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    SubjectRe: Cleanups for APIC
    On Thu, 27 May 2004, Ingo Molnar wrote:

    > > The I/O APIC need not be hooked to PCI ;-) -- I'm not sure about the
    > > i82093AA, but that's definitely true for the i82489DX. The call to
    > > io_apic_sync() is needed for masking to make sure interrupts won't be
    > > dispatched after returning from the call -- this is not needed for
    > > unmasking as a delay here is harmless.
    >
    > well, an APIC message could be on the way to the CPU even with this
    > synchronization. Does it matter whether it's a newly dispatched one due
    > to POST delays or an in-fly one due to APIC bus delays?

    Well, if you'd mask, sync, ack (send EOI) in a handler, then the sync
    would assure the ack wouldn't be in effect before masking, so no further
    interrupt would arrive till unmasking. It would work for level-triggered
    interrupts and the i82093AA, but OTOH for the i82489DX, which uses
    level-deassert messages, it wouldn't.

    Too much hassle for an unreliable result... Just scrap it.

    --
    + Maciej W. Rozycki, Technical University of Gdansk, Poland +
    +--------------------------------------------------------------+
    + e-mail: macro@ds2.pg.gda.pl, PGP key available +
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