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

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Date:	Sun, 21 Jan 2007 23:08:13 +0100
From:	Björn Steinbrink <B.Steinbrink@....de>
To:	Robert Hancock <hancockr@...w.ca>
Cc:	Jeff Garzik <jeff@...zik.org>, Chr <chunkeey@....de>,
	Alistair John Strachan <s0348365@....ed.ac.uk>,
	linux-kernel@...r.kernel.org, htejun@...il.com,
	jens.axboe@...cle.com, lwalton@...l.com
Subject: Re: SATA exceptions with 2.6.20-rc5

On 2007.01.21 13:58:01 -0600, Robert Hancock wrote:
> Björn Steinbrink wrote:
> >All kernels were bad using that approach. So back to square 1. :/
> >
> >Björn
> >
> 
> OK guys, here's a new patch to try against 2.6.20-rc5:
> 
> Right now when switching between ADMA mode and legacy mode (i.e. when 
> going from doing normal DMA reads/writes to doing a FLUSH CACHE) we just 
> set the ADMA GO register bit appropriately and continue with no delay. 
> It looks like in some cases the controller doesn't respond to this 
> immediately, it takes some nanoseconds for the controller's status 
> registers to reflect the change that was made. It's possible that if we 
> were trying to issue commands during this time, the controller might not 
> react properly. This patch adds some code to wait for the status 
> register to change to the state we asked for before continuing.

I went for the "I feel lucky" route and did just add mmio reads after the
mmio writes, posting them. Rationale being that if it is a write posting
issue, the debug patch would/could actually hide it AFAICT.
It's the "I feel lucky" route, because my whole "knowledge" about mmio
and write posting originates from the few things I read up on when you
discovered the comment about write posting in the generic ata code.

Björn
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