[prev in list] [next in list] [prev in thread] [next in thread] 

List:       dmaengine
Subject:    [PATCH 3/6] dmaengine: shdma: Allocate cyclic sg list dynamically
From:       Simon Horman <horms+renesas () verge ! net ! au>
Date:       2014-07-31 0:34:06
Message-ID: 7c32a21a5152589b8d434d0db0c8c5648c5ff2ef.1406766014.git.horms+renesas () verge ! net ! au
[Download RAW message or body]

From: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

The sg list used to prepare cyclic DMA descriptors is currently
allocated statically on the stack as an array of 32 elements. This makes
the shdma_prep_dma_cyclic() function consume a lot of stack space, as
reported by the compiler:

drivers/dma/sh/shdma-base.c: In function ‘shdma_prep_dma_cyclic':
drivers/dma/sh/shdma-base.c:715:1: warning: the frame size of 1056 bytes
is larger than 1024 bytes [-Wframe-larger-than=]

Given the limited Linux kernel stack size, this could lead to stack
overflows. Fix the problem by allocating the sg list dynamically.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
---
 drivers/dma/sh/shdma-base.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/sh/shdma-base.c b/drivers/dma/sh/shdma-base.c
index 94b6bde..e427a03 100644
--- a/drivers/dma/sh/shdma-base.c
+++ b/drivers/dma/sh/shdma-base.c
@@ -672,11 +672,12 @@ static struct dma_async_tx_descriptor *shdma_prep_dma_cyclic(
 {
 	struct shdma_chan *schan = to_shdma_chan(chan);
 	struct shdma_dev *sdev = to_shdma_dev(schan->dma_chan.device);
+	struct dma_async_tx_descriptor *desc;
 	const struct shdma_ops *ops = sdev->ops;
 	unsigned int sg_len = buf_len / period_len;
 	int slave_id = schan->slave_id;
 	dma_addr_t slave_addr;
-	struct scatterlist sgl[SHDMA_MAX_SG_LEN];
+	struct scatterlist *sgl;
 	int i;
 
 	if (!chan)
@@ -700,7 +701,16 @@ static struct dma_async_tx_descriptor *shdma_prep_dma_cyclic(
 
 	slave_addr = ops->slave_addr(schan);
 
+	/*
+	 * Allocate the sg list dynamically as it would consumer too much stack
+	 * space.
+	 */
+	sgl = kcalloc(sg_len, sizeof(*sgl), GFP_KERNEL);
+	if (!sgl)
+		return NULL;
+
 	sg_init_table(sgl, sg_len);
+
 	for (i = 0; i < sg_len; i++) {
 		dma_addr_t src = buf_addr + (period_len * i);
 
@@ -710,8 +720,11 @@ static struct dma_async_tx_descriptor *shdma_prep_dma_cyclic(
 		sg_dma_len(&sgl[i]) = period_len;
 	}
 
-	return shdma_prep_sg(schan, sgl, sg_len, &slave_addr,
+	desc = shdma_prep_sg(schan, sgl, sg_len, &slave_addr,
 			     direction, flags, true);
+
+	kfree(sgl);
+	return desc;
 }
 
 static int shdma_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
-- 
2.0.1

--
To unsubscribe from this list: send the line "unsubscribe dmaengine" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[prev in list] [next in list] [prev in thread] [next in thread]