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>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c
index cd04eb7b182e..926360c2db6a 100644
--- a/drivers/dma/edma.c
+++ b/drivers/dma/edma.c
@@ -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);
         }
 
         /*