linux-kernel - [PATCH 3.12 175/182] dma: edma: fix incorrect SG list handling

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Date:	Tue, 13 May 2014 11:28:47 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Sekhar Nori <nsekhar@...com>,
	Joel Fernandes <joelf@...com>,
	Vinod Koul <vinod.koul@...el.com>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 175/182] dma: edma: fix incorrect SG list handling

From: Sekhar Nori <nsekhar@...com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 5fc68a6cad658e45dca3e0a6607df3a8e5df4ef9 upstream.

The code to handle any length SG lists calls edma_resume()
even before edma_start() is called. This is incorrect
because edma_resume() enables edma events on the channel
after which CPU (in edma_start) cannot clear posted
events by writing to ECR (per the EDMA user's guide).

Because of this EDMA transfers fail to start if due
to some reason there is a pending EDMA event registered
even before EDMA transfers are started. This can happen if
an EDMA event is a byproduct of device initialization.

Fix this by calling edma_resume() only if it is not the
first batch of MAX_NR_SG elements.

Without this patch, MMC/SD fails to function on DA850 EVM
with DMA. The behaviour is triggered by specific IP and
this can explain why the issue was not reported before
(example with MMC/SD on AM335x).

Tested on DA850 EVM and AM335x EVM-SK using MMC/SD card.

Cc: Joel Fernandes <joelf@...com>
Acked-by: Joel Fernandes <joelf@...com>
Tested-by: Jon Ringle <jringle@...dpoint.com>
Tested-by: Alexander Holler <holler@...oftware.de>
Reported-by: Jon Ringle <jringle@...dpoint.com>
Signed-off-by: Sekhar Nori <nsekhar@...com>
Signed-off-by: Vinod Koul <vinod.koul@...el.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/dma/edma.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c
index 10b577fcf48d..0ad40e4a7ae0 100644
--- a/drivers/dma/edma.c
+++ b/drivers/dma/edma.c
@@ -170,11 +170,13 @@ static void edma_execute(struct edma_chan *echan)
 	if (edesc->processed == edesc->pset_nr)
 		edma_link(echan->slot[nslots-1], echan->ecc->dummy_slot);

-	edma_resume(echan->ch_num);
-
 	if (edesc->processed <= MAX_NR_SG) {
 		dev_dbg(dev, "first transfer starting %d\n", echan->ch_num);
 		edma_start(echan->ch_num);
+	} else {
+		dev_dbg(dev, "chan: %d: completed %d elements, resuming\n",
+			echan->ch_num, edesc->processed);
+		edma_resume(echan->ch_num);
 	}

 	/*
-- 
1.9.3

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