linux-kernel - Re: [PATCH] Blacklist DMAR on Intel G31/G33 chipsets

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Date:	Sat, 6 Sep 2008 17:49:35 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	linux-kernel@...r.kernel.org, andi@...stfloor.org,
	arjan@...radead.org, torvalds@...ux-foundation.org,
	sfr@...b.auug.org.au, Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [PATCH] Blacklist DMAR on Intel G31/G33 chipsets


* David Woodhouse <dwmw2@...radead.org> wrote:

> On Fri, 2008-09-05 at 20:34 +0200, Ingo Molnar wrote:
> > * David Woodhouse <dwmw2@...radead.org> wrote:
> > 
> > > Some BIOSes (the Intel DG33BU, for example) wrongly claim to have DMAR
> > > when they don't. Avoid the resulting crashes when it doesn't work as
> > > expected.
> > > 
> > > Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>
> > > ---
> > > 
> > > This time, I build-tested it with CONFIG_DMAR actually enabled. Sorry. 
> > > I'd still be grateful if someone could test it on a DG33BU with the 
> > > old BIOS though, since I've killed mine. I tested the DMI version, but 
> > > not this one.
> > 
> > ok - fixing this makes sense. I have two worries about this patch.
> > 
> > Firstly, the quirk is keyed off an ACPI capability which is quite bad if 
> > someone boots with ACPI off. (which is still quite possible) The DMAR is 
> > PCI enumerated so there's nothing inherently ACPI about this. A DMI 
> > quirk (which will work even if ACPI is disabled) looks more robust.
> 
> No, the intel-iommu code is isn't PCI-enumerated -- it all depends on 
> that ACPI table, unfortunately. [...]

ah, you are right ... and i thought i could trust grep -i acpi 
drivers/pci/intel-iommu.c coming up empty ;-)

Jesse's call obviously, but the DMI thing local to intel-iommu.c still 
looks better to me in all regards. I'm no fan of DMI in general - it 
just doesnt scale - but here a crappy BIOS gets punished with a DMI 
quirk and that's OK.

	Ingo
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