linux-kernel - Re: [RFC][PATCHv2 01/12] videobuf2: add cache management members

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Message-ID: <964aeb73-1474-032f-b2a6-b317cc15f7cb@xs4all.nl>
Date:   Wed, 19 Feb 2020 09:05:35 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Sakari Ailus <sakari.ailus@....fi>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Pawel Osciak <posciak@...omium.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCHv2 01/12] videobuf2: add cache management members

On 2/4/20 3:56 AM, Sergey Senozhatsky wrote:
> Extend vb2_buffer and vb2_queue structs with cache management
> members.
> 
> V4L2 UAPI already contains two buffer flags which user-space,
> supposedly, can use to control buffer cache sync:
> 
> - V4L2_BUF_FLAG_NO_CACHE_INVALIDATE
> - V4L2_BUF_FLAG_NO_CACHE_CLEAN
> 
> None of these, however, do anything at the moment. This patch
> set is intended to change it.
> 
> Since user-space cache management hints are supposed to be
> implemented on a per-buffer basis we need to extend vb2_buffer
> struct with two new memebers ->need_cache_sync_on_prepare and
> ->need_cache_sync_on_finish, which will store corresponding
> user-space hints.
> 
> In order to preserve the existing behaviour, user-space cache
> managements flags will be handled only by those drivers that
> permit user-space cache hints. That's the purpose of vb2_queue
> ->allow_cache_hints member. Driver must set ->allow_cache_hints
> during queue initialisation to enable cache management hints
> mechanism.
> 
> Only drivers that set ->allow_cache_hints during queue initialisation
> will handle user-space cache management hints. Otherwise hints
> will be ignored.
> 
> Change-Id: I52beec2a0d021b7a3715b4f6ae4bfd9dc5e94f0d
> Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> ---
>  include/media/videobuf2-core.h | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index a2b2208b02da..026004180440 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -263,6 +263,10 @@ struct vb2_buffer {
>  	 *			after the 'buf_finish' op is called.
>  	 * copied_timestamp:	the timestamp of this capture buffer was copied
>  	 *			from an output buffer.
> +	 * need_cache_sync_on_prepare: do not sync/invalidate cache from
> +	 * 			buffer's ->prepare() callback.
> +	 * need_cache_sync_on_finish: do not sync/invalidate cache from buffer's
> +	 * 			->finish() callback.

Shouldn't 'do not' be deleted from the flag descriptions? If the flag is set,
then you need to sync/validate, right?

Regards,

	Hans

>  	 * queued_entry:	entry on the queued buffers list, which holds
>  	 *			all buffers queued from userspace
>  	 * done_entry:		entry on the list that stores all buffers ready
> @@ -273,6 +277,8 @@ struct vb2_buffer {
>  	unsigned int		synced:1;
>  	unsigned int		prepared:1;
>  	unsigned int		copied_timestamp:1;
> +	unsigned int		need_cache_sync_on_prepare:1;
> +	unsigned int		need_cache_sync_on_finish:1;
>  
>  	struct vb2_plane	planes[VB2_MAX_PLANES];
>  	struct list_head	queued_entry;
> @@ -491,6 +497,9 @@ struct vb2_buf_ops {
>   * @uses_requests: requests are used for this queue. Set to 1 the first time
>   *		a request is queued. Set to 0 when the queue is canceled.
>   *		If this is 1, then you cannot queue buffers directly.
> + * @allow_cache_hints: when set user-space can pass cache management hints in
> + * 		order to skip cache flush/invalidation on ->prepare() or/and
> + * 		->finish().
>   * @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
> @@ -564,6 +573,7 @@ struct vb2_queue {
>  	unsigned			requires_requests:1;
>  	unsigned			uses_qbuf:1;
>  	unsigned			uses_requests:1;
> +	unsigned			allow_cache_hints:1;
>  
>  	struct mutex			*lock;
>  	void				*owner;
>