Le mercredi 11 mars 2020 à 14:42 -0300, Ezequiel Garcia a écrit : > When the request API is used, typically an OUTPUT (src) buffer > will be part of a request. A userspace process will be typically > blocked, waiting on the request file descriptor. > > Returning the OUTPUT (src) buffer will wake-up such processes, > who will immediately attempt to dequeue the CAPTURE buffer, > only to find it's still unavailable. > > Therefore, change v4l2_m2m_buf_done_and_job_finish returning > the CAPTURE (dst) buffer first, to avoid signalling the request > file descriptor prematurely, i.e. before the CAPTURE buffer is done. > > When the request API is not used, this change should have > no impact. > > Signed-off-by: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx> This was tested with upcoming GStreamer element with O_NONBLOCK flag passed when opening the video node. Before this change, EAGAIN would from time to time be returned when DQBUF(CAPTURE) was called. gst-launch-1.0 filesrc location=somefile.mp4 ! parsebin ! v4l2slh264dec ! fakevideosink https://gitlab.freedesktop.org/ndufresne/gst-plugins-bad/-/blob/v4l2codecs-hantro-v3/sys/v4l2codecs/gstv4l2decoder.c#L139 Tested-by: Nicolas Dufresne <nicolas.dufresne@xxxxxxxxxxxxx> > --- > drivers/media/v4l2-core/v4l2-mem2mem.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2- > core/v4l2-mem2mem.c > index 8986c31176e9..62ac9424c92a 100644 > --- a/drivers/media/v4l2-core/v4l2-mem2mem.c > +++ b/drivers/media/v4l2-core/v4l2-mem2mem.c > @@ -504,12 +504,21 @@ void v4l2_m2m_buf_done_and_job_finish(struct > v4l2_m2m_dev *m2m_dev, > > if (WARN_ON(!src_buf || !dst_buf)) > goto unlock; > - v4l2_m2m_buf_done(src_buf, state); > dst_buf->is_held = src_buf->flags & V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF; > if (!dst_buf->is_held) { > v4l2_m2m_dst_buf_remove(m2m_ctx); > v4l2_m2m_buf_done(dst_buf, state); > } > + /* > + * If the request API is being used, returning the OUTPUT > + * (src) buffer will wake-up any process waiting on the > + * request file descriptor. > + * > + * Therefore, return the CAPTURE (dst) buffer first, > + * to avoid signalling the request file descriptor > + * before the CAPTURE buffer is done. > + */ > + v4l2_m2m_buf_done(src_buf, state); > schedule_next = _v4l2_m2m_job_finish(m2m_dev, m2m_ctx); > unlock: > spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags);
