linux-kernel - Re: [RFC][PATCH 02/15] videobuf2: handle V4L2 buffer cache flags

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Date:   Fri, 10 Jan 2020 11:24:26 +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][PATCH 02/15] videobuf2: handle V4L2 buffer cache flags

On 12/17/19 4:20 AM, Sergey Senozhatsky wrote:
> Set video buffer cache management flags corresponding to V4L2 cache
> flags.
> 
> Both ->prepare() and ->finish() cache management hints should be
> passed during this stage (buffer preparation), because there is no
> other way for user-space to skip ->finish() cache flush.
> 
> There are two possible alternative approaches:
> - The first one is to move cache sync from ->finish() to dqbuf().
>   But this breaks some drivers, that need to fix-up buffers before
>   dequeueing them.
> 
> - The second one is to move ->finish() call from ->done() to dqbuf.

Please combine this patch with patch 13/15!

> 
> Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> ---
>  .../media/common/videobuf2/videobuf2-v4l2.c   | 22 +++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index e652f4318284..2fccfe2a57f8 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -337,6 +337,27 @@ static int vb2_fill_vb2_v4l2_buffer(struct vb2_buffer *vb, struct v4l2_buffer *b
>  	return 0;
>  }
>  
> +static void set_buffer_cache_hints(struct vb2_queue *q,
> +				   struct vb2_buffer *vb,
> +				   struct v4l2_buffer *b)
> +{
> +	vb->need_cache_sync_on_prepare = 1;
> +
> +	if (q->dma_dir != DMA_TO_DEVICE)

What should be done when dma_dir == DMA_BIDIRECTIONAL?

> +		vb->need_cache_sync_on_finish = 1;
> +	else
> +		vb->need_cache_sync_on_finish = 0;
> +
> +	if (!q->allow_cache_hints)
> +		return;
> +
> +	if (b->flags & V4L2_BUF_FLAG_NO_CACHE_INVALIDATE)
> +		vb->need_cache_sync_on_finish = 0;
> +
> +	if (b->flags & V4L2_BUF_FLAG_NO_CACHE_CLEAN)
> +		vb->need_cache_sync_on_prepare = 0;
> +}
> +
>  static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct media_device *mdev,
>  				    struct v4l2_buffer *b, bool is_prepare,
>  				    struct media_request **p_req)
> @@ -381,6 +402,7 @@ static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct media_device *md
>  	}
>  
>  	if (!vb->prepared) {
> +		set_buffer_cache_hints(q, vb, b);
>  		/* Copy relevant information provided by the userspace */
>  		memset(vbuf->planes, 0,
>  		       sizeof(vbuf->planes[0]) * vb->num_planes);
> 

Regards,

	Hans