Re: [PATCH v2 1/1] block: blk-merge: don't merge the pages with non-contiguous descriptors

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Wed, Jan 16, 2013 at 10:32:35AM +0000, James Bottomley wrote:
> On Wed, 2013-01-16 at 12:07 +0530, Subhash Jadavani wrote:
> 
> > Now consider this call stack from MMC block driver (this is on the ARmv7 
> > based board):
> >      [   98.918174] [<c001b50c>] (v7_dma_inv_range+0x30/0x48) from 
> > [<c0017b8c>] (dma_cache_maint_page+0x1c4/0x24c)
> >      [   98.927819] [<c0017b8c>] (dma_cache_maint_page+0x1c4/0x24c) from 
> > [<c0017c28>] (___dma_page_cpu_to_dev+0x14/0x1c)
> >      [   98.937982] [<c0017c28>] (___dma_page_cpu_to_dev+0x14/0x1c) from 
> > [<c0017ff8>] (dma_map_sg+0x3c/0x114)
> 
> OK, so this is showing that ARM itself is making the assumption that the
> pages are contiguous in the page offset map.
> 
> Fix this by doing the increment via the pfn, which will do the right
> thing whatever the memory model.
> 
> Signed-off-by: James Bottomley <JBottomley@Parallels.com>

Ok.  What would you like the patch summary line for this to be -
the existing one seems to be a little wrong given the content of
this patch...

> 
> ---
> 
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index 6b2fb87..ab88c5b 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -809,7 +809,7 @@ static void dma_cache_maint_page(struct page *page, unsigned long offset,
>  			op(vaddr, len, dir);
>  		}
>  		offset = 0;
> -		page++;
> +		page = pfn_to_page(page_to_pfn(page) + 1);
>  		left -= len;
>  	} while (left);
>  }
> 
> 
> 
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