Re: [PATCH v2] tmio_mmc_dma: fix PIO fallback on SDHI

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello.

On 04-08-2013 2:36, 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. The regression was introduced by commit
>> 162f43e31c5a376ec16336e5d0ac973373d54c89 (mmc: tmio: fix a deadlock).
>> Moving tmio_mmc_enable_dma() calls to the top of the PIO fallback code in
>> tmio_mmc_start_dma_{rx|tx}() helps.

>> Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
>> Cc: stable@vger.kernel.org # 3.1+

> Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>

> Not sure though how far back in stable this really has to go. We don't
> have any real-life problem reports with older kernels, do we?

    If we did, that error would have been fixed earlier, wouldn't it?

> I think
> approach to which patches should get into stable changed recently.

    Haven't heard about that (or seen any change in the policy). The issue 
with this bug is its catastrophic consequencies: you can hardly ^C or ^Z out 
of 'bonnie++' when it happens (in fact, you cannot ^C at all). IIRC you can't 
even kill it from another shell.

> Thanks
> Guennadi

WBR, Sergei