Change in coreboot[master]: cpu/x86/lapic: Support switching to X2APIC mode

[Angel Pons (Code Review)]

Attention is currently required from: Kyösti Mälkki.
Angel Pons has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/55262 )

Change subject: cpu/x86/lapic: Support switching to X2APIC mode
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Patch Set 10: Code-Review+1

(1 comment)

Patchset:

PS8:
> Where do you need is_x2apic_mode() to return false? There might be a problem with initial_lapicid() and lapicid() being stashed.

Maybe I didn't explain myself, I don't need `is_x2apic_mode()` to return false at any point. I just explained my train of thought. I noted that `is_x2apic_mode()` never returns false in the X2APIC_RUNTIME case, so the only difference with X2APIC_ONLY is that the `rdmsr(LAPIC_BASE_MSR)` call is omitted.
> This makes X2APIC_ONLY work?
>
> diff --git a/src/include/cpu/x86/lapic.h b/src/include/cpu/x86/lapic.h
>    index 4fbae88ca5..50417acca5 100644
>    --- a/src/include/cpu/x86/lapic.h
>    +++ b/src/include/cpu/x86/lapic.h
>    @@ -75,11 +75,12 @@ static inline bool is_x2apic_mode(void)
>    	if (CONFIG(XAPIC_ONLY))
>    		return false;
>   msr_t msr;
>   msr = rdmsr(LAPIC_BASE_MSR);
> if (CONFIG(X2APIC_ONLY))
> 	return true;
>   msr_t msr;
>   msr = rdmsr(LAPIC_BASE_MSR);
> return ((msr.lo & LAPIC_BASE_X2APIC_ENABLED) == LAPIC_BASE_X2APIC_ENABLED);
> }

Yes, I can try again to be sure.