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* [PATCH AUTOSEL 4.14 08/37] dmaengine: rcar-dmac: Reject zero-length slave DMA requests
       [not found] <>
@ 2019-07-26 13:43 ` Sasha Levin
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From: Sasha Levin @ 2019-07-26 13:43 UTC (permalink / raw)
  To: linux-kernel, stable
  Cc: Geert Uytterhoeven, Eugeniu Rosca, Yoshihiro Shimoda, Vinod Koul,
	Sasha Levin, dmaengine

From: Geert Uytterhoeven <>

[ Upstream commit 78efb76ab4dfb8f74f290ae743f34162cd627f19 ]

While the .device_prep_slave_sg() callback rejects empty scatterlists,
it still accepts single-entry scatterlists with a zero-length segment.
These may happen if a driver calls dmaengine_prep_slave_single() with a
zero len parameter.  The corresponding DMA request will never complete,
leading to messages like:

    rcar-dmac e7300000.dma-controller: Channel Address Error happen

and DMA timeouts.

Although requesting a zero-length DMA request is a driver bug, rejecting
it early eases debugging.  Note that the .device_prep_dma_memcpy()
callback already rejects requests to copy zero bytes.

Reported-by: Eugeniu Rosca <>
Analyzed-by: Yoshihiro Shimoda <>
Signed-off-by: Geert Uytterhoeven <>
Signed-off-by: Vinod Koul <>
Signed-off-by: Sasha Levin <>
 drivers/dma/sh/rcar-dmac.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
index 77b126525dac..19c7433e8309 100644
--- a/drivers/dma/sh/rcar-dmac.c
+++ b/drivers/dma/sh/rcar-dmac.c
@@ -1129,7 +1129,7 @@ rcar_dmac_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
 	struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);
 	/* Someone calling slave DMA on a generic channel? */
-	if (rchan->mid_rid < 0 || !sg_len) {
+	if (rchan->mid_rid < 0 || !sg_len || !sg_dma_len(sgl)) {
 			 "%s: bad parameter: len=%d, id=%d\n",
 			 __func__, sg_len, rchan->mid_rid);

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2019-07-26 13:43 ` [PATCH AUTOSEL 4.14 08/37] dmaengine: rcar-dmac: Reject zero-length slave DMA requests Sasha Levin

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