linux-kernel - Re: sata_svw data corruption, strange problems

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Message-Id: <1214216602.8011.259.camel@pasglop>
Date:	Mon, 23 Jun 2008 20:23:22 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Tejun Heo <tj@...nel.org>, Pavel Machek <pavel@...e.cz>,
	Andreas Schwab <schwab@...e.de>,
	kernel list <linux-kernel@...r.kernel.org>, jgarzik@...ox.com,
	IDE/ATA development list <linux-ide@...r.kernel.org>,
	Trivial patch monkey <trivial@...nel.org>
Subject: Re: sata_svw data corruption, strange problems

On Mon, 2008-06-23 at 10:42 +0100, Alan Cox wrote:
> > > BTW. Tejun, I suppose that usually starting DMA after issuing the
> > > command is a standard practice of legacy/sff type controllers ? Or it's
> > > just because that's how linux did it until now ?
> > 
> > It's how the standard says it should be programmed.  Please take a look
> > at section 3 of the following document.
> > 
> > http://www.centrillium-it.com/Projects/idems100.pdf
> > 
> > It's a non-issue for PATA ones as the host is responsible for running
> 
> It's very much an issue for PATA. If you start the DMA before time things
> go wrong. The DMA has to start after the command is issued (or for ATAPI
> after the command and the cdb are issued). Various ATAPI devices get
> quite cross if you mess this up.
> 
> In some cases the driver code also depends upon this as we software drive
> the data clocks so have to reprogram them after command issue and before
> data transfer begins.

Might explain why those broadcom chipsets are also allergic to ATAPI
DMA :-)

Ben.


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