linux-kernel - Re: SATA exceptions with 2.6.20-rc5

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Date:	Fri, 19 Jan 2007 01:52:51 +0100
From:	Björn Steinbrink <B.Steinbrink@....de>
To:	Robert Hancock <hancockr@...w.ca>
Cc:	linux-kernel@...r.kernel.org, Larry Walton <lwalton@...l.com>,
	jeff@...zik.org, htejun@...il.com, jens.axboe@...cle.com
Subject: Re: SATA exceptions with 2.6.20-rc5

On 2007.01.18 18:09:50 -0600, Robert Hancock wrote:
> I heard from Larry Walton who was apparently seeing this problem as 
> well. He tried my recent "sata_nv: cleanup ADMA error handling v2" patch 
> and originally thought it fixed the problem, but it turned out to only 
> make it happen less often.
> 
> I wouldn't expect that patch to have an effect on this problem. If it 
> seems to reduce the frequency that would tend to be further evidence of 
>  some kind of timing-related issue where the code change just happens 
> to make a difference.
> 
> I'll see if I can come up with a debug patch for people having this 
> problem to try, which prints out when a flush command is issued and what 
> interrupts happen when a flush is pending.
> 
> There is one important difference between ADMA and non-ADMA mode for 
> non-DMA commands like flushes, which didn't come to mind before: ADMA 
> mode uses MMIO registers on the controller whereas non-ADMA mode uses 
> legacy IO registers. Posted write flushing is a concern with MMIO 
> registers but not with PIO, the libata core is supposed to handle this 
> but maybe it doesn't in some case(s). In fact, just looking at 
> libata-sff.c there's this comment on the ata_exec_command_mmio function:
> 
>  *      FIXME: missing write posting for 400nS delay enforcement
> 
> That seems a bit suspicious..

That would imply that disabling adma via a module parameter should make
the issue go away, right? I'll try to have a test run with adma disabled
over night then.

Thanks,
Björn
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