
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     |
                     ------------------------      ------------------------
