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
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