ASPEED video driver

ASPEED Video Engine found on AST2400/2500/2600 SoC supports high performance video compressions with a wide range of video quality and compression ratio options. The adopted compressing algorithm is a modified JPEG algorithm.

There are 2 types of compressions in this IP.

JPEG JFIF standard mode: for single frame and management compression
ASPEED proprietary mode: for multi-frame and differential compression. Support 2-pass (high quality) video compression scheme (Patent pending by ASPEED). Provide visually lossless video compression quality or to reduce the network average loading under intranet KVM applications.

VIDIOC_S_FMT can be used to choose which format you want. V4L2_PIX_FMT_JPEG stands for JPEG JFIF standard mode; V4L2_PIX_FMT_AJPG stands for ASPEED proprietary mode.

More details on the ASPEED video hardware operations can be found in chapter 6.2.16 KVM Video Driver of SDK_User_Guide which available on github <https://github.com/AspeedTech-BMC/openbmc/releases/>__.

The ASPEED video driver implements the following driver-specific control:

`V4L2_CID_ASPEED_HQ_MODE`

Enable/Disable ASPEED's High quality mode. This is a private control
that can be used to enable high quality for aspeed proprietary mode.

.. flat-table:: :header-rows: 0 :stub-columns: 0 :widths: 1 4

* - ``(0)``
  - ASPEED HQ mode is disabled.
* - ``(1)``
  - ASPEED HQ mode is enabled.

`V4L2_CID_ASPEED_HQ_JPEG_QUALITY`

Define the quality of ASPEED's High quality mode. This is a private control
that can be used to decide compression quality if High quality mode enabled
. Higher the value, better the quality and bigger the size.

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* - ``(1)``
  - minimum
* - ``(12)``
  - maximum
* - ``(1)``
  - step
* - ``(1)``
  - default