linux-kernel - Re: something strange in libata-core.c for kernel 2.6.22-rc3

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Date:	Mon, 21 May 2007 11:09:03 +0200
From:	Tejun Heo <htejun@...il.com>
To:	Robert Hancock <hancockr@...w.ca>
CC:	linux-kernel <linux-kernel@...r.kernel.org>,
	ide <linux-ide@...r.kernel.org>, l.genoni@...relinux.com,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: something strange in libata-core.c for kernel 2.6.22-rc3

Robert Hancock wrote:
>> Alan, did you have a chance to test the ACPI cable detection?  It just
>> didn't work when I tried it.  It always returned 80c on my machine.
> 
> On a whim I started poking around in the disassembled ACPI DSDT code for
> my Asus A8N-SLI Deluxe board, which is one of these chipsets. The
> original thought was that the STM/GTM trick on these chipsets is
> supposed to allow us to determine what modes we should use based on what
> modes it sets up appropriately. Unfortunately, unless I'm missing
> something in the AML (which is possible) it doesn't seem like there is
> any validation being done on the settings passed in. The settings appear
> to essentially just get programmed into the controller when STM is
> called and read back on GTM.

Yeah, that's consistent to what I've seen on my machine which is a
variant of A8N.  No matter what value I through at _STM, _GTM just
echoed the result thus always leading to 80c configuration.

> I guess this means that what we have to do is trust that the BIOS set up
> a reasonable mode and base the cable detect on that (either by reading
> back the boot-up controller registers, or by calling GTM). I imagine
> this is what the Windows default IDE driver is doing (just using the
> boot-up mode and feeding it back using GTM/STM on suspend/resume cycles).

Alan, what do you think?

-- 
tejun
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