linux-kernel - Re: [PATCH v5 05/10] media: v4l: Add definition for the Aspeed JPEG format

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Date:   Fri, 19 Nov 2021 10:02:40 +0800
From:   Jammy Huang <jammy_huang@...eedtech.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
CC:     "eajames@...ux.ibm.com" <eajames@...ux.ibm.com>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "joel@....id.au" <joel@....id.au>,
        "andrew@...id.au" <andrew@...id.au>,
        "hverkuil-cisco@...all.nl" <hverkuil-cisco@...all.nl>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "laurent.pinchart@...asonboard.com" 
        <laurent.pinchart@...asonboard.com>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "openbmc@...ts.ozlabs.org" <openbmc@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 05/10] media: v4l: Add definition for the Aspeed JPEG
 format

Hi Sakari,

On 2021/11/18 下午 08:33, Sakari Ailus wrote:
> Hi Jammy,
>
> On Thu, Nov 18, 2021 at 03:40:26PM +0800, Jammy Huang wrote:
>> This introduces support for the Aspeed JPEG format, where the new frame
>> can refer to previous frame to reduce the amount of compressed data. The
>> concept is similar to I/P frame of video compression. I will compare the
>> new frame with previous one to decide which macroblock's data is
>> changed, and only the changed macroblocks will be compressed.
>>
>> This Aspeed JPEG format is used by the video engine on Aspeed platforms,
>> which is generally adapted for remote KVM.
>>
>> Signed-off-by: Jammy Huang <jammy_huang@...eedtech.com>
>> ---
>> v5:
>>    - no update
>> v4:
>>    - new
>> ---
>>   Documentation/media/uapi/v4l/pixfmt-reserved.rst | 12 ++++++++++++
>>   drivers/media/v4l2-core/v4l2-ioctl.c             |  1 +
>>   include/uapi/linux/videodev2.h                   |  1 +
>>   3 files changed, 14 insertions(+)
>>
>> diff --git a/Documentation/media/uapi/v4l/pixfmt-reserved.rst b/Documentation/media/uapi/v4l/pixfmt-reserved.rst
>> index b2cd155e691b..23c05063133d 100644
>> --- a/Documentation/media/uapi/v4l/pixfmt-reserved.rst
>> +++ b/Documentation/media/uapi/v4l/pixfmt-reserved.rst
>> @@ -264,6 +264,18 @@ please make a proposal on the linux-media mailing list.
>>   	of tiles, resulting in 32-aligned resolutions for the luminance plane
>>   	and 16-aligned resolutions for the chrominance plane (with 2x2
>>   	subsampling).
>> +    * .. _V4L2-PIX-FMT-AJPG:
>> +
>> +      - ``V4L2_PIX_FMT_AJPG``
>> +      - 'AJPG'
>> +      - ASPEED JPEG format used by the aspeed-video driver on Aspeed platforms,
>> +        which is generally adapted for remote KVM.
>> +        On each frame compression, I will compare the new frame with previous
>> +        one to decide which macroblock's data is changed, and only the changed
>> +        macroblocks will be compressed.
>> +
>> +        You could reference to chapter 36, Video Engine, of AST2600's datasheet
>> +        for more information.
> Is this datasheet publicly available? Do you have a URL?

Sorry, this datasheet is not publicly available.
Hans mentioned this as well in the discussion below:

https://lkml.org/lkml/2021/11/10/101

-- 
Best Regards
Jammy