linux-kernel - Re: [PATCH 1/3] v4l: Add Qualcomm custom compressed pixel formats

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Date:   Mon, 17 May 2021 18:13:03 +0300
From:   Stanimir Varbanov <stanimir.varbanov@...aro.org>
To:     Nicolas Dufresne <nicolas@...fresne.ca>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-api@...r.kernel.org
Cc:     Hans Verkuil <hverkuil-cisco@...all.nl>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Subject: Re: [PATCH 1/3] v4l: Add Qualcomm custom compressed pixel formats



On 4/29/21 10:10 PM, Nicolas Dufresne wrote:
> Le jeudi 29 avril 2021 à 13:58 +0300, Stanimir Varbanov a écrit :
>> Here we add custom Qualcomm raw compressed pixel formats. They are
>> used in Qualcomm SoCs to optimaize the interconnect bandwidth.
> 
> Wasn't reviewing, just skimming the lists, but s/optimaize/optimize/
> 
>>
>> Signed-off-by: Stanimir Varbanov <stanimir.varbanov@...aro.org>
>> ---
>>  .../userspace-api/media/v4l/pixfmt-reserved.rst      | 12 ++++++++++++
>>  drivers/media/v4l2-core/v4l2-ioctl.c                 |  2 ++
>>  include/uapi/linux/videodev2.h                       |  2 ++
>>  3 files changed, 16 insertions(+)
>>
>> diff --git a/Documentation/userspace-api/media/v4l/pixfmt-reserved.rst b/Documentation/userspace-api/media/v4l/pixfmt-reserved.rst
>> index 0b879c0da713..30b9cef4cbf0 100644
>> --- a/Documentation/userspace-api/media/v4l/pixfmt-reserved.rst
>> +++ b/Documentation/userspace-api/media/v4l/pixfmt-reserved.rst
>> @@ -260,6 +260,18 @@ 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-QC8C:
>> +
>> +      - ``V4L2_PIX_FMT_QC8C``
>> +      - 'QC8C'
>> +      - Compressed Macro-tile 8Bit YUV420 format used by Qualcomm platforms.
>> +	The compression is lossless. It contains four planes.
> 
> Would be nice to document if the bytesperline is meaningful or not. Basically,
> what information need to be carried to other drivers ?

I don't think that bytesperline has some valuable information, the
important thing is the size of the memory buffer and it should be used
to negotiate between v4l2 and drm for example. The layout of the buffer
can be seen at [1].

[1]
https://android.googlesource.com/kernel/msm/+/android-msm-bullhead-3.10-marshmallow-dr/include/media/msm_media_info.h

-- 
regards,
Stan