linux-kernel - Re: [PATCH] i386: add command line option "local_apic_timer_c2

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Date:	Tue, 27 Mar 2007 14:34:27 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Len Brown <lenb@...nel.org>
cc:	Thomas Gleixner <tglx@...utronix.de>, Pavel Machek <pavel@....cz>,
	Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Mingming Cao <cmm@...ibm.com>, Adrian Bunk <bunk@...sta.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
	Mariusz Kozlowski <m.kozlowski@...land.pl>,
	Oliver Pinter <oliver.pntr@...il.com>,
	Sid Boyce <g3vbv@...eyonder.co.uk>,
	Nick Piggin <npiggin@...e.de>,
	Jens Axboe <jens.axboe@...cle.com>,
	Thomas Renninger <trenn@...e.de>
Subject: Re: [PATCH] i386: add command line option "local_apic_timer_c2_ok"



On Tue, 27 Mar 2007, Len Brown wrote:
> 
> I think the only fool-proof way to do this automatically is to

Why not just take the known-good CPUID signature?

Screw firmware or ACPI tables. They're going to be occasionally wrong.

If we know that "Core 2, version X" has a good local APIC timer, we use 
it. Otherwise we don't.

That's generally how we handle other APIC bugs too (the read-after-write 
thing, for example, or the differences between integrated and off-chip 
APIC's). Sometimes we check the APIC version itself, sometimes we check 
the CPUID information, and sometimes we check both ("modern_apic()").

			Linus
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