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

[Andi Kleen <andi@firstfloor.org>]

"Maciej W. Rozycki" <macro@linux-mips.org> writes:
>
>  This single instance of a piece of some HP gear being twisted beyond 
> belief is IMO a minor annoyance and price to pay compared to the gain.  
> Please note that apart from the DSDT being buggy on this machine, it has 
> an incorrect IRQ 0 override in the ACPI table pointing to the pin #2 of 
> the I/O APIC, which is in fact routed to the output of the master 8259A.  
> Additionally the pin #0 of the I/O APIC which is indeed routed to the 
> output of the 8254 does not receive any interrupts, presumably because of 
> some misconfiguration during BIOS initialisation. 

The real reason is actually a workaround in the BIOS for problems
in the older Linux code that caused duplicated timer interrupts. The
old Linux would fall into "enable both IO-APIC and 8259" fallback mode
and the resulted in duplicated timer events, which made everything unhappy.
They instead configured the northbridge in a way that one of the inputs
is ignored.

You won't be able to DMI list it, that workaround is widely used
in lots of different systems.

-andi