linux-kernel - Re: [RFC -tip] x86,apic -- reduce disable

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Message-ID: <20090705190211.GK4791@lenovo>
Date:	Sun, 5 Jul 2009 23:02:11 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Yinghai Lu <yinghai@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC -tip] x86,apic -- reduce disable_apic usage

[H. Peter Anvin - Sun, Jul 05, 2009 at 10:30:11AM -0700]
| Maciej W. Rozycki wrote:
| > 
| >  How do you set cpu_has_apic for systems with discrete local APICs?  The 
| > CPUID flag is not set in this case.
| > 
| 
| Well, should it be?  We do set flags when they're appropriate to us, and
| if the semantics are such as that is inappropriate we can set a custom bit.
| 
| 	-hpa
| 

Peter, Maciej but how kernel behaved on older cpu long time ago?

I mean -- should user pass "lapic" cmdline option too be
able to use apic functionality? (i'm asking since I just
don't know how it had been working before). Current
code (if only I'm not _missing_ something) relies on cpu_has_apic
bit. And even if MP table has been parsed and APIC base found,
cpu_has_apic could be not set so detect_init_APIC will fail
if no "lapic" option passed (in case of old cpu without this cpuid
bit produced) as we eventually stay with pic mode.

	-- Cyrill
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