Re: [PATCHv4 10/11] videobuf2: add begin/end cpu_access callbacks to dma-sg

From: Hans Verkuil <hverkuil@xs4all.nl>
To: Sergey Senozhatsky <senozhatsky@chromium.org>,
	Hans Verkuil <hans.verkuil@cisco.com>,
	Tomasz Figa <tfiga@chromium.org>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>,
	Kyungmin Park <kyungmin.park@samsung.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Sakari Ailus <sakari.ailus@iki.fi>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Pawel Osciak <posciak@chromium.org>,
	linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCHv4 10/11] videobuf2: add begin/end cpu_access callbacks to dma-sg
Date: Fri, 6 Mar 2020 15:04:05 +0100	[thread overview]
Message-ID: <f99cd8d2-26a2-acd1-a986-aee66cd2ba12@xs4all.nl> (raw)
In-Reply-To: <20200302041213.27662-11-senozhatsky@chromium.org>

On 02/03/2020 05:12, Sergey Senozhatsky wrote:
> Provide begin_cpu_access() and end_cpu_access() dma_buf_ops
> callbacks for cache synchronisation on exported buffers.
> 
> V4L2_FLAG_MEMORY_NON_CONSISTENT has no effect on dma-sg buffers.
> dma-sg allocates memory using the page allocator directly, so
> there is no memory consistency guarantee.
> 
> Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> ---
>  .../media/common/videobuf2/videobuf2-dma-sg.c | 28 +++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/drivers/media/common/videobuf2/videobuf2-dma-sg.c b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
> index 6db60e9d5183..ddc67c9aaedb 100644
> --- a/drivers/media/common/videobuf2/videobuf2-dma-sg.c
> +++ b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
> @@ -120,6 +120,12 @@ static void *vb2_dma_sg_alloc(struct device *dev, unsigned long dma_attrs,
>  	buf->num_pages = size >> PAGE_SHIFT;
>  	buf->dma_sgt = &buf->sg_table;
>  
> +	/*
> +	 * NOTE: dma-sg allocates memory using the page allocator directly, so
> +	 * there is no memory consistency guarantee, hence dma-sg ignores DMA
> +	 * attributes passed from the upper layer. That means that
> +	 * V4L2_FLAG_MEMORY_NON_CONSISTENT has no effect on dma-sg buffers.
> +	 */
>  	buf->pages = kvmalloc_array(buf->num_pages, sizeof(struct page *),
>  				    GFP_KERNEL | __GFP_ZERO);
>  	if (!buf->pages)
> @@ -470,6 +476,26 @@ static void vb2_dma_sg_dmabuf_ops_release(struct dma_buf *dbuf)
>  	vb2_dma_sg_put(dbuf->priv);
>  }
>  
> +static int vb2_dma_sg_dmabuf_ops_begin_cpu_access(struct dma_buf *dbuf,
> +					enum dma_data_direction direction)

I suggest you use this style to avoid checkpatch warnings:

static int
vb2_dma_sg_dmabuf_ops_begin_cpu_access(struct dma_buf *dbuf,
				       enum dma_data_direction direction)

> +{
> +	struct vb2_dma_sg_buf *buf = dbuf->priv;
> +	struct sg_table *sgt = buf->dma_sgt;
> +
> +	dma_sync_sg_for_cpu(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
> +	return 0;
> +}
> +
> +static int vb2_dma_sg_dmabuf_ops_end_cpu_access(struct dma_buf *dbuf,
> +					enum dma_data_direction direction)

Ditto.

Regards,

	Hans

> +{
> +	struct vb2_dma_sg_buf *buf = dbuf->priv;
> +	struct sg_table *sgt = buf->dma_sgt;
> +
> +	dma_sync_sg_for_device(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
> +	return 0;
> +}
> +
>  static void *vb2_dma_sg_dmabuf_ops_vmap(struct dma_buf *dbuf)
>  {
>  	struct vb2_dma_sg_buf *buf = dbuf->priv;
> @@ -488,6 +514,8 @@ static const struct dma_buf_ops vb2_dma_sg_dmabuf_ops = {
>  	.detach = vb2_dma_sg_dmabuf_ops_detach,
>  	.map_dma_buf = vb2_dma_sg_dmabuf_ops_map,
>  	.unmap_dma_buf = vb2_dma_sg_dmabuf_ops_unmap,
> +	.begin_cpu_access = vb2_dma_sg_dmabuf_ops_begin_cpu_access,
> +	.end_cpu_access = vb2_dma_sg_dmabuf_ops_end_cpu_access,
>  	.vmap = vb2_dma_sg_dmabuf_ops_vmap,
>  	.mmap = vb2_dma_sg_dmabuf_ops_mmap,
>  	.release = vb2_dma_sg_dmabuf_ops_release,
> 