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media: Documentation: aspeed-video: Add user documentation for the aspeed-video driver
Add user documentation for the aspeed-video driver.
Signed-off-by: Jammy Huang <jammy_huang@aspeedtech.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
authored by
Jammy Huang
and committed by
Hans Verkuil
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Documentation/userspace-api/media/drivers/aspeed-video.rst
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Documentation/userspace-api/media/drivers/aspeed-video.rst
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.. SPDX-License-Identifier: GPL-2.0
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.. include:: <isonum.txt>
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ASPEED video driver
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===================
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ASPEED Video Engine found on AST2400/2500/2600 SoC supports high performance
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video compressions with a wide range of video quality and compression ratio
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options. The adopted compressing algorithm is a modified JPEG algorithm.
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There are 2 types of compressions in this IP.
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* JPEG JFIF standard mode: for single frame and management compression
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* ASPEED proprietary mode: for multi-frame and differential compression.
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Support 2-pass (high quality) video compression scheme (Patent pending by
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ASPEED). Provide visually lossless video compression quality or to reduce
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the network average loading under intranet KVM applications.
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VIDIOC_S_FMT can be used to choose which format you want. V4L2_PIX_FMT_JPEG
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stands for JPEG JFIF standard mode; V4L2_PIX_FMT_AJPG stands for ASPEED
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proprietary mode.
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More details on the ASPEED video hardware operations can be found in
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*chapter 6.2.16 KVM Video Driver* of SDK_User_Guide which available on
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AspeedTech-BMC/openbmc/releases.
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The ASPEED video driver implements the following driver-specific control:
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``V4L2_CID_ASPEED_HQ_MODE``
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---------------------------
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Enable/Disable ASPEED's High quality mode. This is a private control
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that can be used to enable high quality for aspeed proprietary mode.
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.. flat-table::
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 4
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* - ``(0)``
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- ASPEED HQ mode is disabled.
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* - ``(1)``
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- ASPEED HQ mode is enabled.
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``V4L2_CID_ASPEED_HQ_JPEG_QUALITY``
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-----------------------------------
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Define the quality of ASPEED's High quality mode. This is a private control
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that can be used to decide compression quality if High quality mode enabled
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. Higher the value, better the quality and bigger the size.
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.. flat-table::
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 4
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* - ``(1)``
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- minimum
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* - ``(12)``
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- maximum
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* - ``(1)``
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- step
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* - ``(1)``
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- default
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**Copyright** |copy| 2022 ASPEED Technology Inc.