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

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Date:	Sun, 12 Apr 2009 16:06:50 +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 04:00:23PM +0200]
> | 
> | * 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
> | 
> 
> Ingo,
> 
> I think you meant something like the patch below. It's
> not finished yet -- I need to find out right place for
> calling freshly introduced apic_disable_write_op.
> Will continue tomorrow.
> 
> But even having it not completed yet I would like to
> get some feedbackabout code structure in general.

Yeah, the goal now looks good.

Note, i'd suggest to not expose it like this:

>  extern u64 native_apic_icr_read(void);
> +extern void native_apic_write_dummy(u32 reg, u32 v);
>  
>  #define EIM_8BIT_APIC_ID	0
>  #define EIM_32BIT_APIC_ID	1
> @@ -372,6 +373,15 @@ static inline void apic_write(u32 reg, u
>  	apic->write(reg, val);
>  }
>  
> +/*
> + * right after this call apic->write doesn't do anything
> + * note that there is no restore operation it works one way
> + */
> +static inline void apic_disable_write_op(void)
> +{
> +	apic->write = native_apic_write_dummy;
> +}
> +

But have a central and opaque:

	extern void apic_disable(void);

function, defined in apic.c - which does all the internal details 
(like installing a dummy ->write) entry.

	Ingo
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