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

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Date:	Mon, 06 Oct 2008 22:59:37 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	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> 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
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