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SubjectRe: [PATCH 45/79] [PATCH] fix apic acking of irqs
Maciej W. Rozycki wrote:
>> is inherited from x86_64, we call do_boot_cpu with irqs clearly enabled, and
>> check esr in the process.
>
> Please note that ESR may hold some leftover state from whatever happened
> before Linux has taken control, so it is reasonable and I think actually
> recommended by Intel (FWIW) to clear the register before enabling the
> error interrupt. For how to clear the ESR properly, please see
> setup_local_APIC() -- subtle differences and errata in various APIC
> implementations have made it more complicated than necessary, sigh...
which excerpt specifically are you talking about ?
the only ESR mention I see in setup_local_APIC() is this:

/* Pound the ESR really hard over the head with a big hammer -
mbligh */
if (esr_disable) {
apic_write(APIC_ESR, 0);
apic_write(APIC_ESR, 0);
apic_write(APIC_ESR, 0);
apic_write(APIC_ESR, 0);
}
which seems more like a disablement.
the bootup code does clean it, tough, by writing and reading the ESR.

>> But I can understand from the spec you posted that this is clearly an error.
>> So I'd have better come up with a new solution from this
>
> Well, with CONFIG_X86_GOOD_APIC set there is no RMW access to the ESR as
> apic_write_around() expands to apic_write(). And the option is meant to
> be clear only for the original integrated APIC as included in the Pentium
> processor ("Pentium-Classic" in the Kconfig nomenclature). I have no
> means to test such a system, but I still have a working dual-Pentium-MMX
> machine, which features local APICs that should be the same modulo errata.
> I may check and see whether a RMW cycle to the ESR triggers any problems
> with this computer, but the box is currently at the other end of the
> continent, so it will take a while.
>
> I have asked this question already: what kind of CPU are you running on?
> Do you really need to have CONFIG_X86_GOOD_APIC clear with it?
>
My testings that triggered that were with qemu, with randconfigs.
Probably it has a good apic, but it is good that it triggered anyway.
Otherwise I'd never see it.



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