Realtek MST
===========

Introduction
------------

This plugin updates the firmware of DisplayPort MST hub devices made by Realtek,
such as the RTD2141b and RTD2142.

These devices communicate over I²C, via the DisplayPort aux channel. Devices
are declared by system firmware, and quirks specify the aux channel to which
the device is connected for a given system.

System firmware must specify the device's presence because while they can be
identified partially through the presence of Realtek's OUI in the Branch
Device OUI fields of DPCD (DisplayPort Configuration Data), they do not have
unique Device Identification strings.

Firmware Format
---------------

The daemon will decompress the cabinet archive and extract a firmware blob in
an unspecified binary file format, which is written to the partition of the
device flash that is not currently running.

This plugin supports the following protocol ID:

 * com.realtek.rtd2142

GUID Generation
---------------

Devices use custom DeviceInstanceId values derived from device names
provided by system firmware and read from sysfs, like:

 * REALTEK-MST\NAME_10EC2142:00
 * REALTEK-MST\NAME_10EC2142:00&FAMILY_Google_Hatch

Quirk use
---------
This plugin uses the following plugin-specific quirks:

| Quirk                  | Description                                 | Minimum fwupd version |
|------------------------|---------------------------------------------|-----------------------|
| `RealtekMstDpAuxName`  | Specifies the name of the drm_dp_aux_dev channel over which the device should be reached. | 1.6.2 |

Vendor ID security
------------------

The vendor ID is specified by system firmware (such as ACPI tables).

External interface access
---

This plugin requires access to i2c buses associated with the specified
DisplayPort aux channel, usually `/dev/i2c-5` or similar.