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

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Date:	Tue, 16 Jan 2007 02:35:06 +0100
From:	Björn Steinbrink <B.Steinbrink@....de>
To:	Robert Hancock <hancockr@...w.ca>
Cc:	jeff@...zik.org, linux-kernel@...r.kernel.org, htejun@...il.com,
	jens.axboe@...cle.com
Subject: Re: SATA exceptions with 2.6.20-rc5

On 2007.01.15 18:34:43 -0600, Robert Hancock wrote:
> Björn Steinbrink wrote:
> >>My latest bisection attempt actually led to your sata_nv ADMA commit. [1]
> >>I've now backed out that patch from 2.6.20-rc5 and have my stress test
> >>running for 20 minutes now ("record" for a bad kernel surviving that
> >>test is about 40 minutes IIRC). I'll keep it running for at least 2 more
> >>hours.
> >
> >Yep, that one seems to be guilty. 2.6.20-rc5 with that commit backed out
> >survived about 3 hours of testing, while the average was around 5
> >minutes for a failure, sometimes even before I could log in.
> >I took a look at the patch, but I can't really tell anything.
> >nv_adma_check_atapi_dma somehow looks like it should not negate its
> >return value, so that it returns 0 (atapi dma available) when
> >adma_enable was 1. But I'm not exactly confident about that either ;)
> >Will it hurt if I try to remove the negation?
> 
> It should be correct the way it is - that check is trying to prevent 
> ATAPI commands from using DMA until the slave_config function has been 
> called to set up the DMA parameters properly. When the 
> NV_ADMA_ATAPI_SETUP_COMPLETE flag is not set, this returns 1 which 
> disallows DMA transfers. Unless you were using an ATAPI (i.e. CD/DVD) 
> device on the channel this wouldn't affect you anyway.

I wondered about it, because the flag is cleared when adma_enabled is 1,
which seems to be consistent with everything but nv_adma_check_atapi_dma.
Thus I thought that nv_adma_check_atapi_dma might be wrong, but maybe
setting/clearing the flag is wrong instead? *feels lost*

> I'll try your stress test when I get a chance, but I doubt I'll run into 
> the same problem and I haven't seen any similar reports. Perhaps it's 
> some kind of wierd timing issue or incompatibility between the 
> controller and that drive when running in ADMA mode? I seem to remember 
> various reports of issues with certain Maxtor drives and some nForce 
> SATA controllers under Windows at least..

I just checked Maxtor's knowledge base, that incompatibility does not
affect my drive.

Thanks,
Björn
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