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

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

> [Ingo Molnar - Fri, Apr 10, 2009 at 04:00:23PM +0200]
> |
> | * Cyrill Gorcunov <gorcunov@gmail.com> wrote:
> |
> | > [Ingo Molnar - Fri, Apr 10, 2009 at 02:27:50PM +0200]
> | > |
> | > | * Cyrill Gorcunov <gorcunov@openvz.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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