linux-kernel - Re: [PATCH 15/15] Revert "x86: default to reboot via ACPI"

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Date:	Sun, 9 Nov 2008 10:24:23 +0000
From:	Matthew Garrett <mjg@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Zhao Yakui <yakui.zhao@...el.com>, Len Brown <lenb@...nel.org>,
	Andrey Borzenkov <arvidjaar@...l.ru>,
	Ingo Molnar <mingo@...e.hu>,
	Eduardo Habkost <ehabkost@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...l.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH 15/15] Revert "x86: default to reboot via ACPI"

On Sun, Nov 09, 2008 at 12:11:03PM +0200, Avi Kivity wrote:
> Matthew Garrett wrote:
> >Hmm. But we're seeing some machines that end up very confused if 
> >rebooted via ACPI. I guess we need to run Vista on them to find out how 
> >they behave. What OSI strings did your KVM setup expose? We know that 
> >Windows changes behaviour under various circumstances depending on which 
> >OS the firmware requests, so it's almost possible that this is another 
> >of those cases.
> >  
> 
> Isn't it the other way around?  The firmware changes behavior depending 
> on how the OS identifies itself?

That also happens, yes.

> Reboot is a fixed feature IIRC, so it cannot change depending on 
> identification strings.

The ID strings that the firmware requests give a good idea about which 
operating systems the machine has been tested with. If Vista uses the 
ACPI method then having the firmware request the OSI string for Vista 
gives us a good indication that it's safe to use the ACPI method.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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