linux-kernel - RE: ASUS M2NPV-VM APIC/ACPI Bug (patched)

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Date:	Thu, 19 Oct 2006 08:52:11 -0700
From:	"Allen Martin" <AMartin@...dia.com>
To:	"Robert Hancock" <hancockr@...w.ca>, "Len Brown" <lenb@...nel.org>,
	"linux-kernel" <linux-kernel@...r.kernel.org>
Cc:	"Daniel Mierswa" <impulze@...ulze.org>, "Andi Kleen" <ak@...e.de>,
	"Andy Currid" <ACurrid@...dia.com>
Subject: RE: ASUS M2NPV-VM APIC/ACPI Bug (patched)

> > I recall quite clearly that Nvidia told us that that 
> > acpi_skip_timer_override was necessary in NFORCE2 days.  I don't 
> > remember the HPET qualification to that statement -- I 
> guess that came later.
> > Unfortunately, my NFORCE2 board is dead, so I can't really 
> test this out directly.
> > 
> > Perhaps checking for PCI_VENDOR_ID_NVIDIA is too broad and the 
> > workaround is counter-productive on their newer NVIDIA chip-sets?
> > 
> > -Len
> > 
> > ps.
> > One (other) problem with this code is that it checks for an HPET 
> > table, but doesn't check that the kernel has HPET support enabled.
> 
> I think the intent of the HPET check was that the quirk 
> wasn't needed on chipsets new enough to have an HPET. 
> Unfortunately, even if the chipset has an HPET it isn't 
> always enabled by the BIOS.
> 
> Clearly this quirk is too broad, it should likely be only 
> triggering on known chipset revisions with the bad timer 
> overrides and not on all NVIDIA chipsets. What I am wondering 
> is how these boards manage to work fine in Windows, 
> (presumably) without any such chipset-specific tweaks..

The problem is this workaround doesn't fix a chipset issue, it fixes
incorrect entries in the BIOS ACPI tables.  This bug existed in the
NVIDIA reference BIOS for nForce2 and got copied to all customer BIOSes
for nForce2.  Even though our reference BIOSes and documentation for all
chipsets since then have the correct interrupt overrides in the ACPI
tables we still see customer BIOSes that get shipped with incorrect
entries that were probably copied from their nForce2 BIOS code.

I believe the HPET check was because the workaround was causing problems
when enabling HPET on systems that support it.  Andy probably has more
details on that.

-Allen
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