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    SubjectRe: [BUG] Ricoh Cardbus -> Can't get interrupts

    On Mon, 24 Nov 2003, Linus Torvalds wrote:
    > We don't ever try to autoprobe for PCI interrupts, because it's fragile
    > and tends to cause lockups on any hardware where the irq is shared with
    > something else

    Side note as way of explanation: autoprobing for ISA interrupts only works
    because they are edge-triggered, so even if they are shared - which is
    against the ISA spec, but commonly done anyway - the autoprobe would just
    fail, not lock up the machine.

    PCI interrupts are not only _routinely_ shared (making them fundamentally
    harder to probe for), but they are level-triggered, so if you don't shut
    them off in the interrupt handler, you end up with a dead machine that
    constantly takes interrupts.

    These days, our improved irq handler infrastructure could actually pick
    out the shared interrupts from the probed ones (now that drivers return a
    status word saying whether the irq was for an existing driver or not), so
    we could some day allow even PCI drivers to autodetect the irq if
    everything else fails.

    But it's _very_ rare to see it fail. The 2.4.x cardbus driver does the
    same thing, and I don't know of any consistent failure patterns. What kind
    of strange machine is this, Jean? Prototype with a broken BIOS?

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      Last update: 2009-11-18 23:46    [W:0.019 / U:81.984 seconds]
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