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

[Ingo Molnar <mingo@elte.hu>]

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Mon, 6 Oct 2008, Rafael J. Wysocki wrote:
> > 
> > Unfortunately some of the recent IO-APIC changes made the bug show 
> > up.  To prevent this from happening, blacklist machines that are 
> > known to be affected (nx6115 and 6715b in this particular case).
> 
> Can you point to exactly _which_ recent change made it show up? I'd 
> really like to know. _What_ was it that made us suddenly need this 
> quirk when it wasn't necessary before? I'd like to understand the root 
> cause here.
> 
> And how did you even start looking at that strange ACPI override?

i think it was caused by this stream of IO-APIC changes:

 49a66a0: x86: I/O APIC: Always report how the timer has been set up
 17c4469: x86: I/O APIC: Include <asm/i8259.h> required by some code
 593f4a7: x86: APIC: remove apic_write_around(); use alternatives
 ce8b06b: x86: I/O APIC: remove an IRQ2-mask hack
 af17478: x86: I/O APIC: Never configure IRQ2
 c88ac1d: x86: L-APIC: Always fully configure IRQ0
 1baea6e: x86: L-APIC: Set IRQ0 as edge-triggered

Rafael/Maciej, which of these is causing it? ce8b06b ("x86: I/O APIC: 
remove an IRQ2-mask hack")?

Current theory is that this specific flavor of BIOS on HP / AMD / Turion 
laptops (no other type is known to be affected at the moment) somehow 
detects the IO-APIC masking patterns and uses an SMI quirk to change the 
ACPI thermal trip point to very low settings, and thus confusing cpufreq 
to (correctly) go into a very slow frequency.

Activating the quirk works this around. Should we perhaps default to 
this 'quirk' enabled by default?

	Ingo