Re: [PATCH 01/31] staging: bcm2835-camera: Ensure H264 header bytes get a sensible timestamp

[Dave Stevenson <dave.stevenson@raspberrypi.org>]

Hi Nicolas

On Thu, 27 Jun 2019 at 20:55, Nicolas Dufresne <nicolas@ndufresne.ca> wrote:
>
> Hi Dave,
>
> Le jeudi 27 juin 2019 à 20:55 +0200, Stefan Wahren a écrit :
> > From: Dave Stevenson <dave.stevenson@raspberrypi.org>
> >
> > H264 header come from VC with 0 timestamps, which means they get a
> > strange timestamp when processed with VC/kernel start times,
> > particularly if used with the inline header option.
> > Remember the last frame timestamp and use that if set, or otherwise
> > use the kernel start time.
>
> Normally H264 headers are considered to be part of the following frame.
> Giving it the timestamp of the previous frame will likely confuse some
> userspace and cause an off-by-one in timestamp. I understand this is a
> workaround, but am wondering if this can be improved.

Sorry, slight ambiguity in how I'm reading your comment.

Are you saying that the header bytes want to be in the same buffer as
the following frame?
I thought this had also been discussed in the V4L2 stateful codec API
threads along with how many encoded frames were allowed in a single
V4L2 buffer. I certainly hadn't seen a statement about the header
bytes being combined with the next frame.
If the behaviour required by V4L2 is that header bytes and following
frame are in the same buffer, then that is relatively easy to achieve
in the firmware. This workaround can remain for older firmware as it
will never trigger if the firmware has combined the frames.


Or are you saying that the header bytes remain in their own buffer,
but the timestamp wants to be the same as the next frame? That is
harder to achieve in the firmware, but could probably be done in the
kernel driver by holding on to the header bytes frame until the next
buffer had been received, at which point the timestamp can be copied
across. Possible, but just needs slightly careful handling to ensure
we don't lose buffers accidentally.

  Dave

> >
> > Link: https://github.com/raspberrypi/linux/issues/1836
> > Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>
> > ---
> >  .../staging/vc04_services/bcm2835-camera/bcm2835-camera.c  | 14 ++++++++++++--
> >  .../staging/vc04_services/bcm2835-camera/bcm2835-camera.h  |  2 ++
> >  2 files changed, 14 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c b/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c
> > index dce6e6d..0c04815 100644
> > --- a/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c
> > +++ b/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c
> > @@ -359,7 +359,9 @@ static void buffer_cb(struct vchiq_mmal_instance *instance,
> >               }
> >       } else {
> >               if (dev->capture.frame_count) {
> > -                     if (dev->capture.vc_start_timestamp != -1 && pts) {
> > +                     if (dev->capture.vc_start_timestamp != -1) {
> > +                             buf->vb.vb2_buf.timestamp = ktime_get_ns();
> > +                     } else if (pts) {
> >                               ktime_t timestamp;
> >                               s64 runtime_us = pts -
> >                                   dev->capture.vc_start_timestamp;
> > @@ -372,8 +374,15 @@ static void buffer_cb(struct vchiq_mmal_instance *instance,
> >                                        ktime_to_ns(timestamp));
> >                               buf->vb.vb2_buf.timestamp = ktime_to_ns(timestamp);
> >                       } else {
> > -                             buf->vb.vb2_buf.timestamp = ktime_get_ns();
> > +                             if (dev->capture.last_timestamp) {
> > +                                     buf->vb.vb2_buf.timestamp =
> > +                                             dev->capture.last_timestamp;
> > +                             } else {
> > +                                     buf->vb.vb2_buf.timestamp =
> > +                                             ktime_to_ns(dev->capture.kernel_start_ts);
> > +                             }
> >                       }
> > +                     dev->capture.last_timestamp = buf->vb.vb2_buf.timestamp;
> >
> >                       vb2_set_plane_payload(&buf->vb.vb2_buf, 0, length);
> >                       vb2_buffer_done(&buf->vb.vb2_buf, VB2_BUF_STATE_DONE);
> > @@ -541,6 +550,7 @@ static int start_streaming(struct vb2_queue *vq, unsigned int count)
> >                        dev->capture.vc_start_timestamp, parameter_size);
> >
> >       dev->capture.kernel_start_ts = ktime_get();
> > +     dev->capture.last_timestamp = 0;
> >
> >       /* enable the camera port */
> >       dev->capture.port->cb_ctx = dev;
> > diff --git a/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.h b/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.h
> > index 2b5679e..09273b0 100644
> > --- a/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.h
> > +++ b/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.h
> > @@ -90,6 +90,8 @@ struct bm2835_mmal_dev {
> >               s64         vc_start_timestamp;
> >               /* Kernel start timestamp for streaming */
> >               ktime_t kernel_start_ts;
> > +             /* Timestamp of last frame */
> > +             u64             last_timestamp;
> >
> >               struct vchiq_mmal_port  *port; /* port being used for capture */
> >               /* camera port being used for capture */
> > --
> > 2.7.4
> >