linux-kernel - Re: [PATCH] x86 ACPI: Blacklist two HP machines with buggy BIOSes (Re: 2.6.27-rc8+

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Date:	Tue, 7 Oct 2008 06:42:37 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Len Brown <lenb@...nel.org>,
	Jason Vas Dias <jason.vas.dias@...il.com>
Subject: Re: [PATCH] x86 ACPI: Blacklist two HP machines with buggy BIOSes
	(Re: 2.6.27-rc8+ - first impressions)

* Maciej W. Rozycki <macro@...ux-mips.org> wrote:

> > >  Well, perhaps, but the thermal trip point phenomenon seems unique 
> > > to this family of systems.  The other aspects of the problem do 
> > > not really matter anymore as we seem to have addressed them 
> > > robustly enough now.
> > 
> > When you need DMI entries you clearly haven't.
> 
>  You can't just break a piece of hardware randomly (setting the 
> thermal trip points based on an interrupt mask of an I/O APIC input is 
> certainly beyond the ACPI spec), hide its documentation and still 
> demand it to be supported correctly, possibly hurting all the other 
> good equipment.  Sorry -- you have to draw a line somewhere. [...]

agreed. This is a clear example of a complex and hard to track down BIOS 
bug - and even in this case we go out on a limb working it around.

The first approach to such problems is usually a DMI pattern based fix - 
they happen when we dont know the full scope of a particular problem yet 
but have a rough idea and want to react to bugs quickly.

PCI ID based quirks are preferred much more in the long run: DMI pattern 
matching does not scale as the DMI space is human-visible and hence 
changes frequently not for technical/hw-environment but for 
perception/PR reasons, hence it is far less reliable programmatically 
than the PCI ID space.

But PCI ID methods, while more intelligent, they lag behind a bit and 
depend on good cooperation with hw makers. As long as DMI pattern 
matches end up turning into PCI ID based approaches, like here, i'm not 
complaining as a maintainer ;)

Thanks Maciej for your excellent in-depth analysis of this issue, and 
for your many fixes in this area of code - you squashed many difficult, 
long-standing bugs in this space.

	Ingo
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