Re: [PATCH v2] media/doc: Allow sizeimage to be set by v4l clients
From: Hans Verkuil
Date: Thu May 16 2019 - 06:42:50 EST
On 5/16/19 11:56 AM, Tomasz Figa wrote:
> On Thu, May 16, 2019 at 5:09 PM Stanimir Varbanov
> <stanimir.varbanov@xxxxxxxxxx> wrote:
>> Hi Hans,
>> On 5/14/19 11:54 AM, Hans Verkuil wrote:
>>> Hi Stanimir,
>>> On 4/12/19 5:59 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.
>>> I've been reconsidering this change. The sizeimage value in the format
>>> is the minimum size a buffer should have in order to store the data of
>>> an image of the width and height as described in the format.
>>> But there is nothing that prevents userspace from calling VIDIOC_CREATEBUFS
>>> instead of VIDIOC_REQBUFS to allocate larger buffers.
>> Sometimes CREATEBUFS cannot be implemented for a particular fw/hw.
>> CC: Tomasz for his opinion.
> Thanks Stanimir.
> Actually, if called at the same point in time as REQBUFS, CREATE_BUFS
> doesn't really differ to much, except that it gives more flexibility
> for allocating the buffers and that shouldn't depend on any specific
> features of hardware or firmware.
> Actually, one could even allocate any buffers any time regardless of
> hardware/firmware support, but the ability to use such buffers would
> actually depend on such.
> Perhaps we should just let the drivers return -EBUSY from CREATE_BUFS
> if called at the wrong time?
>>> So do we really need this change?
> Yes, because this has worked like this all the time, but it was just
> not documented. Disallowing this would break quite a bit of existing
Which drivers allow this today? I think that would be useful information
for the commit log of a v4 of this patch.
> Best regards,
>>> The more I think about this, the more uncomfortable I become with this change.