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: <sta...@vger.kernel.org> # v3.12.x+
> Cc: Joel Fernandes <jo...@ti.com>
> Reported-by: Jon Ringle <jrin...@gridpoint.com>
> Signed-off-by: Sekhar Nori <nsek...@ti.com>
> ---
> 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
>
>
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