Re: [PATCH] x86 ACPI: Blacklist two HP machines with buggy BIOSes (Re: 2.6.27-rc8+ - first impressions)

[Ingo Molnar <mingo@elte.hu>]

* Maciej W. Rozycki <macro@linux-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