From 593f47355467b9ef44293698817e2bdb347e2d11 Mon Sep 17 00:00:00 2001 From: Marek Szyprowski Date: Thu, 21 Jun 2012 11:48:11 +0200 Subject: [PATCH] ARM: dma-mapping: fix buffer chunk allocation order IOMMU-aware dma_alloc_attrs() implementation allocates buffers in power-of-two chunks to improve performance and take advantage of large page mappings provided by some IOMMU hardware. However current code, due to a subtle bug, allocated those chunks in the smallest-to-largest order, what completely killed all the advantages of using larger than page chunks. If a 4KiB chunk has been mapped as a first chunk, the consecutive chunks are not aligned correctly to the power-of-two which match their size and IOMMU drivers were not able to use internal mappings of size other than the 4KiB (largest common denominator of alignment and chunk size). This patch fixes this issue by changing to the correct largest-to-smallest chunk size allocation sequence. Signed-off-by: Marek Szyprowski --- arch/arm/mm/dma-mapping.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c index d766e4256b74..4044abcf6f9d 100644 --- a/arch/arm/mm/dma-mapping.c +++ b/arch/arm/mm/dma-mapping.c @@ -1067,7 +1067,7 @@ static struct page **__iommu_alloc_buffer(struct device *dev, size_t size, gfp_t return NULL; while (count) { - int j, order = __ffs(count); + int j, order = __fls(count); pages[i] = alloc_pages(gfp | __GFP_NOWARN, order); while (!pages[i] && order) -- 2.39.2