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

[Paul Menzel <pmenzel@molgen.mpg.de>]

Dear Jammy,


Am 19.11.21 um 03:02 schrieb Jammy Huang:

> On 2021/11/18 下午 08:33, Sakari Ailus wrote:

>> 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@aspeedtech.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

If questions come up during review, please also add the answers to the 
commit message of the next iteration. ;-) Maybe:

> The implementation is based on datasheet *Name goes here*, revision
> X, which is not publicly available.

Kind regards,

Paul