Re: [PATCH 04/12] v4l: vb2-dma-contig: add setup of sglist for MMAP buffers

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

Hi Tomasz,

Thanks for the patch.

On Wednesday 23 May 2012 15:07:27 Tomasz Stanislawski wrote:
> This patch adds the setup of sglist list for MMAP buffers.
> It is needed for buffer exporting via DMABUF mechanism.
> 
> Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
> ---
>  drivers/media/video/videobuf2-dma-contig.c |   70 ++++++++++++++++++++++++-
>  1 file changed, 68 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/video/videobuf2-dma-contig.c
> b/drivers/media/video/videobuf2-dma-contig.c index 52b4f59..ae656be 100644
> --- a/drivers/media/video/videobuf2-dma-contig.c
> +++ b/drivers/media/video/videobuf2-dma-contig.c
> @@ -32,6 +32,7 @@ struct vb2_dc_buf {
>  	/* MMAP related */
>  	struct vb2_vmarea_handler	handler;
>  	atomic_t			refcount;
> +	struct sg_table			*sgt_base;
> 
>  	/* USERPTR related */
>  	struct vm_area_struct		*vma;
> @@ -189,14 +190,37 @@ static void vb2_dc_put(void *buf_priv)
>  	if (!atomic_dec_and_test(&buf->refcount))
>  		return;
> 
> +	vb2_dc_release_sgtable(buf->sgt_base);
>  	dma_free_coherent(buf->dev, buf->size, buf->vaddr, buf->dma_addr);
>  	kfree(buf);
>  }
> 
> +static int vb2_dc_kaddr_to_pages(unsigned long kaddr,
> +	struct page **pages, unsigned int n_pages)
> +{
> +	unsigned int i;
> +	unsigned long pfn;
> +	struct vm_area_struct vma = {
> +		.vm_flags = VM_IO | VM_PFNMAP,
> +		.vm_mm = current->mm,
> +	};
> +
> +	for (i = 0; i < n_pages; ++i, kaddr += PAGE_SIZE) {

The follow_pfn() kerneldoc mentions that it looks up a PFN for a user address. 
The only users I've found in the kernel sources pass a user address. Is it 
legal to use it for kernel addresses ?

> +		if (follow_pfn(&vma, kaddr, &pfn))
> +			break;
> +		pages[i] = pfn_to_page(pfn);
> +	}
> +
> +	return i;
> +}
> +
>  static void *vb2_dc_alloc(void *alloc_ctx, unsigned long size)
>  {
>  	struct device *dev = alloc_ctx;
>  	struct vb2_dc_buf *buf;
> +	int ret = -ENOMEM;
> +	int n_pages;
> +	struct page **pages = NULL;
> 
>  	buf = kzalloc(sizeof *buf, GFP_KERNEL);
>  	if (!buf)
> @@ -205,10 +229,41 @@ static void *vb2_dc_alloc(void *alloc_ctx, unsigned
> long size) buf->vaddr = dma_alloc_coherent(dev, size, &buf->dma_addr,
> GFP_KERNEL); if (!buf->vaddr) {
>  		dev_err(dev, "dma_alloc_coherent of size %ld failed\n", size);
> -		kfree(buf);
> -		return ERR_PTR(-ENOMEM);
> +		goto fail_buf;
> +	}
> +
> +	WARN_ON((unsigned long)buf->vaddr & ~PAGE_MASK);
> +	WARN_ON(buf->dma_addr & ~PAGE_MASK);
> +
> +	n_pages = PAGE_ALIGN(size) >> PAGE_SHIFT;
> +
> +	pages = kmalloc(n_pages * sizeof pages[0], GFP_KERNEL);
> +	if (!pages) {
> +		dev_err(dev, "failed to alloc page table\n");
> +		goto fail_dma;
> +	}
> +
> +	ret = vb2_dc_kaddr_to_pages((unsigned long)buf->vaddr, pages, n_pages);
> +	if (ret < 0) {
> +		dev_err(dev, "failed to get buffer pages from DMA API\n");
> +		goto fail_pages;
> +	}
> +	if (ret != n_pages) {
> +		ret = -EFAULT;
> +		dev_err(dev, "failed to get all pages from DMA API\n");
> +		goto fail_pages;
> +	}
> +
> +	buf->sgt_base = vb2_dc_pages_to_sgt(pages, n_pages, 0, size);
> +	if (IS_ERR(buf->sgt_base)) {
> +		ret = PTR_ERR(buf->sgt_base);
> +		dev_err(dev, "failed to prepare sg table\n");
> +		goto fail_pages;
>  	}
> 
> +	/* pages are no longer needed */
> +	kfree(pages);
> +
>  	buf->dev = dev;
>  	buf->size = size;
> 
> @@ -219,6 +274,17 @@ static void *vb2_dc_alloc(void *alloc_ctx, unsigned
> long size) atomic_inc(&buf->refcount);
> 
>  	return buf;
> +
> +fail_pages:
> +	kfree(pages);
> +
> +fail_dma:

You can merge the fail_pages and fail_dma labels, as kfree(NULL) is valid.

> +	dma_free_coherent(dev, size, buf->vaddr, buf->dma_addr);
> +
> +fail_buf:
> +	kfree(buf);
> +
> +	return ERR_PTR(ret);
>  }
> 
>  static int vb2_dc_mmap(void *buf_priv, struct vm_area_struct *vma)

-- 
Regards,

Laurent Pinchart