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Date: Wed, 6 Jan 2010 20:29:18 +0000
From: Matthew Garrett <mjg59@srcf.ucam.org>
To: Len Brown <lenb@kernel.org>
Cc: Arjan van de Ven <arjan@infradead.org>, "H. Peter Anvin" <hpa@zytor.com>,
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Subject: Re: [PATCH] Add DMI quirk for Intel DP55KG mainboard
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On Wed, Jan 06, 2010 at 03:22:30PM -0500, Len Brown wrote:

> I've looked at _OSI use in over a hundred DSDTs and never
> seen run-time re-configuration of reset support.

The point isn't that the firmware changes its behaviour - the point is 
that the OS does.

> I do not think the BIOS has a run-time decision to make here.
> If a box is designed to support Windows XP and newer, it is
> likely that ACPI_RESET is simply valid and XP blindly uses it.
> If reset fails, the box doesn't pass WHQL and the box is fixed.
> If W2K is run on that box, ACPI_RESET is still valid, just that
> W2K chooses to not write to it.

And if ACPI_RESET is set but untested (because 2000 never used it)?

> We can't rely on blind use of _OSI to mean "new enough", since
> it was supported back in W2K era.  That means we have to parse
> the OSI strings.  But what happens when a BIOS writer decides to
> evaluate _OSI("Windows Future") without evaluating any of the
> old strings we know about?  We would disable ACPI reset on such
> a future box?

Potentially, yes. But since such a machine would clearly expect to be 
treated as "Windows Future", we'd be running it in an untested 
configuration anyway.

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