linux-kernel - Re: [PATCH v9 05/15] vb2: add unordered vb2

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Message-ID: <4e3fa169-00f9-daef-134f-3bdcbc53bd8e@xs4all.nl>
Date:   Mon, 7 May 2018 13:03:17 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Ezequiel Garcia <ezequiel@...labora.com>,
        linux-media@...r.kernel.org
Cc:     kernel@...labora.com,
        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: [PATCH v9 05/15] vb2: add unordered vb2_queue property for
 drivers

On 04/05/18 22:06, Ezequiel Garcia wrote:
> From: Gustavo Padovan <gustavo.padovan@...labora.com>
> 
> Explicit synchronization benefits a lot from ordered queues, they fit
> better in a pipeline with DRM for example so create a opt-in way for
> drivers notify videobuf2 that the queue is unordered.
> 
> v5: go back to a bitfield property for the unordered property.

This needs to be a callback. Whether or not the queue is unordered depends
on the current format (see the next two patches). So if a queue can e.g.
capture both raw/MJPEG and compressed (MPEG-like) data, then it has to call
a callback.

Regards,

	Hans

> 
> v4: rename it to vb2_ops_is_unordered() (Hans Verkuil)
> 
> v3: - make it bool (Hans)
>     - create vb2_ops_set_unordered() helper
> 
> v2: improve comments for is_unordered flag (Hans Verkuil)
> 
> Signed-off-by: Gustavo Padovan <gustavo.padovan@...labora.com>
> Signed-off-by: Ezequiel Garcia <ezequiel@...labora.com>
> ---
>  include/media/videobuf2-core.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index f9633de0386c..364e4cb41b10 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -467,6 +467,8 @@ struct vb2_buf_ops {
>   * @quirk_poll_must_check_waiting_for_buffers: Return %EPOLLERR at poll when QBUF
>   *              has not been called. This is a vb1 idiom that has been adopted
>   *              also by vb2.
> + * @unordered:	tell if the queue is unordered, i.e. buffers can be
> + *		dequeued in a different order from how they were queued.
>   * @lock:	pointer to a mutex that protects the &struct vb2_queue. The
>   *		driver can set this to a mutex to let the v4l2 core serialize
>   *		the queuing ioctls. If the driver wants to handle locking
> @@ -533,6 +535,7 @@ struct vb2_queue {
>  	unsigned			fileio_read_once:1;
>  	unsigned			fileio_write_immediately:1;
>  	unsigned			allow_zero_bytesused:1;
> +	unsigned			unordered:1;
>  	unsigned		   quirk_poll_must_check_waiting_for_buffers:1;
>  
>  	struct mutex			*lock;
>