linux-kernel - Re: [RFC PATCH] media/doc: Allow sizeimage to be set by v4l clients

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Message-ID: <adecdc4e-1aed-fc33-b14b-083322797c70@linaro.org>
Date:   Mon, 21 Jan 2019 12:48:26 +0200
From:   Stanimir Varbanov <stanimir.varbanov@...aro.org>
To:     Hans Verkuil <hverkuil@...all.nl>, linux-media@...r.kernel.org
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Vikash Garodia <vgarodia@...eaurora.org>,
        Tomasz Figa <tfiga@...omium.org>,
        Alexandre Courbot <acourbot@...omium.org>,
        Malathi Gottam <mgottam@...eaurora.org>
Subject: Re: [RFC PATCH] media/doc: Allow sizeimage to be set by v4l clients

Hi Hans,

On 1/18/19 11:13 AM, Hans Verkuil wrote:
> On 1/16/19 1:37 PM, Stanimir Varbanov wrote:
>> This changes v4l2_pix_format and v4l2_plane_pix_format sizeimage
>> field description to allow v4l clients to set bigger image size
>> in case of variable length compressed data.
>>
>> Signed-off-by: Stanimir Varbanov <stanimir.varbanov@...aro.org>
>> ---
>>  Documentation/media/uapi/v4l/pixfmt-v4l2-mplane.rst | 5 ++++-
>>  Documentation/media/uapi/v4l/pixfmt-v4l2.rst        | 3 ++-
>>  2 files changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/media/uapi/v4l/pixfmt-v4l2-mplane.rst b/Documentation/media/uapi/v4l/pixfmt-v4l2-mplane.rst
>> index 7f82dad9013a..dbe0b74e9ba4 100644
>> --- a/Documentation/media/uapi/v4l/pixfmt-v4l2-mplane.rst
>> +++ b/Documentation/media/uapi/v4l/pixfmt-v4l2-mplane.rst
>> @@ -30,7 +30,10 @@ describing all planes of that format.
>>  
>>      * - __u32
>>        - ``sizeimage``
>> -      - Maximum size in bytes required for image data in this plane.
>> +      - Maximum size in bytes required for image data in this plane,
>> +        set by the driver. When the image consists of variable length
>> +        compressed data this is the maximum number of bytes required
>> +        to hold an image, and it is allowed to be set by the client.
>>      * - __u32
>>        - ``bytesperline``
>>        - Distance in bytes between the leftmost pixels in two adjacent
>> diff --git a/Documentation/media/uapi/v4l/pixfmt-v4l2.rst b/Documentation/media/uapi/v4l/pixfmt-v4l2.rst
>> index 71eebfc6d853..54b6d2b67bd7 100644
>> --- a/Documentation/media/uapi/v4l/pixfmt-v4l2.rst
>> +++ b/Documentation/media/uapi/v4l/pixfmt-v4l2.rst
>> @@ -89,7 +89,8 @@ Single-planar format structure
>>        - Size in bytes of the buffer to hold a complete image, set by the
>>  	driver. Usually this is ``bytesperline`` times ``height``. When
>>  	the image consists of variable length compressed data this is the
>> -	maximum number of bytes required to hold an image.
>> +	maximum number of bytes required to hold an image, and it is
>> +	allowed to be set by the client.
>>      * - __u32
>>        - ``colorspace``
>>        - Image colorspace, from enum :c:type:`v4l2_colorspace`.
>>
> 
> Hmm. "maximum number of bytes required to hold an image": that's not actually true
> for bitstream formats like MPEG. It's just the size of the buffer used to store the
> bitstream, i.e. one buffer may actually contain multiple compressed images, or a
> compressed image is split over multiple buffers.
> 

Do you want me to change something in the current documentation, i.e.
the quoted above?

> Only for MJPEG is this statement true since each buffer will contain a single
> compressed JPEG image.
> 
> Regards,
> 
> 	Hans
> 

-- 
regards,
Stan