On Mon, 17 Mar 2014, Sekhar Nori wrote: > 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@xxxxxxxxxxxxxxx> # v3.12.x+ > Cc: Joel Fernandes <joelf@xxxxxx> > Reported-by: Jon Ringle <jringle@xxxxxxxxxxxxx> > Signed-off-by: Sekhar Nori <nsekhar@xxxxxx> > --- > Jon, can you please confirm this fixes the issue you > reported? The patch does not apply on linux-3.12 due to changes to the 3 context lines at the start of the hunk. But, I manually fixed up the code and it does fix the issue on our AM1808 board. > Joel, can you ack this please? In particular, I was > not able to test with SG list greater than MAX_NR_SG. > > drivers/dma/edma.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c > index cd8da45..bf5ad0f 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); > } > The above 3 lines are different on linux-3.12. I have the following in my linux-3.12 tree: if (edesc->processed == edesc->pset_nr) edma_link(echan->slot[nslots-1], 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); > } > > /* > -- > 1.7.10.1 > > -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html