Hi Hans,
On Do, 2022-04-21 at 11:44 +0200, Hans Verkuil wrote:
> On 04/04/2022 18:35, Philipp Zabel wrote:
> > The V4L2 specification states:
> >
> > "If the application sets this to 0 for an output stream, then bytesused
> > will be set to the size of the buffer (see the length field of this
> > struct) by the driver."
> >
> > Since we set allow_zero_bytesused, we have to handle this ourselves.
> >
> > Signed-off-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>
> > ---
> > drivers/media/platform/chips-media/coda-bit.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/media/platform/chips-media/coda-bit.c b/drivers/media/platform/chips-media/coda-bit.c
> > index c484c008ab02..705a179ea8f0 100644
> > --- a/drivers/media/platform/chips-media/coda-bit.c
> > +++ b/drivers/media/platform/chips-media/coda-bit.c
> > @@ -381,6 +381,9 @@ void coda_fill_bitstream(struct coda_ctx *ctx, struct list_head *buffer_list)
> > /* Dump empty buffers */
> > if (!vb2_get_plane_payload(&src_buf->vb2_buf, 0)) {
> > src_buf = v4l2_m2m_src_buf_remove(ctx->fh.m2m_ctx);
> > + vb2_set_plane_payload(&src_buf->vb2_buf, 0,
> > + vb2_plane_size(&src_buf->vb2_buf,
> > + 0));
>
> Would it be possible to stop using allow_zero_bytesused altogether?
>
> Are there still applications that rely on zero-sized output buffers to stop the
> decoder?
This was used by GStreamer 1.8. The code is still left in current
versions, but is never executed unless the decoder stop command fails:
https://gitlab.freedesktop.org/gstreamer/gstreamer/-/blob/main/subprojects/gst-plugins-good/sys/v4l2/gstv4l2videodec.c#L446-454
Whether there are still any applications using GStreamer 1.8 for V4L2
video decoding on devices that get kernel updates, I don't know.
> I'm not actually sure that I want this in the driver, perhaps v4l2-compliance
> can be modified to turn a fail into a warn if the driver is the coda driver.
Same for nxp/imx-jpeg, qcom/venus and samsung/s5p-mfc?
> Patching the driver is hiding the fact that the coda driver does something
> non-standard for legacy reasons. It doesn't make sense either to change
> bytesused to the buffer size since there really is nothing in the buffer.
>
> v4l2-compliance already has checks for two drivers, search for is_vivid and
> is_uvcvideo.
Ok.
> I'm skipping this patch for now.
regards
Philipp
