Re: [PATCH v3 1/1] vb2: Only requeue buffers immediately once streaming is started

[Hans Verkuil <hverkuil@xs4all.nl>]

On 07/03/2015 04:50 PM, Sakari Ailus wrote:
> Buffers can be returned back to videobuf2 in driver's streamon handler. In
> this case vb2_buffer_done() with buffer state VB2_BUF_STATE_QUEUED will
> cause the driver's buf_queue vb2 operation to be called, queueing the same
> buffer again only to be returned to videobuf2 using vb2_buffer_done() and so
> on.
> 
> Add a new buffer state VB2_BUF_STATE_REQUEUEING which, when used as the
> state argument to vb2_buffer_done(), will result in buffers queued to the
> driver. Using VB2_BUF_STATE_QUEUED will leave the buffer to videobuf2, as it
> was before "[media] vb2: allow requeuing buffers while streaming".
> 
> Fixes: ce0eff016f72 ("[media] vb2: allow requeuing buffers while streaming")
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> Cc: stable@vger.kernel.org # for v4.1
> ---
> since v2:
> 
> - Replace the if's at the end of v4l2_buffer_done() by a pretty-looking
>   switch.
> 
>  drivers/media/pci/cobalt/cobalt-irq.c    |  2 +-
>  drivers/media/v4l2-core/videobuf2-core.c | 24 ++++++++++++++++--------
>  include/media/videobuf2-core.h           |  2 ++
>  3 files changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/media/pci/cobalt/cobalt-irq.c b/drivers/media/pci/cobalt/cobalt-irq.c
> index e18f49e..2687cb0 100644
> --- a/drivers/media/pci/cobalt/cobalt-irq.c
> +++ b/drivers/media/pci/cobalt/cobalt-irq.c
> @@ -134,7 +134,7 @@ done:
>  	   also know about dropped frames. */
>  	cb->vb.v4l2_buf.sequence = s->sequence++;
>  	vb2_buffer_done(&cb->vb, (skip || s->unstable_frame) ?
> -			VB2_BUF_STATE_QUEUED : VB2_BUF_STATE_DONE);
> +			VB2_BUF_STATE_REQUEUEING : VB2_BUF_STATE_DONE);
>  }
>  
>  irqreturn_t cobalt_irq_handler(int irq, void *dev_id)
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
> index 1a096a6..bbd22ff 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -1182,7 +1182,8 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
>  
>  	if (WARN_ON(state != VB2_BUF_STATE_DONE &&
>  		    state != VB2_BUF_STATE_ERROR &&
> -		    state != VB2_BUF_STATE_QUEUED))
> +		    state != VB2_BUF_STATE_QUEUED &&
> +		    state != VB2_BUF_STATE_REQUEUEING))
>  		state = VB2_BUF_STATE_ERROR;
>  
>  #ifdef CONFIG_VIDEO_ADV_DEBUG
> @@ -1199,22 +1200,29 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
>  	for (plane = 0; plane < vb->num_planes; ++plane)
>  		call_void_memop(vb, finish, vb->planes[plane].mem_priv);
>  
> -	/* Add the buffer to the done buffers list */
>  	spin_lock_irqsave(&q->done_lock, flags);
> -	vb->state = state;
> -	if (state != VB2_BUF_STATE_QUEUED)
> +	if (state == VB2_BUF_STATE_QUEUED ||
> +	    state == VB2_BUF_STATE_REQUEUEING) {
> +		vb->state = VB2_BUF_STATE_QUEUED;
> +	} else {
> +		/* Add the buffer to the done buffers list */
>  		list_add_tail(&vb->done_entry, &q->done_list);
> +		vb->state = state;
> +	}
>  	atomic_dec(&q->owned_by_drv_count);
>  	spin_unlock_irqrestore(&q->done_lock, flags);
>  
> -	if (state == VB2_BUF_STATE_QUEUED) {
> +	switch (state) {
> +	case VB2_BUF_STATE_QUEUED:
> +		return;
> +	case VB2_BUF_STATE_REQUEUEING:
>  		if (q->start_streaming_called)
>  			__enqueue_in_driver(vb);
>  		return;
> +	default:
> +		/* Inform any processes that may be waiting for buffers */
> +		wake_up(&q->done_wq);

Either add a break here, or keep the wake_up where it was and just have a:

	default:
		break;

Switch cases that do not end with return or break are always bad practice since it
is all too easy to add a new case in the future and miss that there was no
break in the case before, thus creating an unwanted fall-through.

With that change:

Acked-by: Hans Verkuil <hans.verkuil@cisco.com>

Regards,

	Hans

>  	}
> -
> -	/* Inform any processes that may be waiting for buffers */
> -	wake_up(&q->done_wq);
>  }
>  EXPORT_SYMBOL_GPL(vb2_buffer_done);
>  
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 22a44c2..c192e1b 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -139,6 +139,7 @@ enum vb2_io_modes {
>   * @VB2_BUF_STATE_PREPARING:	buffer is being prepared in videobuf
>   * @VB2_BUF_STATE_PREPARED:	buffer prepared in videobuf and by the driver
>   * @VB2_BUF_STATE_QUEUED:	buffer queued in videobuf, but not in driver
> + * @VB2_BUF_STATE_REQUEUEING:	re-queue a buffer to the driver
>   * @VB2_BUF_STATE_ACTIVE:	buffer queued in driver and possibly used
>   *				in a hardware operation
>   * @VB2_BUF_STATE_DONE:		buffer returned from driver to videobuf, but
> @@ -152,6 +153,7 @@ enum vb2_buffer_state {
>  	VB2_BUF_STATE_PREPARING,
>  	VB2_BUF_STATE_PREPARED,
>  	VB2_BUF_STATE_QUEUED,
> +	VB2_BUF_STATE_REQUEUEING,
>  	VB2_BUF_STATE_ACTIVE,
>  	VB2_BUF_STATE_DONE,
>  	VB2_BUF_STATE_ERROR,
>