linux-kernel - Re: [RFC -tip] x86: do_IRQ - send APIC EOI for x86-32 on irq without handler v3

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Message-ID: <20090410140023.GA29090@elte.hu>
Date:	Fri, 10 Apr 2009 16:00:23 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	Yinghai Lu <yhlu.kernel@...il.com>
Subject: Re: [RFC -tip] x86: do_IRQ - send APIC EOI for x86-32 on irq
	without handler v3


* Cyrill Gorcunov <gorcunov@...il.com> wrote:

> [Ingo Molnar - Fri, Apr 10, 2009 at 02:27:50PM +0200]
> | 
> | * Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
> | 
> | > Ingo, I've checked the sources and as far as I see
> | > we could NOP'ify apic->write indeed but I have
> | > an internal feeling that this will bring us more problem
> | > in future (for example it could be the following scenario:
> | > some screwed APIC would require cleaning of LVT's or
> | > IRR after resume regardless if it was initialized
> | > or not at all). Mostly I mean that the idea of making
> | > apic->write NOP'ified is quite elegant indeed but
> | > cut off the subset of apic operations (we need
> | > apic->read anyway) somehow bothering me from inside :)
> | 
> | it's as if assigned a special type of 'dummy apic' struct apic. It 
> | wont cause problems down the line: we use the new APIC driver 
> | infrastructure to abstract out quirks.
> 
> Well, it's not that new actually :-)

Yeah, i mean the new unified/modernized code in 2.6.30-to-be.

> | 
> | one small detail:
> | 
> | > +/* Ack APIC irq if it's enabled only */
> | > +static inline void ack_APIC_irq_safe(void)
> | > +{
> | > +#ifdef CONFIG_X86_LOCAL_APIC
> | > +	if (cpu_has_apic)
> | > +		ack_APIC_irq();
> | > +#endif
> | 
> | we dont need the cpu_has_apic check there, do we? In the 
> | !cpu_has_apic the ->write method should be a dummy.
> 
> Yes. In case you're talking about it'll not be needed
> (we will find earlier whether cpu_has_apic or not).

yeah.

	Ingo
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