org/projects/downloads/UIO/user/
+
+With ``lsuio`` you can quickly check if your kernel module is loaded and
+which attributes it exports. Have a look at the manpage for details.
+
+The source code of ``lsuio`` can serve as an example for getting
+information about an UIO device. The file ``uio_helper.c`` contains a
+lot of functions you could use in your userspace driver code.
+
+mmap() device memory
+--------------------
+
+After you made sure you've got the right device with the memory mappings
+you need, all you have to do is to call :c:func:`mmap()` to map the
+device's memory to userspace.
+
+The parameter ``offset`` of the :c:func:`mmap()` call has a special
+meaning for UIO devices: It is used to select which mapping of your
+device you want to map. To map the memory of mapping N, you have to use
+N times the page size as your offset::
+
+        offset = N * getpagesize();
+
+N starts from zero, so if you've got only one memory range to map, set
+``offset = 0``. A drawback of this technique is that memory is always
+mapped beginning with its start address.
+
+Waiting for interrupts
+----------------------
+
+After you successfully mapped your devices memory, you can access it
+like an ordinary array. Usually, you will perform some initialization.
+After that, your hardware starts working and will generate an interrupt
+as soon as it's finished, has some data available, or needs your
+attention because an error occurred.
+
+``/dev/uioX`` is a read-only file. A :c:func:`read()` will always
+block until an interrupt occurs. There is only one legal value for the
+``count`` parameter of :c:func:`read()`, and that is the size of a
+signed 32 bit integer (4). Any other value for ``count`` causes
+:c:func:`read()` to fail. The signed 32 bit integer read is the
+interrupt count of your device. If the value is one more than the value
+you read the last time, everything is OK. If the difference is greater
+than one, you missed interrupts.
+
+You can also use :c:func:`select()` on ``/dev/uioX``.
+
+Generic PCI UIO driver
+======================
+
+The generic driver is a kernel module named uio_pci_generic. It can
+work with any device compliant to PCI 2.3 (circa 2002) and any compliant
+PCI Express device. Using this, you only need to write the userspace
+driver, removing the need to write a hardware-specific kernel module.
+
+Making the driver recognize the device
+--------------------------------------
+
+Since the driver does not declare any device ids, it will not get loaded
+automatically and will not automatically bind to any devices, you must
+load it and allocate id to the driver yourself. For example::
+
+     modprobe uio_pci_generic
+     echo "8086 10f5" > /sys/bus/pci/drivers/uio_pci_generic/new_id
+
+If there already is a hardware specific kernel driver for your device,
+the generic driver still won't bind to it, in this case if you want to
+use the generic driver (why would you?) you'll have to manually unbind
+the hardware specific driver and bind the generic driver, like this::
+
+        echo -n 0000:00:19.0 > /sys/bus/pci/drivers/e1000e/unbind
+        echo -n 0000:00:19.0 > /sys/bus/pci/drivers/uio_pci_generic/bind
+
+You can verify that the device has been bound to the driver by looking
+for it in sysfs, for example like the following::
+
+        ls -l /sys/bus/pci/devices/0000:00:19.0/driver
+
+Which if successful should print::
+
+      .../0000:00:19.0/driver -> ../../../bus/pci/drivers/uio_pci_generic
+
+Note that the generic driver will not bind to old PCI 2.2 devices. If
+binding the device failed, run the following command::
+
+      dmesg
+
+and look in the output for failure reasons.
+
+Things to know about uio_pci_generic
+------------------------------------
+
+Interrupts are handled using the Interrupt Disable bit in the PCI
+command register and Interrupt Status bit in the PCI status register.
+All devices compliant to PCI 2.3 (circa 2002) and all compliant PCI
+Express devices should support these bits. uio_pci_generic detects
+this support, and won't bind to devices which do not support the
+Interrupt Disable Bit in the command register.
+
+On each interrupt, uio_pci_generic sets the Interrupt Disable bit.
+This prevents the device from generating further interrupts until the
+bit is cleared. The userspace driver should clear this bit before
+blocking and waiting for more interrupts.
+
+Writing userspace driver using uio_pci_generic
+------------------------------------------------
+
+Userspace driver can use pci sysfs interface, or the libpci library that
+wraps it, to talk to the device and to re-enable interrupts by writing
+to the command register.
+
+Example code using uio_pci_generic
+----------------------------------
+
+Here is some sample userspace driver code using uio_pci_generic::
+
+    #include <stdlib.h>
+    #include <stdio.h>
+    #include <unistd.h>
+    #include <sys/types.h>
+    #include <sys/stat.h>
+    #include <fcntl.h>
+    #include <errno.h>
+
+    int main()
+    {
+        int uiofd;
+        int configfd;
+        int err;
+        int i;
+        unsigned icount;
+        unsigned char command_high;
+
+        uiofd = open("/dev/uio0", O_RDONLY);
+        if (uiofd < 0) {
+            perror("uio open:");
+            return errno;
+        }
+        configfd = open("/sys/class/uio/uio0/device/config", O_RDWR);
+        if (configfd < 0) {
+            perror("config open:");
+            return errno;
+        }
+
+        /* Read and cache command value */
+        err = pread(configfd, &command_high, 1, 5);
+        if (err != 1) {
+            perror("command config read:");
+            return errno;
+        }
+        command_high &= ~0x4;
+
+        for(i = 0;; ++i) {
+            /* Print out a message, for debugging. */
+            if (i == 0)
+                fprintf(stderr, "Started uio test driver.\n");
+            else
+                fprintf(stderr, "Interrupts: %d\n", icount);
+
+            /****************************************/
+            /* Here we got an interrupt from the
+               device. Do something to it. */
+            /****************************************/
+
+            /* Re-enable interrupts. */
+            err = pwrite(configfd, &command_high, 1, 5);
+            if (err != 1) {
+                perror("config write:");
+                break;
+            }
+
+            /* Wait for next interrupt. */
+            err = read(uiofd, &icount, 4);
+            if (err != 4) {
+                perror("uio read:");
+                break;
+            }
+
+        }
+        return errno;
+    }
+
+Generic Hyper-V UIO driver
+==========================
+
+The generic driver is a kernel module named uio_hv_generic. It
+supports devices on the Hyper-V VMBus similar to uio_pci_generic on
+PCI bus.
+
+Making the driver recognize the device
+--------------------------------------
+
+Since the driver does not declare any device GUID's, it will not get
+loaded automatically and will not automatically bind to any devices, you
+must load it and allocate id to the driver yourself. For example, to use
+the network device class GUID::
+
+     modprobe uio_hv_generic
+     echo "f8615163-df3e-46c5-913f-f2d2f965ed0e" > /sys/bus/vmbus/drivers/uio_hv_generic/new_id
+
+If there already is a hardware specific kernel driver for the device,
+the generic driver still won't bind to it, in this case if you want to
+use the generic driver for a userspace library you'll have to manually unbind
+the hardware specific driver and bind the generic driver, using the device specific GUID
+like this::
+
+          echo -n ed963694-e847-4b2a-85af-bc9cfc11d6f3 > /sys/bus/vmbus/drivers/hv_netvsc/unbind
+          echo -n ed963694-e847-4b2a-85af-bc9cfc11d6f3 > /sys/bus/vmbus/drivers/uio_hv_generic/bind
+
+You can verify that the device has been bound to the driver by looking
+for it in sysfs, for example like the following::
+
+        ls -l /sys/bus/vmbus/devices/ed963694-e847-4b2a-85af-bc9cfc11d6f3/driver
+
+Which if successful should print::
+
+      .../ed963694-e847-4b2a-85af-bc9cfc11d6f3/driver -> ../../../bus/vmbus/drivers/uio_hv_generic
+
+Things to know about uio_hv_generic
+-----------------------------------
+
+On each interrupt, uio_hv_generic sets the Interrupt Disable bit. This
+prevents the device from generating further interrupts until the bit is
+cleared. The userspace driver should clear this bit before blocking and
+waiting for more interrupts.
+
+When host rescinds a device, the interrupt file descriptor is marked down
+and any reads of the interrupt file descriptor will return -EIO. Similar
+to a closed socket or disconnected serial device.
+
+The vmbus device regions are mapped into uio device resources:
+    0) Channel ring buffers: guest to host and host to guest
+    1) Guest to host interrupt signalling pages
+    2) Guest to host monitor page
+    3) Network receive buffer region
+    4) Network send buffer region
+
+If a subchannel is created by a request to host, then the uio_hv_generic
+device driver will create a sysfs binary file for the per-channel ring buffer.
+For example::
+
+	/sys/bus/vmbus/devices/3811fe4d-0fa0-4b62-981a-74fc1084c757/channels/21/ring
+
+Further information
+===================
+
+-  `OSADL homepage. <http://www.osadl.org>`_
+
+-  `Linutronix homepage. <http://www.linutronix.de>`_

Documentation/driver-api/usb/URB.rst

@@ -0,0 +1,290 @@
+.. _usb-urb:
+
+USB Request Block (URB)
+~~~~~~~~~~~~~~~~~~~~~~~
+
+:Revised: 2000-Dec-05
+:Again:   2002-Jul-06
+:Again:   2005-Sep-19
+:Again:   2017-Mar-29
+
+
+.. note::
+
+    The USB subsystem now has a substantial section at :ref:`usb-hostside-api`
+    section, generated from the current source code.
+    This particular documentation file isn't complete and may not be
+    updated to the last version; don't rely on it except for a quick
+    overview.
+
+Basic concept or 'What is an URB?'
+==================================
+
+The basic idea of the new driver is message passing, the message itself is
+called USB Request Block, or URB for short.
+
+- An URB consists of all relevant information to execute any USB transaction
+  and deliver the data and status back.
+
+- Execution of an URB is inherently an asynchronous operation, i.e. the
+  :c:func:`usb_submit_urb` call returns immediately after it has successfully
+  queued the requested action.
+
+- Transfers for one URB can be canceled with :c:func:`usb_unlink_urb`
+  at any time.
+
+- Each URB has a completion handler, which is called after the action
+  has been successfully completed or canceled. The URB also contains a
+  context-pointer for passing information to the completion handler.
+
+- Each endpoint for a device logically supports a queue of requests.
+  You can fill that queue, so that the USB hardware can still transfer
+  data to an endpoint while your driver handles completion of another.
+  This maximizes use of USB bandwidth, and supports seamless streaming
+  of data to (or from) devices when using periodic transfer modes.
+
+
+The URB structure
+=================
+
+Some of the fields in struct :c:type:`urb` are::
+
+  struct urb
+  {
+  // (IN) device and pipe specify the endpoint queue
+	struct usb_device *dev;         // pointer to associated USB device
+	unsigned int pipe;              // endpoint information
+
+	unsigned int transfer_flags;    // URB_ISO_ASAP, URB_SHORT_NOT_OK, etc.
+
+  // (IN) all urbs need completion routines
+	void *context;                  // context for completion routine
+	usb_complete_t complete;        // pointer to completion routine
+
+  // (OUT) status after each completion
+	int status;                     // returned status
+
+  // (IN) buffer used for data transfers
+	void *transfer_buffer;          // associated data buffer
+	u32 transfer_buffer_length;     // data buffer length
+	int number_of_packets;          // size of iso_frame_desc
+
+  // (OUT) sometimes only part of CTRL/BULK/INTR transfer_buffer is used
+	u32 actual_length;              // actual data buffer length
+
+  // (IN) setup stage for CTRL (pass a struct usb_ctrlrequest)
+	unsigned char *setup_packet;    // setup packet (control only)
+
+  // Only for PERIODIC transfers (ISO, INTERRUPT)
+    // (IN/OUT) start_frame is set unless URB_ISO_ASAP isn't set
+	int start_frame;                // start frame
+	int interval;                   // polling interval
+
+    // ISO only: packets are only "best effort"; each can have errors
+	int error_count;                // number of errors
+	struct usb_iso_packet_descriptor iso_frame_desc[0];
+  };
+
+Your driver must create the "pipe" value using values from the appropriate
+endpoint descriptor in an interface that it's claimed.
+
+
+How to get an URB?
+==================
+
+URBs are allocated by calling :c:func:`usb_alloc_urb`::
+
+	struct urb *usb_alloc_urb(int isoframes, int mem_flags)
+
+Return value is a pointer to the allocated URB, 0 if allocation failed.
+The parameter isoframes specifies the number of isochronous transfer frames
+you want to schedule. For CTRL/BULK/INT, use 0.  The mem_flags parameter
+holds standard memory allocation flags, letting you control (among other
+things) whether the underlying code may block or not.
+
+To free an URB, use :c:func:`usb_free_urb`::
+
+	void usb_free_urb(struct urb *urb)
+
+You may free an urb that you've submitted, but which hasn't yet been
+returned to you in a completion callback.  It will automatically be
+deallocated when it is no longer in use.
+
+
+What has to be filled in?
+=========================
+
+Depending on the type of transaction, there are some inline functions
+defined in ``linux/usb.h`` to simplify the initialization, such as
+:c:func:`usb_fill_control_urb`, :c:func:`usb_fill_bulk_urb` and
+:c:func:`usb_fill_int_urb`.  In general, they need the usb device pointer,
+the pipe (usual format from usb.h), the transfer buffer, the desired transfer
+length, the completion handler, and its context. Take a look at the some
+existing drivers to see how they're used.
+
+Flags:
+
+- For ISO there are two startup behaviors: Specified start_frame or ASAP.
+- For ASAP set ``URB_ISO_ASAP`` in transfer_flags.
+
+If short packets should NOT be tolerated, set ``URB_SHORT_NOT_OK`` in
+transfer_flags.
+
+
+How to submit an URB?
+=====================
+
+Just call :c:func:`usb_submit_urb`::
+
+	int usb_submit_urb(struct urb *urb, int mem_flags)
+
+The ``mem_flags`` parameter, such as ``GFP_ATOMIC``, controls memory
+allocation, such as whether the lower levels may block when memory is tight.
+
+It immediately returns, either with status 0 (request queued) or some
+error code, usually caused by the following:
+
+- Out of memory (``-ENOMEM``)
+- Unplugged device (``-ENODEV``)
+- Stalled endpoint (``-EPIPE``)
+- Too many queued ISO transfers (``-EAGAIN``)
+- Too many requested ISO frames (``-EFBIG``)
+- Invalid INT interval (``-EINVAL``)
+- More than one packet for INT (``-EINVAL``)
+
+After submission, ``urb->status`` is ``-EINPROGRESS``; however, you should
+never look at that value except in your completion callback.
+
+For isochronous endpoints, your completion handlers should (re)submit
+URBs to the same endpoint with the ``URB_ISO_ASAP`` flag, using
+multi-buffering, to get seamless ISO streaming.
+
+
+How to cancel an already running URB?
+=====================================
+
+There are two ways to cancel an URB you've submitted but which hasn't
+been returned to your driver yet.  For an asynchronous cancel, call
+:c:func:`usb_unlink_urb`::
+
+	int usb_unlink_urb(struct urb *urb)
+
+It removes the urb from the internal list and frees all allocated
+HW descriptors. The status is changed to reflect unlinking.  Note
+that the URB will not normally have finished when :c:func:`usb_unlink_urb`
+returns; you must still wait for the completion handler to be called.
+
+To cancel an URB synchronously, call :c:func:`usb_kill_urb`::
+
+	void usb_kill_urb(struct urb *urb)
+
+It does everything :c:func:`usb_unlink_urb` does, and in addition it waits
+until after the URB has been returned and the completion handler
+has finished.  It also marks the URB as temporarily unusable, so
+that if the completion handler or anyone else tries to resubmit it
+they will get a ``-EPERM`` error.  Thus you can be sure that when
+:c:func:`usb_kill_urb` returns, the URB is totally idle.
+
+There is a lifetime issue to consider.  An URB may complete at any
+time, and the completion handler may free the URB.  If this happens
+while :c:func:`usb_unlink_urb` or :c:func:`usb_kill_urb` is running, it will
+cause a memory-access violation.  The driver is responsible for avoiding this,
+which often means some sort of lock will be needed to prevent the URB
+from being deallocated while it is still in use.
+
+On the other hand, since usb_unlink_urb may end up calling the
+completion handler, the handler must not take any lock that is held
+when usb_unlink_urb is invoked.  The general solution to this problem
+is to increment the URB's reference count while holding the lock, then
+drop the lock and call usb_unlink_urb or usb_kill_urb, and then
+decrement the URB's reference count.  You increment the reference
+count by calling :c:func`usb_get_urb`::
+
+	struct urb *usb_get_urb(struct urb *urb)
+
+(ignore the return value; it is the same as the argument) and
+decrement the reference count by calling :c:func:`usb_free_urb`.  Of course,
+none of this is necessary if there's no danger of the URB being freed
+by the completion handler.
+
+
+What about the completion handler?
+==================================
+
+The handler is of the following type::
+
+	typedef void (*usb_complete_t)(struct urb *)
+
+I.e., it gets the URB that caused the completion call. In the completion
+handler, you should have a look at ``urb->status`` to detect any USB errors.
+Since the context parameter is included in the URB, you can pass
+information to the completion handler.
+
+Note that even when an error (or unlink) is reported, data may have been
+transferred.  That's because USB transfers are packetized; it might take
+sixteen packets to transfer your 1KByte buffer, and ten of them might
+have transferred successfully before the completion was called.
+
+
+.. warning::
+
+   NEVER SLEEP IN A COMPLETION HANDLER.
+
+   These are often called in atomic context.
+
+In the current kernel, completion handlers run with local interrupts
+disabled, but in the future this will be changed, so don't assume that
+local IRQs are always disabled inside completion handlers.
+
+How to do isochronous (ISO) transfers?
+======================================
+
+Besides the fields present on a bulk transfer, for ISO, you also
+also have to set ``urb->interval`` to say how often to make transfers; it's
+often one per frame (which is once every microframe for highspeed devices).
+The actual interval used will be a power of two that's no bigger than what
+you specify. You can use the :c:func:`usb_fill_int_urb` macro to fill
+most ISO transfer fields.
+
+For ISO transfers you also have to fill a :c:type:`usb_iso_packet_descriptor`
+structure, allocated at the end of the URB by :c:func:`usb_alloc_urb`, for
+each packet you want to schedule.
+
+The :c:func:`usb_submit_urb` call modifies ``urb->interval`` to the implemented
+interval value that is less than or equal to the requested interval value.  If
+``URB_ISO_ASAP`` scheduling is used, ``urb->start_frame`` is also updated.
+
+For each entry you have to specify the data offset for this frame (base is
+transfer_buffer), and the length you want to write/expect to read.
+After completion, actual_length contains the actual transferred length and
+status contains the resulting status for the ISO transfer for this frame.
+It is allowed to specify a varying length from frame to frame (e.g. for
+audio synchronisation/adaptive transfer rates). You can also use the length
+0 to omit one or more frames (striping).
+
+For scheduling you can choose your own start frame or ``URB_ISO_ASAP``. As
+explained earlier, if you always keep at least one URB queued and your
+completion keeps (re)submitting a later URB, you'll get smooth ISO streaming
+(if usb bandwidth utilization allows).
+
+If you specify your own start frame, make sure it's several frames in advance
+of the current frame.  You might want this model if you're synchronizing
+ISO data with some other event stream.
+
+
+How to start interrupt (INT) transfers?
+=======================================
+
+Interrupt transfers, like isochronous transfers, are periodic, and happen
+in intervals that are powers of two (1, 2, 4 etc) units.  Units are frames
+for full and low speed devices, and microframes for high speed ones.
+You can use the :c:func:`usb_fill_int_urb` macro to fill INT transfer fields.
+
+The :c:func:`usb_submit_urb` call modifies ``urb->interval`` to the implemented
+interval value that is less than or equal to the requested interval value.
+
+In Linux 2.6, unlike earlier versions, interrupt URBs are not automagically
+restarted when they complete.  They end when the completion handler is
+called, just like other URBs.  If you want an interrupt URB to be restarted,
+your completion handler must resubmit it.
+s

Documentation/driver-api/usb/anchors.rst

@@ -0,0 +1,83 @@
+USB Anchors
+~~~~~~~~~~~
+
+What is anchor?
+===============
+
+A USB driver needs to support some callbacks requiring
+a driver to cease all IO to an interface. To do so, a
+driver has to keep track of the URBs it has submitted
+to know they've all completed or to call usb_kill_urb
+for them. The anchor is a data structure takes care of
+keeping track of URBs and provides methods to deal with
+multiple URBs.
+
+Allocation and Initialisation
+=============================
+
+There's no API to allocate an anchor. It is simply declared
+as struct usb_anchor. :c:func:`init_usb_anchor` must be called to
+initialise the data structure.
+
+Deallocation
+============
+
+Once it has no more URBs associated with it, the anchor can be
+freed with normal memory management operations.
+
+Association and disassociation of URBs with anchors
+===================================================
+
+An association of URBs to an anchor is made by an explicit
+call to :c:func:`usb_anchor_urb`. The association is maintained until
+an URB is finished by (successful) completion. Thus disassociation
+is automatic. A function is provided to forcibly finish (kill)
+all URBs associated with an anchor.
+Furthermore, disassociation can be made with :c:func:`usb_unanchor_urb`
+
+Operations on multitudes of URBs
+================================
+
+:c:func:`usb_kill_anchored_urbs`
+--------------------------------
+
+This function kills all URBs associated with an anchor. The URBs
+are called in the reverse temporal order they were submitted.
+This way no data can be reordered.
+
+:c:func:`usb_unlink_anchored_urbs`
+----------------------------------
+
+
+This function unlinks all URBs associated with an anchor. The URBs
+are processed in the reverse temporal order they were submitted.
+This is similar to :c:func:`usb_kill_anchored_urbs`, but it will not sleep.
+Therefore no guarantee is made that the URBs have been unlinked when
+the call returns. They may be unlinked later but will be unlinked in
+finite time.
+
+:c:func:`usb_scuttle_anchored_urbs`
+-----------------------------------
+
+All URBs of an anchor are unanchored en masse.
+
+:c:func:`usb_wait_anchor_empty_timeout`
+---------------------------------------
+
+This function waits for all URBs associated with an anchor to finish
+or a timeout, whichever comes first. Its return value will tell you
+whether the timeout was reached.
+
+:c:func:`usb_anchor_empty`
+--------------------------
+
+Returns true if no URBs are associated with an anchor. Locking
+is the caller's responsibility.
+
+:c:func:`usb_get_from_anchor`
+-----------------------------
+
+Returns the oldest anchored URB of an anchor. The URB is unanchored
+and returned with a reference. As you may mix URBs to several
+destinations in one anchor you have no guarantee the chronologically
+first submitted URB is returned.

Documentation/driver-api/usb/bulk-streams.rst

@@ -0,0 +1,83 @@
+USB bulk streams
+~~~~~~~~~~~~~~~~
+
+Background
+==========
+
+Bulk endpoint streams were added in the USB 3.0 specification.  Streams allow a
+device driver to overload a bulk endpoint so that multiple transfers can be
+queued at once.
+
+Streams are defined in sections 4.4.6.4 and 8.12.1.4 of the Universal Serial Bus
+3.0 specification at http://www.usb.org/developers/docs/  The USB Attached SCSI
+Protocol, which uses streams to queue multiple SCSI commands, can be found on
+the T10 website (http://t10.org/).
+
+
+Device-side implications
+========================
+
+Once a buffer has been queued to a stream ring, the device is notified (through
+an out-of-band mechanism on another endpoint) that data is ready for that stream
+ID.  The device then tells the host which "stream" it wants to start.  The host
+can also initiate a transfer on a stream without the device asking, but the
+device can refuse that transfer.  Devices can switch between streams at any
+time.
+
+
+Driver implications
+===================
+
+::
+
+  int usb_alloc_streams(struct usb_interface *interface,
+		struct usb_host_endpoint **eps, unsigned int num_eps,
+		unsigned int num_streams, gfp_t mem_flags);
+
+Device drivers will call this API to request that the host controller driver
+allocate memory so the driver can use up to num_streams stream IDs.  They must
+pass an array of usb_host_endpoints that need to be setup with similar stream
+IDs.  This is to ensure that a UASP driver will be able to use the same stream
+ID for the bulk IN and OUT endpoints used in a Bi-directional command sequence.
+
+The return value is an error condition (if one of the endpoints doesn't support
+streams, or the xHCI driver ran out of memory), or the number of streams the
+host controller allocated for this endpoint.  The xHCI host controller hardware
+declares how many stream IDs it can support, and each bulk endpoint on a
+SuperSpeed device will say how many stream IDs it can handle.  Therefore,
+drivers should be able to deal with being allocated less stream IDs than they
+requested.
+
+Do NOT call this function if you have URBs enqueued for any of the endpoints
+passed in as arguments.  Do not call this function to request less than two
+streams.
+
+Drivers will only be allowed to call this API once for the same endpoint
+without calling usb_free_streams().  This is a simplification for the xHCI host
+controller driver, and may change in the future.
+
+
+Picking new Stream IDs to use
+=============================
+
+Stream ID 0 is reserved, and should not be used to communicate with devices.  If
+usb_alloc_streams() returns with a value of N, you may use streams 1 though N.
+To queue an URB for a specific stream, set the urb->stream_id value.  If the
+endpoint does not support streams, an error will be returned.
+
+Note that new API to choose the next stream ID will have to be added if the xHCI
+driver supports secondary stream IDs.
+
+
+Clean up
+========
+
+If a driver wishes to stop using streams to communicate with the device, it
+should call::
+
+  void usb_free_streams(struct usb_interface *interface,
+		struct usb_host_endpoint **eps, unsigned int num_eps,
+		gfp_t mem_flags);
+
+All stream IDs will be deallocated when the driver releases the interface, to
+ensure that drivers that don't support streams will be able to use the endpoint.

Documentation/driver-api/usb/callbacks.rst

@@ -0,0 +1,157 @@
+USB core callbacks
+~~~~~~~~~~~~~~~~~~
+
+What callbacks will usbcore do?
+===============================
+
+Usbcore will call into a driver through callbacks defined in the driver
+structure and through the completion handler of URBs a driver submits.
+Only the former are in the scope of this document. These two kinds of
+callbacks are completely independent of each other. Information on the
+completion callback can be found in :ref:`usb-urb`.
+
+The callbacks defined in the driver structure are:
+
+1. Hotplugging callbacks:
+
+ - @probe:
+	Called to see if the driver is willing to manage a particular
+	interface on a device.
+
+ - @disconnect:
+	Called when the interface is no longer accessible, usually
+	because its device has been (or is being) disconnected or the
+	driver module is being unloaded.
+
+2. Odd backdoor through usbfs:
+
+ - @ioctl:
+	Used for drivers that want to talk to userspace through
+	the "usbfs" filesystem.  This lets devices provide ways to
+	expose information to user space regardless of where they
+	do (or don't) show up otherwise in the filesystem.
+
+3. Power management (PM) callbacks:
+
+ - @suspend:
+	Called when the device is going to be suspended.
+
+ - @resume:
+	Called when the device is being resumed.
+
+ - @reset_resume:
+	Called when the suspended device has been reset instead
+	of being resumed.
+
+4. Device level operations:
+
+ - @pre_reset:
+	Called when the device is about to be reset.
+
+ - @post_reset:
+	Called after the device has been reset
+
+The ioctl interface (2) should be used only if you have a very good
+reason. Sysfs is preferred these days. The PM callbacks are covered
+separately in :ref:`usb-power-management`.
+
+Calling conventions
+===================
+
+All callbacks are mutually exclusive. There's no need for locking
+against other USB callbacks. All callbacks are called from a task
+context. You may sleep. However, it is important that all sleeps have a
+small fixed upper limit in time. In particular you must not call out to
+user space and await results.
+
+Hotplugging callbacks
+=====================
+
+These callbacks are intended to associate and disassociate a driver with
+an interface. A driver's bond to an interface is exclusive.
+
+The probe() callback
+--------------------
+
+::
+
+  int (*probe) (struct usb_interface *intf,
+		const struct usb_device_id *id);
+
+Accept or decline an interface. If you accept the device return 0,
+otherwise -ENODEV or -ENXIO. Other error codes should be used only if a
+genuine error occurred during initialisation which prevented a driver
+from accepting a device that would else have been accepted.
+You are strongly encouraged to use usbcore's facility,
+usb_set_intfdata(), to associate a data structure with an interface, so
+that you know which internal state and identity you associate with a
+particular interface. The device will not be suspended and you may do IO
+to the interface you are called for and endpoint 0 of the device. Device
+initialisation that doesn't take too long is a good idea here.
+
+The disconnect() callback
+-------------------------
+
+::
+
+  void (*disconnect) (struct usb_interface *intf);
+
+This callback is a signal to break any connection with an interface.
+You are not allowed any IO to a device after returning from this
+callback. You also may not do any other operation that may interfere
+with another driver bound the interface, eg. a power management
+operation.
+If you are called due to a physical disconnection, all your URBs will be
+killed by usbcore. Note that in this case disconnect will be called some
+time after the physical disconnection. Thus your driver must be prepared
+to deal with failing IO even prior to the callback.
+
+Device level callbacks
+======================
+
+pre_reset
+---------
+
+::
+
+  int (*pre_reset)(struct usb_interface *intf);
+
+A driver or user space is triggering a reset on the device which
+contains the interface passed as an argument. Cease IO, wait for all
+outstanding URBs to complete, and save any device state you need to
+restore.  No more URBs may be submitted until the post_reset method
+is called.
+
+If you need to allocate memory here, use GFP_NOIO or GFP_ATOMIC, if you
+are in atomic context.
+
+post_reset
+----------
+
+::
+
+  int (*post_reset)(struct usb_interface *intf);
+
+The reset has completed.  Restore any saved device state and begin
+using the device again.
+
+If you need to allocate memory here, use GFP_NOIO or GFP_ATOMIC, if you
+are in atomic context.
+
+Call sequences
+==============
+
+No callbacks other than probe will be invoked for an interface
+that isn't bound to your driver.
+
+Probe will never be called for an interface bound to a driver.
+Hence following a successful probe, disconnect will be called
+before there is another probe for the same interface.
+
+Once your driver is bound to an interface, disconnect can be
+called at any time except in between pre_reset and post_reset.
+pre_reset is always followed by post_reset, even if the reset
+failed or the device has been unplugged.
+
+suspend is always followed by one of: resume, reset_resume, or
+disconnect.

Documentation/driver-api/usb/dma.rst

@@ -0,0 +1,136 @@
+USB DMA
+~~~~~~~
+
+In Linux 2.5 kernels (and later), USB device drivers have additional control
+over how DMA may be used to perform I/O operations.  The APIs are detailed
+in the kernel usb programming guide (kerneldoc, from the source code).
+
+API overview
+============
+
+The big picture is that USB drivers can continue to ignore most DMA issues,
+though they still must provide DMA-ready buffers (see
+``Documentation/DMA-API-HOWTO.txt``).  That's how they've worked through
+the 2.4 (and earlier) kernels, or they can now be DMA-aware.
+
+DMA-aware usb drivers:
+
+- New calls enable DMA-aware drivers, letting them allocate dma buffers and
+  manage dma mappings for existing dma-ready buffers (see below).
+
+- URBs have an additional "transfer_dma" field, as well as a transfer_flags
+  bit saying if it's valid.  (Control requests also have "setup_dma", but
+  drivers must not use it.)
+
+- "usbcore" will map this DMA address, if a DMA-aware driver didn't do
+  it first and set ``URB_NO_TRANSFER_DMA_MAP``.  HCDs
+  don't manage dma mappings for URBs.
+
+- There's a new "generic DMA API", parts of which are usable by USB device
+  drivers.  Never use dma_set_mask() on any USB interface or device; that
+  would potentially break all devices sharing that bus.
+
+Eliminating copies
+==================
+
+It's good to avoid making CPUs copy data needlessly.  The costs can add up,
+and effects like cache-trashing can impose subtle penalties.
+
+- If you're doing lots of small data transfers from the same buffer all
+  the time, that can really burn up resources on systems which use an
+  IOMMU to manage the DMA mappings.  It can cost MUCH more to set up and
+  tear down the IOMMU mappings with each request than perform the I/O!
+
+  For those specific cases, USB has primitives to allocate less expensive
+  memory.  They work like kmalloc and kfree versions that give you the right
+  kind of addresses to store in urb->transfer_buffer and urb->transfer_dma.
+  You'd also set ``URB_NO_TRANSFER_DMA_MAP`` in urb->transfer_flags::
+
+	void *usb_alloc_coherent (struct usb_device *dev, size_t size,
+		int mem_flags, dma_addr_t *dma);
+
+	void usb_free_coherent (struct usb_device *dev, size_t size,
+		void *addr, dma_addr_t dma);
+
+  Most drivers should **NOT** be using these primitives; they don't need
+  to use this type of memory ("dma-coherent"), and memory returned from
+  :c:func:`kmalloc` will work just fine.
+
+  The memory buffer returned is "dma-coherent"; sometimes you might need to
+  force a consistent memory access ordering by using memory barriers.  It's
+  not using a streaming DMA mapping, so it's good for small transfers on
+  systems where the I/O would otherwise thrash an IOMMU mapping.  (See
+  ``Documentation/DMA-API-HOWTO.txt`` for definitions of "coherent" and
+  "streaming" DMA mappings.)
+
+  Asking for 1/Nth of a page (as well as asking for N pages) is reasonably
+  space-efficient.
+
+  On most systems the memory returned will be uncached, because the
+  semantics of dma-coherent memory require either bypassing CPU caches
+  or using cache hardware with bus-snooping support.  While x86 hardware
+  has such bus-snooping, many other systems use software to flush cache
+  lines to prevent DMA conflicts.
+
+- Devices on some EHCI controllers could handle DMA to/from high memory.
+
+  Unfortunately, the current Linux DMA infrastructure doesn't have a sane
+  way to expose these capabilities ... and in any case, HIGHMEM is mostly a
+  design wart specific to x86_32.  So your best bet is to ensure you never
+  pass a highmem buffer into a USB driver.  That's easy; it's the default
+  behavior.  Just don't override it; e.g. with ``NETIF_F_HIGHDMA``.
+
+  This may force your callers to do some bounce buffering, copying from
+  high memory to "normal" DMA memory.  If you can come up with a good way
+  to fix this issue (for x86_32 machines with over 1 GByte of memory),
+  feel free to submit patches.
+
+Working with existing buffers
+=============================
+
+Existing buffers aren't usable for DMA without first being mapped into the
+DMA address space of the device.  However, most buffers passed to your
+driver can safely be used with such DMA mapping.  (See the first section
+of Documentation/DMA-API-HOWTO.txt, titled "What memory is DMA-able?")
+
+- When you're using scatterlists, you can map everything at once.  On some
+  systems, this kicks in an IOMMU and turns the scatterlists into single
+  DMA transactions::
+
+	int usb_buffer_map_sg (struct usb_device *dev, unsigned pipe,
+		struct scatterlist *sg, int nents);
+
+	void usb_buffer_dmasync_sg (struct usb_device *dev, unsigned pipe,
+		struct scatterlist *sg, int n_hw_ents);
+
+	void usb_buffer_unmap_sg (struct usb_device *dev, unsigned pipe,
+		struct scatterlist *sg, int n_hw_ents);
+
+  It's probably easier to use the new ``usb_sg_*()`` calls, which do the DMA
+  mapping and apply other tweaks to make scatterlist i/o be fast.
+
+- Some drivers may prefer to work with the model that they're mapping large
+  buffers, synchronizing their safe re-use.  (If there's no re-use, then let
+  usbcore do the map/unmap.)  Large periodic transfers make good examples
+  here, since it's cheaper to just synchronize the buffer than to unmap it
+  each time an urb completes and then re-map it on during resubmission.
+
+  These calls all work with initialized urbs:  ``urb->dev``, ``urb->pipe``,
+  ``urb->transfer_buffer``, and ``urb->transfer_buffer_length`` must all be
+  valid when these calls are used (``urb->setup_packet`` must be valid too
+  if urb is a control request)::
+
+	struct urb *usb_buffer_map (struct urb *urb);
+
+	void usb_buffer_dmasync (struct urb *urb);
+
+	void usb_buffer_unmap (struct urb *urb);
+
+  The calls manage ``urb->transfer_dma`` for you, and set
+  ``URB_NO_TRANSFER_DMA_MAP`` so that usbcore won't map or unmap the buffer.
+  They cannot be used for setup_packet buffers in control requests.
+
+Note that several of those interfaces are currently commented out, since
+they don't have current users.  See the source code.  Other than the dmasync
+calls (where the underlying DMA primitives have changed), most of them can
+easily be commented back in if you want to use them.

Documentation/driver-api/usb/dwc3.rst

@@ -0,0 +1,711 @@
+===============================================================
+Synopsys DesignWare Core SuperSpeed USB 3.0 Controller
+===============================================================
+
+:Author: Felipe Balbi <felipe.balbi@linux.intel.com>
+:Date: April 2017
+
+Introduction
+============
+
+The *Synopsys DesignWare Core SuperSpeed USB 3.0 Controller*
+(hereinafter referred to as *DWC3*) is a USB SuperSpeed compliant
+controller which can be configured in one of 4 ways:
+
+	1. Peripheral-only configuration
+	2. Host-only configuration
+	3. Dual-Role configuration
+	4. Hub configuration
+
+Linux currently supports several versions of this controller. In all
+likelyhood, the version in your SoC is already supported. At the time
+of this writing, known tested versions range from 2.02a to 3.10a. As a
+rule of thumb, anything above 2.02a should work reliably well.
+
+Currently, we have many known users for this driver. In alphabetical
+order:
+
+	1. Cavium
+	2. Intel Corporation
+	3. Qualcomm
+	4. Rockchip
+	5. ST
+	6. Samsung
+	7. Texas Instruments
+	8. Xilinx
+
+Summary of Features
+======================
+
+For details about features supported by your version of DWC3, consult
+your IP team and/or *Synopsys DesignWare Core SuperSpeed USB 3.0
+Controller Databook*. Following is a list of features supported by the
+driver at the time of this writing:
+
+	1. Up to 16 bidirectional endpoints (including the control
+	   pipe - ep0)
+	2. Flexible endpoint configuration
+	3. Simultaneous IN and OUT transfer support
+	4. Scatter-list support
+	5. Up to 256 TRBs [#trb]_ per endpoint
+	6. Support for all transfer types (*Control*, *Bulk*,
+	   *Interrupt*, and *Isochronous*)
+	7. SuperSpeed Bulk Streams
+	8. Link Power Management
+	9. Trace Events for debugging
+	10. DebugFS [#debugfs]_ interface
+
+These features have all been exercised with many of the **in-tree**
+gadget drivers. We have verified both *ConfigFS* [#configfs]_ and
+legacy gadget drivers.
+
+Driver Design
+==============
+
+The DWC3 driver sits on the *drivers/usb/dwc3/* directory. All files
+related to this driver are in this one directory. This makes it easy
+for new-comers to read the code and understand how it behaves.
+
+Because of DWC3's configuration flexibility, the driver is a little
+complex in some places but it should be rather straightforward to
+understand.
+
+The biggest part of the driver refers to the Gadget API.
+
+Known Limitations
+===================
+
+Like any other HW, DWC3 has its own set of limitations. To avoid
+constant questions about such problems, we decided to document them
+here and have a single location to where we could point users.
+
+OUT Transfer Size Requirements
+---------------------------------
+
+According to Synopsys Databook, all OUT transfer TRBs [#trb]_ must
+have their *size* field set to a value which is integer divisible by
+the endpoint's *wMaxPacketSize*. This means that *e.g.* in order to
+receive a Mass Storage *CBW* [#cbw]_, req->length must either be set
+to a value that's divisible by *wMaxPacketSize* (1024 on SuperSpeed,
+512 on HighSpeed, etc), or DWC3 driver must add a Chained TRB pointing
+to a throw-away buffer for the remaining length. Without this, OUT
+transfers will **NOT** start.
+
+Note that as of this writing, this won't be a problem because DWC3 is
+fully capable of appending a chained TRB for the remaining length and
+completely hide this detail from the gadget driver. It's still worth
+mentioning because this seems to be the largest source of queries
+about DWC3 and *non-working transfers*.
+
+TRB Ring Size Limitation
+-------------------------
+
+We, currently, have a hard limit of 256 TRBs [#trb]_ per endpoint,
+with the last TRB being a Link TRB [#link_trb]_ pointing back to the
+first. This limit is arbitrary but it has the benefit of adding up to
+exactly 4096 bytes, or 1 Page.
+
+DWC3 driver will try its best to cope with more than 255 requests and,
+for the most part, it should work normally. However this is not
+something that has been exercised very frequently. If you experience
+any problems, see section **Reporting Bugs** below.
+
+Reporting Bugs
+================
+
+Whenever you encounter a problem with DWC3, first and foremost you
+should make sure that:
+
+	1. You're running latest tag from `Linus' tree`_
+	2. You can reproduce the error without any out-of-tree changes
+	   to DWC3
+	3. You have checked that it's not a fault on the host machine
+
+After all these are verified, then here's how to capture enough
+information so we can be of any help to you.
+
+Required Information
+---------------------
+
+DWC3 relies exclusively on Trace Events for debugging. Everything is
+exposed there, with some extra bits being exposed to DebugFS
+[#debugfs]_.
+
+In order to capture DWC3's Trace Events you should run the following
+commands **before** plugging the USB cable to a host machine:
+
+.. code-block:: sh
+
+		 # mkdir -p /d
+		 # mkdir -p /t
+		 # mount -t debugfs none /d
+		 # mount -t tracefs none /t
+		 # echo 81920 > /t/buffer_size_kb
+		 # echo 1 > /t/events/dwc3/enable
+
+After this is done, you can connect your USB cable and reproduce the
+problem. As soon as the fault is reproduced, make a copy of files
+``trace`` and ``regdump``, like so:
+
+.. code-block:: sh
+
+		# cp /t/trace /root/trace.txt
+		# cat /d/*dwc3*/regdump > /root/regdump.txt
+
+Make sure to compress ``trace.txt`` and ``regdump.txt`` in a tarball
+and email it to `me`_ with `linux-usb`_ in Cc. If you want to be extra
+sure that I'll help you, write your subject line in the following
+format:
+
+	**[BUG REPORT] usb: dwc3: Bug while doing XYZ**
+
+On the email body, make sure to detail what you doing, which gadget
+driver you were using, how to reproduce the problem, what SoC you're
+using, which OS (and its version) was running on the Host machine.
+
+With all this information, we should be able to understand what's
+going on and be helpful to you.
+
+Debugging
+===========
+
+First and foremost a disclaimer::
+
+  DISCLAIMER: The information available on DebugFS and/or TraceFS can
+  change at any time at any Major Linux Kernel Release. If writing
+  scripts, do **NOT** assume information to be available in the
+  current format.
+
+With that out of the way, let's carry on.
+
+If you're willing to debug your own problem, you deserve a round of
+applause :-)
+
+Anyway, there isn't much to say here other than Trace Events will be
+really helpful in figuring out issues with DWC3. Also, access to
+Synopsys Databook will be **really** valuable in this case.
+
+A USB Sniffer can be helpful at times but it's not entirely required,
+there's a lot that can be understood without looking at the wire.
+
+Feel free to email `me`_ and Cc `linux-usb`_ if you need any help.
+
+``DebugFS``
+-------------
+
+``DebugFS`` is very good for gathering snapshots of what's going on
+with DWC3 and/or any endpoint.
+
+On DWC3's ``DebugFS`` directory, you will find the following files and
+directories:
+
+``ep[0..15]{in,out}/``
+``link_state``
+``regdump``
+``testmode``
+
+``link_state``
+``````````````
+
+When read, ``link_state`` will print out one of ``U0``, ``U1``,
+``U2``, ``U3``, ``SS.Disabled``, ``RX.Detect``, ``SS.Inactive``,
+``Polling``, ``Recovery``, ``Hot Reset``, ``Compliance``,
+``Loopback``, ``Reset``, ``Resume`` or ``UNKNOWN link state``.
+
+This file can also be written to in order to force link to one of the
+states above.
+
+``regdump``
+`````````````
+
+File name is self-explanatory. When read, ``regdump`` will print out a
+register dump of DWC3. Note that this file can be grepped to find the
+information you want.
+
+``testmode``
+``````````````
+
+When read, ``testmode`` will print out a name of one of the specified
+USB 2.0 Testmodes (``test_j``, ``test_k``, ``test_se0_nak``,
+``test_packet``, ``test_force_enable``) or the string ``no test`` in
+case no tests are currently being executed.
+
+In order to start any of these test modes, the same strings can be
+written to the file and DWC3 will enter the requested test mode.
+
+
+``ep[0..15]{in,out}``
+``````````````````````
+
+For each endpoint we expose one directory following the naming
+convention ``ep$num$dir`` *(ep0in, ep0out, ep1in, ...)*. Inside each
+of these directories you will find the following files:
+
+``descriptor_fetch_queue``
+``event_queue``
+``rx_fifo_queue``
+``rx_info_queue``
+``rx_request_queue``
+``transfer_type``
+``trb_ring``
+``tx_fifo_queue``
+``tx_request_queue``
+
+With access to Synopsys Databook, you can decode the information on
+them.
+
+``transfer_type``
+~~~~~~~~~~~~~~~~~~
+
+When read, ``transfer_type`` will print out one of ``control``,
+``bulk``, ``interrupt`` or ``isochronous`` depending on what the
+endpoint descriptor says. If the endpoint hasn't been enabled yet, it
+will print ``--``.
+
+``trb_ring``
+~~~~~~~~~~~~~
+
+When read, ``trb_ring`` will print out details about all TRBs on the
+ring. It will also tell you where our enqueue and dequeue pointers are
+located in the ring:
+
+.. code-block:: sh
+   
+		buffer_addr,size,type,ioc,isp_imi,csp,chn,lst,hwo
+		000000002c754000,481,normal,1,0,1,0,0,0         
+		000000002c75c000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c78c000,481,normal,1,0,1,0,0,0         
+		000000002c754000,481,normal,1,0,1,0,0,0         
+		000000002c75c000,481,normal,1,0,1,0,0,0         
+		000000002c784000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c78c000,481,normal,1,0,1,0,0,0         
+		000000002c790000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c790000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c784000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c78c000,481,normal,1,0,1,0,0,0         
+		000000002c754000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c784000,481,normal,1,0,1,0,0,0         
+		000000002c78c000,481,normal,1,0,1,0,0,0         
+		000000002c790000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c790000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c790000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c790000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c790000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c790000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c790000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c790000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c78c000,481,normal,1,0,1,0,0,0         
+		000000002c784000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c78c000,481,normal,1,0,1,0,0,0         
+		000000002c754000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c790000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c78c000,481,normal,1,0,1,0,0,0         
+		000000002c75c000,481,normal,1,0,1,0,0,0         
+		000000002c78c000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c754000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c754000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c78c000,481,normal,1,0,1,0,0,0         
+		000000002c790000,481,normal,1,0,1,0,0,0         
+		000000002c754000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c75c000,481,normal,1,0,1,0,0,0         
+		000000002c780000,481,normal,1,0,1,0,0,0         
+		000000002c784000,481,normal,1,0,1,0,0,0         
+		000000002c788000,481,normal,1,0,1,0,0,0         
+		000000002c78c000,481,normal,1,0,1,0,0,0         
+		000000002c790000,481,normal,1,0,1,0,0,0         
+		000000002c754000,481,normal,1,0,1,0,0,0         
+		000000002c758000,481,normal,1,0,1,0,0,0         
+		000000002c75c000,512,normal,1,0,1,0,0,1        D
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0       E 
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		0000000000000000,0,UNKNOWN,0,0,0,0,0,0         
+		00000000381ab000,0,link,0,0,0,0,0,1
+
+
+Trace Events
+-------------
+
+DWC3 also provides several trace events which help us gathering
+information about the behavior of the driver during runtime.
+
+In order to use these events, you must enable ``CONFIG_FTRACE`` in
+your kernel config.
+
+For details about how enable DWC3 events, see section **Reporting
+Bugs**.
+
+The following subsections will give details about each Event Class and
+each Event defined by DWC3.
+
+MMIO
+```````
+
+It is sometimes useful to look at every MMIO access when looking for
+bugs. Because of that, DWC3 offers two Trace Events (one for
+dwc3_readl() and one for dwc3_writel()). ``TP_printk`` follows::
+
+  TP_printk("addr %p value %08x", __entry->base + __entry->offset,
+  		__entry->value)
+
+Interrupt Events
+````````````````
+
+Every IRQ event can be logged and decoded into a human readable
+string. Because every event will be different, we don't give an
+example other than the ``TP_printk`` format used::
+
+  TP_printk("event (%08x): %s", __entry->event,
+  		dwc3_decode_event(__entry->event, __entry->ep0state))
+
+Control Request
+`````````````````
+
+Every USB Control Request can be logged to the trace buffer. The
+output format is::
+
+  TP_printk("%s", dwc3_decode_ctrl(__entry->bRequestType,
+  				__entry->bRequest, __entry->wValue,
+  				__entry->wIndex, __entry->wLength)
+  )
+
+Note that Standard Control Requests will be decoded into
+human-readable strings with their respective arguments. Class and
+Vendor requests will be printed out a sequence of 8 bytes in hex
+format.
+
+Lifetime of a ``struct usb_request``
+```````````````````````````````````````
+
+The entire lifetime of a ``struct usb_request`` can be tracked on the
+trace buffer. We have one event for each of allocation, free,
+queueing, dequeueing, and giveback. Output format is::
+
+  TP_printk("%s: req %p length %u/%u %s%s%s ==> %d",
+  	__get_str(name), __entry->req, __entry->actual, __entry->length,
+  	__entry->zero ? "Z" : "z",
+  	__entry->short_not_ok ? "S" : "s",
+  	__entry->no_interrupt ? "i" : "I",
+  	__entry->status
+  )
+
+Generic Commands
+````````````````````
+
+We can log and decode every Generic Command with its completion
+code. Format is::
+
+  TP_printk("cmd '%s' [%x] param %08x --> status: %s",
+  	dwc3_gadget_generic_cmd_string(__entry->cmd),
+  	__entry->cmd, __entry->param,
+  	dwc3_gadget_generic_cmd_status_string(__entry->status)
+  )
+
+Endpoint Commands
+````````````````````
+
+Endpoints commands can also be logged together with completion
+code. Format is::
+
+  TP_printk("%s: cmd '%s' [%d] params %08x %08x %08x --> status: %s",
+  	__get_str(name), dwc3_gadget_ep_cmd_string(__entry->cmd),
+  	__entry->cmd, __entry->param0,
+  	__entry->param1, __entry->param2,
+  	dwc3_ep_cmd_status_string(__entry->cmd_status)
+  )
+
+Lifetime of a ``TRB``
+``````````````````````
+
+A ``TRB`` Lifetime is simple. We are either preparing a ``TRB`` or
+completing it. With these two events, we can see how a ``TRB`` changes
+over time. Format is::
+
+  TP_printk("%s: %d/%d trb %p buf %08x%08x size %s%d ctrl %08x (%c%c%c%c:%c%c:%s)",
+  	__get_str(name), __entry->queued, __entry->allocated,
+  	__entry->trb, __entry->bph, __entry->bpl,
+  	({char *s;
+  	int pcm = ((__entry->size >> 24) & 3) + 1;
+  	switch (__entry->type) {
+  	case USB_ENDPOINT_XFER_INT:
+  	case USB_ENDPOINT_XFER_ISOC:
+  		switch (pcm) {
+  		case 1:
+  			s = "1x ";
+  			break;
+  		case 2:
+  			s = "2x ";
+  			break;
+  		case 3:
+  			s = "3x ";
+  			break;
+  		}
+  	default:
+  		s = "";
+  	} s; }),
+  	DWC3_TRB_SIZE_LENGTH(__entry->size), __entry->ctrl,
+  	__entry->ctrl & DWC3_TRB_CTRL_HWO ? 'H' : 'h',
+  	__entry->ctrl & DWC3_TRB_CTRL_LST ? 'L' : 'l',
+  	__entry->ctrl & DWC3_TRB_CTRL_CHN ? 'C' : 'c',
+  	__entry->ctrl & DWC3_TRB_CTRL_CSP ? 'S' : 's',
+  	__entry->ctrl & DWC3_TRB_CTRL_ISP_IMI ? 'S' : 's',
+  	__entry->ctrl & DWC3_TRB_CTRL_IOC ? 'C' : 'c',
+      dwc3_trb_type_string(DWC3_TRBCTL_TYPE(__entry->ctrl))
+  )  
+
+Lifetime of an Endpoint
+```````````````````````
+
+And endpoint's lifetime is summarized with enable and disable
+operations, both of which can be traced. Format is::
+
+  TP_printk("%s: mps %d/%d streams %d burst %d ring %d/%d flags %c:%c%c%c%c%c:%c:%c",
+  	__get_str(name), __entry->maxpacket,
+  	__entry->maxpacket_limit, __entry->max_streams,
+  	__entry->maxburst, __entry->trb_enqueue,
+  	__entry->trb_dequeue,
+  	__entry->flags & DWC3_EP_ENABLED ? 'E' : 'e',
+  	__entry->flags & DWC3_EP_STALL ? 'S' : 's',
+  	__entry->flags & DWC3_EP_WEDGE ? 'W' : 'w',
+  	__entry->flags & DWC3_EP_TRANSFER_STARTED ? 'B' : 'b',
+  	__entry->flags & DWC3_EP_PENDING_REQUEST ? 'P' : 'p',
+  	__entry->flags & DWC3_EP_END_TRANSFER_PENDING ? 'E' : 'e',
+  	__entry->direction ? '<' : '>'
+  )
+
+
+Structures, Methods and Definitions
+====================================
+
+.. kernel-doc:: drivers/usb/dwc3/core.h
+   :doc: main data structures
+   :internal:
+
+.. kernel-doc:: drivers/usb/dwc3/gadget.h
+   :doc: gadget-only helpers
+   :internal:
+
+.. kernel-doc:: drivers/usb/dwc3/gadget.c
+   :doc: gadget-side implementation
+   :internal:
+
+.. kernel-doc:: drivers/usb/dwc3/core.c
+   :doc: core driver (probe, PM, etc)
+   :internal:
+   
+.. [#trb] Transfer Request Block
+.. [#link_trb] Transfer Request Block pointing to another Transfer
+	       Request Block.
+.. [#debugfs] The Debug File System
+.. [#configfs] The Config File System
+.. [#cbw] Command Block Wrapper
+.. _Linus' tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
+.. _me: felipe.balbi@linux.intel.com
+.. _linux-usb: linux-usb@vger.kernel.org

Documentation/driver-api/usb/error-codes.rst

@@ -0,0 +1,207 @@
+.. _usb-error-codes:
+
+USB Error codes
+~~~~~~~~~~~~~~~
+
+:Revised: 2004-Oct-21
+
+This is the documentation of (hopefully) all possible error codes (and
+their interpretation) that can be returned from usbcore.
+
+Some of them are returned by the Host Controller Drivers (HCDs), which
+device drivers only see through usbcore.  As a rule, all the HCDs should
+behave the same except for transfer speed dependent behaviors and the
+way certain faults are reported.
+
+
+Error codes returned by :c:func:`usb_submit_urb`
+================================================
+
+Non-USB-specific:
+
+
+=============== ===============================================
+0		URB submission went fine
+
+``-ENOMEM``	no memory for allocation of internal structures
+=============== ===============================================
+
+USB-specific:
+
+=======================	=======================================================
+``-EBUSY``		The URB is already active.
+
+``-ENODEV``		specified USB-device or bus doesn't exist
+
+``-ENOENT``		specified interface or endpoint does not exist or
+			is not enabled
+
+``-ENXIO``		host controller driver does not support queuing of
+			this type of urb.  (treat as a host controller bug.)
+
+``-EINVAL``		a) Invalid transfer type specified (or not supported)
+			b) Invalid or unsupported periodic transfer interval
+			c) ISO: attempted to change transfer interval
+			d) ISO: ``number_of_packets`` is < 0
+			e) various other cases
+
+``-EXDEV``		ISO: ``URB_ISO_ASAP`` wasn't specified and all the
+			frames the URB would be scheduled in have already
+			expired.
+
+``-EFBIG``		Host controller driver can't schedule that many ISO
+			frames.
+
+``-EPIPE``		The pipe type specified in the URB doesn't match the
+			endpoint's actual type.
+
+``-EMSGSIZE``		(a) endpoint maxpacket size is zero; it is not usable
+			    in the current interface altsetting.
+			(b) ISO packet is larger than the endpoint maxpacket.
+			(c) requested data transfer length is invalid: negative
+			    or too large for the host controller.
+
+``-ENOSPC``		This request would overcommit the usb bandwidth reserved
+			for periodic transfers (interrupt, isochronous).
+
+``-ESHUTDOWN``		The device or host controller has been disabled due to
+			some problem that could not be worked around.
+
+``-EPERM``		Submission failed because ``urb->reject`` was set.
+
+``-EHOSTUNREACH``	URB was rejected because the device is suspended.
+
+``-ENOEXEC``		A control URB doesn't contain a Setup packet.
+=======================	=======================================================
+
+Error codes returned by ``in urb->status`` or in ``iso_frame_desc[n].status`` (for ISO)
+=======================================================================================
+
+USB device drivers may only test urb status values in completion handlers.
+This is because otherwise there would be a race between HCDs updating
+these values on one CPU, and device drivers testing them on another CPU.
+
+A transfer's actual_length may be positive even when an error has been
+reported.  That's because transfers often involve several packets, so that
+one or more packets could finish before an error stops further endpoint I/O.
+
+For isochronous URBs, the urb status value is non-zero only if the URB is
+unlinked, the device is removed, the host controller is disabled, or the total
+transferred length is less than the requested length and the
+``URB_SHORT_NOT_OK`` flag is set.  Completion handlers for isochronous URBs
+should only see ``urb->status`` set to zero, ``-ENOENT``, ``-ECONNRESET``,
+``-ESHUTDOWN``, or ``-EREMOTEIO``. Individual frame descriptor status fields
+may report more status codes.
+
+
+===============================	===============================================
+0				Transfer completed successfully
+
+``-ENOENT``			URB was synchronously unlinked by
+				:c:func:`usb_unlink_urb`
+
+``-EINPROGRESS``		URB still pending, no results yet
+				(That is, if drivers see this it's a bug.)
+
+``-EPROTO`` [#f1]_, [#f2]_	a) bitstuff error
+				b) no response packet received within the
+				   prescribed bus turn-around time
+				c) unknown USB error
+
+``-EILSEQ`` [#f1]_, [#f2]_	a) CRC mismatch
+				b) no response packet received within the
+				   prescribed bus turn-around time
+				c) unknown USB error
+
+				Note that often the controller hardware does
+				not distinguish among cases a), b), and c), so
+				a driver cannot tell whether there was a
+				protocol error, a failure to respond (often
+				caused by device disconnect), or some other
+				fault.
+
+``-ETIME`` [#f2]_		No response packet received within the
+				prescribed bus turn-around time.  This error
+				may instead be reported as
+				``-EPROTO`` or ``-EILSEQ``.
+
+``-ETIMEDOUT``			Synchronous USB message functions use this code
+				to indicate timeout expired before the transfer
+				completed, and no other error was reported
+				by HC.
+
+``-EPIPE`` [#f2]_		Endpoint stalled.  For non-control endpoints,
+				reset this status with
+				:c:func:`usb_clear_halt`.
+
+``-ECOMM``			During an IN transfer, the host controller
+				received data from an endpoint faster than it
+				could be written to system memory
+
+``-ENOSR``			During an OUT transfer, the host controller
+				could not retrieve data from system memory fast
+				enough to keep up with the USB data rate
+
+``-EOVERFLOW`` [#f1]_		The amount of data returned by the endpoint was
+				greater than either the max packet size of the
+				endpoint or the remaining buffer size.
+				"Babble".
+
+``-EREMOTEIO``			The data read from the endpoint did not fill
+				the specified buffer, and ``URB_SHORT_NOT_OK``
+				was set in ``urb->transfer_flags``.
+
+``-ENODEV``			Device was removed.  Often preceded by a burst
+				of other errors, since the hub driver doesn't
+				detect device removal events immediately.
+
+``-EXDEV``			ISO transfer only partially completed
+				(only set in ``iso_frame_desc[n].status``,
+				not ``urb->status``)
+
+``-EINVAL``			ISO madness, if this happens: Log off and
+				go home
+
+``-ECONNRESET``			URB was asynchronously unlinked by
+				:c:func:`usb_unlink_urb`
+
+``-ESHUTDOWN``			The device or host controller has been
+				disabled due to some problem that could not
+				be worked around, such as a physical
+				disconnect.
+===============================	===============================================
+
+
+.. [#f1]
+
+   Error codes like ``-EPROTO``, ``-EILSEQ`` and ``-EOVERFLOW`` normally
+   indicate hardware problems such as bad devices (including firmware)
+   or cables.
+
+.. [#f2]
+
+   This is also one of several codes that different kinds of host
+   controller use to indicate a transfer has failed because of device
+   disconnect.  In the interval before the hub driver starts disconnect
+   processing, devices may receive such fault reports for every request.
+
+
+
+Error codes returned by usbcore-functions
+=========================================
+
+.. note:: expect also other submit and transfer status codes
+
+:c:func:`usb_register`:
+
+======================= ===================================
+``-EINVAL``		error during registering new driver
+======================= ===================================
+
+``usb_get_*/usb_set_*()``,
+:c:func:`usb_control_msg`,
+:c:func:`usb_bulk_msg()`:
+
+======================= ==============================================
+``-ETIMEDOUT``		Timeout expired before the transfer completed.
+======================= ==============================================

Documentation/driver-api/usb/gadget.rst

@@ -0,0 +1,510 @@
+========================
+USB Gadget API for Linux
+========================
+
+:Author: David Brownell
+:Date:   20 August 2004
+
+Introduction
+============
+
+This document presents a Linux-USB "Gadget" kernel mode API, for use
+within peripherals and other USB devices that embed Linux. It provides
+an overview of the API structure, and shows how that fits into a system
+development project. This is the first such API released on Linux to
+address a number of important problems, including:
+
+-  Supports USB 2.0, for high speed devices which can stream data at
+   several dozen megabytes per second.
+
+-  Handles devices with dozens of endpoints just as well as ones with
+   just two fixed-function ones. Gadget drivers can be written so
+   they're easy to port to new hardware.
+
+-  Flexible enough to expose more complex USB device capabilities such
+   as multiple configurations, multiple interfaces, composite devices,
+   and alternate interface settings.
+
+-  USB "On-The-Go" (OTG) support, in conjunction with updates to the
+   Linux-USB host side.
+
+-  Sharing data structures and API models with the Linux-USB host side
+   API. This helps the OTG support, and looks forward to more-symmetric
+   frameworks (where the same I/O model is used by both host and device
+   side drivers).
+
+-  Minimalist, so it's easier to support new device controller hardware.
+   I/O processing doesn't imply large demands for memory or CPU
+   resources.
+
+Most Linux developers will not be able to use this API, since they have
+USB ``host`` hardware in a PC, workstation, or server. Linux users with
+embedded systems are more likely to have USB peripheral hardware. To
+distinguish drivers running inside such hardware from the more familiar
+Linux "USB device drivers", which are host side proxies for the real USB
+devices, a different term is used: the drivers inside the peripherals
+are "USB gadget drivers". In USB protocol interactions, the device
+driver is the master (or "client driver") and the gadget driver is the
+slave (or "function driver").
+
+The gadget API resembles the host side Linux-USB API in that both use
+queues of request objects to package I/O buffers, and those requests may
+be submitted or canceled. They share common definitions for the standard
+USB *Chapter 9* messages, structures, and constants. Also, both APIs
+bind and unbind drivers to devices. The APIs differ in detail, since the
+host side's current URB framework exposes a number of implementation
+details and assumptions that are inappropriate for a gadget API. While
+the model for control transfers and configuration management is
+necessarily different (one side is a hardware-neutral master, the other
+is a hardware-aware slave), the endpoint I/0 API used here should also
+be usable for an overhead-reduced host side API.
+
+Structure of Gadget Drivers
+===========================
+
+A system running inside a USB peripheral normally has at least three
+layers inside the kernel to handle USB protocol processing, and may have
+additional layers in user space code. The ``gadget`` API is used by the
+middle layer to interact with the lowest level (which directly handles
+hardware).
+
+In Linux, from the bottom up, these layers are:
+
+*USB Controller Driver*
+    This is the lowest software level. It is the only layer that talks
+    to hardware, through registers, fifos, dma, irqs, and the like. The
+    ``<linux/usb/gadget.h>`` API abstracts the peripheral controller
+    endpoint hardware. That hardware is exposed through endpoint
+    objects, which accept streams of IN/OUT buffers, and through
+    callbacks that interact with gadget drivers. Since normal USB
+    devices only have one upstream port, they only have one of these
+    drivers. The controller driver can support any number of different
+    gadget drivers, but only one of them can be used at a time.
+
+    Examples of such controller hardware include the PCI-based NetChip
+    2280 USB 2.0 high speed controller, the SA-11x0 or PXA-25x UDC
+    (found within many PDAs), and a variety of other products.
+
+*Gadget Driver*
+    The lower boundary of this driver implements hardware-neutral USB
+    functions, using calls to the controller driver. Because such
+    hardware varies widely in capabilities and restrictions, and is used
+    in embedded environments where space is at a premium, the gadget
+    driver is often configured at compile time to work with endpoints
+    supported by one particular controller. Gadget drivers may be
+    portable to several different controllers, using conditional
+    compilation. (Recent kernels substantially simplify the work
+    involved in supporting new hardware, by *autoconfiguring* endpoints
+    automatically for many bulk-oriented drivers.) Gadget driver
+    responsibilities include:
+
+    -  handling setup requests (ep0 protocol responses) possibly
+       including class-specific functionality
+
+    -  returning configuration and string descriptors
+
+    -  (re)setting configurations and interface altsettings, including
+       enabling and configuring endpoints
+
+    -  handling life cycle events, such as managing bindings to
+       hardware, USB suspend/resume, remote wakeup, and disconnection
+       from the USB host.
+
+    -  managing IN and OUT transfers on all currently enabled endpoints
+
+    Such drivers may be modules of proprietary code, although that
+    approach is discouraged in the Linux community.
+
+*Upper Level*
+    Most gadget drivers have an upper boundary that connects to some
+    Linux driver or framework in Linux. Through that boundary flows the
+    data which the gadget driver produces and/or consumes through
+    protocol transfers over USB. Examples include:
+
+    -  user mode code, using generic (gadgetfs) or application specific
+       files in ``/dev``
+
+    -  networking subsystem (for network gadgets, like the CDC Ethernet
+       Model gadget driver)
+
+    -  data capture drivers, perhaps video4Linux or a scanner driver; or
+       test and measurement hardware.
+
+    -  input subsystem (for HID gadgets)
+
+    -  sound subsystem (for audio gadgets)
+
+    -  file system (for PTP gadgets)
+
+    -  block i/o subsystem (for usb-storage gadgets)
+
+    -  ... and more
+
+*Additional Layers*
+    Other layers may exist. These could include kernel layers, such as
+    network protocol stacks, as well as user mode applications building
+    on standard POSIX system call APIs such as ``open()``, ``close()``,
+    ``read()`` and ``write()``. On newer systems, POSIX Async I/O calls may
+    be an option. Such user mode code will not necessarily be subject to
+    the GNU General Public License (GPL).
+
+OTG-capable systems will also need to include a standard Linux-USB host
+side stack, with ``usbcore``, one or more *Host Controller Drivers*
+(HCDs), *USB Device Drivers* to support the OTG "Targeted Peripheral
+List", and so forth. There will also be an *OTG Controller Driver*,
+which is visible to gadget and device driver developers only indirectly.
+That helps the host and device side USB controllers implement the two
+new OTG protocols (HNP and SRP). Roles switch (host to peripheral, or
+vice versa) using HNP during USB suspend processing, and SRP can be
+viewed as a more battery-friendly kind of device wakeup protocol.
+
+Over time, reusable utilities are evolving to help make some gadget
+driver tasks simpler. For example, building configuration descriptors
+from vectors of descriptors for the configurations interfaces and
+endpoints is now automated, and many drivers now use autoconfiguration
+to choose hardware endpoints and initialize their descriptors. A
+potential example of particular interest is code implementing standard
+USB-IF protocols for HID, networking, storage, or audio classes. Some
+developers are interested in KDB or KGDB hooks, to let target hardware
+be remotely debugged. Most such USB protocol code doesn't need to be
+hardware-specific, any more than network protocols like X11, HTTP, or
+NFS are. Such gadget-side interface drivers should eventually be
+combined, to implement composite devices.
+
+Kernel Mode Gadget API
+======================
+
+Gadget drivers declare themselves through a struct
+:c:type:`usb_gadget_driver`, which is responsible for most parts of enumeration
+for a struct :c:type:`usb_gadget`. The response to a set_configuration usually
+involves enabling one or more of the struct :c:type:`usb_ep` objects exposed by
+the gadget, and submitting one or more struct :c:type:`usb_request` buffers to
+transfer data. Understand those four data types, and their operations,
+and you will understand how this API works.
+
+.. Note::
+
+    Other than the "Chapter 9" data types, most of the significant data
+    types and functions are described here.
+
+    However, some relevant information is likely omitted from what you
+    are reading. One example of such information is endpoint
+    autoconfiguration. You'll have to read the header file, and use
+    example source code (such as that for "Gadget Zero"), to fully
+    understand the API.
+
+    The part of the API implementing some basic driver capabilities is
+    specific to the version of the Linux kernel that's in use. The 2.6
+    and upper kernel versions include a *driver model* framework that has
+    no analogue on earlier kernels; so those parts of the gadget API are
+    not fully portable. (They are implemented on 2.4 kernels, but in a
+    different way.) The driver model state is another part of this API that is
+    ignored by the kerneldoc tools.
+
+The core API does not expose every possible hardware feature, only the
+most widely available ones. There are significant hardware features,
+such as device-to-device DMA (without temporary storage in a memory
+buffer) that would be added using hardware-specific APIs.
+
+This API allows drivers to use conditional compilation to handle
+endpoint capabilities of different hardware, but doesn't require that.
+Hardware tends to have arbitrary restrictions, relating to transfer
+types, addressing, packet sizes, buffering, and availability. As a rule,
+such differences only matter for "endpoint zero" logic that handles
+device configuration and management. The API supports limited run-time
+detection of capabilities, through naming conventions for endpoints.
+Many drivers will be able to at least partially autoconfigure
+themselves. In particular, driver init sections will often have endpoint
+autoconfiguration logic that scans the hardware's list of endpoints to
+find ones matching the driver requirements (relying on those
+conventions), to eliminate some of the most common reasons for
+conditional compilation.
+
+Like the Linux-USB host side API, this API exposes the "chunky" nature
+of USB messages: I/O requests are in terms of one or more "packets", and
+packet boundaries are visible to drivers. Compared to RS-232 serial
+protocols, USB resembles synchronous protocols like HDLC (N bytes per
+frame, multipoint addressing, host as the primary station and devices as
+secondary stations) more than asynchronous ones (tty style: 8 data bits
+per frame, no parity, one stop bit). So for example the controller
+drivers won't buffer two single byte writes into a single two-byte USB
+IN packet, although gadget drivers may do so when they implement
+protocols where packet boundaries (and "short packets") are not
+significant.
+
+Driver Life Cycle
+-----------------
+
+Gadget drivers make endpoint I/O requests to hardware without needing to
+know many details of the hardware, but driver setup/configuration code
+needs to handle some differences. Use the API like this:
+
+1. Register a driver for the particular device side usb controller
+   hardware, such as the net2280 on PCI (USB 2.0), sa11x0 or pxa25x as
+   found in Linux PDAs, and so on. At this point the device is logically
+   in the USB ch9 initial state (``attached``), drawing no power and not
+   usable (since it does not yet support enumeration). Any host should
+   not see the device, since it's not activated the data line pullup
+   used by the host to detect a device, even if VBUS power is available.
+
+2. Register a gadget driver that implements some higher level device
+   function. That will then bind() to a :c:type:`usb_gadget`, which activates
+   the data line pullup sometime after detecting VBUS.
+
+3. The hardware driver can now start enumerating. The steps it handles
+   are to accept USB ``power`` and ``set_address`` requests. Other steps are
+   handled by the gadget driver. If the gadget driver module is unloaded
+   before the host starts to enumerate, steps before step 7 are skipped.
+
+4. The gadget driver's ``setup()`` call returns usb descriptors, based both
+   on what the bus interface hardware provides and on the functionality
+   being implemented. That can involve alternate settings or
+   configurations, unless the hardware prevents such operation. For OTG
+   devices, each configuration descriptor includes an OTG descriptor.
+
+5. The gadget driver handles the last step of enumeration, when the USB
+   host issues a ``set_configuration`` call. It enables all endpoints used
+   in that configuration, with all interfaces in their default settings.
+   That involves using a list of the hardware's endpoints, enabling each
+   endpoint according to its descriptor. It may also involve using
+   ``usb_gadget_vbus_draw`` to let more power be drawn from VBUS, as
+   allowed by that configuration. For OTG devices, setting a
+   configuration may also involve reporting HNP capabilities through a
+   user interface.
+
+6. Do real work and perform data transfers, possibly involving changes
+   to interface settings or switching to new configurations, until the
+   device is disconnect()ed from the host. Queue any number of transfer
+   requests to each endpoint. It may be suspended and resumed several
+   times before being disconnected. On disconnect, the drivers go back
+   to step 3 (above).
+
+7. When the gadget driver module is being unloaded, the driver unbind()
+   callback is issued. That lets the controller driver be unloaded.
+
+Drivers will normally be arranged so that just loading the gadget driver
+module (or statically linking it into a Linux kernel) allows the
+peripheral device to be enumerated, but some drivers will defer
+enumeration until some higher level component (like a user mode daemon)
+enables it. Note that at this lowest level there are no policies about
+how ep0 configuration logic is implemented, except that it should obey
+USB specifications. Such issues are in the domain of gadget drivers,
+including knowing about implementation constraints imposed by some USB
+controllers or understanding that composite devices might happen to be
+built by integrating reusable components.
+
+Note that the lifecycle above can be slightly different for OTG devices.
+Other than providing an additional OTG descriptor in each configuration,
+only the HNP-related differences are particularly visible to driver
+code. They involve reporting requirements during the ``SET_CONFIGURATION``
+request, and the option to invoke HNP during some suspend callbacks.
+Also, SRP changes the semantics of ``usb_gadget_wakeup`` slightly.
+
+USB 2.0 Chapter 9 Types and Constants
+-------------------------------------
+
+Gadget drivers rely on common USB structures and constants defined in
+the :ref:`linux/usb/ch9.h <usb_chapter9>` header file, which is standard in
+Linux 2.6+ kernels. These are the same types and constants used by host side
+drivers (and usbcore).
+
+Core Objects and Methods
+------------------------
+
+These are declared in ``<linux/usb/gadget.h>``, and are used by gadget
+drivers to interact with USB peripheral controller drivers.
+
+.. kernel-doc:: include/linux/usb/gadget.h
+   :internal:
+
+Optional Utilities
+------------------
+
+The core API is sufficient for writing a USB Gadget Driver, but some
+optional utilities are provided to simplify common tasks. These
+utilities include endpoint autoconfiguration.
+
+.. kernel-doc:: drivers/usb/gadget/usbstring.c
+   :export:
+
+.. kernel-doc:: drivers/usb/gadget/config.c
+   :export:
+
+Composite Device Framework
+--------------------------
+
+The core API is sufficient for writing drivers for composite USB devices
+(with more than one function in a given configuration), and also
+multi-configuration devices (also more than one function, but not
+necessarily sharing a given configuration). There is however an optional
+framework which makes it easier to reuse and combine functions.
+
+Devices using this framework provide a struct :c:type:`usb_composite_driver`,
+which in turn provides one or more struct :c:type:`usb_configuration`
+instances. Each such configuration includes at least one struct
+:c:type:`usb_function`, which packages a user visible role such as "network
+link" or "mass storage device". Management functions may also exist,
+such as "Device Firmware Upgrade".
+
+.. kernel-doc:: include/linux/usb/composite.h
+   :internal:
+
+.. kernel-doc:: drivers/usb/gadget/composite.c
+   :export:
+
+Composite Device Functions
+--------------------------
+
+At this writing, a few of the current gadget drivers have been converted
+to this framework. Near-term plans include converting all of them,
+except for ``gadgetfs``.
+
+Peripheral Controller Drivers
+=============================
+
+The first hardware supporting this API was the NetChip 2280 controller,
+which supports USB 2.0 high speed and is based on PCI. This is the
+``net2280`` driver module. The driver supports Linux kernel versions 2.4
+and 2.6; contact NetChip Technologies for development boards and product
+information.
+
+Other hardware working in the ``gadget`` framework includes: Intel's PXA
+25x and IXP42x series processors (``pxa2xx_udc``), Toshiba TC86c001
+"Goku-S" (``goku_udc``), Renesas SH7705/7727 (``sh_udc``), MediaQ 11xx
+(``mq11xx_udc``), Hynix HMS30C7202 (``h7202_udc``), National 9303/4
+(``n9604_udc``), Texas Instruments OMAP (``omap_udc``), Sharp LH7A40x
+(``lh7a40x_udc``), and more. Most of those are full speed controllers.
+
+At this writing, there are people at work on drivers in this framework
+for several other USB device controllers, with plans to make many of
+them be widely available.
+
+A partial USB simulator, the ``dummy_hcd`` driver, is available. It can
+act like a net2280, a pxa25x, or an sa11x0 in terms of available
+endpoints and device speeds; and it simulates control, bulk, and to some
+extent interrupt transfers. That lets you develop some parts of a gadget
+driver on a normal PC, without any special hardware, and perhaps with
+the assistance of tools such as GDB running with User Mode Linux. At
+least one person has expressed interest in adapting that approach,
+hooking it up to a simulator for a microcontroller. Such simulators can
+help debug subsystems where the runtime hardware is unfriendly to
+software development, or is not yet available.
+
+Support for other controllers is expected to be developed and
+contributed over time, as this driver framework evolves.
+
+Gadget Drivers
+==============
+
+In addition to *Gadget Zero* (used primarily for testing and development
+with drivers for usb controller hardware), other gadget drivers exist.
+
+There's an ``ethernet`` gadget driver, which implements one of the most
+useful *Communications Device Class* (CDC) models. One of the standards
+for cable modem interoperability even specifies the use of this ethernet
+model as one of two mandatory options. Gadgets using this code look to a
+USB host as if they're an Ethernet adapter. It provides access to a
+network where the gadget's CPU is one host, which could easily be
+bridging, routing, or firewalling access to other networks. Since some
+hardware can't fully implement the CDC Ethernet requirements, this
+driver also implements a "good parts only" subset of CDC Ethernet. (That
+subset doesn't advertise itself as CDC Ethernet, to avoid creating
+problems.)
+
+Support for Microsoft's ``RNDIS`` protocol has been contributed by
+Pengutronix and Auerswald GmbH. This is like CDC Ethernet, but it runs
+on more slightly USB hardware (but less than the CDC subset). However,
+its main claim to fame is being able to connect directly to recent
+versions of Windows, using drivers that Microsoft bundles and supports,
+making it much simpler to network with Windows.
+
+There is also support for user mode gadget drivers, using ``gadgetfs``.
+This provides a *User Mode API* that presents each endpoint as a single
+file descriptor. I/O is done using normal ``read()`` and ``read()`` calls.
+Familiar tools like GDB and pthreads can be used to develop and debug
+user mode drivers, so that once a robust controller driver is available
+many applications for it won't require new kernel mode software. Linux
+2.6 *Async I/O (AIO)* support is available, so that user mode software
+can stream data with only slightly more overhead than a kernel driver.
+
+There's a USB Mass Storage class driver, which provides a different
+solution for interoperability with systems such as MS-Windows and MacOS.
+That *Mass Storage* driver uses a file or block device as backing store
+for a drive, like the ``loop`` driver. The USB host uses the BBB, CB, or
+CBI versions of the mass storage class specification, using transparent
+SCSI commands to access the data from the backing store.
+
+There's a "serial line" driver, useful for TTY style operation over USB.
+The latest version of that driver supports CDC ACM style operation, like
+a USB modem, and so on most hardware it can interoperate easily with
+MS-Windows. One interesting use of that driver is in boot firmware (like
+a BIOS), which can sometimes use that model with very small systems
+without real serial lines.
+
+Support for other kinds of gadget is expected to be developed and
+contributed over time, as this driver framework evolves.
+
+USB On-The-GO (OTG)
+===================
+
+USB OTG support on Linux 2.6 was initially developed by Texas
+Instruments for `OMAP <http://www.omap.com>`__ 16xx and 17xx series
+processors. Other OTG systems should work in similar ways, but the
+hardware level details could be very different.
+
+Systems need specialized hardware support to implement OTG, notably
+including a special *Mini-AB* jack and associated transceiver to support
+*Dual-Role* operation: they can act either as a host, using the standard
+Linux-USB host side driver stack, or as a peripheral, using this
+``gadget`` framework. To do that, the system software relies on small
+additions to those programming interfaces, and on a new internal
+component (here called an "OTG Controller") affecting which driver stack
+connects to the OTG port. In each role, the system can re-use the
+existing pool of hardware-neutral drivers, layered on top of the
+controller driver interfaces (:c:type:`usb_bus` or :c:type:`usb_gadget`).
+Such drivers need at most minor changes, and most of the calls added to
+support OTG can also benefit non-OTG products.
+
+-  Gadget drivers test the ``is_otg`` flag, and use it to determine
+   whether or not to include an OTG descriptor in each of their
+   configurations.
+
+-  Gadget drivers may need changes to support the two new OTG protocols,
+   exposed in new gadget attributes such as ``b_hnp_enable`` flag. HNP
+   support should be reported through a user interface (two LEDs could
+   suffice), and is triggered in some cases when the host suspends the
+   peripheral. SRP support can be user-initiated just like remote
+   wakeup, probably by pressing the same button.
+
+-  On the host side, USB device drivers need to be taught to trigger HNP
+   at appropriate moments, using ``usb_suspend_device()``. That also
+   conserves battery power, which is useful even for non-OTG
+   configurations.
+
+-  Also on the host side, a driver must support the OTG "Targeted
+   Peripheral List". That's just a whitelist, used to reject peripherals
+   not supported with a given Linux OTG host. *This whitelist is
+   product-specific; each product must modify* ``otg_whitelist.h`` *to
+   match its interoperability specification.*
+
+   Non-OTG Linux hosts, like PCs and workstations, normally have some
+   solution for adding drivers, so that peripherals that aren't
+   recognized can eventually be supported. That approach is unreasonable
+   for consumer products that may never have their firmware upgraded,
+   and where it's usually unrealistic to expect traditional
+   PC/workstation/server kinds of support model to work. For example,
+   it's often impractical to change device firmware once the product has
+   been distributed, so driver bugs can't normally be fixed if they're
+   found after shipment.
+
+Additional changes are needed below those hardware-neutral :c:type:`usb_bus`
+and :c:type:`usb_gadget` driver interfaces; those aren't discussed here in any
+detail. Those affect the hardware-specific code for each USB Host or
+Peripheral controller, and how the HCD initializes (since OTG can be
+active only on a single port). They also involve what may be called an
+*OTG Controller Driver*, managing the OTG transceiver and the OTG state
+machine logic as well as much of the root hub behavior for the OTG port.
+The OTG controller driver needs to activate and deactivate USB
+controllers depending on the relevant device role. Some related changes
+were needed inside usbcore, so that it can identify OTG-capable devices
+and respond appropriately to HNP or SRP protocols.

Documentation/driver-api/usb/hotplug.rst

@@ -0,0 +1,154 @@
+USB hotplugging
+~~~~~~~~~~~~~~~
+
+Linux Hotplugging
+=================
+
+
+In hotpluggable busses like USB (and Cardbus PCI), end-users plug devices
+into the bus with power on.  In most cases, users expect the devices to become
+immediately usable.  That means the system must do many things, including:
+
+    - Find a driver that can handle the device.  That may involve
+      loading a kernel module; newer drivers can use module-init-tools
+      to publish their device (and class) support to user utilities.
+
+    - Bind a driver to that device.  Bus frameworks do that using a
+      device driver's probe() routine.
+
+    - Tell other subsystems to configure the new device.  Print
+      queues may need to be enabled, networks brought up, disk
+      partitions mounted, and so on.  In some cases these will
+      be driver-specific actions.
+
+This involves a mix of kernel mode and user mode actions.  Making devices
+be immediately usable means that any user mode actions can't wait for an
+administrator to do them:  the kernel must trigger them, either passively
+(triggering some monitoring daemon to invoke a helper program) or
+actively (calling such a user mode helper program directly).
+
+Those triggered actions must support a system's administrative policies;
+such programs are called "policy agents" here.  Typically they involve
+shell scripts that dispatch to more familiar administration tools.
+
+Because some of those actions rely on information about drivers (metadata)
+that is currently available only when the drivers are dynamically linked,
+you get the best hotplugging when you configure a highly modular system.
+
+Kernel Hotplug Helper (``/sbin/hotplug``)
+=========================================
+
+There is a kernel parameter: ``/proc/sys/kernel/hotplug``, which normally
+holds the pathname ``/sbin/hotplug``.  That parameter names a program
+which the kernel may invoke at various times.
+
+The /sbin/hotplug program can be invoked by any subsystem as part of its
+reaction to a configuration change, from a thread in that subsystem.
+Only one parameter is required: the name of a subsystem being notified of
+some kernel event.  That name is used as the first key for further event
+dispatch; any other argument and environment parameters are specified by
+the subsystem making that invocation.
+
+Hotplug software and other resources is available at:
+
+	http://linux-hotplug.sourceforge.net
+
+Mailing list information is also available at that site.
+
+
+USB Policy Agent
+================
+
+The USB subsystem currently invokes ``/sbin/hotplug`` when USB devices
+are added or removed from system.  The invocation is done by the kernel
+hub workqueue [hub_wq], or else as part of root hub initialization
+(done by init, modprobe, kapmd, etc).  Its single command line parameter
+is the string "usb", and it passes these environment variables:
+
+========== ============================================
+ACTION     ``add``, ``remove``
+PRODUCT    USB vendor, product, and version codes (hex)
+TYPE       device class codes (decimal)
+INTERFACE  interface 0 class codes (decimal)
+========== ============================================
+
+If "usbdevfs" is configured, DEVICE and DEVFS are also passed.  DEVICE is
+the pathname of the device, and is useful for devices with multiple and/or
+alternate interfaces that complicate driver selection.  By design, USB
+hotplugging is independent of ``usbdevfs``:  you can do most essential parts
+of USB device setup without using that filesystem, and without running a
+user mode daemon to detect changes in system configuration.
+
+Currently available policy agent implementations can load drivers for
+modules, and can invoke driver-specific setup scripts.  The newest ones
+leverage USB module-init-tools support.  Later agents might unload drivers.
+
+
+USB Modutils Support
+====================
+
+Current versions of module-init-tools will create a ``modules.usbmap`` file
+which contains the entries from each driver's ``MODULE_DEVICE_TABLE``.  Such
+files can be used by various user mode policy agents to make sure all the
+right driver modules get loaded, either at boot time or later.
+
+See ``linux/usb.h`` for full information about such table entries; or look
+at existing drivers.  Each table entry describes one or more criteria to
+be used when matching a driver to a device or class of devices.  The
+specific criteria are identified by bits set in "match_flags", paired
+with field values.  You can construct the criteria directly, or with
+macros such as these, and use driver_info to store more information::
+
+    USB_DEVICE (vendorId, productId)
+	... matching devices with specified vendor and product ids
+    USB_DEVICE_VER (vendorId, productId, lo, hi)
+	... like USB_DEVICE with lo <= productversion <= hi
+    USB_INTERFACE_INFO (class, subclass, protocol)
+	... matching specified interface class info
+    USB_DEVICE_INFO (class, subclass, protocol)
+	... matching specified device class info
+
+A short example, for a driver that supports several specific USB devices
+and their quirks, might have a MODULE_DEVICE_TABLE like this::
+
+    static const struct usb_device_id mydriver_id_table[] = {
+	{ USB_DEVICE (0x9999, 0xaaaa), driver_info: QUIRK_X },
+	{ USB_DEVICE (0xbbbb, 0x8888), driver_info: QUIRK_Y|QUIRK_Z },
+	...
+	{ } /* end with an all-zeroes entry */
+    };
+    MODULE_DEVICE_TABLE(usb, mydriver_id_table);
+
+Most USB device drivers should pass these tables to the USB subsystem as
+well as to the module management subsystem.  Not all, though: some driver
+frameworks connect using interfaces layered over USB, and so they won't
+need such a struct :c:type:`usb_driver`.
+
+Drivers that connect directly to the USB subsystem should be declared
+something like this::
+
+    static struct usb_driver mydriver = {
+	.name		= "mydriver",
+	.id_table	= mydriver_id_table,
+	.probe		= my_probe,
+	.disconnect	= my_disconnect,
+
+	/*
+	if using the usb chardev framework:
+	    .minor		= MY_USB_MINOR_START,
+	    .fops		= my_file_ops,
+	if exposing any operations through usbdevfs:
+	    .ioctl		= my_ioctl,
+	*/
+    };
+
+When the USB subsystem knows about a driver's device ID table, it's used when
+choosing drivers to probe().  The thread doing new device processing checks
+drivers' device ID entries from the ``MODULE_DEVICE_TABLE`` against interface
+and device descriptors for the device.  It will only call ``probe()`` if there
+is a match, and the third argument to ``probe()`` will be the entry that
+matched.
+
+If you don't provide an ``id_table`` for your driver, then your driver may get
+probed for each new device; the third parameter to ``probe()`` will be
+``NULL``.

Documentation/driver-api/usb/index.rst

@@ -0,0 +1,29 @@
+=============
+Linux USB API
+=============
+
+.. toctree::
+
+   usb
+   gadget
+   anchors
+   bulk-streams
+   callbacks
+   dma
+   URB
+   power-management
+   hotplug
+   persist
+   error-codes
+   writing_usb_driver
+   dwc3
+   writing_musb_glue_layer
+   typec
+   usb3-debug-port
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`

Documentation/driver-api/usb/persist.rst

@@ -0,0 +1,171 @@
+.. _usb-persist:
+
+USB device persistence during system suspend
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+:Author: Alan Stern <stern@rowland.harvard.edu>
+:Date: September 2, 2006 (Updated February 25, 2008)
+
+
+What is the problem?
+====================
+
+According to the USB specification, when a USB bus is suspended the
+bus must continue to supply suspend current (around 1-5 mA).  This
+is so that devices can maintain their internal state and hubs can
+detect connect-change events (devices being plugged in or unplugged).
+The technical term is "power session".
+
+If a USB device's power session is interrupted then the system is
+required to behave as though the device has been unplugged.  It's a
+conservative approach; in the absence of suspend current the computer
+has no way to know what has actually happened.  Perhaps the same
+device is still attached or perhaps it was removed and a different
+device plugged into the port.  The system must assume the worst.
+
+By default, Linux behaves according to the spec.  If a USB host
+controller loses power during a system suspend, then when the system
+wakes up all the devices attached to that controller are treated as
+though they had disconnected.  This is always safe and it is the
+"officially correct" thing to do.
+
+For many sorts of devices this behavior doesn't matter in the least.
+If the kernel wants to believe that your USB keyboard was unplugged
+while the system was asleep and a new keyboard was plugged in when the
+system woke up, who cares?  It'll still work the same when you type on
+it.
+
+Unfortunately problems _can_ arise, particularly with mass-storage
+devices.  The effect is exactly the same as if the device really had
+been unplugged while the system was suspended.  If you had a mounted
+filesystem on the device, you're out of luck -- everything in that
+filesystem is now inaccessible.  This is especially annoying if your
+root filesystem was located on the device, since your system will
+instantly crash.
+
+Loss of power isn't the only mechanism to worry about.  Anything that
+interrupts a power session will have the same effect.  For example,
+even though suspend current may have been maintained while the system
+was asleep, on many systems during the initial stages of wakeup the
+firmware (i.e., the BIOS) resets the motherboard's USB host
+controllers.  Result: all the power sessions are destroyed and again
+it's as though you had unplugged all the USB devices.  Yes, it's
+entirely the BIOS's fault, but that doesn't do _you_ any good unless
+you can convince the BIOS supplier to fix the problem (lots of luck!).
+
+On many systems the USB host controllers will get reset after a
+suspend-to-RAM.  On almost all systems, no suspend current is
+available during hibernation (also known as swsusp or suspend-to-disk).
+You can check the kernel log after resuming to see if either of these
+has happened; look for lines saying "root hub lost power or was reset".
+
+In practice, people are forced to unmount any filesystems on a USB
+device before suspending.  If the root filesystem is on a USB device,
+the system can't be suspended at all.  (All right, it _can_ be
+suspended -- but it will crash as soon as it wakes up, which isn't
+much better.)
+
+
+What is the solution?
+=====================
+
+The kernel includes a feature called USB-persist.  It tries to work
+around these issues by allowing the core USB device data structures to
+persist across a power-session disruption.
+
+It works like this.  If the kernel sees that a USB host controller is
+not in the expected state during resume (i.e., if the controller was
+reset or otherwise had lost power) then it applies a persistence check
+to each of the USB devices below that controller for which the
+"persist" attribute is set.  It doesn't try to resume the device; that
+can't work once the power session is gone.  Instead it issues a USB
+port reset and then re-enumerates the device.  (This is exactly the
+same thing that happens whenever a USB device is reset.)  If the
+re-enumeration shows that the device now attached to that port has the
+same descriptors as before, including the Vendor and Product IDs, then
+the kernel continues to use the same device structure.  In effect, the
+kernel treats the device as though it had merely been reset instead of
+unplugged.
+
+The same thing happens if the host controller is in the expected state
+but a USB device was unplugged and then replugged, or if a USB device
+fails to carry out a normal resume.
+
+If no device is now attached to the port, or if the descriptors are
+different from what the kernel remembers, then the treatment is what
+you would expect.  The kernel destroys the old device structure and
+behaves as though the old device had been unplugged and a new device
+plugged in.
+
+The end result is that the USB device remains available and usable.
+Filesystem mounts and memory mappings are unaffected, and the world is
+now a good and happy place.
+
+Note that the "USB-persist" feature will be applied only to those
+devices for which it is enabled.  You can enable the feature by doing
+(as root)::
+
+	echo 1 >/sys/bus/usb/devices/.../power/persist
+
+where the "..." should be filled in the with the device's ID.  Disable
+the feature by writing 0 instead of 1.  For hubs the feature is
+automatically and permanently enabled and the power/persist file
+doesn't even exist, so you only have to worry about setting it for
+devices where it really matters.
+
+
+Is this the best solution?
+==========================
+
+Perhaps not.  Arguably, keeping track of mounted filesystems and
+memory mappings across device disconnects should be handled by a
+centralized Logical Volume Manager.  Such a solution would allow you
+to plug in a USB flash device, create a persistent volume associated
+with it, unplug the flash device, plug it back in later, and still
+have the same persistent volume associated with the device.  As such
+it would be more far-reaching than USB-persist.
+
+On the other hand, writing a persistent volume manager would be a big
+job and using it would require significant input from the user.  This
+solution is much quicker and easier -- and it exists now, a giant
+point in its favor!
+
+Furthermore, the USB-persist feature applies to _all_ USB devices, not
+just mass-storage devices.  It might turn out to be equally useful for
+other device types, such as network interfaces.
+
+
+WARNING: USB-persist can be dangerous!!
+=======================================
+
+When recovering an interrupted power session the kernel does its best
+to make sure the USB device hasn't been changed; that is, the same
+device is still plugged into the port as before.  But the checks
+aren't guaranteed to be 100% accurate.
+
+If you replace one USB device with another of the same type (same
+manufacturer, same IDs, and so on) there's an excellent chance the
+kernel won't detect the change.  The serial number string and other
+descriptors are compared with the kernel's stored values, but this
+might not help since manufacturers frequently omit serial numbers
+entirely in their devices.
+
+Furthermore it's quite possible to leave a USB device exactly the same
+while changing its media.  If you replace the flash memory card in a
+USB card reader while the system is asleep, the kernel will have no
+way to know you did it.  The kernel will assume that nothing has
+happened and will continue to use the partition tables, inodes, and
+memory mappings for the old card.
+
+If the kernel gets fooled in this way, it's almost certain to cause
+data corruption and to crash your system.  You'll have no one to blame
+but yourself.
+
+For those devices with avoid_reset_quirk attribute being set, persist
+maybe fail because they may morph after reset.
+
+YOU HAVE BEEN WARNED!  USE AT YOUR OWN RISK!
+
+That having been said, most of the time there shouldn't be any trouble
+at all.  The USB-persist feature can be extremely useful.  Make the
+most of it.

Documentation/driver-api/usb/power-management.rst

@@ -0,0 +1,798 @@
+.. _usb-power-management:
+
+Power Management for USB
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+:Author: Alan Stern <stern@rowland.harvard.edu>
+:Date: Last-updated: February 2014
+
+..
+	Contents:
+	---------
+	* What is Power Management?
+	* What is Remote Wakeup?
+	* When is a USB device idle?
+	* Forms of dynamic PM
+	* The user interface for dynamic PM
+	* Changing the default idle-delay time
+	* Warnings
+	* The driver interface for Power Management
+	* The driver interface for autosuspend and autoresume
+	* Other parts of the driver interface
+	* Mutual exclusion
+	* Interaction between dynamic PM and system PM
+	* xHCI hardware link PM
+	* USB Port Power Control
+	* User Interface for Port Power Control
+	* Suggested Userspace Port Power Policy
+
+
+What is Power Management?
+-------------------------
+
+Power Management (PM) is the practice of saving energy by suspending
+parts of a computer system when they aren't being used.  While a
+component is ``suspended`` it is in a nonfunctional low-power state; it
+might even be turned off completely.  A suspended component can be
+``resumed`` (returned to a functional full-power state) when the kernel
+needs to use it.  (There also are forms of PM in which components are
+placed in a less functional but still usable state instead of being
+suspended; an example would be reducing the CPU's clock rate.  This
+document will not discuss those other forms.)
+
+When the parts being suspended include the CPU and most of the rest of
+the system, we speak of it as a "system suspend".  When a particular
+device is turned off while the system as a whole remains running, we
+call it a "dynamic suspend" (also known as a "runtime suspend" or
+"selective suspend").  This document concentrates mostly on how
+dynamic PM is implemented in the USB subsystem, although system PM is
+covered to some extent (see ``Documentation/power/*.txt`` for more
+information about system PM).
+
+System PM support is present only if the kernel was built with
+``CONFIG_SUSPEND`` or ``CONFIG_HIBERNATION`` enabled.  Dynamic PM support
+
+for USB is present whenever
+the kernel was built with ``CONFIG_PM`` enabled.
+
+[Historically, dynamic PM support for USB was present only if the
+kernel had been built with ``CONFIG_USB_SUSPEND`` enabled (which depended on
+``CONFIG_PM_RUNTIME``).  Starting with the 3.10 kernel release, dynamic PM
+support for USB was present whenever the kernel was built with
+``CONFIG_PM_RUNTIME`` enabled.  The ``CONFIG_USB_SUSPEND`` option had been
+eliminated.]
+
+
+What is Remote Wakeup?
+----------------------
+
+When a device has been suspended, it generally doesn't resume until
+the computer tells it to.  Likewise, if the entire computer has been
+suspended, it generally doesn't resume until the user tells it to, say
+by pressing a power button or opening the cover.
+
+However some devices have the capability of resuming by themselves, or
+asking the kernel to resume them, or even telling the entire computer
+to resume.  This capability goes by several names such as "Wake On
+LAN"; we will refer to it generically as "remote wakeup".  When a
+device is enabled for remote wakeup and it is suspended, it may resume
+itself (or send a request to be resumed) in response to some external
+event.  Examples include a suspended keyboard resuming when a key is
+pressed, or a suspended USB hub resuming when a device is plugged in.
+
+
+When is a USB device idle?
+--------------------------
+
+A device is idle whenever the kernel thinks it's not busy doing
+anything important and thus is a candidate for being suspended.  The
+exact definition depends on the device's driver; drivers are allowed
+to declare that a device isn't idle even when there's no actual
+communication taking place.  (For example, a hub isn't considered idle
+unless all the devices plugged into that hub are already suspended.)
+In addition, a device isn't considered idle so long as a program keeps
+its usbfs file open, whether or not any I/O is going on.
+
+If a USB device has no driver, its usbfs file isn't open, and it isn't
+being accessed through sysfs, then it definitely is idle.
+
+
+Forms of dynamic PM
+-------------------
+
+Dynamic suspends occur when the kernel decides to suspend an idle
+device.  This is called ``autosuspend`` for short.  In general, a device
+won't be autosuspended unless it has been idle for some minimum period
+of time, the so-called idle-delay time.
+
+Of course, nothing the kernel does on its own initiative should
+prevent the computer or its devices from working properly.  If a
+device has been autosuspended and a program tries to use it, the
+kernel will automatically resume the device (autoresume).  For the
+same reason, an autosuspended device will usually have remote wakeup
+enabled, if the device supports remote wakeup.
+
+It is worth mentioning that many USB drivers don't support
+autosuspend.  In fact, at the time of this writing (Linux 2.6.23) the
+only drivers which do support it are the hub driver, kaweth, asix,
+usblp, usblcd, and usb-skeleton (which doesn't count).  If a
+non-supporting driver is bound to a device, the device won't be
+autosuspended.  In effect, the kernel pretends the device is never
+idle.
+
+We can categorize power management events in two broad classes:
+external and internal.  External events are those triggered by some
+agent outside the USB stack: system suspend/resume (triggered by
+userspace), manual dynamic resume (also triggered by userspace), and
+remote wakeup (triggered by the device).  Internal events are those
+triggered within the USB stack: autosuspend and autoresume.  Note that
+all dynamic suspend events are internal; external agents are not
+allowed to issue dynamic suspends.
+
+
+The user interface for dynamic PM
+---------------------------------
+
+The user interface for controlling dynamic PM is located in the ``power/``
+subdirectory of each USB device's sysfs directory, that is, in
+``/sys/bus/usb/devices/.../power/`` where "..." is the device's ID.  The
+relevant attribute files are: wakeup, control, and
+``autosuspend_delay_ms``.  (There may also be a file named ``level``; this
+file was deprecated as of the 2.6.35 kernel and replaced by the
+``control`` file.  In 2.6.38 the ``autosuspend`` file will be deprecated
+and replaced by the ``autosuspend_delay_ms`` file.  The only difference
+is that the newer file expresses the delay in milliseconds whereas the
+older file uses seconds.  Confusingly, both files are present in 2.6.37
+but only ``autosuspend`` works.)
+
+	``power/wakeup``
+
+		This file is empty if the device does not support
+		remote wakeup.  Otherwise the file contains either the
+		word ``enabled`` or the word ``disabled``, and you can
+		write those words to the file.  The setting determines
+		whether or not remote wakeup will be enabled when the
+		device is next suspended.  (If the setting is changed
+		while the device is suspended, the change won't take
+		effect until the following suspend.)
+
+	``power/control``
+
+		This file contains one of two words: ``on`` or ``auto``.
+		You can write those words to the file to change the
+		device's setting.
+
+		- ``on`` means that the device should be resumed and
+		  autosuspend is not allowed.  (Of course, system
+		  suspends are still allowed.)
+
+		- ``auto`` is the normal state in which the kernel is
+		  allowed to autosuspend and autoresume the device.
+
+		(In kernels up to 2.6.32, you could also specify
+		``suspend``, meaning that the device should remain
+		suspended and autoresume was not allowed.  This
+		setting is no longer supported.)
+
+	``power/autosuspend_delay_ms``
+
+		This file contains an integer value, which is the
+		number of milliseconds the device should remain idle
+		before the kernel will autosuspend it (the idle-delay
+		time).  The default is 2000.  0 means to autosuspend
+		as soon as the device becomes idle, and negative
+		values mean never to autosuspend.  You can write a
+		number to the file to change the autosuspend
+		idle-delay time.
+
+Writing ``-1`` to ``power/autosuspend_delay_ms`` and writing ``on`` to
+``power/control`` do essentially the same thing -- they both prevent the
+device from being autosuspended.  Yes, this is a redundancy in the
+API.
+
+(In 2.6.21 writing ``0`` to ``power/autosuspend`` would prevent the device
+from being autosuspended; the behavior was changed in 2.6.22.  The
+``power/autosuspend`` attribute did not exist prior to 2.6.21, and the
+``power/level`` attribute did not exist prior to 2.6.22.  ``power/control``
+was added in 2.6.34, and ``power/autosuspend_delay_ms`` was added in
+2.6.37 but did not become functional until 2.6.38.)
+
+
+Changing the default idle-delay time
+------------------------------------
+
+The default autosuspend idle-delay time (in seconds) is controlled by
+a module parameter in usbcore.  You can specify the value when usbcore
+is loaded.  For example, to set it to 5 seconds instead of 2 you would
+do::
+
+	modprobe usbcore autosuspend=5
+
+Equivalently, you could add to a configuration file in /etc/modprobe.d
+a line saying::
+
+	options usbcore autosuspend=5
+
+Some distributions load the usbcore module very early during the boot
+process, by means of a program or script running from an initramfs
+image.  To alter the parameter value you would have to rebuild that
+image.
+
+If usbcore is compiled into the kernel rather than built as a loadable
+module, you can add::
+
+	usbcore.autosuspend=5
+
+to the kernel's boot command line.
+
+Finally, the parameter value can be changed while the system is
+running.  If you do::
+
+	echo 5 >/sys/module/usbcore/parameters/autosuspend
+
+then each new USB device will have its autosuspend idle-delay
+initialized to 5.  (The idle-delay values for already existing devices
+will not be affected.)
+
+Setting the initial default idle-delay to -1 will prevent any
+autosuspend of any USB device.  This has the benefit of allowing you
+then to enable autosuspend for selected devices.
+
+
+Warnings
+--------
+
+The USB specification states that all USB devices must support power
+management.  Nevertheless, the sad fact is that many devices do not
+support it very well.  You can suspend them all right, but when you
+try to resume them they disconnect themselves from the USB bus or
+they stop working entirely.  This seems to be especially prevalent
+among printers and scanners, but plenty of other types of device have
+the same deficiency.
+
+For this reason, by default the kernel disables autosuspend (the
+``power/control`` attribute is initialized to ``on``) for all devices other
+than hubs.  Hubs, at least, appear to be reasonably well-behaved in
+this regard.
+
+(In 2.6.21 and 2.6.22 this wasn't the case.  Autosuspend was enabled
+by default for almost all USB devices.  A number of people experienced
+problems as a result.)
+
+This means that non-hub devices won't be autosuspended unless the user
+or a program explicitly enables it.  As of this writing there aren't
+any widespread programs which will do this; we hope that in the near
+future device managers such as HAL will take on this added
+responsibility.  In the meantime you can always carry out the
+necessary operations by hand or add them to a udev script.  You can
+also change the idle-delay time; 2 seconds is not the best choice for
+every device.
+
+If a driver knows that its device has proper suspend/resume support,
+it can enable autosuspend all by itself.  For example, the video
+driver for a laptop's webcam might do this (in recent kernels they
+do), since these devices are rarely used and so should normally be
+autosuspended.
+
+Sometimes it turns out that even when a device does work okay with
+autosuspend there are still problems.  For example, the usbhid driver,
+which manages keyboards and mice, has autosuspend support.  Tests with
+a number of keyboards show that typing on a suspended keyboard, while
+causing the keyboard to do a remote wakeup all right, will nonetheless
+frequently result in lost keystrokes.  Tests with mice show that some
+of them will issue a remote-wakeup request in response to button
+presses but not to motion, and some in response to neither.
+
+The kernel will not prevent you from enabling autosuspend on devices
+that can't handle it.  It is even possible in theory to damage a
+device by suspending it at the wrong time.  (Highly unlikely, but
+possible.)  Take care.
+
+
+The driver interface for Power Management
+-----------------------------------------
+
+The requirements for a USB driver to support external power management
+are pretty modest; the driver need only define::
+
+	.suspend
+	.resume
+	.reset_resume
+
+methods in its :c:type:`usb_driver` structure, and the ``reset_resume`` method
+is optional.  The methods' jobs are quite simple:
+
+      - The ``suspend`` method is called to warn the driver that the
+	device is going to be suspended.  If the driver returns a
+	negative error code, the suspend will be aborted.  Normally
+	the driver will return 0, in which case it must cancel all
+	outstanding URBs (:c:func:`usb_kill_urb`) and not submit any more.
+
+      - The ``resume`` method is called to tell the driver that the
+	device has been resumed and the driver can return to normal
+	operation.  URBs may once more be submitted.
+
+      - The ``reset_resume`` method is called to tell the driver that
+	the device has been resumed and it also has been reset.
+	The driver should redo any necessary device initialization,
+	since the device has probably lost most or all of its state
+	(although the interfaces will be in the same altsettings as
+	before the suspend).
+
+If the device is disconnected or powered down while it is suspended,
+the ``disconnect`` method will be called instead of the ``resume`` or
+``reset_resume`` method.  This is also quite likely to happen when
+waking up from hibernation, as many systems do not maintain suspend
+current to the USB host controllers during hibernation.  (It's
+possible to work around the hibernation-forces-disconnect problem by
+using the USB Persist facility.)
+
+The ``reset_resume`` method is used by the USB Persist facility (see
+:ref:`usb-persist`) and it can also be used under certain
+circumstances when ``CONFIG_USB_PERSIST`` is not enabled.  Currently, if a
+device is reset during a resume and the driver does not have a
+``reset_resume`` method, the driver won't receive any notification about
+the resume.  Later kernels will call the driver's ``disconnect`` method;
+2.6.23 doesn't do this.
+
+USB drivers are bound to interfaces, so their ``suspend`` and ``resume``
+methods get called when the interfaces are suspended or resumed.  In
+principle one might want to suspend some interfaces on a device (i.e.,
+force the drivers for those interface to stop all activity) without
+suspending the other interfaces.  The USB core doesn't allow this; all
+interfaces are suspended when the device itself is suspended and all
+interfaces are resumed when the device is resumed.  It isn't possible
+to suspend or resume some but not all of a device's interfaces.  The
+closest you can come is to unbind the interfaces' drivers.
+
+
+The driver interface for autosuspend and autoresume
+---------------------------------------------------
+
+To support autosuspend and autoresume, a driver should implement all
+three of the methods listed above.  In addition, a driver indicates
+that it supports autosuspend by setting the ``.supports_autosuspend`` flag
+in its usb_driver structure.  It is then responsible for informing the
+USB core whenever one of its interfaces becomes busy or idle.  The
+driver does so by calling these six functions::
+
+	int  usb_autopm_get_interface(struct usb_interface *intf);
+	void usb_autopm_put_interface(struct usb_interface *intf);
+	int  usb_autopm_get_interface_async(struct usb_interface *intf);
+	void usb_autopm_put_interface_async(struct usb_interface *intf);
+	void usb_autopm_get_interface_no_resume(struct usb_interface *intf);
+	void usb_autopm_put_interface_no_suspend(struct usb_interface *intf);
+
+The functions work by maintaining a usage counter in the
+usb_interface's embedded device structure.  When the counter is > 0
+then the interface is deemed to be busy, and the kernel will not
+autosuspend the interface's device.  When the usage counter is = 0
+then the interface is considered to be idle, and the kernel may
+autosuspend the device.
+
+Drivers must be careful to balance their overall changes to the usage
+counter.  Unbalanced "get"s will remain in effect when a driver is
+unbound from its interface, preventing the device from going into
+runtime suspend should the interface be bound to a driver again.  On
+the other hand, drivers are allowed to achieve this balance by calling
+the ``usb_autopm_*`` functions even after their ``disconnect`` routine
+has returned -- say from within a work-queue routine -- provided they
+retain an active reference to the interface (via ``usb_get_intf`` and
+``usb_put_intf``).
+
+Drivers using the async routines are responsible for their own
+synchronization and mutual exclusion.
+
+	:c:func:`usb_autopm_get_interface` increments the usage counter and
+	does an autoresume if the device is suspended.  If the
+	autoresume fails, the counter is decremented back.
+
+	:c:func:`usb_autopm_put_interface` decrements the usage counter and
+	attempts an autosuspend if the new value is = 0.
+
+	:c:func:`usb_autopm_get_interface_async` and
+	:c:func:`usb_autopm_put_interface_async` do almost the same things as
+	their non-async counterparts.  The big difference is that they
+	use a workqueue to do the resume or suspend part of their
+	jobs.  As a result they can be called in an atomic context,
+	such as an URB's completion handler, but when they return the
+	device will generally not yet be in the desired state.
+
+	:c:func:`usb_autopm_get_interface_no_resume` and
+	:c:func:`usb_autopm_put_interface_no_suspend` merely increment or
+	decrement the usage counter; they do not attempt to carry out
+	an autoresume or an autosuspend.  Hence they can be called in
+	an atomic context.
+
+The simplest usage pattern is that a driver calls
+:c:func:`usb_autopm_get_interface` in its open routine and
+:c:func:`usb_autopm_put_interface` in its close or release routine.  But other
+patterns are possible.
+
+The autosuspend attempts mentioned above will often fail for one
+reason or another.  For example, the ``power/control`` attribute might be
+set to ``on``, or another interface in the same device might not be
+idle.  This is perfectly normal.  If the reason for failure was that
+the device hasn't been idle for long enough, a timer is scheduled to
+carry out the operation automatically when the autosuspend idle-delay
+has expired.
+
+Autoresume attempts also can fail, although failure would mean that
+the device is no longer present or operating properly.  Unlike
+autosuspend, there's no idle-delay for an autoresume.
+
+
+Other parts of the driver interface
+-----------------------------------
+
+Drivers can enable autosuspend for their devices by calling::
+
+	usb_enable_autosuspend(struct usb_device *udev);
+
+in their :c:func:`probe` routine, if they know that the device is capable of
+suspending and resuming correctly.  This is exactly equivalent to
+writing ``auto`` to the device's ``power/control`` attribute.  Likewise,
+drivers can disable autosuspend by calling::
+
+	usb_disable_autosuspend(struct usb_device *udev);
+
+This is exactly the same as writing ``on`` to the ``power/control`` attribute.
+
+Sometimes a driver needs to make sure that remote wakeup is enabled
+during autosuspend.  For example, there's not much point
+autosuspending a keyboard if the user can't cause the keyboard to do a
+remote wakeup by typing on it.  If the driver sets
+``intf->needs_remote_wakeup`` to 1, the kernel won't autosuspend the
+device if remote wakeup isn't available.  (If the device is already
+autosuspended, though, setting this flag won't cause the kernel to
+autoresume it.  Normally a driver would set this flag in its ``probe``
+method, at which time the device is guaranteed not to be
+autosuspended.)
+
+If a driver does its I/O asynchronously in interrupt context, it
+should call :c:func:`usb_autopm_get_interface_async` before starting output and
+:c:func:`usb_autopm_put_interface_async` when the output queue drains.  When
+it receives an input event, it should call::
+
+	usb_mark_last_busy(struct usb_device *udev);
+
+in the event handler.  This tells the PM core that the device was just
+busy and therefore the next autosuspend idle-delay expiration should
+be pushed back.  Many of the usb_autopm_* routines also make this call,
+so drivers need to worry only when interrupt-driven input arrives.
+
+Asynchronous operation is always subject to races.  For example, a
+driver may call the :c:func:`usb_autopm_get_interface_async` routine at a time
+when the core has just finished deciding the device has been idle for
+long enough but not yet gotten around to calling the driver's ``suspend``
+method.  The ``suspend`` method must be responsible for synchronizing with
+the I/O request routine and the URB completion handler; it should
+cause autosuspends to fail with -EBUSY if the driver needs to use the
+device.
+
+External suspend calls should never be allowed to fail in this way,
+only autosuspend calls.  The driver can tell them apart by applying
+the :c:func:`PMSG_IS_AUTO` macro to the message argument to the ``suspend``
+method; it will return True for internal PM events (autosuspend) and
+False for external PM events.
+
+
+Mutual exclusion
+----------------
+
+For external events -- but not necessarily for autosuspend or
+autoresume -- the device semaphore (udev->dev.sem) will be held when a
+``suspend`` or ``resume`` method is called.  This implies that external
+suspend/resume events are mutually exclusive with calls to ``probe``,
+``disconnect``, ``pre_reset``, and ``post_reset``; the USB core guarantees that
+this is true of autosuspend/autoresume events as well.
+
+If a driver wants to block all suspend/resume calls during some
+critical section, the best way is to lock the device and call
+:c:func:`usb_autopm_get_interface` (and do the reverse at the end of the
+critical section).  Holding the device semaphore will block all
+external PM calls, and the :c:func:`usb_autopm_get_interface` will prevent any
+internal PM calls, even if it fails.  (Exercise: Why?)
+
+
+Interaction between dynamic PM and system PM
+--------------------------------------------
+
+Dynamic power management and system power management can interact in
+a couple of ways.
+
+Firstly, a device may already be autosuspended when a system suspend
+occurs.  Since system suspends are supposed to be as transparent as
+possible, the device should remain suspended following the system
+resume.  But this theory may not work out well in practice; over time
+the kernel's behavior in this regard has changed.  As of 2.6.37 the
+policy is to resume all devices during a system resume and let them
+handle their own runtime suspends afterward.
+
+Secondly, a dynamic power-management event may occur as a system
+suspend is underway.  The window for this is short, since system
+suspends don't take long (a few seconds usually), but it can happen.
+For example, a suspended device may send a remote-wakeup signal while
+the system is suspending.  The remote wakeup may succeed, which would
+cause the system suspend to abort.  If the remote wakeup doesn't
+succeed, it may still remain active and thus cause the system to
+resume as soon as the system suspend is complete.  Or the remote
+wakeup may fail and get lost.  Which outcome occurs depends on timing
+and on the hardware and firmware design.
+
+
+xHCI hardware link PM
+---------------------
+
+xHCI host controller provides hardware link power management to usb2.0
+(xHCI 1.0 feature) and usb3.0 devices which support link PM. By
+enabling hardware LPM, the host can automatically put the device into
+lower power state(L1 for usb2.0 devices, or U1/U2 for usb3.0 devices),
+which state device can enter and resume very quickly.
+
+The user interface for controlling hardware LPM is located in the
+``power/`` subdirectory of each USB device's sysfs directory, that is, in
+``/sys/bus/usb/devices/.../power/`` where "..." is the device's ID. The
+relevant attribute files are ``usb2_hardware_lpm`` and ``usb3_hardware_lpm``.
+
+	``power/usb2_hardware_lpm``
+
+		When a USB2 device which support LPM is plugged to a
+		xHCI host root hub which support software LPM, the
+		host will run a software LPM test for it; if the device
+		enters L1 state and resume successfully and the host
+		supports USB2 hardware LPM, this file will show up and
+		driver will enable hardware LPM	for the device. You
+		can write y/Y/1 or n/N/0 to the file to	enable/disable
+		USB2 hardware LPM manually. This is for	test purpose mainly.
+
+	``power/usb3_hardware_lpm_u1``
+	``power/usb3_hardware_lpm_u2``
+
+		When a USB 3.0 lpm-capable device is plugged in to a
+		xHCI host which supports link PM, it will check if U1
+		and U2 exit latencies have been set in the BOS
+		descriptor; if the check is passed and the host
+		supports USB3 hardware LPM, USB3 hardware LPM will be
+		enabled for the device and these files will be created.
+		The files hold a string value (enable or disable)
+		indicating whether or not USB3 hardware LPM U1 or U2
+		is enabled for the device.
+
+USB Port Power Control
+----------------------
+
+In addition to suspending endpoint devices and enabling hardware
+controlled link power management, the USB subsystem also has the
+capability to disable power to ports under some conditions.  Power is
+controlled through ``Set/ClearPortFeature(PORT_POWER)`` requests to a hub.
+In the case of a root or platform-internal hub the host controller
+driver translates ``PORT_POWER`` requests into platform firmware (ACPI)
+method calls to set the port power state. For more background see the
+Linux Plumbers Conference 2012 slides [#f1]_ and video [#f2]_:
+
+Upon receiving a ``ClearPortFeature(PORT_POWER)`` request a USB port is
+logically off, and may trigger the actual loss of VBUS to the port [#f3]_.
+VBUS may be maintained in the case where a hub gangs multiple ports into
+a shared power well causing power to remain until all ports in the gang
+are turned off.  VBUS may also be maintained by hub ports configured for
+a charging application.  In any event a logically off port will lose
+connection with its device, not respond to hotplug events, and not
+respond to remote wakeup events.
+
+.. warning::
+
+   turning off a port may result in the inability to hot add a device.
+   Please see "User Interface for Port Power Control" for details.
+
+As far as the effect on the device itself it is similar to what a device
+goes through during system suspend, i.e. the power session is lost.  Any
+USB device or driver that misbehaves with system suspend will be
+similarly affected by a port power cycle event.  For this reason the
+implementation shares the same device recovery path (and honors the same
+quirks) as the system resume path for the hub.
+
+.. [#f1]
+
+  http://dl.dropbox.com/u/96820575/sarah-sharp-lpt-port-power-off2-mini.pdf
+
+.. [#f2]
+
+  http://linuxplumbers.ubicast.tv/videos/usb-port-power-off-kerneluserspace-api/
+
+.. [#f3]
+
+  USB 3.1 Section 10.12
+
+  wakeup note: if a device is configured to send wakeup events the port
+  power control implementation will block poweroff attempts on that
+  port.
+
+
+User Interface for Port Power Control
+-------------------------------------
+
+The port power control mechanism uses the PM runtime system.  Poweroff is
+requested by clearing the ``power/pm_qos_no_power_off`` flag of the port device
+(defaults to 1).  If the port is disconnected it will immediately receive a
+``ClearPortFeature(PORT_POWER)`` request.  Otherwise, it will honor the pm
+runtime rules and require the attached child device and all descendants to be
+suspended. This mechanism is dependent on the hub advertising port power
+switching in its hub descriptor (wHubCharacteristics logical power switching
+mode field).
+
+Note, some interface devices/drivers do not support autosuspend.  Userspace may
+need to unbind the interface drivers before the :c:type:`usb_device` will
+suspend.  An unbound interface device is suspended by default.  When unbinding,
+be careful to unbind interface drivers, not the driver of the parent usb
+device.  Also, leave hub interface drivers bound.  If the driver for the usb
+device (not interface) is unbound the kernel is no longer able to resume the
+device.  If a hub interface driver is unbound, control of its child ports is
+lost and all attached child-devices will disconnect.  A good rule of thumb is
+that if the 'driver/module' link for a device points to
+``/sys/module/usbcore`` then unbinding it will interfere with port power
+control.
+
+Example of the relevant files for port power control.  Note, in this example
+these files are relative to a usb hub device (prefix)::
+
+     prefix=/sys/devices/pci0000:00/0000:00:14.0/usb3/3-1
+
+                      attached child device +
+                  hub port device +         |
+     hub interface device +       |         |
+                          v       v         v
+                  $prefix/3-1:1.0/3-1-port1/device
+
+     $prefix/3-1:1.0/3-1-port1/power/pm_qos_no_power_off
+     $prefix/3-1:1.0/3-1-port1/device/power/control
+     $prefix/3-1:1.0/3-1-port1/device/3-1.1:<intf0>/driver/unbind
+     $prefix/3-1:1.0/3-1-port1/device/3-1.1:<intf1>/driver/unbind
+     ...
+     $prefix/3-1:1.0/3-1-port1/device/3-1.1:<intfN>/driver/unbind
+
+In addition to these files some ports may have a 'peer' link to a port on
+another hub.  The expectation is that all superspeed ports have a
+hi-speed peer::
+
+  $prefix/3-1:1.0/3-1-port1/peer -> ../../../../usb2/2-1/2-1:1.0/2-1-port1
+  ../../../../usb2/2-1/2-1:1.0/2-1-port1/peer -> ../../../../usb3/3-1/3-1:1.0/3-1-port1
+
+Distinct from 'companion ports', or 'ehci/xhci shared switchover ports'
+peer ports are simply the hi-speed and superspeed interface pins that
+are combined into a single usb3 connector.  Peer ports share the same
+ancestor XHCI device.
+
+While a superspeed port is powered off a device may downgrade its
+connection and attempt to connect to the hi-speed pins.  The
+implementation takes steps to prevent this:
+
+1. Port suspend is sequenced to guarantee that hi-speed ports are powered-off
+   before their superspeed peer is permitted to power-off.  The implication is
+   that the setting ``pm_qos_no_power_off`` to zero on a superspeed port may
+   not cause the port to power-off until its highspeed peer has gone to its
+   runtime suspend state.  Userspace must take care to order the suspensions
+   if it wants to guarantee that a superspeed port will power-off.
+
+2. Port resume is sequenced to force a superspeed port to power-on prior to its
+   highspeed peer.
+
+3. Port resume always triggers an attached child device to resume.  After a
+   power session is lost the device may have been removed, or need reset.
+   Resuming the child device when the parent port regains power resolves those
+   states and clamps the maximum port power cycle frequency at the rate the
+   child device can suspend (autosuspend-delay) and resume (reset-resume
+   latency).
+
+Sysfs files relevant for port power control:
+
+	``<hubdev-portX>/power/pm_qos_no_power_off``:
+		This writable flag controls the state of an idle port.
+		Once all children and descendants have suspended the
+		port may suspend/poweroff provided that
+		pm_qos_no_power_off is '0'.  If pm_qos_no_power_off is
+		'1' the port will remain active/powered regardless of
+		the stats of descendants.  Defaults to 1.
+
+	``<hubdev-portX>/power/runtime_status``:
+		This file reflects whether the port is 'active' (power is on)
+		or 'suspended' (logically off).  There is no indication to
+		userspace whether VBUS is still supplied.
+
+	``<hubdev-portX>/connect_type``:
+		An advisory read-only flag to userspace indicating the
+		location and connection type of the port.  It returns
+		one of four values 'hotplug', 'hardwired', 'not used',
+		and 'unknown'.  All values, besides unknown, are set by
+		platform firmware.
+
+		``hotplug`` indicates an externally connectable/visible
+		port on the platform.  Typically userspace would choose
+		to keep such a port powered to handle new device
+		connection events.
+
+		``hardwired`` refers to a port that is not visible but
+		connectable. Examples are internal ports for USB
+		bluetooth that can be disconnected via an external
+		switch or a port with a hardwired USB camera.  It is
+		expected to be safe to allow these ports to suspend
+		provided pm_qos_no_power_off is coordinated with any
+		switch that gates connections.  Userspace must arrange
+		for the device to be connected prior to the port
+		powering off, or to activate the port prior to enabling
+		connection via a switch.
+
+		``not used`` refers to an internal port that is expected
+		to never have a device connected to it.  These may be
+		empty internal ports, or ports that are not physically
+		exposed on a platform.  Considered safe to be
+		powered-off at all times.
+
+		``unknown`` means platform firmware does not provide
+		information for this port.  Most commonly refers to
+		external hub ports which should be considered 'hotplug'
+		for policy decisions.
+
+		.. note::
+
+			- since we are relying on the BIOS to get this ACPI
+			  information correct, the USB port descriptions may
+			  be missing or wrong.
+
+			- Take care in clearing ``pm_qos_no_power_off``. Once
+			  power is off this port will
+			  not respond to new connect events.
+
+	Once a child device is attached additional constraints are
+	applied before the port is allowed to poweroff.
+
+	``<child>/power/control``:
+		Must be ``auto``, and the port will not
+		power down until ``<child>/power/runtime_status``
+		reflects the 'suspended' state.  Default
+		value is controlled by child device driver.
+
+	``<child>/power/persist``:
+		This defaults to ``1`` for most devices and indicates if
+		kernel can persist the device's configuration across a
+		power session loss (suspend / port-power event).  When
+		this value is ``0`` (quirky devices), port poweroff is
+		disabled.
+
+	``<child>/driver/unbind``:
+		Wakeup capable devices will block port poweroff.  At
+		this time the only mechanism to clear the usb-internal
+		wakeup-capability for an interface device is to unbind
+		its driver.
+
+Summary of poweroff pre-requisite settings relative to a port device::
+
+	echo 0 > power/pm_qos_no_power_off
+	echo 0 > peer/power/pm_qos_no_power_off # if it exists
+	echo auto > power/control # this is the default value
+	echo auto > <child>/power/control
+	echo 1 > <child>/power/persist # this is the default value
+
+Suggested Userspace Port Power Policy
+-------------------------------------
+
+As noted above userspace needs to be careful and deliberate about what
+ports are enabled for poweroff.
+
+The default configuration is that all ports start with
+``power/pm_qos_no_power_off`` set to ``1`` causing ports to always remain
+active.
+
+Given confidence in the platform firmware's description of the ports
+(ACPI _PLD record for a port populates 'connect_type') userspace can
+clear pm_qos_no_power_off for all 'not used' ports.  The same can be
+done for 'hardwired' ports provided poweroff is coordinated with any
+connection switch for the port.
+
+A more aggressive userspace policy is to enable USB port power off for
+all ports (set ``<hubdev-portX>/power/pm_qos_no_power_off`` to ``0``) when
+some external factor indicates the user has stopped interacting with the
+system.  For example, a distro may want to enable power off all USB
+ports when the screen blanks, and re-power them when the screen becomes
+active.  Smart phones and tablets may want to power off USB ports when
+the user pushes the power button.

Documentation/driver-api/usb/typec.rst

@@ -0,0 +1,233 @@
+
+USB Type-C connector class
+==========================
+
+Introduction
+------------
+
+The typec class is meant for describing the USB Type-C ports in a system to the
+user space in unified fashion. The class is designed to provide nothing else
+except the user space interface implementation in hope that it can be utilized
+on as many platforms as possible.
+
+The platforms are expected to register every USB Type-C port they have with the
+class. In a normal case the registration will be done by a USB Type-C or PD PHY
+driver, but it may be a driver for firmware interface such as UCSI, driver for
+USB PD controller or even driver for Thunderbolt3 controller. This document
+considers the component registering the USB Type-C ports with the class as "port
+driver".
+
+On top of showing the capabilities, the class also offer user space control over
+the roles and alternate modes of ports, partners and cable plugs when the port
+driver is capable of supporting those features.
+
+The class provides an API for the port drivers described in this document. The
+attributes are described in Documentation/ABI/testing/sysfs-class-typec.
+
+User space interface
+--------------------
+Every port will be presented as its own device under /sys/class/typec/. The
+first port will be named "port0", the second "port1" and so on.
+
+When connected, the partner will be presented also as its own device under
+/sys/class/typec/. The parent of the partner device will always be the port it
+is attached to. The partner attached to port "port0" will be named
+"port0-partner". Full path to the device would be
+/sys/class/typec/port0/port0-partner/.
+
+The cable and the two plugs on it may also be optionally presented as their own
+devices under /sys/class/typec/. The cable attached to the port "port0" port
+will be named port0-cable and the plug on the SOP Prime end (see USB Power
+Delivery Specification ch. 2.4) will be named "port0-plug0" and on the SOP
+Double Prime end "port0-plug1". The parent of a cable will always be the port,
+and the parent of the cable plugs will always be the cable.
+
+If the port, partner or cable plug supports Alternate Modes, every supported
+Alternate Mode SVID will have their own device describing them. Note that the
+Alternate Mode devices will not be attached to the typec class. The parent of an
+alternate mode will be the device that supports it, so for example an alternate
+mode of port0-partner will be presented under /sys/class/typec/port0-partner/.
+Every mode that is supported will have its own group under the Alternate Mode
+device named "mode<index>", for example /sys/class/typec/port0/<alternate
+mode>/mode1/. The requests for entering/exiting a mode can be done with "active"
+attribute file in that group.
+
+Driver API
+----------
+
+Registering the ports
+~~~~~~~~~~~~~~~~~~~~~
+
+The port drivers will describe every Type-C port they control with struct
+typec_capability data structure, and register them with the following API:
+
+.. kernel-doc:: drivers/usb/typec/class.c
+   :functions: typec_register_port typec_unregister_port
+
+When registering the ports, the prefer_role member in struct typec_capability
+deserves special notice. If the port that is being registered does not have
+initial role preference, which means the port does not execute Try.SNK or
+Try.SRC by default, the member must have value TYPEC_NO_PREFERRED_ROLE.
+Otherwise if the port executes Try.SNK by default, the member must have value
+TYPEC_DEVICE, and with Try.SRC the value must be TYPEC_HOST.
+
+Registering Partners
+~~~~~~~~~~~~~~~~~~~~
+
+After successful connection of a partner, the port driver needs to register the
+partner with the class. Details about the partner need to be described in struct
+typec_partner_desc. The class copies the details of the partner during
+registration. The class offers the following API for registering/unregistering
+partners.
+
+.. kernel-doc:: drivers/usb/typec/class.c
+   :functions: typec_register_partner typec_unregister_partner
+
+The class will provide a handle to struct typec_partner if the registration was
+successful, or NULL.
+
+If the partner is USB Power Delivery capable, and the port driver is able to
+show the result of Discover Identity command, the partner descriptor structure
+should include handle to struct usb_pd_identity instance. The class will then
+create a sysfs directory for the identity under the partner device. The result
+of Discover Identity command can then be reported with the following API:
+
+.. kernel-doc:: drivers/usb/typec/class.c
+   :functions: typec_partner_set_identity
+
+Registering Cables
+~~~~~~~~~~~~~~~~~~
+
+After successful connection of a cable that supports USB Power Delivery
+Structured VDM "Discover Identity", the port driver needs to register the cable
+and one or two plugs, depending if there is CC Double Prime controller present
+in the cable or not. So a cable capable of SOP Prime communication, but not SOP
+Double Prime communication, should only have one plug registered. For more
+information about SOP communication, please read chapter about it from the
+latest USB Power Delivery specification.
+
+The plugs are represented as their own devices. The cable is registered first,
+followed by registration of the cable plugs. The cable will be the parent device
+for the plugs. Details about the cable need to be described in struct
+typec_cable_desc and about a plug in struct typec_plug_desc. The class copies
+the details during registration. The class offers the following API for
+registering/unregistering cables and their plugs:
+
+.. kernel-doc:: drivers/usb/typec/class.c
+   :functions: typec_register_cable typec_unregister_cable typec_register_plug typec_unregister_plug
+
+The class will provide a handle to struct typec_cable and struct typec_plug if
+the registration is successful, or NULL if it isn't.
+
+If the cable is USB Power Delivery capable, and the port driver is able to show
+the result of Discover Identity command, the cable descriptor structure should
+include handle to struct usb_pd_identity instance. The class will then create a
+sysfs directory for the identity under the cable device. The result of Discover
+Identity command can then be reported with the following API:
+
+.. kernel-doc:: drivers/usb/typec/class.c
+   :functions: typec_cable_set_identity
+
+Notifications
+~~~~~~~~~~~~~
+
+When the partner has executed a role change, or when the default roles change
+during connection of a partner or cable, the port driver must use the following
+APIs to report it to the class:
+
+.. kernel-doc:: drivers/usb/typec/class.c
+   :functions: typec_set_data_role typec_set_pwr_role typec_set_vconn_role typec_set_pwr_opmode
+
+Alternate Modes
+~~~~~~~~~~~~~~~
+
+USB Type-C ports, partners and cable plugs may support Alternate Modes. Each
+Alternate Mode will have identifier called SVID, which is either a Standard ID
+given by USB-IF or vendor ID, and each supported SVID can have 1 - 6 modes. The
+class provides struct typec_mode_desc for describing individual mode of a SVID,
+and struct typec_altmode_desc which is a container for all the supported modes.
+
+Ports that support Alternate Modes need to register each SVID they support with
+the following API:
+
+.. kernel-doc:: drivers/usb/typec/class.c
+   :functions: typec_port_register_altmode
+
+If a partner or cable plug provides a list of SVIDs as response to USB Power
+Delivery Structured VDM Discover SVIDs message, each SVID needs to be
+registered.
+
+API for the partners:
+
+.. kernel-doc:: drivers/usb/typec/class.c
+   :functions: typec_partner_register_altmode
+
+API for the Cable Plugs:
+
+.. kernel-doc:: drivers/usb/typec/class.c
+   :functions: typec_plug_register_altmode
+
+So ports, partners and cable plugs will register the alternate modes with their
+own functions, but the registration will always return a handle to struct
+typec_altmode on success, or NULL. The unregistration will happen with the same
+function:
+
+.. kernel-doc:: drivers/usb/typec/class.c
+   :functions: typec_unregister_altmode
+
+If a partner or cable plug enters or exits a mode, the port driver needs to
+notify the class with the following API:
+
+.. kernel-doc:: drivers/usb/typec/class.c
+   :functions: typec_altmode_update_active
+
+Multiplexer/DeMultiplexer Switches
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+USB Type-C connectors may have one or more mux/demux switches behind them. Since
+the plugs can be inserted right-side-up or upside-down, a switch is needed to
+route the correct data pairs from the connector to the USB controllers. If
+Alternate or Accessory Modes are supported, another switch is needed that can
+route the pins on the connector to some other component besides USB. USB Type-C
+Connector Class supplies an API for registering those switches.
+
+.. kernel-doc:: drivers/usb/typec/mux.c
+   :functions: typec_switch_register typec_switch_unregister typec_mux_register typec_mux_unregister
+
+In most cases the same physical mux will handle both the orientation and mode.
+However, as the port drivers will be responsible for the orientation, and the
+alternate mode drivers for the mode, the two are always separated into their
+own logical components: "mux" for the mode and "switch" for the orientation.
+
+When a port is registered, USB Type-C Connector Class requests both the mux and
+the switch for the port. The drivers can then use the following API for
+controlling them:
+
+.. kernel-doc:: drivers/usb/typec/class.c
+   :functions: typec_set_orientation typec_set_mode
+
+If the connector is dual-role capable, there may also be a switch for the data
+role. USB Type-C Connector Class does not supply separate API for them. The
+port drivers can use USB Role Class API with those.
+
+Illustration of the muxes behind a connector that supports an alternate mode::
+
+                     ------------------------
+                     |       Connector      |
+                     ------------------------
+                            |         |
+                     ------------------------
+                      \     Orientation    /
+                       --------------------
+                                |
+                       --------------------
+                      /        Mode        \
+                     ------------------------
+                         /              \
+      ------------------------        --------------------
+      |       Alt Mode       |       /      USB Role      \
+      ------------------------      ------------------------
+                                         /            \
+                     ------------------------      ------------------------
+                     |       USB Host       |      |       USB Device     |
+                     ------------------------      ------------------------

Documentation/driver-api/usb/typec_bus.rst

@@ -0,0 +1,136 @@
+
+API for USB Type-C Alternate Mode drivers
+=========================================
+
+Introduction
+------------
+
+Alternate modes require communication with the partner using Vendor Defined
+Messages (VDM) as defined in USB Type-C and USB Power Delivery Specifications.
+The communication is SVID (Standard or Vendor ID) specific, i.e. specific for
+every alternate mode, so every alternate mode will need a custom driver.
+
+USB Type-C bus allows binding a driver to the discovered partner alternate
+modes by using the SVID and the mode number.
+
+USB Type-C Connector Class provides a device for every alternate mode a port
+supports, and separate device for every alternate mode the partner supports.
+The drivers for the alternate modes are bound to the partner alternate mode
+devices, and the port alternate mode devices must be handled by the port
+drivers.
+
+When a new partner alternate mode device is registered, it is linked to the
+alternate mode device of the port that the partner is attached to, that has
+matching SVID and mode. Communication between the port driver and alternate mode
+driver will happen using the same API.
+
+The port alternate mode devices are used as a proxy between the partner and the
+alternate mode drivers, so the port drivers are only expected to pass the SVID
+specific commands from the alternate mode drivers to the partner, and from the
+partners to the alternate mode drivers. No direct SVID specific communication is
+needed from the port drivers, but the port drivers need to provide the operation
+callbacks for the port alternate mode devices, just like the alternate mode
+drivers need to provide them for the partner alternate mode devices.
+
+Usage:
+------
+
+General
+~~~~~~~
+
+By default, the alternate mode drivers are responsible for entering the mode.
+It is also possible to leave the decision about entering the mode to the user
+space (See Documentation/ABI/testing/sysfs-class-typec). Port drivers should not
+enter any modes on their own.
+
+``->vdm`` is the most important callback in the operation callbacks vector. It
+will be used to deliver all the SVID specific commands from the partner to the
+alternate mode driver, and vice versa in case of port drivers. The drivers send
+the SVID specific commands to each other using :c:func:`typec_altmode_vmd()`.
+
+If the communication with the partner using the SVID specific commands results
+in need to reconfigure the pins on the connector, the alternate mode driver
+needs to notify the bus using :c:func:`typec_altmode_notify()`. The driver
+passes the negotiated SVID specific pin configuration value to the function as
+parameter. The bus driver will then configure the mux behind the connector using
+that value as the state value for the mux, and also call blocking notification
+chain to notify the external drivers about the state of the connector that need
+to know it.
+
+NOTE: The SVID specific pin configuration values must always start from
+``TYPEC_STATE_MODAL``. USB Type-C specification defines two default states for
+the connector: ``TYPEC_STATE_USB`` and ``TYPEC_STATE_SAFE``. These values are
+reserved by the bus as the first possible values for the state. When the
+alternate mode is entered, the bus will put the connector into
+``TYPEC_STATE_SAFE`` before sending Enter or Exit Mode command as defined in USB
+Type-C Specification, and also put the connector back to ``TYPEC_STATE_USB``
+after the mode has been exited.
+
+An example of working definitions for SVID specific pin configurations would
+look like this:
+
+enum {
+	ALTMODEX_CONF_A = TYPEC_STATE_MODAL,
+	ALTMODEX_CONF_B,
+	...
+};
+
+Helper macro ``TYPEC_MODAL_STATE()`` can also be used:
+
+#define ALTMODEX_CONF_A = TYPEC_MODAL_STATE(0);
+#define ALTMODEX_CONF_B = TYPEC_MODAL_STATE(1);
+
+Notification chain
+~~~~~~~~~~~~~~~~~~
+
+The drivers for the components that the alternate modes are designed for need to
+get details regarding the results of the negotiation with the partner, and the
+pin configuration of the connector. In case of DisplayPort alternate mode for
+example, the GPU drivers will need to know those details. In case of
+Thunderbolt alternate mode, the thunderbolt drivers will need to know them, and
+so on.
+
+The notification chain is designed for this purpose. The drivers can register
+notifiers with :c:func:`typec_altmode_register_notifier()`.
+
+Cable plug alternate modes
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The alternate mode drivers are not bound to cable plug alternate mode devices,
+only to the partner alternate mode devices. If the alternate mode supports, or
+requires, a cable that responds to SOP Prime, and optionally SOP Double Prime
+messages, the driver for that alternate mode must request handle to the cable
+plug alternate modes using :c:func:`typec_altmode_get_plug()`, and take over
+their control.
+
+Driver API
+----------
+
+Alternate mode driver registering/unregistering
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/usb/typec/bus.c
+   :functions: typec_altmode_register_driver typec_altmode_unregister_driver
+
+Alternate mode driver operations
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/usb/typec/bus.c
+   :functions: typec_altmode_enter typec_altmode_exit typec_altmode_attention typec_altmode_vdm typec_altmode_notify
+
+API for the port drivers
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/usb/typec/bus.c
+   :functions: typec_match_altmode
+
+Cable Plug operations
+~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/usb/typec/bus.c
+   :functions: typec_altmode_get_plug typec_altmode_put_plug
+
+Notifications
+~~~~~~~~~~~~~
+.. kernel-doc:: drivers/usb/typec/class.c
+   :functions: typec_altmode_register_notifier typec_altmode_unregister_notifier

Documentation/driver-api/usb/usb3-debug-port.rst

@@ -0,0 +1,152 @@
+===============
+USB3 debug port
+===============
+
+:Author: Lu Baolu <baolu.lu@linux.intel.com>
+:Date: March 2017
+
+GENERAL
+=======
+
+This is a HOWTO for using the USB3 debug port on x86 systems.
+
+Before using any kernel debugging functionality based on USB3
+debug port, you need to::
+
+	1) check whether any USB3 debug port is available in
+	   your system;
+	2) check which port is used for debugging purposes;
+	3) have a USB 3.0 super-speed A-to-A debugging cable.
+
+INTRODUCTION
+============
+
+The xHCI debug capability (DbC) is an optional but standalone
+functionality provided by the xHCI host controller. The xHCI
+specification describes DbC in the section 7.6.
+
+When DbC is initialized and enabled, it will present a debug
+device through the debug port (normally the first USB3
+super-speed port). The debug device is fully compliant with
+the USB framework and provides the equivalent of a very high
+performance full-duplex serial link between the debug target
+(the system under debugging) and a debug host.
+
+EARLY PRINTK
+============
+
+DbC has been designed to log early printk messages. One use for
+this feature is kernel debugging. For example, when your machine
+crashes very early before the regular console code is initialized.
+Other uses include simpler, lockless logging instead of a full-
+blown printk console driver and klogd.
+
+On the debug target system, you need to customize a debugging
+kernel with CONFIG_EARLY_PRINTK_USB_XDBC enabled. And, add below
+kernel boot parameter::
+
+	"earlyprintk=xdbc"
+
+If there are multiple xHCI controllers in your system, you can
+append a host contoller index to this kernel parameter. This
+index starts from 0.
+
+Current design doesn't support DbC runtime suspend/resume. As
+the result, you'd better disable runtime power management for
+USB subsystem by adding below kernel boot parameter::
+
+	"usbcore.autosuspend=-1"
+
+Before starting the debug target, you should connect the debug
+port to a USB port (root port or port of any external hub) on
+the debug host. The cable used to connect these two ports
+should be a USB 3.0 super-speed A-to-A debugging cable.
+
+During early boot of the debug target, DbC will be detected and
+initialized. After initialization, the debug host should be able
+to enumerate the debug device in debug target. The debug host
+will then bind the debug device with the usb_debug driver module
+and create the /dev/ttyUSB device.
+
+If the debug device enumeration goes smoothly, you should be able
+to see below kernel messages on the debug host::
+
+	# tail -f /var/log/kern.log
+	[ 1815.983374] usb 4-3: new SuperSpeed USB device number 4 using xhci_hcd
+	[ 1815.999595] usb 4-3: LPM exit latency is zeroed, disabling LPM.
+	[ 1815.999899] usb 4-3: New USB device found, idVendor=1d6b, idProduct=0004
+	[ 1815.999902] usb 4-3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
+	[ 1815.999903] usb 4-3: Product: Remote GDB
+	[ 1815.999904] usb 4-3: Manufacturer: Linux
+	[ 1815.999905] usb 4-3: SerialNumber: 0001
+	[ 1816.000240] usb_debug 4-3:1.0: xhci_dbc converter detected
+	[ 1816.000360] usb 4-3: xhci_dbc converter now attached to ttyUSB0
+
+You can use any communication program, for example minicom, to
+read and view the messages. Below simple bash scripts can help
+you to check the sanity of the setup.
+
+.. code-block:: sh
+
+	===== start of bash scripts =============
+	#!/bin/bash
+
+	while true ; do
+		while [ ! -d /sys/class/tty/ttyUSB0 ] ; do
+			:
+		done
+	cat /dev/ttyUSB0
+	done
+	===== end of bash scripts ===============
+
+Serial TTY
+==========
+
+The DbC support has been added to the xHCI driver. You can get a
+debug device provided by the DbC at runtime.
+
+In order to use this, you need to make sure your kernel has been
+configured to support USB_XHCI_DBGCAP. A sysfs attribute under
+the xHCI device node is used to enable or disable DbC. By default,
+DbC is disabled::
+
+	root@target:/sys/bus/pci/devices/0000:00:14.0# cat dbc
+	disabled
+
+Enable DbC with the following command::
+
+	root@target:/sys/bus/pci/devices/0000:00:14.0# echo enable > dbc
+
+You can check the DbC state at anytime::
+
+	root@target:/sys/bus/pci/devices/0000:00:14.0# cat dbc
+	enabled
+
+Connect the debug target to the debug host with a USB 3.0 super-
+speed A-to-A debugging cable. You can see /dev/ttyDBC0 created
+on the debug target. You will see below kernel message lines::
+
+	root@target: tail -f /var/log/kern.log
+	[  182.730103] xhci_hcd 0000:00:14.0: DbC connected
+	[  191.169420] xhci_hcd 0000:00:14.0: DbC configured
+	[  191.169597] xhci_hcd 0000:00:14.0: DbC now attached to /dev/ttyDBC0
+
+Accordingly, the DbC state has been brought up to::
+
+	root@target:/sys/bus/pci/devices/0000:00:14.0# cat dbc
+	configured
+
+On the debug host, you will see the debug device has been enumerated.
+You will see below kernel message lines::
+
+	root@host: tail -f /var/log/kern.log
+	[   79.454780] usb 2-2.1: new SuperSpeed USB device number 3 using xhci_hcd
+	[   79.475003] usb 2-2.1: LPM exit latency is zeroed, disabling LPM.
+	[   79.475389] usb 2-2.1: New USB device found, idVendor=1d6b, idProduct=0010
+	[   79.475390] usb 2-2.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
+	[   79.475391] usb 2-2.1: Product: Linux USB Debug Target
+	[   79.475392] usb 2-2.1: Manufacturer: Linux Foundation
+	[   79.475393] usb 2-2.1: SerialNumber: 0001
+
+The debug device works now. You can use any communication or debugging
+program to talk between the host and the target.

Documentation/driver-api/usb/writing_musb_glue_layer.rst

@@ -0,0 +1,720 @@
+=========================
+Writing a MUSB Glue Layer
+=========================
+
+:Author: Apelete Seketeli
+
+Introduction
+============
+
+The Linux MUSB subsystem is part of the larger Linux USB subsystem. It
+provides support for embedded USB Device Controllers (UDC) that do not
+use Universal Host Controller Interface (UHCI) or Open Host Controller
+Interface (OHCI).
+
+Instead, these embedded UDC rely on the USB On-the-Go (OTG)
+specification which they implement at least partially. The silicon
+reference design used in most cases is the Multipoint USB Highspeed
+Dual-Role Controller (MUSB HDRC) found in the Mentor Graphics Inventra™
+design.
+
+As a self-taught exercise I have written an MUSB glue layer for the
+Ingenic JZ4740 SoC, modelled after the many MUSB glue layers in the
+kernel source tree. This layer can be found at
+``drivers/usb/musb/jz4740.c``. In this documentation I will walk through the
+basics of the ``jz4740.c`` glue layer, explaining the different pieces and
+what needs to be done in order to write your own device glue layer.
+
+.. _musb-basics:
+
+Linux MUSB Basics
+=================
+
+To get started on the topic, please read USB On-the-Go Basics (see
+Resources) which provides an introduction of USB OTG operation at the
+hardware level. A couple of wiki pages by Texas Instruments and Analog
+Devices also provide an overview of the Linux kernel MUSB configuration,
+albeit focused on some specific devices provided by these companies.
+Finally, getting acquainted with the USB specification at USB home page
+may come in handy, with practical instance provided through the Writing
+USB Device Drivers documentation (again, see Resources).
+
+Linux USB stack is a layered architecture in which the MUSB controller
+hardware sits at the lowest. The MUSB controller driver abstract the
+MUSB controller hardware to the Linux USB stack::
+
+	  ------------------------
+	  |                      | <------- drivers/usb/gadget
+	  | Linux USB Core Stack | <------- drivers/usb/host
+	  |                      | <------- drivers/usb/core
+	  ------------------------
+		     ⬍
+	 --------------------------
+	 |                        | <------ drivers/usb/musb/musb_gadget.c
+	 | MUSB Controller driver | <------ drivers/usb/musb/musb_host.c
+	 |                        | <------ drivers/usb/musb/musb_core.c
+	 --------------------------
+		     ⬍
+      ---------------------------------
+      | MUSB Platform Specific Driver |
+      |                               | <-- drivers/usb/musb/jz4740.c
+      |       aka "Glue Layer"        |
+      ---------------------------------
+		     ⬍
+      ---------------------------------
+      |   MUSB Controller Hardware    |
+      ---------------------------------
+
+As outlined above, the glue layer is actually the platform specific code
+sitting in between the controller driver and the controller hardware.
+
+Just like a Linux USB driver needs to register itself with the Linux USB
+subsystem, the MUSB glue layer needs first to register itself with the
+MUSB controller driver. This will allow the controller driver to know
+about which device the glue layer supports and which functions to call
+when a supported device is detected or released; remember we are talking
+about an embedded controller chip here, so no insertion or removal at
+run-time.
+
+All of this information is passed to the MUSB controller driver through
+a :c:type:`platform_driver` structure defined in the glue layer as::
+
+    static struct platform_driver jz4740_driver = {
+	.probe      = jz4740_probe,
+	.remove     = jz4740_remove,
+	.driver     = {
+	    .name   = "musb-jz4740",
+	},
+    };
+
+The probe and remove function pointers are called when a matching device
+is detected and, respectively, released. The name string describes the
+device supported by this glue layer. In the current case it matches a
+platform_device structure declared in ``arch/mips/jz4740/platform.c``. Note
+that we are not using device tree bindings here.
+
+In order to register itself to the controller driver, the glue layer
+goes through a few steps, basically allocating the controller hardware
+resources and initialising a couple of circuits. To do so, it needs to
+keep track of the information used throughout these steps. This is done
+by defining a private ``jz4740_glue`` structure::
+
+    struct jz4740_glue {
+	struct device           *dev;
+	struct platform_device  *musb;
+	struct clk      *clk;
+    };
+
+
+The dev and musb members are both device structure variables. The first
+one holds generic information about the device, since it's the basic
+device structure, and the latter holds information more closely related
+to the subsystem the device is registered to. The clk variable keeps
+information related to the device clock operation.
+
+Let's go through the steps of the probe function that leads the glue
+layer to register itself to the controller driver.
+
+.. note::
+
+   For the sake of readability each function will be split in logical
+   parts, each part being shown as if it was independent from the others.
+
+.. code-block:: c
+    :emphasize-lines: 8,12,18
+
+    static int jz4740_probe(struct platform_device *pdev)
+    {
+	struct platform_device      *musb;
+	struct jz4740_glue      *glue;
+	struct clk                      *clk;
+	int             ret;
+
+	glue = devm_kzalloc(&pdev->dev, sizeof(*glue), GFP_KERNEL);
+	if (!glue)
+	    return -ENOMEM;
+
+	musb = platform_device_alloc("musb-hdrc", PLATFORM_DEVID_AUTO);
+	if (!musb) {
+	    dev_err(&pdev->dev, "failed to allocate musb device\n");
+	    return -ENOMEM;
+	}
+
+	clk = devm_clk_get(&pdev->dev, "udc");
+	if (IS_ERR(clk)) {
+	    dev_err(&pdev->dev, "failed to get clock\n");
+	    ret = PTR_ERR(clk);
+	    goto err_platform_device_put;
+	}
+
+	ret = clk_prepare_enable(clk);
+	if (ret) {
+	    dev_err(&pdev->dev, "failed to enable clock\n");
+	    goto err_platform_device_put;
+	}
+
+	musb->dev.parent        = &pdev->dev;
+
+	glue->dev           = &pdev->dev;
+	glue->musb          = musb;
+	glue->clk           = clk;
+
+	return 0;
+
+    err_platform_device_put:
+	platform_device_put(musb);
+	return ret;
+    }
+
+The first few lines of the probe function allocate and assign the glue,
+musb and clk variables. The ``GFP_KERNEL`` flag (line 8) allows the
+allocation process to sleep and wait for memory, thus being usable in a
+locking situation. The ``PLATFORM_DEVID_AUTO`` flag (line 12) allows
+automatic allocation and management of device IDs in order to avoid
+device namespace collisions with explicit IDs. With :c:func:`devm_clk_get`
+(line 18) the glue layer allocates the clock -- the ``devm_`` prefix
+indicates that :c:func:`clk_get` is managed: it automatically frees the
+allocated clock resource data when the device is released -- and enable
+it.
+
+
+
+Then comes the registration steps:
+
+.. code-block:: c
+    :emphasize-lines: 3,5,7,9,16
+
+    static int jz4740_probe(struct platform_device *pdev)
+    {
+	struct musb_hdrc_platform_data  *pdata = &jz4740_musb_platform_data;
+
+	pdata->platform_ops     = &jz4740_musb_ops;
+
+	platform_set_drvdata(pdev, glue);
+
+	ret = platform_device_add_resources(musb, pdev->resource,
+			    pdev->num_resources);
+	if (ret) {
+	    dev_err(&pdev->dev, "failed to add resources\n");
+	    goto err_clk_disable;
+	}
+
+	ret = platform_device_add_data(musb, pdata, sizeof(*pdata));
+	if (ret) {
+	    dev_err(&pdev->dev, "failed to add platform_data\n");
+	    goto err_clk_disable;
+	}
+
+	return 0;
+
+    err_clk_disable:
+	clk_disable_unprepare(clk);
+    err_platform_device_put:
+	platform_device_put(musb);
+	return ret;
+    }
+
+The first step is to pass the device data privately held by the glue
+layer on to the controller driver through :c:func:`platform_set_drvdata`
+(line 7). Next is passing on the device resources information, also privately
+held at that point, through :c:func:`platform_device_add_resources` (line 9).
+
+Finally comes passing on the platform specific data to the controller
+driver (line 16). Platform data will be discussed in
+:ref:`musb-dev-platform-data`, but here we are looking at the
+``platform_ops`` function pointer (line 5) in ``musb_hdrc_platform_data``
+structure (line 3). This function pointer allows the MUSB controller
+driver to know which function to call for device operation::
+
+    static const struct musb_platform_ops jz4740_musb_ops = {
+	.init       = jz4740_musb_init,
+	.exit       = jz4740_musb_exit,
+    };
+
+Here we have the minimal case where only init and exit functions are
+called by the controller driver when needed. Fact is the JZ4740 MUSB
+controller is a basic controller, lacking some features found in other
+controllers, otherwise we may also have pointers to a few other
+functions like a power management function or a function to switch
+between OTG and non-OTG modes, for instance.
+
+At that point of the registration process, the controller driver
+actually calls the init function:
+
+   .. code-block:: c
+    :emphasize-lines: 12,14
+
+    static int jz4740_musb_init(struct musb *musb)
+    {
+	musb->xceiv = usb_get_phy(USB_PHY_TYPE_USB2);
+	if (!musb->xceiv) {
+	    pr_err("HS UDC: no transceiver configured\n");
+	    return -ENODEV;
+	}
+
+	/* Silicon does not implement ConfigData register.
+	 * Set dyn_fifo to avoid reading EP config from hardware.
+	 */
+	musb->dyn_fifo = true;
+
+	musb->isr = jz4740_musb_interrupt;
+
+	return 0;
+    }
+
+The goal of ``jz4740_musb_init()`` is to get hold of the transceiver
+driver data of the MUSB controller hardware and pass it on to the MUSB
+controller driver, as usual. The transceiver is the circuitry inside the
+controller hardware responsible for sending/receiving the USB data.
+Since it is an implementation of the physical layer of the OSI model,
+the transceiver is also referred to as PHY.
+
+Getting hold of the ``MUSB PHY`` driver data is done with ``usb_get_phy()``
+which returns a pointer to the structure containing the driver instance
+data. The next couple of instructions (line 12 and 14) are used as a
+quirk and to setup IRQ handling respectively. Quirks and IRQ handling
+will be discussed later in :ref:`musb-dev-quirks` and
+:ref:`musb-handling-irqs`\ ::
+
+    static int jz4740_musb_exit(struct musb *musb)
+    {
+	usb_put_phy(musb->xceiv);
+
+	return 0;
+    }
+
+Acting as the counterpart of init, the exit function releases the MUSB
+PHY driver when the controller hardware itself is about to be released.
+
+Again, note that init and exit are fairly simple in this case due to the
+basic set of features of the JZ4740 controller hardware. When writing an
+musb glue layer for a more complex controller hardware, you might need
+to take care of more processing in those two functions.
+
+Returning from the init function, the MUSB controller driver jumps back
+into the probe function::
+
+    static int jz4740_probe(struct platform_device *pdev)
+    {
+	ret = platform_device_add(musb);
+	if (ret) {
+	    dev_err(&pdev->dev, "failed to register musb device\n");
+	    goto err_clk_disable;
+	}
+
+	return 0;
+
+    err_clk_disable:
+	clk_disable_unprepare(clk);
+    err_platform_device_put:
+	platform_device_put(musb);
+	return ret;
+    }
+
+This is the last part of the device registration process where the glue
+layer adds the controller hardware device to Linux kernel device
+hierarchy: at this stage, all known information about the device is
+passed on to the Linux USB core stack:
+
+   .. code-block:: c
+    :emphasize-lines: 5,6
+
+    static int jz4740_remove(struct platform_device *pdev)
+    {
+	struct jz4740_glue  *glue = platform_get_drvdata(pdev);
+
+	platform_device_unregister(glue->musb);
+	clk_disable_unprepare(glue->clk);
+
+	return 0;
+    }
+
+Acting as the counterpart of probe, the remove function unregister the
+MUSB controller hardware (line 5) and disable the clock (line 6),
+allowing it to be gated.
+
+.. _musb-handling-irqs:
+
+Handling IRQs
+=============
+
+Additionally to the MUSB controller hardware basic setup and
+registration, the glue layer is also responsible for handling the IRQs:
+
+   .. code-block:: c
+    :emphasize-lines: 7,9-11,14,24
+
+    static irqreturn_t jz4740_musb_interrupt(int irq, void *__hci)
+    {
+	unsigned long   flags;
+	irqreturn_t     retval = IRQ_NONE;
+	struct musb     *musb = __hci;
+
+	spin_lock_irqsave(&musb->lock, flags);
+
+	musb->int_usb = musb_readb(musb->mregs, MUSB_INTRUSB);
+	musb->int_tx = musb_readw(musb->mregs, MUSB_INTRTX);
+	musb->int_rx = musb_readw(musb->mregs, MUSB_INTRRX);
+
+	/*
+	 * The controller is gadget only, the state of the host mode IRQ bits is
+	 * undefined. Mask them to make sure that the musb driver core will
+	 * never see them set
+	 */
+	musb->int_usb &= MUSB_INTR_SUSPEND | MUSB_INTR_RESUME |
+	    MUSB_INTR_RESET | MUSB_INTR_SOF;
+
+	if (musb->int_usb || musb->int_tx || musb->int_rx)
+	    retval = musb_interrupt(musb);
+
+	spin_unlock_irqrestore(&musb->lock, flags);
+
+	return retval;
+    }
+
+Here the glue layer mostly has to read the relevant hardware registers
+and pass their values on to the controller driver which will handle the
+actual event that triggered the IRQ.
+
+The interrupt handler critical section is protected by the
+:c:func:`spin_lock_irqsave` and counterpart :c:func:`spin_unlock_irqrestore`
+functions (line 7 and 24 respectively), which prevent the interrupt
+handler code to be run by two different threads at the same time.
+
+Then the relevant interrupt registers are read (line 9 to 11):
+
+-  ``MUSB_INTRUSB``: indicates which USB interrupts are currently active,
+
+-  ``MUSB_INTRTX``: indicates which of the interrupts for TX endpoints are
+   currently active,
+
+-  ``MUSB_INTRRX``: indicates which of the interrupts for TX endpoints are
+   currently active.
+
+Note that :c:func:`musb_readb` is used to read 8-bit registers at most, while
+:c:func:`musb_readw` allows us to read at most 16-bit registers. There are
+other functions that can be used depending on the size of your device
+registers. See ``musb_io.h`` for more information.
+
+Instruction on line 18 is another quirk specific to the JZ4740 USB
+device controller, which will be discussed later in :ref:`musb-dev-quirks`.
+
+The glue layer still needs to register the IRQ handler though. Remember
+the instruction on line 14 of the init function::
+
+    static int jz4740_musb_init(struct musb *musb)
+    {
+	musb->isr = jz4740_musb_interrupt;
+
+	return 0;
+    }
+
+This instruction sets a pointer to the glue layer IRQ handler function,
+in order for the controller hardware to call the handler back when an
+IRQ comes from the controller hardware. The interrupt handler is now
+implemented and registered.
+
+.. _musb-dev-platform-data:
+
+Device Platform Data
+====================
+
+In order to write an MUSB glue layer, you need to have some data
+describing the hardware capabilities of your controller hardware, which
+is called the platform data.
+
+Platform data is specific to your hardware, though it may cover a broad
+range of devices, and is generally found somewhere in the ``arch/``
+directory, depending on your device architecture.
+
+For instance, platform data for the JZ4740 SoC is found in
+``arch/mips/jz4740/platform.c``. In the ``platform.c`` file each device of the
+JZ4740 SoC is described through a set of structures.
+
+Here is the part of ``arch/mips/jz4740/platform.c`` that covers the USB
+Device Controller (UDC):
+
+   .. code-block:: c
+    :emphasize-lines: 2,7,14-17,21,22,25,26,28,29
+
+    /* USB Device Controller */
+    struct platform_device jz4740_udc_xceiv_device = {
+	.name = "usb_phy_gen_xceiv",
+	.id   = 0,
+    };
+
+    static struct resource jz4740_udc_resources[] = {
+	[0] = {
+	    .start = JZ4740_UDC_BASE_ADDR,
+	    .end   = JZ4740_UDC_BASE_ADDR + 0x10000 - 1,
+	    .flags = IORESOURCE_MEM,
+	},
+	[1] = {
+	    .start = JZ4740_IRQ_UDC,
+	    .end   = JZ4740_IRQ_UDC,
+	    .flags = IORESOURCE_IRQ,
+	    .name  = "mc",
+	},
+    };
+
+    struct platform_device jz4740_udc_device = {
+	.name = "musb-jz4740",
+	.id   = -1,
+	.dev  = {
+	    .dma_mask          = &jz4740_udc_device.dev.coherent_dma_mask,
+	    .coherent_dma_mask = DMA_BIT_MASK(32),
+	},
+	.num_resources = ARRAY_SIZE(jz4740_udc_resources),
+	.resource      = jz4740_udc_resources,
+    };
+
+The ``jz4740_udc_xceiv_device`` platform device structure (line 2)
+describes the UDC transceiver with a name and id number.
+
+At the time of this writing, note that ``usb_phy_gen_xceiv`` is the
+specific name to be used for all transceivers that are either built-in
+with reference USB IP or autonomous and doesn't require any PHY
+programming. You will need to set ``CONFIG_NOP_USB_XCEIV=y`` in the
+kernel configuration to make use of the corresponding transceiver
+driver. The id field could be set to -1 (equivalent to
+``PLATFORM_DEVID_NONE``), -2 (equivalent to ``PLATFORM_DEVID_AUTO``) or
+start with 0 for the first device of this kind if we want a specific id
+number.
+
+The ``jz4740_udc_resources`` resource structure (line 7) defines the UDC
+registers base addresses.
+
+The first array (line 9 to 11) defines the UDC registers base memory
+addresses: start points to the first register memory address, end points
+to the last register memory address and the flags member defines the
+type of resource we are dealing with. So ``IORESOURCE_MEM`` is used to
+define the registers memory addresses. The second array (line 14 to 17)
+defines the UDC IRQ registers addresses. Since there is only one IRQ
+register available for the JZ4740 UDC, start and end point at the same
+address. The ``IORESOURCE_IRQ`` flag tells that we are dealing with IRQ
+resources, and the name ``mc`` is in fact hard-coded in the MUSB core in
+order for the controller driver to retrieve this IRQ resource by
+querying it by its name.
+
+Finally, the ``jz4740_udc_device`` platform device structure (line 21)
+describes the UDC itself.
+
+The ``musb-jz4740`` name (line 22) defines the MUSB driver that is used
+for this device; remember this is in fact the name that we used in the
+``jz4740_driver`` platform driver structure in :ref:`musb-basics`.
+The id field (line 23) is set to -1 (equivalent to ``PLATFORM_DEVID_NONE``)
+since we do not need an id for the device: the MUSB controller driver was
+already set to allocate an automatic id in :ref:`musb-basics`. In the dev field
+we care for DMA related information here. The ``dma_mask`` field (line 25)
+defines the width of the DMA mask that is going to be used, and
+``coherent_dma_mask`` (line 26) has the same purpose but for the
+``alloc_coherent`` DMA mappings: in both cases we are using a 32 bits mask.
+Then the resource field (line 29) is simply a pointer to the resource
+structure defined before, while the ``num_resources`` field (line 28) keeps
+track of the number of arrays defined in the resource structure (in this
+case there were two resource arrays defined before).
+
+With this quick overview of the UDC platform data at the ``arch/`` level now
+done, let's get back to the MUSB glue layer specific platform data in
+``drivers/usb/musb/jz4740.c``:
+
+   .. code-block:: c
+    :emphasize-lines: 3,5,7-9,11
+
+    static struct musb_hdrc_config jz4740_musb_config = {
+	/* Silicon does not implement USB OTG. */
+	.multipoint = 0,
+	/* Max EPs scanned, driver will decide which EP can be used. */
+	.num_eps    = 4,
+	/* RAMbits needed to configure EPs from table */
+	.ram_bits   = 9,
+	.fifo_cfg = jz4740_musb_fifo_cfg,
+	.fifo_cfg_size = ARRAY_SIZE(jz4740_musb_fifo_cfg),
+    };
+
+    static struct musb_hdrc_platform_data jz4740_musb_platform_data = {
+	.mode   = MUSB_PERIPHERAL,
+	.config = &jz4740_musb_config,
+    };
+
+First the glue layer configures some aspects of the controller driver
+operation related to the controller hardware specifics. This is done
+through the ``jz4740_musb_config`` :c:type:`musb_hdrc_config` structure.
+
+Defining the OTG capability of the controller hardware, the multipoint
+member (line 3) is set to 0 (equivalent to false) since the JZ4740 UDC
+is not OTG compatible. Then ``num_eps`` (line 5) defines the number of USB
+endpoints of the controller hardware, including endpoint 0: here we have
+3 endpoints + endpoint 0. Next is ``ram_bits`` (line 7) which is the width
+of the RAM address bus for the MUSB controller hardware. This
+information is needed when the controller driver cannot automatically
+configure endpoints by reading the relevant controller hardware
+registers. This issue will be discussed when we get to device quirks in
+:ref:`musb-dev-quirks`. Last two fields (line 8 and 9) are also
+about device quirks: ``fifo_cfg`` points to the USB endpoints configuration
+table and ``fifo_cfg_size`` keeps track of the size of the number of
+entries in that configuration table. More on that later in
+:ref:`musb-dev-quirks`.
+
+Then this configuration is embedded inside ``jz4740_musb_platform_data``
+:c:type:`musb_hdrc_platform_data` structure (line 11): config is a pointer to
+the configuration structure itself, and mode tells the controller driver
+if the controller hardware may be used as ``MUSB_HOST`` only,
+``MUSB_PERIPHERAL`` only or ``MUSB_OTG`` which is a dual mode.
+
+Remember that ``jz4740_musb_platform_data`` is then used to convey
+platform data information as we have seen in the probe function in
+:ref:`musb-basics`.
+
+.. _musb-dev-quirks:
+
+Device Quirks
+=============
+
+Completing the platform data specific to your device, you may also need
+to write some code in the glue layer to work around some device specific
+limitations. These quirks may be due to some hardware bugs, or simply be
+the result of an incomplete implementation of the USB On-the-Go
+specification.
+
+The JZ4740 UDC exhibits such quirks, some of which we will discuss here
+for the sake of insight even though these might not be found in the
+controller hardware you are working on.
+
+Let's get back to the init function first:
+
+   .. code-block:: c
+    :emphasize-lines: 12
+
+    static int jz4740_musb_init(struct musb *musb)
+    {
+	musb->xceiv = usb_get_phy(USB_PHY_TYPE_USB2);
+	if (!musb->xceiv) {
+	    pr_err("HS UDC: no transceiver configured\n");
+	    return -ENODEV;
+	}
+
+	/* Silicon does not implement ConfigData register.
+	 * Set dyn_fifo to avoid reading EP config from hardware.
+	 */
+	musb->dyn_fifo = true;
+
+	musb->isr = jz4740_musb_interrupt;
+
+	return 0;
+    }
+
+Instruction on line 12 helps the MUSB controller driver to work around
+the fact that the controller hardware is missing registers that are used
+for USB endpoints configuration.
+
+Without these registers, the controller driver is unable to read the
+endpoints configuration from the hardware, so we use line 12 instruction
+to bypass reading the configuration from silicon, and rely on a
+hard-coded table that describes the endpoints configuration instead::
+
+    static struct musb_fifo_cfg jz4740_musb_fifo_cfg[] = {
+	{ .hw_ep_num = 1, .style = FIFO_TX, .maxpacket = 512, },
+	{ .hw_ep_num = 1, .style = FIFO_RX, .maxpacket = 512, },
+	{ .hw_ep_num = 2, .style = FIFO_TX, .maxpacket = 64, },
+    };
+
+Looking at the configuration table above, we see that each endpoints is
+described by three fields: ``hw_ep_num`` is the endpoint number, style is
+its direction (either ``FIFO_TX`` for the controller driver to send packets
+in the controller hardware, or ``FIFO_RX`` to receive packets from
+hardware), and maxpacket defines the maximum size of each data packet
+that can be transmitted over that endpoint. Reading from the table, the
+controller driver knows that endpoint 1 can be used to send and receive
+USB data packets of 512 bytes at once (this is in fact a bulk in/out
+endpoint), and endpoint 2 can be used to send data packets of 64 bytes
+at once (this is in fact an interrupt endpoint).
+
+Note that there is no information about endpoint 0 here: that one is
+implemented by default in every silicon design, with a predefined
+configuration according to the USB specification. For more examples of
+endpoint configuration tables, see ``musb_core.c``.
+
+Let's now get back to the interrupt handler function:
+
+   .. code-block:: c
+    :emphasize-lines: 18-19
+
+    static irqreturn_t jz4740_musb_interrupt(int irq, void *__hci)
+    {
+	unsigned long   flags;
+	irqreturn_t     retval = IRQ_NONE;
+	struct musb     *musb = __hci;
+
+	spin_lock_irqsave(&musb->lock, flags);
+
+	musb->int_usb = musb_readb(musb->mregs, MUSB_INTRUSB);
+	musb->int_tx = musb_readw(musb->mregs, MUSB_INTRTX);
+	musb->int_rx = musb_readw(musb->mregs, MUSB_INTRRX);
+
+	/*
+	 * The controller is gadget only, the state of the host mode IRQ bits is
+	 * undefined. Mask them to make sure that the musb driver core will
+	 * never see them set
+	 */
+	musb->int_usb &= MUSB_INTR_SUSPEND | MUSB_INTR_RESUME |
+	    MUSB_INTR_RESET | MUSB_INTR_SOF;
+
+	if (musb->int_usb || musb->int_tx || musb->int_rx)
+	    retval = musb_interrupt(musb);
+
+	spin_unlock_irqrestore(&musb->lock, flags);
+
+	return retval;
+    }
+
+Instruction on line 18 above is a way for the controller driver to work
+around the fact that some interrupt bits used for USB host mode
+operation are missing in the ``MUSB_INTRUSB`` register, thus left in an
+undefined hardware state, since this MUSB controller hardware is used in
+peripheral mode only. As a consequence, the glue layer masks these
+missing bits out to avoid parasite interrupts by doing a logical AND
+operation between the value read from ``MUSB_INTRUSB`` and the bits that
+are actually implemented in the register.
+
+These are only a couple of the quirks found in the JZ4740 USB device
+controller. Some others were directly addressed in the MUSB core since
+the fixes were generic enough to provide a better handling of the issues
+for others controller hardware eventually.
+
+Conclusion
+==========
+
+Writing a Linux MUSB glue layer should be a more accessible task, as
+this documentation tries to show the ins and outs of this exercise.
+
+The JZ4740 USB device controller being fairly simple, I hope its glue
+layer serves as a good example for the curious mind. Used with the
+current MUSB glue layers, this documentation should provide enough
+guidance to get started; should anything gets out of hand, the linux-usb
+mailing list archive is another helpful resource to browse through.
+
+Acknowledgements
+================
+
+Many thanks to Lars-Peter Clausen and Maarten ter Huurne for answering
+my questions while I was writing the JZ4740 glue layer and for helping
+me out getting the code in good shape.
+
+I would also like to thank the Qi-Hardware community at large for its
+cheerful guidance and support.
+
+Resources
+=========
+
+USB Home Page: http://www.usb.org
+
+linux-usb Mailing List Archives: http://marc.info/?l=linux-usb
+
+USB On-the-Go Basics:
+http://www.maximintegrated.com/app-notes/index.mvp/id/1822
+
+:ref:`Writing USB Device Drivers <writing-usb-driver>`
+
+Texas Instruments USB Configuration Wiki Page:
+http://processors.wiki.ti.com/index.php/Usbgeneralpage

Documentation/driver-api/usb/writing_usb_driver.rst

@@ -0,0 +1,326 @@
+.. _writing-usb-driver:
+
+==========================
+Writing USB Device Drivers
+==========================
+
+:Author: Greg Kroah-Hartman
+
+Introduction
+============
+
+The Linux USB subsystem has grown from supporting only two different
+types of devices in the 2.2.7 kernel (mice and keyboards), to over 20
+different types of devices in the 2.4 kernel. Linux currently supports
+almost all USB class devices (standard types of devices like keyboards,
+mice, modems, printers and speakers) and an ever-growing number of
+vendor-specific devices (such as USB to serial converters, digital
+cameras, Ethernet devices and MP3 players). For a full list of the
+different USB devices currently supported, see Resources.
+
+The remaining kinds of USB devices that do not have support on Linux are
+almost all vendor-specific devices. Each vendor decides to implement a
+custom protocol to talk to their device, so a custom driver usually
+needs to be created. Some vendors are open with their USB protocols and
+help with the creation of Linux drivers, while others do not publish
+them, and developers are forced to reverse-engineer. See Resources for
+some links to handy reverse-engineering tools.
+
+Because each different protocol causes a new driver to be created, I
+have written a generic USB driver skeleton, modelled after the
+pci-skeleton.c file in the kernel source tree upon which many PCI
+network drivers have been based. This USB skeleton can be found at
+drivers/usb/usb-skeleton.c in the kernel source tree. In this article I
+will walk through the basics of the skeleton driver, explaining the
+different pieces and what needs to be done to customize it to your
+specific device.
+
+Linux USB Basics
+================
+
+If you are going to write a Linux USB driver, please become familiar
+with the USB protocol specification. It can be found, along with many
+other useful documents, at the USB home page (see Resources). An
+excellent introduction to the Linux USB subsystem can be found at the
+USB Working Devices List (see Resources). It explains how the Linux USB
+subsystem is structured and introduces the reader to the concept of USB
+urbs (USB Request Blocks), which are essential to USB drivers.
+
+The first thing a Linux USB driver needs to do is register itself with
+the Linux USB subsystem, giving it some information about which devices
+the driver supports and which functions to call when a device supported
+by the driver is inserted or removed from the system. All of this
+information is passed to the USB subsystem in the :c:type:`usb_driver`
+structure. The skeleton driver declares a :c:type:`usb_driver` as::
+
+    static struct usb_driver skel_driver = {
+	    .name        = "skeleton",
+	    .probe       = skel_probe,
+	    .disconnect  = skel_disconnect,
+	    .fops        = &skel_fops,
+	    .minor       = USB_SKEL_MINOR_BASE,
+	    .id_table    = skel_table,
+    };
+
+
+The variable name is a string that describes the driver. It is used in
+informational messages printed to the system log. The probe and
+disconnect function pointers are called when a device that matches the
+information provided in the ``id_table`` variable is either seen or
+removed.
+
+The fops and minor variables are optional. Most USB drivers hook into
+another kernel subsystem, such as the SCSI, network or TTY subsystem.
+These types of drivers register themselves with the other kernel
+subsystem, and any user-space interactions are provided through that
+interface. But for drivers that do not have a matching kernel subsystem,
+such as MP3 players or scanners, a method of interacting with user space
+is needed. The USB subsystem provides a way to register a minor device
+number and a set of :c:type:`file_operations` function pointers that enable
+this user-space interaction. The skeleton driver needs this kind of
+interface, so it provides a minor starting number and a pointer to its
+:c:type:`file_operations` functions.
+
+The USB driver is then registered with a call to :c:func:`usb_register`,
+usually in the driver's init function, as shown here::
+
+    static int __init usb_skel_init(void)
+    {
+	    int result;
+
+	    /* register this driver with the USB subsystem */
+	    result = usb_register(&skel_driver);
+	    if (result < 0) {
+		    err("usb_register failed for the "__FILE__ "driver."
+			"Error number %d", result);
+		    return -1;
+	    }
+
+	    return 0;
+    }
+    module_init(usb_skel_init);
+
+
+When the driver is unloaded from the system, it needs to deregister
+itself with the USB subsystem. This is done with the :c:func:`usb_deregister`
+function::
+
+    static void __exit usb_skel_exit(void)
+    {
+	    /* deregister this driver with the USB subsystem */
+	    usb_deregister(&skel_driver);
+    }
+    module_exit(usb_skel_exit);
+
+
+To enable the linux-hotplug system to load the driver automatically when
+the device is plugged in, you need to create a ``MODULE_DEVICE_TABLE``.
+The following code tells the hotplug scripts that this module supports a
+single device with a specific vendor and product ID::
+
+    /* table of devices that work with this driver */
+    static struct usb_device_id skel_table [] = {
+	    { USB_DEVICE(USB_SKEL_VENDOR_ID, USB_SKEL_PRODUCT_ID) },
+	    { }                      /* Terminating entry */
+    };
+    MODULE_DEVICE_TABLE (usb, skel_table);
+
+
+There are other macros that can be used in describing a struct
+:c:type:`usb_device_id` for drivers that support a whole class of USB
+drivers. See :ref:`usb.h <usb_header>` for more information on this.
+
+Device operation
+================
+
+When a device is plugged into the USB bus that matches the device ID
+pattern that your driver registered with the USB core, the probe
+function is called. The :c:type:`usb_device` structure, interface number and
+the interface ID are passed to the function::
+
+    static int skel_probe(struct usb_interface *interface,
+	const struct usb_device_id *id)
+
+
+The driver now needs to verify that this device is actually one that it
+can accept. If so, it returns 0. If not, or if any error occurs during
+initialization, an errorcode (such as ``-ENOMEM`` or ``-ENODEV``) is
+returned from the probe function.
+
+In the skeleton driver, we determine what end points are marked as
+bulk-in and bulk-out. We create buffers to hold the data that will be
+sent and received from the device, and a USB urb to write data to the
+device is initialized.
+
+Conversely, when the device is removed from the USB bus, the disconnect
+function is called with the device pointer. The driver needs to clean
+any private data that has been allocated at this time and to shut down
+any pending urbs that are in the USB system.
+
+Now that the device is plugged into the system and the driver is bound
+to the device, any of the functions in the :c:type:`file_operations` structure
+that were passed to the USB subsystem will be called from a user program
+trying to talk to the device. The first function called will be open, as
+the program tries to open the device for I/O. We increment our private
+usage count and save a pointer to our internal structure in the file
+structure. This is done so that future calls to file operations will
+enable the driver to determine which device the user is addressing. All
+of this is done with the following code::
+
+    /* increment our usage count for the module */
+    ++skel->open_count;
+
+    /* save our object in the file's private structure */
+    file->private_data = dev;
+
+
+After the open function is called, the read and write functions are
+called to receive and send data to the device. In the ``skel_write``
+function, we receive a pointer to some data that the user wants to send
+to the device and the size of the data. The function determines how much
+data it can send to the device based on the size of the write urb it has
+created (this size depends on the size of the bulk out end point that
+the device has). Then it copies the data from user space to kernel
+space, points the urb to the data and submits the urb to the USB
+subsystem. This can be seen in the following code::
+
+    /* we can only write as much as 1 urb will hold */
+    bytes_written = (count > skel->bulk_out_size) ? skel->bulk_out_size : count;
+
+    /* copy the data from user space into our urb */
+    copy_from_user(skel->write_urb->transfer_buffer, buffer, bytes_written);
+
+    /* set up our urb */
+    usb_fill_bulk_urb(skel->write_urb,
+		      skel->dev,
+		      usb_sndbulkpipe(skel->dev, skel->bulk_out_endpointAddr),
+		      skel->write_urb->transfer_buffer,
+		      bytes_written,
+		      skel_write_bulk_callback,
+		      skel);
+
+    /* send the data out the bulk port */
+    result = usb_submit_urb(skel->write_urb);
+    if (result) {
+	    err("Failed submitting write urb, error %d", result);
+    }
+
+
+When the write urb is filled up with the proper information using the
+:c:func:`usb_fill_bulk_urb` function, we point the urb's completion callback
+to call our own ``skel_write_bulk_callback`` function. This function is
+called when the urb is finished by the USB subsystem. The callback
+function is called in interrupt context, so caution must be taken not to
+do very much processing at that time. Our implementation of
+``skel_write_bulk_callback`` merely reports if the urb was completed
+successfully or not and then returns.
+
+The read function works a bit differently from the write function in
+that we do not use an urb to transfer data from the device to the
+driver. Instead we call the :c:func:`usb_bulk_msg` function, which can be used
+to send or receive data from a device without having to create urbs and
+handle urb completion callback functions. We call the :c:func:`usb_bulk_msg`
+function, giving it a buffer into which to place any data received from
+the device and a timeout value. If the timeout period expires without
+receiving any data from the device, the function will fail and return an
+error message. This can be shown with the following code::
+
+    /* do an immediate bulk read to get data from the device */
+    retval = usb_bulk_msg (skel->dev,
+			   usb_rcvbulkpipe (skel->dev,
+			   skel->bulk_in_endpointAddr),
+			   skel->bulk_in_buffer,
+			   skel->bulk_in_size,
+			   &count, HZ*10);
+    /* if the read was successful, copy the data to user space */
+    if (!retval) {
+	    if (copy_to_user (buffer, skel->bulk_in_buffer, count))
+		    retval = -EFAULT;
+	    else
+		    retval = count;
+    }
+
+
+The :c:func:`usb_bulk_msg` function can be very useful for doing single reads
+or writes to a device; however, if you need to read or write constantly to
+a device, it is recommended to set up your own urbs and submit them to
+the USB subsystem.
+
+When the user program releases the file handle that it has been using to
+talk to the device, the release function in the driver is called. In
+this function we decrement our private usage count and wait for possible
+pending writes::
+
+    /* decrement our usage count for the device */
+    --skel->open_count;
+
+
+One of the more difficult problems that USB drivers must be able to
+handle smoothly is the fact that the USB device may be removed from the
+system at any point in time, even if a program is currently talking to
+it. It needs to be able to shut down any current reads and writes and
+notify the user-space programs that the device is no longer there. The
+following code (function ``skel_delete``) is an example of how to do
+this::
+
+    static inline void skel_delete (struct usb_skel *dev)
+    {
+	kfree (dev->bulk_in_buffer);
+	if (dev->bulk_out_buffer != NULL)
+	    usb_free_coherent (dev->udev, dev->bulk_out_size,
+		dev->bulk_out_buffer,
+		dev->write_urb->transfer_dma);
+	usb_free_urb (dev->write_urb);
+	kfree (dev);
+    }
+
+
+If a program currently has an open handle to the device, we reset the
+flag ``device_present``. For every read, write, release and other
+functions that expect a device to be present, the driver first checks
+this flag to see if the device is still present. If not, it releases
+that the device has disappeared, and a ``-ENODEV`` error is returned to the
+user-space program. When the release function is eventually called, it
+determines if there is no device and if not, it does the cleanup that
+the ``skel_disconnect`` function normally does if there are no open files
+on the device (see Listing 5).
+
+Isochronous Data
+================
+
+This usb-skeleton driver does not have any examples of interrupt or
+isochronous data being sent to or from the device. Interrupt data is
+sent almost exactly as bulk data is, with a few minor exceptions.
+Isochronous data works differently with continuous streams of data being
+sent to or from the device. The audio and video camera drivers are very
+good examples of drivers that handle isochronous data and will be useful
+if you also need to do this.
+
+Conclusion
+==========
+
+Writing Linux USB device drivers is not a difficult task as the
+usb-skeleton driver shows. This driver, combined with the other current
+USB drivers, should provide enough examples to help a beginning author
+create a working driver in a minimal amount of time. The linux-usb-devel
+mailing list archives also contain a lot of helpful information.
+
+Resources
+=========
+
+The Linux USB Project:
+http://www.linux-usb.org/
+
+Linux Hotplug Project:
+http://linux-hotplug.sourceforge.net/
+
+Linux USB Working Devices List:
+http://www.qbik.ch/usb/devices/
+
+linux-usb-devel Mailing List Archives:
+http://marc.theaimsgroup.com/?l=linux-usb-devel
+
+Programming Guide for Linux USB Device Drivers:
+http://lmu.web.psi.ch/docu/manuals/software_manuals/linux_sl/usb_linux_programming_guide.pdf
+
+USB Home Page: http://www.usb.org

Documentation/driver-api/vme.rst

@@ -0,0 +1,297 @@
+VME Device Drivers
+==================
+
+Driver registration
+-------------------
+
+As with other subsystems within the Linux kernel, VME device drivers register
+with the VME subsystem, typically called from the devices init routine.  This is
+achieved via a call to :c:func:`vme_register_driver`.
+
+A pointer to a structure of type :c:type:`struct vme_driver <vme_driver>` must
+be provided to the registration function. Along with the maximum number of
+devices your driver is able to support.
+
+At the minimum, the '.name', '.match' and '.probe' elements of
+:c:type:`struct vme_driver <vme_driver>` should be correctly set. The '.name'
+element is a pointer to a string holding the device driver's name.
+
+The '.match' function allows control over which VME devices should be registered
+with the driver. The match function should return 1 if a device should be
+probed and 0 otherwise. This example match function (from vme_user.c) limits
+the number of devices probed to one:
+
+.. code-block:: c
+
+	#define USER_BUS_MAX	1
+	...
+	static int vme_user_match(struct vme_dev *vdev)
+	{
+		if (vdev->id.num >= USER_BUS_MAX)
+			return 0;
+		return 1;
+	}
+
+The '.probe' element should contain a pointer to the probe routine. The
+probe routine is passed a :c:type:`struct vme_dev <vme_dev>` pointer as an
+argument.
+
+Here, the 'num' field refers to the sequential device ID for this specific
+driver. The bridge number (or bus number) can be accessed using
+dev->bridge->num.
+
+A function is also provided to unregister the driver from the VME core called
+:c:func:`vme_unregister_driver` and should usually be called from the device
+driver's exit routine.
+
+
+Resource management
+-------------------
+
+Once a driver has registered with the VME core the provided match routine will
+be called the number of times specified during the registration. If a match
+succeeds, a non-zero value should be returned. A zero return value indicates
+failure. For all successful matches, the probe routine of the corresponding
+driver is called. The probe routine is passed a pointer to the devices
+device structure. This pointer should be saved, it will be required for
+requesting VME resources.
+
+The driver can request ownership of one or more master windows
+(:c:func:`vme_master_request`), slave windows (:c:func:`vme_slave_request`)
+and/or dma channels (:c:func:`vme_dma_request`). Rather than allowing the device
+driver to request a specific window or DMA channel (which may be used by a
+different driver) the API allows a resource to be assigned based on the required
+attributes of the driver in question. For slave windows these attributes are
+split into the VME address spaces that need to be accessed in 'aspace' and VME
+bus cycle types required in 'cycle'. Master windows add a further set of
+attributes in 'width' specifying the required data transfer widths. These
+attributes are defined as bitmasks and as such any combination of the
+attributes can be requested for a single window, the core will assign a window
+that meets the requirements, returning a pointer of type vme_resource that
+should be used to identify the allocated resource when it is used. For DMA
+controllers, the request function requires the potential direction of any
+transfers to be provided in the route attributes. This is typically VME-to-MEM
+and/or MEM-to-VME, though some hardware can support VME-to-VME and MEM-to-MEM
+transfers as well as test pattern generation. If an unallocated window fitting
+the requirements can not be found a NULL pointer will be returned.
+
+Functions are also provided to free window allocations once they are no longer
+required. These functions (:c:func:`vme_master_free`, :c:func:`vme_slave_free`
+and :c:func:`vme_dma_free`) should be passed the pointer to the resource
+provided during resource allocation.
+
+
+Master windows
+--------------
+
+Master windows provide access from the local processor[s] out onto the VME bus.
+The number of windows available and the available access modes is dependent on
+the underlying chipset. A window must be configured before it can be used.
+
+
+Master window configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Once a master window has been assigned :c:func:`vme_master_set` can be used to
+configure it and :c:func:`vme_master_get` to retrieve the current settings. The
+address spaces, transfer widths and cycle types are the same as described
+under resource management, however some of the options are mutually exclusive.
+For example, only one address space may be specified.
+
+
+Master window access
+~~~~~~~~~~~~~~~~~~~~
+
+The function :c:func:`vme_master_read` can be used to read from and
+:c:func:`vme_master_write` used to write to configured master windows.
+
+In addition to simple reads and writes, :c:func:`vme_master_rmw` is provided to
+do a read-modify-write transaction. Parts of a VME window can also be mapped
+into user space memory using :c:func:`vme_master_mmap`.
+
+
+Slave windows
+-------------
+
+Slave windows provide devices on the VME bus access into mapped portions of the
+local memory. The number of windows available and the access modes that can be
+used is dependent on the underlying chipset. A window must be configured before
+it can be used.
+
+
+Slave window configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Once a slave window has been assigned :c:func:`vme_slave_set` can be used to
+configure it and :c:func:`vme_slave_get` to retrieve the current settings.
+
+The address spaces, transfer widths and cycle types are the same as described
+under resource management, however some of the options are mutually exclusive.
+For example, only one address space may be specified.
+
+
+Slave window buffer allocation
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Functions are provided to allow the user to allocate
+(:c:func:`vme_alloc_consistent`) and free (:c:func:`vme_free_consistent`)
+contiguous buffers which will be accessible by the VME bridge. These functions
+do not have to be used, other methods can be used to allocate a buffer, though
+care must be taken to ensure that they are contiguous and accessible by the VME
+bridge.
+
+
+Slave window access
+~~~~~~~~~~~~~~~~~~~
+
+Slave windows map local memory onto the VME bus, the standard methods for
+accessing memory should be used.
+
+
+DMA channels
+------------
+
+The VME DMA transfer provides the ability to run link-list DMA transfers. The
+API introduces the concept of DMA lists. Each DMA list is a link-list which can
+be passed to a DMA controller. Multiple lists can be created, extended,
+executed, reused and destroyed.
+
+
+List Management
+~~~~~~~~~~~~~~~
+
+The function :c:func:`vme_new_dma_list` is provided to create and
+:c:func:`vme_dma_list_free` to destroy DMA lists. Execution of a list will not
+automatically destroy the list, thus enabling a list to be reused for repetitive
+tasks.
+
+
+List Population
+~~~~~~~~~~~~~~~
+
+An item can be added to a list using :c:func:`vme_dma_list_add` (the source and
+destination attributes need to be created before calling this function, this is
+covered under "Transfer Attributes").
+
+.. note::
+
+	The detailed attributes of the transfers source and destination
+	are not checked until an entry is added to a DMA list, the request
+	for a DMA channel purely checks the directions in which the
+	controller is expected to transfer data. As a result it is
+	possible for this call to return an error, for example if the
+	source or destination is in an unsupported VME address space.
+
+Transfer Attributes
+~~~~~~~~~~~~~~~~~~~
+
+The attributes for the source and destination are handled separately from adding
+an item to a list. This is due to the diverse attributes required for each type
+of source and destination. There are functions to create attributes for PCI, VME
+and pattern sources and destinations (where appropriate):
+
+ - PCI source or destination: :c:func:`vme_dma_pci_attribute`
+ - VME source or destination: :c:func:`vme_dma_vme_attribute`
+ - Pattern source: :c:func:`vme_dma_pattern_attribute`
+
+The function :c:func:`vme_dma_free_attribute` should be used to free an
+attribute.
+
+
+List Execution
+~~~~~~~~~~~~~~
+
+The function :c:func:`vme_dma_list_exec` queues a list for execution and will
+return once the list has been executed.
+
+
+Interrupts
+----------
+
+The VME API provides functions to attach and detach callbacks to specific VME
+level and status ID combinations and for the generation of VME interrupts with
+specific VME level and status IDs.
+
+
+Attaching Interrupt Handlers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The function :c:func:`vme_irq_request` can be used to attach and
+:c:func:`vme_irq_free` to free a specific VME level and status ID combination.
+Any given combination can only be assigned a single callback function. A void
+pointer parameter is provided, the value of which is passed to the callback
+function, the use of this pointer is user undefined. The callback parameters are
+as follows. Care must be taken in writing a callback function, callback
+functions run in interrupt context:
+
+.. code-block:: c
+
+	void callback(int level, int statid, void *priv);
+
+
+Interrupt Generation
+~~~~~~~~~~~~~~~~~~~~
+
+The function :c:func:`vme_irq_generate` can be used to generate a VME interrupt
+at a given VME level and VME status ID.
+
+
+Location monitors
+-----------------
+
+The VME API provides the following functionality to configure the location
+monitor.
+
+
+Location Monitor Management
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The function :c:func:`vme_lm_request` is provided to request the use of a block
+of location monitors and :c:func:`vme_lm_free` to free them after they are no
+longer required. Each block may provide a number of location monitors,
+monitoring adjacent locations. The function :c:func:`vme_lm_count` can be used
+to determine how many locations are provided.
+
+
+Location Monitor Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Once a bank of location monitors has been allocated, the function
+:c:func:`vme_lm_set` is provided to configure the location and mode of the
+location monitor. The function :c:func:`vme_lm_get` can be used to retrieve
+existing settings.
+
+
+Location Monitor Use
+~~~~~~~~~~~~~~~~~~~~
+
+The function :c:func:`vme_lm_attach` enables a callback to be attached and
+:c:func:`vme_lm_detach` allows on to be detached from each location monitor
+location. Each location monitor can monitor a number of adjacent locations. The
+callback function is declared as follows.
+
+.. code-block:: c
+
+	void callback(void *data);
+
+
+Slot Detection
+--------------
+
+The function :c:func:`vme_slot_num` returns the slot ID of the provided bridge.
+
+
+Bus Detection
+-------------
+
+The function :c:func:`vme_bus_num` returns the bus ID of the provided bridge.
+
+
+VME API
+-------
+
+.. kernel-doc:: include/linux/vme.h
+   :internal:
+
+.. kernel-doc:: drivers/vme/vme.c
+   :export: