linux-kernel - Re: [RFC v4 08/17] [media] vb2: add 'ordered_in

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Date:   Tue, 24 Oct 2017 15:11:05 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Gustavo Padovan <gustavo@...ovan.org>, linux-media@...r.kernel.org
Cc:     Mauro Carvalho Chehab <mchehab@....samsung.com>,
        Shuah Khan <shuahkh@....samsung.com>,
        Pawel Osciak <pawel@...iak.com>,
        Alexandre Courbot <acourbot@...omium.org>,
        Sakari Ailus <sakari.ailus@....fi>,
        Brian Starkey <brian.starkey@....com>,
        linux-kernel@...r.kernel.org,
        Gustavo Padovan <gustavo.padovan@...labora.com>
Subject: Re: [RFC v4 08/17] [media] vb2: add 'ordered_in_driver' property to
 queues

On 10/20/2017 11:50 PM, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@...labora.com>
> 
> 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.
> 
> v2: rename property to 'ordered_in_driver' to avoid confusion
> 
> Signed-off-by: Gustavo Padovan <gustavo.padovan@...labora.com>
> ---
>  include/media/videobuf2-core.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 96af4eb49e52..6dd3f0181107 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -500,6 +500,11 @@ 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_in_driver: if the driver can guarantee that the queue will be
> + *		ordered or not, i.e., the buffers are queued to the driver in
> + *		the same order they are dequeued from the driver. The default

I'd swap the words 'queued' and 'dequeued'. It's more logical that way.

Regards,

	Hans

> + *		is not ordered unless the driver sets this flag. As of now it
> + *		is mandatory for using explicit fences.
>   * @fileio:	file io emulator internal data, used only if emulator is active
>   * @threadio:	thread io internal data, used only if thread is active
>   */
> @@ -552,6 +557,7 @@ struct vb2_queue {
>  	unsigned int			is_output:1;
>  	unsigned int			copy_timestamp:1;
>  	unsigned int			last_buffer_dequeued:1;
> +	unsigned int			ordered_in_driver:1;
>  
>  	struct vb2_fileio_data		*fileio;
>  	struct vb2_threadio_data	*threadio;
>