Hi Hans, On 5/16/19 1:40 PM, Hans Verkuil wrote: > 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 >> userspace. > > Which drivers allow this today? I think that would be useful information > for the commit log of a v4 of this patch. > I'd say s5p-mfc and mtk-vcodec at least. -- regards, Stan
