Re: [PATCH v3 10/15] [media] vb2: add 'ordered' property to queues

[Brian Starkey]

Hi,

On Thu, Sep 07, 2017 at 03:42:21PM -0300, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxx>
>
> For explicit synchronization (and soon for HAL3/Request API) we need
> the v4l2-driver to guarantee the ordering in which the buffers were queued
> by userspace. This is already true for many drivers, but we never needed
> to say it.
>
> Signed-off-by: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxx>
> ---
> include/media/videobuf2-core.h | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 5ed8d3402474..20099dc22f26 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -508,6 +508,9 @@ struct vb2_buf_ops {
>  * @last_buffer_dequeued: used in poll() and DQBUF to immediately return if the
>  *		last decoded buffer was already dequeued. Set for capture queues
>  *		when a buffer with the V4L2_BUF_FLAG_LAST is dequeued.
> + * @ordered: if the driver can guarantee that the queue will be ordered or not.
> + *		The default is not ordered unless the driver sets this flag. It
> + *		is mandatory for using explicit fences.

If it's mandatory for fences (why is that?), then I guess this patch
should come before any of the fence implementation?

But it's not entirely clear to me what this flag means - ordered with
respect to what? Ordered such that the order in which the buffers are
queued in the driver are the same order that they will be dequeued by
userspace?

I think the order they are queued from userspace can still be
different from both the order they are queued in the driver (because
the in-fences can signal in any order), and dequeued again in
userspace, so "ordered" seems a bit ambiguous.

I think it should be more clear.

Cheers
-Brian

>  * @fileio:	file io emulator internal data, used only if emulator is active
>  * @threadio:	thread io internal data, used only if thread is active
>  */
> @@ -560,6 +563,7 @@ struct vb2_queue {
> 	unsigned int			is_output:1;
> 	unsigned int			copy_timestamp:1;
> 	unsigned int			last_buffer_dequeued:1;
> +	unsigned int			ordered:1;
>
> 	struct vb2_fileio_data		*fileio;
> 	struct vb2_threadio_data	*threadio;
> --
> 2.13.5