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    SubjectRe: [RT] MPIC edge sensitive issues with hardirq preemption
    On Tue, Jul 01, 2008 at 02:41:19PM +0400, Sergei Shtylyov wrote:
    > Hello.
    > Anton Vorontsov wrote:
    >> But how this could be a bug in the PIC code? IMO this is a bug in the
    >> kernel/irq code, since it assumes that fasteoi PIC will retrigger masked
    >> edge sources... This isn't true for at least MPIC. To make this work for
    >> all fasteoi PICs, we should mask edge sensitive interrupts very very
    >> carefully.
    > I guess it assumed this based on 8259's behavior (not sure about I/O
    > APIC).
    > Hm, but the 8259 code never used "fasteoi" path for some obscure
    > reason...
    >> jammed with the idea that MPIC irq type 0 is low level sensitive, but the
    >> true thing is that it is rising edge sensitive. (Ah, I know where I got
    >> confused, type 0 is active-low for ISA PICs).
    > You mean in the device tree?

    Yes, simply changing device tree.

    >> So in all my previous emails I was wrong when I was saying "mpic is
    >> programmed to low level sensitive". It was programmed for rising edge
    >> sensitive. An all my further reasonings were flawed because of this.
    > Gah. I'm surprised how it could work at all then...
    >> Re-programming MPIC to high level sensitive also makes IDE work. But
    >> this doesn't mean that IRQ code is correct.
    > I wonder why. :-O
    > Your ULi IDE is in native mode, so it should be generating a PCI
    > interrupt -- which is *low* level sensitive.

    Exactly. This is another reason why I was so confused.

    Anton Vorontsov

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