
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 th                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 