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

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Date:	Mon, 23 Jun 2008 22:05:40 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	benh@...nel.crashing.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

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.

I was saying drive getting ready before command issue was non issue.

-- 
tejun
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