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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
commit | 2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch) | |
tree | 848558de17fb3008cdf4d861b01ac7781903ce39 /Documentation/driver-api/usb/typec_bus.rst | |
parent | Initial commit. (diff) | |
download | linux-upstream.tar.xz linux-upstream.zip |
Adding upstream version 6.1.76.upstream/6.1.76upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | Documentation/driver-api/usb/typec_bus.rst | 122 |
1 files changed, 122 insertions, 0 deletions
diff --git a/Documentation/driver-api/usb/typec_bus.rst b/Documentation/driver-api/usb/typec_bus.rst new file mode 100644 index 000000000..21c890ae1 --- /dev/null +++ b/Documentation/driver-api/usb/typec_bus.rst @@ -0,0 +1,122 @@ + +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. + +:ref:`USB Type-C Connector Class <typec>` 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_vdm()`. + +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. + +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); + +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 structs +~~~~~~~~~~~~~~~~~~~~~~ + +.. kernel-doc:: include/linux/usb/typec_altmode.h + :functions: typec_altmode_driver typec_altmode_ops + +Alternate mode driver registering/unregistering +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +.. kernel-doc:: include/linux/usb/typec_altmode.h + :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 |