Re: [RFCv2 PATCH 3/9] v4l: vb2: Add dma-contig allocator as dma_buf user

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Tomasz,

On Tuesday 13 March 2012 11:17:01 Tomasz Stanislawski wrote:
> From: Sumit Semwal <sumit.semwal@ti.com>
> 
> This patch makes changes for adding dma-contig as a dma_buf user. It
> provides function implementations for the {attach, detach, map,
> unmap}_dmabuf() mem_ops of DMABUF memory type.
> 
> Signed-off-by: Sumit Semwal <sumit.semwal@ti.com>
> Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
> 	[author of the original patch]
> Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com>
> 	[integration with refactored dma-contig allocator]
> ---
>  drivers/media/video/videobuf2-dma-contig.c |  116
> ++++++++++++++++++++++++++++ 1 files changed, 116 insertions(+), 0
> deletions(-)
> 
> diff --git a/drivers/media/video/videobuf2-dma-contig.c
> b/drivers/media/video/videobuf2-dma-contig.c index c1dc043..746dd5f 100644
> --- a/drivers/media/video/videobuf2-dma-contig.c
> +++ b/drivers/media/video/videobuf2-dma-contig.c
> @@ -35,6 +35,9 @@ struct vb2_dc_buf {
> 
>  	/* USERPTR related */
>  	struct vm_area_struct		*vma;
> +
> +	/* DMABUF related */
> +	struct dma_buf_attachment	*db_attach;
>  };
> 
>  /*********************************************/
> @@ -485,6 +488,115 @@ fail_buf:
>  }
> 
>  /*********************************************/
> +/*       callbacks for DMABUF buffers        */
> +/*********************************************/
> +
> +static int vb2_dc_map_dmabuf(void *mem_priv)
> +{
> +	struct vb2_dc_buf *buf = mem_priv;
> +	struct sg_table *sgt;
> +	unsigned long contig_size;
> +	int ret = 0;
> +
> +	if (WARN_ON(!buf->db_attach)) {
> +		printk(KERN_ERR "trying to pin a non attached buffer\n");
> +		return -EINVAL;
> +	}
> +
> +	if (WARN_ON(buf->dma_sgt)) {
> +		printk(KERN_ERR "dmabuf buffer is already pinned\n");
> +		return 0;
> +	}
> +
> +	/* get the associated scatterlist for this buffer */
> +	sgt = dma_buf_map_attachment(buf->db_attach, buf->dma_dir);
> +	if (IS_ERR_OR_NULL(sgt)) {
> +		printk(KERN_ERR "Error getting dmabuf scatterlist\n");
> +		return -EINVAL;
> +	}

I've checked why dma_map_sg() was missing from here, and then remembered that 
the exporter is still responsible for mapping the buffer to the importer's 
device address space :-) I'll raise that topic separately.

> +
> +	/* checking if dmabuf is big enough to store contiguous chunk */
> +	contig_size = vb2_dc_get_contiguous_size(sgt);
> +	if (contig_size < buf->size) {
> +		printk(KERN_ERR "contiguous chunk of dmabuf is too small\n");
> +		ret = -EFAULT;
> +		goto fail_map;
> +	}
> +
> +	buf->dma_addr = sg_dma_address(sgt->sgl);
> +	buf->dma_sgt = sgt;
> +
> +	return 0;
> +
> +fail_map:
> +	dma_buf_unmap_attachment(buf->db_attach, sgt);
> +
> +	return ret;
> +}
> +
> +static void vb2_dc_unmap_dmabuf(void *mem_priv)
> +{
> +	struct vb2_dc_buf *buf = mem_priv;
> +	struct sg_table *sgt = buf->dma_sgt;
> +
> +	if (WARN_ON(!buf->db_attach)) {
> +		printk(KERN_ERR "trying to unpin a not attached buffer\n");
> +		return;
> +	}
> +
> +	if (WARN_ON(!sgt)) {
> +		printk(KERN_ERR "dmabuf buffer is already unpinned\n");
> +		return;
> +	}
> +
> +	dma_buf_unmap_attachment(buf->db_attach, sgt);
> +
> +	buf->dma_addr = 0;
> +	buf->dma_sgt = NULL;
> +}
> +
> +static void vb2_dc_detach_dmabuf(void *mem_priv)
> +{
> +	struct vb2_dc_buf *buf = mem_priv;
> +
> +	if (buf->dma_addr)
> +		vb2_dc_unmap_dmabuf(buf);

Can detach() be called with the buffer still mapped() ? Wouldn't that be a bug 
in the caller ?

> +
> +	/* detach this attachment */
> +	dma_buf_detach(buf->db_attach->dmabuf, buf->db_attach);
> +	kfree(buf);
> +}

There's nothing allocator-specific in the attach/detach operations. Shouldn't 
they be moved to the vb2 core ?

> +
> +static void *vb2_dc_attach_dmabuf(void *alloc_ctx, struct dma_buf *dbuf,
> +	unsigned long size, int write)
> +{
> +	struct vb2_dc_buf *buf;
> +	struct dma_buf_attachment *dba;
> +
> +	if (dbuf->size < size)
> +		return ERR_PTR(-EFAULT);
> +
> +	buf = kzalloc(sizeof *buf, GFP_KERNEL);
> +	if (!buf)
> +		return ERR_PTR(-ENOMEM);
> +
> +	buf->dev = alloc_ctx;
> +	/* create attachment for the dmabuf with the user device */
> +	dba = dma_buf_attach(dbuf, buf->dev);
> +	if (IS_ERR(dba)) {
> +		printk(KERN_ERR "failed to attach dmabuf\n");
> +		kfree(buf);
> +		return dba;
> +	}
> +
> +	buf->dma_dir = write ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
> +	buf->size = size;
> +	buf->db_attach = dba;
> +
> +	return buf;
> +}
> +
> +/*********************************************/
>  /*       DMA CONTIG exported functions       */
>  /*********************************************/
> 
> @@ -498,6 +610,10 @@ const struct vb2_mem_ops vb2_dma_contig_memops = {
>  	.put_userptr	= vb2_dc_put_userptr,
>  	.prepare	= vb2_dc_prepare,
>  	.finish		= vb2_dc_finish,
> +	.map_dmabuf	= vb2_dc_map_dmabuf,
> +	.unmap_dmabuf	= vb2_dc_unmap_dmabuf,
> +	.attach_dmabuf	= vb2_dc_attach_dmabuf,
> +	.detach_dmabuf	= vb2_dc_detach_dmabuf,
>  	.num_users	= vb2_dc_num_users,
>  };
>  EXPORT_SYMBOL_GPL(vb2_dma_contig_memops);

-- 
Regards,

Laurent Pinchart