Re: [PATCH v4 4/4] media: videobuf2-core: attach once if multiple planes share the same dbuf

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On 14/06/2024 09:37, Yunke Cao wrote:
> When multiple planes use the same dma buf, each plane will have its own dma
> buf attachment and mapping. It is a waste of IOVA space.
> 
> This patch adds a dbuf_duplicated boolean in vb2_plane. If a plane's dbuf
> is the same as an existing plane, do not create another attachment and
> mapping.

I'm getting two documentation warnings:

include/media/videobuf2-core.h:194: warning: Function parameter or struct member 'dbuf_duplicated' not described in 'vb2_plane'
include/media/videobuf2-core.h:194: warning: Excess struct member 'duplicated_dbuf' description in 'vb2_plane'
2 warnings as Errors

Clearly a typo.

So please post a v5 to fix this issue as well.

Regards,

	Hans

> 
> Signed-off-by: Yunke Cao <yunkec@xxxxxxxxxxxx>
> ---
> v4
> - Only set dbuf_duplicated when alloc_devs are equal.
> 
> v3
> - Adjust the patch according to the previous patches to resolve conflicts.
> - Add comment to explain the purpose of the change.
> 
> v2
> - Separate out the refactor changes out to previous patches.
> - Fix mem_priv check.
> ---
>  .../media/common/videobuf2/videobuf2-core.c   | 30 ++++++++++++++++---
>  include/media/videobuf2-core.h                |  3 ++
>  2 files changed, 29 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index cbc8928f0418..c19f1df3a4d2 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -304,10 +304,13 @@ static void __vb2_plane_dmabuf_put(struct vb2_buffer *vb, struct vb2_plane *p)
>  	if (!p->mem_priv)
>  		return;
>  
> -	if (p->dbuf_mapped)
> -		call_void_memop(vb, unmap_dmabuf, p->mem_priv);
> +	if (!p->dbuf_duplicated) {
> +		if (p->dbuf_mapped)
> +			call_void_memop(vb, unmap_dmabuf, p->mem_priv);
> +
> +		call_void_memop(vb, detach_dmabuf, p->mem_priv);
> +	}
>  
> -	call_void_memop(vb, detach_dmabuf, p->mem_priv);
>  	dma_buf_put(p->dbuf);
>  	p->mem_priv = NULL;
>  	p->dbuf = NULL;
> @@ -316,6 +319,7 @@ static void __vb2_plane_dmabuf_put(struct vb2_buffer *vb, struct vb2_plane *p)
>  	p->length = 0;
>  	p->m.fd = 0;
>  	p->data_offset = 0;
> +	p->dbuf_duplicated = false;
>  }
>  
>  /*
> @@ -1374,7 +1378,7 @@ static int __prepare_dmabuf(struct vb2_buffer *vb)
>  	struct vb2_plane planes[VB2_MAX_PLANES];
>  	struct vb2_queue *q = vb->vb2_queue;
>  	void *mem_priv;
> -	unsigned int plane;
> +	unsigned int plane, i;
>  	int ret = 0;
>  	bool reacquired = vb->planes[0].mem_priv == NULL;
>  
> @@ -1427,6 +1431,24 @@ static int __prepare_dmabuf(struct vb2_buffer *vb)
>  		}
>  
>  		for (plane = 0; plane < vb->num_planes; ++plane) {
> +			/*
> +			 * This is an optimization to reduce dma_buf attachment/mapping.
> +			 * When the same dma_buf is used for multiple planes, there is no need
> +			 * to create duplicated attachments.
> +			 */
> +			for (i = 0; i < plane; ++i) {
> +				if (planes[plane].dbuf == vb->planes[i].dbuf &&
> +				    q->alloc_devs[plane] == q->alloc_devs[i]) {
> +					vb->planes[plane].dbuf_duplicated = true;
> +					vb->planes[plane].dbuf = vb->planes[i].dbuf;
> +					vb->planes[plane].mem_priv = vb->planes[i].mem_priv;
> +					break;
> +				}
> +			}
> +
> +			if (vb->planes[plane].dbuf_duplicated)
> +				continue;
> +
>  			/* Acquire each plane's memory */
>  			mem_priv = call_ptr_memop(attach_dmabuf,
>  						  vb,
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 955237ac503d..053ced60595f 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -154,6 +154,8 @@ struct vb2_mem_ops {
>   * @mem_priv:	private data with this plane.
>   * @dbuf:	dma_buf - shared buffer object.
>   * @dbuf_mapped:	flag to show whether dbuf is mapped or not
> + * @duplicated_dbuf:	boolean to show whether dbuf is duplicated with a
> + *		previous plane of the buffer.
>   * @bytesused:	number of bytes occupied by data in the plane (payload).
>   * @length:	size of this plane (NOT the payload) in bytes. The maximum
>   *		valid size is MAX_UINT - PAGE_SIZE.
> @@ -179,6 +181,7 @@ struct vb2_plane {
>  	void			*mem_priv;
>  	struct dma_buf		*dbuf;
>  	unsigned int		dbuf_mapped;
> +	bool			dbuf_duplicated;
>  	unsigned int		bytesused;
>  	unsigned int		length;
>  	unsigned int		min_length;





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