Re: [PATCH] tmio_mmc_dma: fix PIO fallback on SDHI

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On 08/02/2013 03:35 PM, Guennadi Liakhovetski wrote:

I'm testing SH-Mobile SDHI driver in DMA mode with a  new DMA controller  using
'bonnie++' and getting DMA error after which the tmio_mmc_dma.c code falls back
to PIO but all commands time out after that.  It turned out that the fallback
code calls tmio_mmc_enable_dma() with RX/TX channels already freed and pointers
to them cleared, so that the function bails out early instead  of clearing the
DMA bit in the CTL_DMA_ENABLE register.  Fixing the RX/TX channel check so that
it takes place only when enabling DMA helps with the PIO fallback.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@xxxxxxxxxxxxxxxxxx>

---
The patch is against Chris Ball's 'mmc.git' repo, 'master' branch.

  drivers/mmc/host/tmio_mmc_dma.c |    2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

Index: mmc/drivers/mmc/host/tmio_mmc_dma.c
===================================================================
--- mmc.orig/drivers/mmc/host/tmio_mmc_dma.c
+++ mmc/drivers/mmc/host/tmio_mmc_dma.c
@@ -25,7 +25,7 @@

  void tmio_mmc_enable_dma(struct tmio_mmc_host *host, bool enable)
  {
-	if (!host->chan_tx || !host->chan_rx)
+	if (enable && !(host->chan_tx && host->chan_rx))
  		return;

Ok, I see the problem and this does fix it. But it adds complexity to the
driver - one more condition to an if.

   So what?

Whereas, I think, it can be avoided if we just move calls to

tmio_mmc_enable_dma(host, false);

in tmio_mmc_start_dma_rx() and tmio_mmc_start_dma_tx() a couple of lines

   Well, not couple. :-P

up - before clearing ->chan_rx and ->chan_tx pointers? That should work
too at no cost.

Well, it was my first variant. However, not knowing the hardware well, I deemed it not quite safe to clear the DMA bit before shutting down the DMA channels, so came up with the second version (which I consider more logically correct).

I think that would be a better fix, could you, please, try?

I tried it but mystically fixing the PIO fallback makes DMA error less frequent. IIRC, I didn't see DMA error with the first variant of the fix, so I'll have to retry it...

Thanks
Guennadi

WBR, Sergei

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