[RFC 4/5] dma: edma: Find missed events and issue them

[RFC 4/5] dma: edma: Find missed events and issue them

[Joel Fernandes]

In an effort to move to using Scatter gather lists of any size with
EDMA as discussed at [1] instead of placing limitations on the driver,
we work through the limitations of the EDMAC hardware to find missed
events and issue them.

The sequence of events that require this are:

For the scenario where MAX slots for an EDMA channel is 3:

SG1 -> SG2 -> SG3 -> SG4 -> SG5 -> SG6 -> Null

The above SG list will have to be DMA'd in 2 sets:

(1) SG1 -> SG2 -> SG3 -> Null
(2) SG4 -> SG5 -> SG6 -> Null

After (1) is succesfully transferred, the events from the MMC controller
donot stop coming and are missed by the time we have setup the transfer
for (2). So here, we catch the events missed as an error condition and
issue them manually.

[1] http://marc.info/?l=linux-omap&m=137416733628831&w=2

Signed-off-by: Joel Fernandes <joelf@ti.com>
---
 drivers/dma/edma.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c
index 0e7ed79..b0b5bcd 100644
--- a/drivers/dma/edma.c
+++ b/drivers/dma/edma.c
@@ -414,7 +414,15 @@ static void edma_callback(unsigned ch_num, u16 ch_status, void *data)
 
 		break;
 	case DMA_CC_ERROR:
-		dev_dbg(dev, "transfer error on channel %d\n", ch_num);
+		if (echan->edesc) {
+			dev_dbg(dev, "Missed event on %d, retrying\n",
+				ch_num);
+			edma_clean_channel(echan->ch_num);
+			edma_stop(echan->ch_num);
+			edma_start(echan->ch_num);
+			edma_manual_trigger(echan->ch_num);
+		}
+		dev_dbg(dev, "handled error on channel %d\n", ch_num);
 		break;
 	default:
 		break;
-- 
1.7.9.5