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SubjectRe: [RFC v5 10/11] [media] vb2: add out-fence support to QBUF
2017-11-17 Alexandre Courbot <acourbot@chromium.org>:

> On Thursday, November 16, 2017 2:10:56 AM JST, Gustavo Padovan wrote:
> > From: Gustavo Padovan <gustavo.padovan@collabora.com>
> >
> > If V4L2_BUF_FLAG_OUT_FENCE flag is present on the QBUF call we create
> > an out_fence and send its fd to userspace on the fence_fd field as a
> > return arg for the QBUF call.
> >
> > The fence is signaled on buffer_done(), when the job on the buffer is
> > finished.
> >
> > With out-fences we do not allow drivers to requeue buffers through vb2,
> > instead we flag an error on the buffer, signals it fence with error and
>
> s/it/its
>
> > return it to userspace.
> >
> > v6
> > - get rid of the V4L2_EVENT_OUT_FENCE event. We always keep the
> > ordering in vb2 for queueing in the driver, so the event is not
> > necessary anymore and the out_fence_fd is sent back to userspace
> > on QBUF call return arg
> > - do not allow requeueing with out-fences, instead mark the buffer
> > with an error and wake up to userspace.
> > - send the out_fence_fd back to userspace on the fence_fd field
> >
> > v5:
> > - delay fd_install to DQ_EVENT (Hans)
> > - if queue is fully ordered send OUT_FENCE event right away
> > (Brian)
> > - rename 'q->ordered' to 'q->ordered_in_driver'
> > - merge change to implement OUT_FENCE event here
> >
> > v4:
> > - return the out_fence_fd in the BUF_QUEUED event(Hans)
> >
> > v3: - add WARN_ON_ONCE(q->ordered) on requeueing (Hans)
> > - set the OUT_FENCE flag if there is a fence pending (Hans)
> > - call fd_install() after vb2_core_qbuf() (Hans)
> > - clean up fence if vb2_core_qbuf() fails (Hans)
> > - add list to store sync_file and fence for the next queued buffer
> >
> > v2: check if the queue is ordered.
> >
> > Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
> > ---
> > drivers/media/v4l2-core/videobuf2-core.c | 42
> > +++++++++++++++++++++++++++++---
> > drivers/media/v4l2-core/videobuf2-v4l2.c | 21 +++++++++++++++-
> > 2 files changed, 58 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/media/v4l2-core/videobuf2-core.c
> > b/drivers/media/v4l2-core/videobuf2-core.c
> > index 8b4f0e9bcb36..2eb5ffa8e028 100644
> > --- a/drivers/media/v4l2-core/videobuf2-core.c
> > +++ b/drivers/media/v4l2-core/videobuf2-core.c
> > @@ -354,6 +354,7 @@ static int __vb2_queue_alloc(struct vb2_queue *q,
> > enum vb2_memory memory,
> > vb->planes[plane].length = plane_sizes[plane];
> > vb->planes[plane].min_length = plane_sizes[plane];
> > }
> > + vb->out_fence_fd = -1;
> > q->bufs[vb->index] = vb;
> > /* Allocate video buffer memory for the MMAP type */
> > @@ -934,10 +935,26 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum
> > vb2_buffer_state state)
> > case VB2_BUF_STATE_QUEUED:
> > return;
> > case VB2_BUF_STATE_REQUEUEING:
> > - if (q->start_streaming_called)
> > - __enqueue_in_driver(vb);
> > - return;
> > +
> > + if (!vb->out_fence) {
> > + if (q->start_streaming_called)
> > + __enqueue_in_driver(vb);
> > + return;
> > + }
> > +
> > + /* Do not allow requeuing with explicit synchronization,
> > + * report it as an error to userspace */
> > + state = VB2_BUF_STATE_ERROR;
> > +
> > + /* fall through */
> > default:
> > + if (state == VB2_BUF_STATE_ERROR)
> > + dma_fence_set_error(vb->out_fence, -EFAULT);
> > + dma_fence_signal(vb->out_fence);
> > + dma_fence_put(vb->out_fence);
> > + vb->out_fence = NULL;
> > + vb->out_fence_fd = -1;
> > +
> > /* Inform any processes that may be waiting for buffers */
> > wake_up(&q->done_wq);
> > break;
> > @@ -1325,12 +1342,18 @@ EXPORT_SYMBOL_GPL(vb2_core_prepare_buf);
> > int vb2_setup_out_fence(struct vb2_queue *q, unsigned int index)
> > {
> > struct vb2_buffer *vb;
> > + u64 context;
> > vb = q->bufs[index];
> > vb->out_fence_fd = get_unused_fd_flags(O_CLOEXEC);
> > - vb->out_fence = vb2_fence_alloc(q->out_fence_context);
> > + if (q->ordered_in_driver)
> > + context = q->out_fence_context;
> > + else
> > + context = dma_fence_context_alloc(1);
> > +
> > + vb->out_fence = vb2_fence_alloc(context);
> > if (!vb->out_fence) {
> > put_unused_fd(vb->out_fence_fd);
> > return -ENOMEM;
> > @@ -1594,6 +1617,9 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned
> > int index, void *pb,
> > if (pb)
> > call_void_bufop(q, fill_user_buffer, vb, pb);
> > + fd_install(vb->out_fence_fd, vb->sync_file->file);
>
> What happens if the buffer does not have an output fence? Shouldn't this be
> protected by a check on whether the buffer has been queued with
> V4L2_BUF_FLAG_OUT_FENCE?

Ouch, I think we would have a nice crash. We should protect it, yes.


Gustavo

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