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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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