2017-07-06 Hans Verkuil <[email protected]>:
> On 06/16/17 09:39, Gustavo Padovan wrote:
> > From: Gustavo Padovan <[email protected]>
> >
> > If V4L2_BUF_FLAG_OUT_FENCE flag is present on the QBUF call we create
> > an out_fence for the buffer and return it to userspace on the fence_fd
> > field. It only works with ordered queues.
> >
> > The fence is signaled on buffer_done(), when the job on the buffer is
> > finished.
> >
> > v2: check if the queue is ordered.
> >
> > Signed-off-by: Gustavo Padovan <[email protected]>
> > ---
> > drivers/media/v4l2-core/videobuf2-core.c | 6 ++++++
> > drivers/media/v4l2-core/videobuf2-v4l2.c | 22 +++++++++++++++++++++-
> > 2 files changed, 27 insertions(+), 1 deletion(-)
> >
>
> <snip>
>
> > diff --git a/drivers/media/v4l2-core/videobuf2-v4l2.c
> > b/drivers/media/v4l2-core/videobuf2-v4l2.c
> > index e6ad77f..e2733dd 100644
> > --- a/drivers/media/v4l2-core/videobuf2-v4l2.c
> > +++ b/drivers/media/v4l2-core/videobuf2-v4l2.c
> > @@ -204,9 +204,14 @@ static void __fill_v4l2_buffer(struct vb2_buffer *vb,
> > void *pb)
> > b->timestamp = ns_to_timeval(vb->timestamp);
> > b->timecode = vbuf->timecode;
> > b->sequence = vbuf->sequence;
> > - b->fence_fd = -1;
> > + b->fence_fd = vb->out_fence_fd;
>
> I forgot to ask: can a buffer have both an in and an out fence? If so, then we
> have a problem here since we can report only one fence fd.
>
> If it is not allowed, then we need a check for that somewhere.
It is perfect fine to have both, I just wasn't expecting to get them out
from the kernel at the same time. In-fence is set by userspace in the
fence_fd field and then sent to the kernel, the field is then reused to
send the out-fence created in the kernel to userspace. That is how GPU
drivers do it.
Gustavo
