linux-kernel - Re: [PATCH v2 1/1] V4L: videobuf, don't use dma addr as physical

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Message-ID: <4D6CACC2.7010307@gmail.com>
Date:	Tue, 01 Mar 2011 09:22:26 +0100
From:	Jiri Slaby <jirislaby@...il.com>
To:	Jiri Slaby <jslaby@...e.cz>
CC:	mchehab@...radead.org, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH v2 1/1] V4L: videobuf, don't use dma addr as physical

On 03/01/2011 09:21 AM, Jiri Slaby wrote:
> mem->dma_handle is a dma address obtained by dma_alloc_coherent which
> needn't be a physical address as a hardware IOMMU can (and most
> likely will) return a bus address where physical != bus address. So
> ensure we are remapping (remap_pfn_range) the right page in
> __videobuf_mmap_mapper by using virt_to_phys(mem->vaddr) and not
> mem->dma_handle.
> 
> While at it, use PFN_DOWN instead of explicit shift to obtain a frame
> number.
> 
> This was discovered by a random review of the code when looking for
> something completely different. I'm not aware of any bug reports for
> this.
> 
> However it is a bug because many v4l drivers use this layer and have
> no idea whether IOMMU is in the system and running or not.
> 
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
> Cc: Mauro Carvalho Chehab <mchehab@...radead.org>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>

Ah, this is rather:
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>

> ---
> 
> This is a version with updated changelog.
> 
>  drivers/media/video/videobuf-dma-contig.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/media/video/videobuf-dma-contig.c b/drivers/media/video/videobuf-dma-contig.c
> index c969111..19d3e4a 100644
> --- a/drivers/media/video/videobuf-dma-contig.c
> +++ b/drivers/media/video/videobuf-dma-contig.c
> @@ -300,7 +300,7 @@ static int __videobuf_mmap_mapper(struct videobuf_queue *q,
>  
>  	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
>  	retval = remap_pfn_range(vma, vma->vm_start,
> -				 mem->dma_handle >> PAGE_SHIFT,
> +				 PFN_DOWN(virt_to_phys(mem->vaddr))
>  				 size, vma->vm_page_prot);
>  	if (retval) {
>  		dev_err(q->dev, "mmap: remap failed with error %d. ", retval);


-- 
js
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