linux-kernel - Re: [PATCHv4 3/8] videobuf2: split buffer cache

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Date:   Tue, 3 Aug 2021 10:10:19 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Tomasz Figa <tfiga@...omium.org>
Cc:     Dafna Hirschfeld <dafna.hirschfeld@...labora.com>,
        Ricardo Ribalda <ribalda@...omium.org>,
        Christoph Hellwig <hch@....de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 3/8] videobuf2: split buffer cache_hints initialisation

On 27/07/2021 09:05, Sergey Senozhatsky wrote:
> V4L2 is not the perfect place to manage vb2 buffer cache hints.
> It works for V4L2 users, but there are backends that use vb2 core

use -> use the

> and don't use V4L2. Factor buffer cache hints init and call it

Factor? You mean Refactor?

Regards,

	Hans

> when we allocate vb2 buffer.
> 
> Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> ---
>  .../media/common/videobuf2/videobuf2-core.c   | 22 +++++++++++++++++++
>  .../media/common/videobuf2/videobuf2-v4l2.c   | 18 ---------------
>  2 files changed, 22 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index 23e41fec9880..76210c006958 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -382,6 +382,27 @@ static void __setup_offsets(struct vb2_buffer *vb)
>  	}
>  }
>  
> +static void init_buffer_cache_hints(struct vb2_queue *q, struct vb2_buffer *vb)
> +{
> +	/*
> +	 * DMA exporter should take care of cache syncs, so we can avoid
> +	 * explicit ->prepare()/->finish() syncs. For other ->memory types
> +	 * we always need ->prepare() or/and ->finish() cache sync.
> +	 */
> +	if (q->memory == VB2_MEMORY_DMABUF) {
> +		vb->skip_cache_sync_on_finish = 1;
> +		vb->skip_cache_sync_on_prepare = 1;
> +		return;
> +	}
> +
> +	/*
> +	 * ->finish() cache sync can be avoided when queue direction is
> +	 * TO_DEVICE.
> +	 */
> +	if (q->dma_dir == DMA_TO_DEVICE)
> +		vb->skip_cache_sync_on_finish = 1;
> +}
> +
>  /*
>   * __vb2_queue_alloc() - allocate videobuf buffer structures and (for MMAP type)
>   * video buffer memory for all buffers/planes on the queue and initializes the
> @@ -415,6 +436,7 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
>  		vb->index = q->num_buffers + buffer;
>  		vb->type = q->type;
>  		vb->memory = memory;
> +		init_buffer_cache_hints(q, vb);
>  		for (plane = 0; plane < num_planes; ++plane) {
>  			vb->planes[plane].length = plane_sizes[plane];
>  			vb->planes[plane].min_length = plane_sizes[plane];
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index 454d58268602..2fbae9bd7b52 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -345,17 +345,6 @@ static void set_buffer_cache_hints(struct vb2_queue *q,
>  				   struct vb2_buffer *vb,
>  				   struct v4l2_buffer *b)
>  {
> -	/*
> -	 * DMA exporter should take care of cache syncs, so we can avoid
> -	 * explicit ->prepare()/->finish() syncs. For other ->memory types
> -	 * we always need ->prepare() or/and ->finish() cache sync.
> -	 */
> -	if (q->memory == VB2_MEMORY_DMABUF) {
> -		vb->skip_cache_sync_on_finish = 1;
> -		vb->skip_cache_sync_on_prepare = 1;
> -		return;
> -	}
> -
>  	if (!vb2_queue_allows_cache_hints(q)) {
>  		/*
>  		 * Clear buffer cache flags if queue does not support user
> @@ -367,13 +356,6 @@ static void set_buffer_cache_hints(struct vb2_queue *q,
>  		return;
>  	}
>  
> -	/*
> -	 * ->finish() cache sync can be avoided when queue direction is
> -	 * TO_DEVICE.
> -	 */
> -	if (q->dma_dir == DMA_TO_DEVICE)
> -		vb->skip_cache_sync_on_finish = 1;
> -
>  	if (b->flags & V4L2_BUF_FLAG_NO_CACHE_INVALIDATE)
>  		vb->skip_cache_sync_on_finish = 1;
>  
>