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

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Date:	Wed, 16 Jan 2013 10:32:35 +0000
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Subhash Jadavani <subhashj@...eaurora.org>
Cc:	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-mmc@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	martin.petersen@...cle.com, asias@...hat.com, tj@...nel.org,
	linux-arm-kernel@...ts.infradead.org,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH v2 1/1] block: blk-merge: don't merge the pages with
 non-contiguous descriptors

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@...allels.com>

---

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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