linux-kernel - Re: [PATCH] x86: Add reboot quirk for Dell Precision M4600

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Date:	Mon, 08 Aug 2011 11:40:58 -0500
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Matthew Garrett <mjg59@...f.ucam.org>
CC:	Ingo Molnar <mingo@...e.hu>, Mel Gorman <mgorman@...e.de>,
	tglx@...utronix.de, bruno@...a-net.ch, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Add reboot quirk for Dell Precision M4600

On 08/06/2011 10:30 AM, Matthew Garrett wrote:
> On Sat, Aug 06, 2011 at 08:56:35AM +0200, Ingo Molnar wrote:
>> Weird - ACPI is the default Windows method of reboot - how come it 
>> does not work on that box? Does Windows work around this specific 
>> machine (unlikely), or is our ACPI boot sequence not 100% compatible 
>> with the Windows method (more likely IMO)?
> 
> The ACPI reboot method on these machines hits the keyboard controller 
> rather than PCI, which is unusual. What I suspect is that the write 
> triggers some SMM or EC code that's making assumptions about system 
> state, and we're not quite identical. Bouncing on the keyboard 
> controller from userspace with init=/bin/bash wedges in the same way.
> 

I have a vague suspicion that Windows might have a meta-quirk for this
class of machines, i.e. if the ACPI reboot method, say, points at the
keyboard controller or points at the "PCI" reboot port then it actually
uses its own special-purpose routines rather than general routines.  It
would be extremely interesting to know if "reboot=kbd" works on these boxen.

	-hpa

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