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

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Message-ID: <b6a231ea-c039-d276-313d-1b6dd19cab14@linaro.org>
Date:   Wed, 10 Apr 2019 17:21:20 +0300
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 3/14/19 3:11 PM, Hans Verkuil wrote:
> On 1/21/19 11:48 AM, Stanimir Varbanov wrote:
>> 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?
> 
> Hmm, it looks like this discussion stalled (i.e. I forgot to reply).
> 
> How about this:
> 
> "When the image consists of variable length compressed data this is the
> number of bytes required by the encoder to support the worst-case

I don't think 'encoder' is the right word here:

s/encoder/encoder or decoder

> compression scenario. Clients are allowed to set this field. However,
> drivers may ignore the value or modify it."

Can we rephrase to:

"Clients are allowed to set sizeimage field, but however drivers my
ignore the value or modify it."

-- 
regards,
Stan