Re: SATA exceptions with 2.6.20-rc5

From: Robert Hancock
Date: Thu Jan 18 2007 - 19:11:57 EST


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..

--
Robert Hancock Saskatoon, SK, Canada
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Home Page: http://www.roberthancock.com/

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