Commit 5fc68a6c authored Mar 19, 2014 by Sekhar Nori Committed by Vinod Koul Apr 14, 2014

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>

parent c9eaa447

drivers/dma/edma.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -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);
		}

		/*

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