[PATCH 6/9] dma: edma: Detect null slot errors and handle them correctly

From: Joel Fernandes
Date: Mon Jul 29 2013 - 09:31:56 EST

For crypto IP, we continue to receive events even continuously in
NULL slot, and request lines don't get de-asserted unlike omap_hsmmc.
Due to this, we continously receive error interrupts when we
manually trigger an event.

We fix this, by first detecting if the Channel is currently transferring
from a NULL slot or not, that's where the edma_read_slot in the error
callback from interrupt handler comes in.

Second thing we do is, if we detect if we are on a NULL slot, we don't
forcefully trigger as this will only result in more error conditions.
Instead we set a missed flag and allow the manual triggerring to happen
in edma_execute which will eventually be called. This fixes the issue
where we are on a NULL slot and continue to receive events from
modules like crypto that don't stop their request events after a
transfer is completed.

Signed-off-by: Joel Fernandes <joelf@xxxxxx>
drivers/dma/edma.c | 42 ++++++++++++++++++++++++++++++++++++++----
1 file changed, 38 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c
index 1eda5cc..c72e8c9 100644
--- a/drivers/dma/edma.c
+++ b/drivers/dma/edma.c
@@ -70,6 +70,7 @@ struct edma_chan {
int ch_num;
bool alloced;
int slot[EDMA_MAX_SLOTS];
+ int missed;
struct dma_slave_config cfg;

@@ -169,6 +170,18 @@ static void edma_execute(struct edma_chan *echan)
dev_dbg(dev, "first transfer starting %d\n", echan->ch_num);
+ /* This happens due to setup times between intermediate transfers
+ in long SG lists which have to be broken up into transfers of
+ MAX_NR_SG */
+ if (echan->missed) {
+ dev_dbg(dev, "missed event in execute detected\n");
+ edma_clean_channel(echan->ch_num);
+ edma_stop(echan->ch_num);
+ edma_start(echan->ch_num);
+ edma_manual_trigger(echan->ch_num);
+ echan->missed = 0;
+ }

static int edma_terminate_all(struct edma_chan *echan)
@@ -387,6 +400,7 @@ static void edma_callback(unsigned ch_num, u16 ch_status, void *data)
struct device *dev = echan->vchan.chan.device->dev;
struct edma_desc *edesc;
unsigned long flags;
+ struct edmacc_param p;

/* Pause the channel */
@@ -414,15 +428,35 @@ static void edma_callback(unsigned ch_num, u16 ch_status, void *data)

- if (echan->edesc) {
- dev_dbg(dev, "Missed event on %d, retrying\n",
- ch_num);
+ spin_lock_irqsave(&echan->vchan.lock, flags);
+ edma_read_slot(EDMA_CHAN_SLOT(echan->slot[0]), &p);
+ if (p.a_b_cnt == 0 && p.ccnt == 0) {
+ dev_dbg(dev, "Error occurred, looks like slot is null, just setting miss\n");
+ /*
+ Issue later based on missed flag which will be sure
+ to happen as:
+ (1) we finished transmitting an intermediate slot and
+ edma_execute is coming up.
+ (2) or we finished current transfer and issue will
+ call edma_execute.
+ Important note: issuing can be dangerous here and
+ lead to some nasty recursion as this is a NULL slot
+ at this point.
+ */
+ echan->missed = 1;
+ } else {
+ dev_dbg(dev, "Error occurred but slot is non-null, TRIGGERING\n");
- dev_dbg(dev, "handled error on channel %d\n", ch_num);
+ spin_unlock_irqrestore(&echan->vchan.lock, flags);

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