Re: [RFC PATCH 2/2 -mm] RapidIO: TSI721 Add DMA Engine support

From: Andrew Morton
Date: Tue Oct 04 2011 - 21:55:54 EST

On Tue, 4 Oct 2011 18:38:09 -0700 "Bounine, Alexandre" <Alexandre.Bounine@xxxxxxx> wrote:

> > No, it can be used all over the place: drivers/net/irda/w83977af_ir.c,
> > drivers/scsi/bnx2fc/bnx2fc_tgt.c,
> > drivers/net/wireless/rt2x00/rt2x00pci.c,
> > drivers/crypto/amcc/crypto4xx_core.c and many nmore.
> In this case I will happily use dma_zalloc_coherent() as soon as
> it is available

geeze, which of us is more lazy?

Here we go...

From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: include/linux/dma-mapping.h: add dma_zalloc_coherent()

Lots of driver code does a dma_alloc_coherent() and then zeroes out the
memory with a memset. Make it easy for them.

Cc: Alexandre Bounine <alexandre.bounine@xxxxxxx>
From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: include-linux-dma-mappingh-add-dma_zalloc_coherent
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

Documentation/DMA-API.txt | 7 +++++++
include/linux/dma-mapping.h | 10 ++++++++++
2 files changed, 17 insertions(+)

diff -puN include/linux/dma-mapping.h~include-linux-dma-mappingh-add-dma_zalloc_coherent include/linux/dma-mapping.h
--- a/include/linux/dma-mapping.h~include-linux-dma-mappingh-add-dma_zalloc_coherent
+++ a/include/linux/dma-mapping.h
@@ -1,6 +1,7 @@

+#include <linux/string.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/dma-attrs.h>
@@ -117,6 +118,15 @@ static inline int dma_set_seg_boundary(s
return -EIO;

+static inline void *dma_zalloc_coherent(struct device *dev, size_t size,
+ dma_addr_t *dma_handle, gfp_t flag)
+ void *ret = dma_alloc_coherent(dev, size, dma_handle, flag);
+ if (ret)
+ memset(ret, 0, size);
+ return ret;
static inline int dma_get_cache_alignment(void)
diff -puN Documentation/DMA-API.txt~include-linux-dma-mappingh-add-dma_zalloc_coherent Documentation/DMA-API.txt
--- a/Documentation/DMA-API.txt~include-linux-dma-mappingh-add-dma_zalloc_coherent
+++ a/Documentation/DMA-API.txt
@@ -50,6 +50,13 @@ specify the GFP_ flags (see kmalloc) for
implementation may choose to ignore flags that affect the location of
the returned memory, like GFP_DMA).

+void *
+dma_zalloc_coherent(struct device *dev, size_t size,
+ dma_addr_t *dma_handle, gfp_t flag)
+Wraps dma_alloc_coherent() and also zeroes the returned memory if the
+allocation attempt succeeded.
dma_free_coherent(struct device *dev, size_t size, void *cpu_addr,
dma_addr_t dma_handle)

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