linux-kernel - Re: [RFC v5 03/11] [media] vb2: add 'ordered_in

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Date:   Fri, 17 Nov 2017 10:15:59 -0200
From:   Mauro Carvalho Chehab <mchehab@....samsung.com>
To:     Gustavo Padovan <gustavo@...ovan.org>
Cc:     linux-media@...r.kernel.org, Hans Verkuil <hverkuil@...all.nl>,
        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>,
        Thierry Escande <thierry.escande@...labora.com>,
        linux-kernel@...r.kernel.org,
        Gustavo Padovan <gustavo.padovan@...labora.com>
Subject: Re: [RFC v5 03/11] [media] vb2: add 'ordered_in_driver' property to
 queues

Em Wed, 15 Nov 2017 15:10:49 -0200
Gustavo Padovan <gustavo@...ovan.org> escreveu:

> From: Gustavo Padovan <gustavo.padovan@...labora.com>
> 
> We use ordered_in_driver property to optimize for the case where
> the driver can deliver the buffers in an ordered fashion. When it
> is ordered we can use the same fence context for all fences, but
> when it is not we need to a new context for each out-fence.
> 
> So the ordered_in_driver flag will help us with identifying the queues
> that can be optimized and use the same fence context.
> 
> v4: make the property a vector for optimization and not a mandatory thing
> that drivers need to set if they want to use explicit synchronization.
> 
> v3: improve doc (Hans Verkuil)
> 
> v2: rename property to 'ordered_in_driver' to avoid confusion
> 
> Signed-off-by: Gustavo Padovan <gustavo.padovan@...labora.com>
> ---
>  include/media/videobuf2-core.h | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index ef9b64398c8c..38b9c8dd42c6 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -440,6 +440,12 @@ struct vb2_buf_ops {
>   * @fileio_read_once:		report EOF after reading the first buffer
>   * @fileio_write_immediately:	queue buffer after each write() call
>   * @allow_zero_bytesused:	allow bytesused == 0 to be passed to the driver
> + * @ordered_in_driver: if the driver can guarantee that the queue will be
> + *		ordered or not, i.e., the buffers are dequeued from the driver
> + *		in the same order they are queued to the driver. The default
> + *		is not ordered unless the driver sets this flag. Setting it
> + *		when ordering can be guaranted helps to optimize explicit
> + *		fences.
>   * @quirk_poll_must_check_waiting_for_buffers: Return POLLERR at poll when QBUF
>   *              has not been called. This is a vb1 idiom that has been adopted
>   *              also by vb2.
> @@ -510,6 +516,7 @@ struct vb2_queue {
>  	unsigned			fileio_read_once:1;
>  	unsigned			fileio_write_immediately:1;
>  	unsigned			allow_zero_bytesused:1;
> +	unsigned			ordered_in_driver:1;

As this may depend on the format, it is probably a good idea to set
this flag either via a function argument or by a function that
would be meant to update it, as video format changes.

>  	unsigned		   quirk_poll_must_check_waiting_for_buffers:1;
>  
>  	struct mutex			*lock;


-- 
Thanks,
Mauro