On 07/20/2016 08:22 PM, Javier Martinez Canillas wrote:
> Currently the dma-buf is unmapped when the buffer is dequeued by userspace
> but it's not used anymore after the driver finished processing the buffer.
>
> So instead of doing the dma-buf unmapping in __vb2_dqbuf(), it can be made
> in vb2_buffer_done() after the driver notified that buf processing is done.
>
> Decoupling the buffer dequeue from the dma-buf unmapping has also the side
> effect of making possible to add dma-buf fence support in the future since
> the buffer could be dequeued even before the driver has finished using it.
>
> Signed-off-by: Javier Martinez Canillas <javier@xxxxxxxxxxxxxxx>
>
> ---
> Hello,
>
> I've tested this patch doing DMA buffer sharing between a
> vivid input and output device with both v4l2-ctl and gst:
>
> $ v4l2-ctl -d0 -e1 --stream-dmabuf --stream-out-mmap
> $ v4l2-ctl -d0 -e1 --stream-mmap --stream-out-dmabuf
> $ gst-launch-1.0 v4l2src device=/dev/video0 io-mode=dmabuf ! v4l2sink device=/dev/video1 io-mode=dmabuf-import
>
> And I didn't find any issues but more testing will be appreciated.
>
> Best regards,
> Javier
>
> drivers/media/v4l2-core/videobuf2-core.c | 34 +++++++++++++++++++++-----------
> 1 file changed, 22 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
> index 7128b09810be..973331efaf79 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -958,6 +958,22 @@ void *vb2_plane_cookie(struct vb2_buffer *vb, unsigned int plane_no)
> EXPORT_SYMBOL_GPL(vb2_plane_cookie);
>
> /**
> + * __vb2_unmap_dmabuf() - unmap dma-buf attached to buffer planes
> + */
> +static void __vb2_unmap_dmabuf(struct vb2_buffer *vb)
> +{
> + int i;
> +
> + for (i = 0; i < vb->num_planes; ++i) {
> + if (!vb->planes[i].dbuf_mapped)
> + continue;
> + call_void_memop(vb, unmap_dmabuf,
> + vb->planes[i].mem_priv);
Does unmap_dmabuf work in interrupt context? Since vb2_buffer_done can be called from
an irq handler this is a concern.
That said, vb2_buffer_done already calls call_void_memop(vb, finish, vb->planes[plane].mem_priv);
to sync buffers, and that can take a long time as well. So it is not a good idea to
have this in vb2_buffer_done.
What I would like to see is to have vb2 handle this finish() call and the vb2_unmap_dmabuf
in some workthread or equivalent.
It would complicate matters somewhat in vb2, but it would simplify drivers since these
actions would not longer take place in interrupt context.
I think this patch makes sense, but I would prefer that this is moved out of the interrupt
context.
Regards,
Hans
> + vb->planes[i].dbuf_mapped = 0;
> + }
> +}
> +
> +/**
> * vb2_buffer_done() - inform videobuf that an operation on a buffer is finished
> * @vb: vb2_buffer returned from the driver
> * @state: either VB2_BUF_STATE_DONE if the operation finished successfully,
> @@ -1028,6 +1044,9 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
> __enqueue_in_driver(vb);
> return;
> default:
> + if (q->memory == VB2_MEMORY_DMABUF)
> + __vb2_unmap_dmabuf(vb);
> +
> /* Inform any processes that may be waiting for buffers */
> wake_up(&q->done_wq);
> break;
> @@ -1708,23 +1727,11 @@ EXPORT_SYMBOL_GPL(vb2_wait_for_all_buffers);
> */
> static void __vb2_dqbuf(struct vb2_buffer *vb)
> {
> - struct vb2_queue *q = vb->vb2_queue;
> - unsigned int i;
> -
> /* nothing to do if the buffer is already dequeued */
> if (vb->state == VB2_BUF_STATE_DEQUEUED)
> return;
>
> vb->state = VB2_BUF_STATE_DEQUEUED;
> -
> - /* unmap DMABUF buffer */
> - if (q->memory == VB2_MEMORY_DMABUF)
> - for (i = 0; i < vb->num_planes; ++i) {
> - if (!vb->planes[i].dbuf_mapped)
> - continue;
> - call_void_memop(vb, unmap_dmabuf, vb->planes[i].mem_priv);
> - vb->planes[i].dbuf_mapped = 0;
> - }
> }
>
> /**
> @@ -1861,6 +1868,9 @@ static void __vb2_queue_cancel(struct vb2_queue *q)
> call_void_vb_qop(vb, buf_finish, vb);
> }
> __vb2_dqbuf(vb);
> +
> + if (q->memory == VB2_MEMORY_DMABUF)
> + __vb2_unmap_dmabuf(vb);
> }
> }
>
>
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