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

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Date:	Mon, 15 Jan 2007 18:34:43 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Björn Steinbrink <B.Steinbrink@....de>,
	jeff@...zik.org, linux-kernel@...r.kernel.org, htejun@...il.com,
	jens.axboe@...cle.com
Subject: Re: SATA exceptions with 2.6.20-rc5

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'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..

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@...pamshaw.ca
Home Page: http://www.roberthancock.com/

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