On 21/04/2022 12:24, Philipp Zabel wrote: > 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? Yes for venus and s5p, but why would imx-jpeg use this? It makes no sense for a jpeg codec. I think it should just be removed for imx-jpeg. IMHO, once a decoder supports the STOP command, it should no longer set allow_zero_bytesused to true. But that decision is up to you for the coda driver. Regards, Hans > >> 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