linux-kernel - [PATCH 5/4] Provide __dma

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Date:	Wed, 19 May 2010 14:49:08 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Herbert Xu <herbert@...dor.apana.org.au>,
	Mike Frysinger <vapier@...too.org>,
	Nick Piggin <npiggin@...e.de>, os@...ix.com
Cc:	David Miller <davem@...emloft.net>, penberg@...helsinki.fi,
	mpm@...enic.com, ken@...elabs.ch, geert@...ux-m68k.org,
	michael-dev@...i-braun.de, linux-kernel@...r.kernel.org,
	linux-crypto@...r.kernel.org, anemo@....ocn.ne.jp
Subject: [PATCH 5/4] Provide __dma_aligned macro

Commit 3843384a055496dfed3c93ae883d964d8290fdab ("Input: ad7877 - keep
dma rx buffers in seperate cache lines")[sic] introduced the use of
____cacheline_aligned to ensure that buffers used for DMA as part of a
structure were suitably separated from the rest of the structure.

However, aligning to the cache line size isn't necessary on
cache-coherent architectures. To avoid wasting space, the correct value
to use for the alignment is ARCH_KMALLOC_MINALIGN.

This patch provides a __dma_aligned macro which does the right thing.

Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index ca32ed7..4487cf3 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -5,6 +5,9 @@
 #include <linux/err.h>
 #include <linux/dma-attrs.h>
 #include <linux/scatterlist.h>
+#include <linux/slab.h>
+
+#define __dma_aligned __attribute__((__aligned__(ARCH_KMALLOC_MINALIGN)))
 
 /* These definitions mirror those in pci.h, so they can be used
  * interchangeably with their PCI_ counterparts */

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@...el.com                              Intel Corporation

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