usb: move ReST documentation to Documentation/driver-api/usb/

This is where all other USB ReST documentation has moved to.

Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

3 files changed, 286 insertions, 0 deletions

diff --git a/Documentation/driver-api/usb/index.rst b/Documentation/driver-api/usb/index.rst
index 3d357a83046b..8fe995a1ec94 100644
--- a/Documentation/driver-api/usb/index.rst
+++ b/Documentation/driver-api/usb/index.rst
@@ -18,6 +18,8 @@ Linux USB API
    writing_usb_driver
    dwc3
    writing_musb_glue_layer
+   typec
+   usb3-debug-port
 
 .. only::  subproject and html
 
diff --git a/Documentation/driver-api/usb/typec.rst b/Documentation/driver-api/usb/typec.rst
new file mode 100644
index 000000000000..b67a46779de9
--- /dev/null
+++ b/Documentation/driver-api/usb/typec.rst
@@ -0,0 +1,184 @@
+
+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/typec.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/typec.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/typec.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/typec.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/typec.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/typec.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/typec.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/typec.c
+   :functions: typec_partner_register_altmode
+
+API for the Cable Plugs:
+
+.. kernel-doc:: drivers/usb/typec/typec.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/typec.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/typec.c
+   :functions: typec_altmode_update_active
diff --git a/Documentation/driver-api/usb/usb3-debug-port.rst b/Documentation/driver-api/usb/usb3-debug-port.rst
new file mode 100644
index 000000000000..feb1a36a65b7
--- /dev/null
+++ b/Documentation/driver-api/usb/usb3-debug-port.rst
@@ -0,0 +1,100 @@
+===============
+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 ===============