linux-kernel - Re: [PATCH] [media] videobuf-dma-contig: replace vm_iomap_memory() with remap_pfn

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Date:	Wed, 10 Sep 2014 09:00:30 +0200
From:	Hans Verkuil <hverkuil@...all.nl>
To:	Fancy Fang <chen.fang@...escale.com>, m.chehab@...sung.com,
	viro@...IV.linux.org.uk
CC:	shawn.guo@...escale.com, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH] [media] videobuf-dma-contig: replace vm_iomap_memory()
 with remap_pfn_range().

On 09/10/14 07:28, Fancy Fang wrote:
> When user requests V4L2_MEMORY_MMAP type buffers, the videobuf-core
> will assign the corresponding offset to the 'boff' field of the
> videobuf_buffer for each requested buffer sequentially. Later, user
> may call mmap() to map one or all of the buffers with the 'offset'
> parameter which is equal to its 'boff' value. Obviously, the 'offset'
> value is only used to find the matched buffer instead of to be the
> real offset from the buffer's physical start address as used by
> vm_iomap_memory(). So, in some case that if the offset is not zero,
> vm_iomap_memory() will fail.

Is this just a fix for something that can fail theoretically, or do you
actually have a case where this happens? I am very reluctant to make
any changes to videobuf. Drivers should all migrate to vb2.

I have CC-ed Marek as well since he knows a lot more about this stuff
than I do.

Regards,

	Hans

> 
> Signed-off-by: Fancy Fang <chen.fang@...escale.com>
> ---
>  drivers/media/v4l2-core/videobuf-dma-contig.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/v4l2-core/videobuf-dma-contig.c b/drivers/media/v4l2-core/videobuf-dma-contig.c
> index bf80f0f..8bd9889 100644
> --- a/drivers/media/v4l2-core/videobuf-dma-contig.c
> +++ b/drivers/media/v4l2-core/videobuf-dma-contig.c
> @@ -305,7 +305,9 @@ static int __videobuf_mmap_mapper(struct videobuf_queue *q,
>  	/* Try to remap memory */
>  	size = vma->vm_end - vma->vm_start;
>  	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> -	retval = vm_iomap_memory(vma, mem->dma_handle, size);
> +	retval = remap_pfn_range(vma, vma->vm_start,
> +				 mem->dma_handle >> PAGE_SHIFT,
> +				 size, vma->vm_page_prot);
>  	if (retval) {
>  		dev_err(q->dev, "mmap: remap failed with error %d. ",
>  			retval);
> 

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