Re: [PATCH 03/12] [media] vb2: add in-fence support to QBUF

[Gustavo Padovan <gustavo@padovan.org>]

2017-07-06 Hans Verkuil <hverkuil@xs4all.nl>:

> On 07/03/17 20:16, Gustavo Padovan wrote:
> >>> @@ -1436,6 +1481,11 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
> >>>  	if (pb)
> >>>  		call_void_bufop(q, fill_user_buffer, vb, pb);
> >>>  
> >>> +	vb->in_fence = fence;
> >>> +	if (fence && !dma_fence_add_callback(fence, &vb->fence_cb,
> >>> +					     vb2_qbuf_fence_cb))
> >>> +		return 0;
> >>
> >> Maybe we should provide some error or debug log here or a WARN_ON(), if 
> >> dma_fence_add_callback() fails instead of silently ignore any errors.
> > 
> > This is not an error. If the if succeeds it mean we have installed a
> > callback for the fence. If not, it means the fence signaled already and
> > we don't can call __vb2_core_qbuf right away.
> 
> I had the same question as Mauro. After looking at the dma_fence_add_callback
> code I see what you mean, but a comment would certainly be helpful.

Sure, I'll add a comment explaining it.

> 
> Also, should you set vb->in_fence to NULL if the fence signaled already?
> I'm not sure if you need to call 'dma_fence_put(vb->in_fence);' as well.
> You would know that better than I do.

You got it right. I should be doing that.

Gustavo