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

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Date:	Fri, 10 Apr 2009 14:27:50 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
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@...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.

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.

> -#ifdef CONFIG_X86_64
> -		if (!disable_apic)
> -			ack_APIC_irq();
> -#endif
> -
> +		ack_APIC_irq_safe();

Please keep the ack_APIC_irq() name - it is inherently safe to call 
it if we always give it a meaningful ->write method.

	Ingo
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