linux-kernel - [PATCH 3/3] dmaengine: Fixup dmaengine_prep_slave

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Date:	Wed, 25 Apr 2012 20:50:53 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Vinod Koul <vinod.koul@...el.com>,
	Russell King <linux@....linux.org.uk>
Cc:	Viresh Kumar <viresh.kumar@...com>,
	Srinidhi Kasagar <srinidhi.kasagar@...ricsson.com>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Shawn Guo <shawn.guo@...aro.org>,
	Javier Martin <javier.martin@...ta-silicon.com>,
	Richard Zhao <richard.zhao@...aro.org>,
	Yong Wang <yong.y.wang@...el.com>,
	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
	linux-kernel@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>
Subject: [PATCH 3/3] dmaengine: Fixup dmaengine_prep_slave_single() to be actually useful

From: Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>

dmaengine_prep_slave_single() is a helper function which is supposed to be used
to prepare a transfer of a single contingous buffer. Currently the function
takes a pointer to such a buffer from which it builds a scatterlist and passes
it on to device_prep_slave_sg. The dmaengine framework requires that any
scatterlist that is passed to device_prep_slave_sg is mapped and it may not be
unmapped until the DMA operation has completed. This is not the here and any use
of dmaengine_prep_slave_single() will lead to undefined behaviour (Most likely a
system crash).

This patch changes dmaengine_prep_slave_single() to take a dma_addr_t instead of
a pointer to a buffer and moves the responsibility of mapping and unmapping the
buffer up to the caller.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
Signed-off-by: Lars-Peter Clausen <lars@...afoo.de>

---
Changes since v1:
	* Drop call to sg_set_page
	* Slightly reword commit message
---
 include/linux/dmaengine.h |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 676f967..0e6b595 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -615,11 +615,13 @@ static inline int dmaengine_slave_config(struct dma_chan *chan,
 }
 
 static inline struct dma_async_tx_descriptor *dmaengine_prep_slave_single(
-	struct dma_chan *chan, void *buf, size_t len,
+	struct dma_chan *chan, dma_addr_t buf, size_t len,
 	enum dma_transfer_direction dir, unsigned long flags)
 {
 	struct scatterlist sg;
-	sg_init_one(&sg, buf, len);
+	sg_init_table(&sg, 1);
+	sg_dma_address(&sg) = buf;
+	sg_dma_len(&sg) = len;
 
 	return chan->device->device_prep_slave_sg(chan, &sg, 1,
 						  dir, flags, NULL);
-- 
1.7.9.5

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