From b0b3ddf8fb37283d0d488d667fac4c069d612ba3 Mon Sep 17 00:00:00 2001 From: Felipe Balbi Date: Tue, 9 May 2017 16:30:24 +0300 Subject: 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 --- Documentation/driver-api/usb/index.rst | 2 + Documentation/driver-api/usb/typec.rst | 184 +++++++++++++++++++++++ Documentation/driver-api/usb/usb3-debug-port.rst | 100 ++++++++++++ 3 files changed, 286 insertions(+) create mode 100644 Documentation/driver-api/usb/typec.rst create mode 100644 Documentation/driver-api/usb/usb3-debug-port.rst (limited to 'Documentation/driver-api/usb') 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", for example /sys/class/typec/port0//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 +: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 =============== -- cgit v1.2.3