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dma: edma: fix incorrect SG list handling 

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: stable@vger.kernel.org # v3.12.x+
Cc: Joel Fernandes <joelf@ti.com>
Acked-by: Joel Fernandes <joelf@ti.com>
Tested-by: Jon Ringle <jringle@gridpoint.com>
Tested-by: Alexander Holler <holler@ahsoftware.de>
Reported-by: Jon Ringle <jringle@gridpoint.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
This commit is contained in:
Sekhar Nori 2014-03-19 11:25:50 +05:30 committed by Vinod Koul
parent c9eaa447e7
commit 5fc68a6cad
1 changed files with 4 additions and 2 deletions
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6
drivers/dma/edma.c
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@ -182,11 +182,13 @@ static void edma_execute(struct edma_chan *echan)
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);
}
/*