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    SubjectRe: [PATCH] 2.6.18-rt7: PowerPC: fix breakage in threaded fasteoi type IRQ handlers

    > it's a compatibility hack only. Threaded handlers are a different type
    > of flow, but often the fasteoi handler is not changed to the threaded
    > handler so i changed it to be a threaded handler too.
    > threaded handlers need a mask() + an ack(), because that's the correct
    > model to map them to kernel threads - threaded handlers can be delayed
    > for a long time if something higher-prio is preempting them.

    I've re-read the old thread and I disagree with you there. I think the
    right approach was proposed initially by Daniel Walker.

    If my understanding of "threaded handlers" is correct, that is delaying
    the delivery of the interrupt to a thread while restoring the ability to
    process further interrupts of the same or lower priority immediately.

    There is no such thing as an explicit "ack" on fasteoi controllers. The
    ack is implicit with the reading of the vector (either via a special
    cycle on the bus or via reading the intack register for example on

    So by doing a mask followed by an eoi, you essentially mask the
    interrupt preventing further delivery of that interrupt and lower the
    CPU priority in the PIC thus allowing processing of further interrupts.

    Are there other fasteoi controllers than the ones I have on powerpc
    anyway ?

    There is one thing I disagree with in the initial patch from Daniel
    however, it's the fact that he can't deal with fasteoi handlers that
    have no mask/unmask.

    I have such a controller, on Cell, though currently I do have an empty
    mask and unmask for it, I've been thinking about removing them (and
    fixing callers to test for NULL). This is the Cell's top level
    controller and it is edge only (at this level, on Cell, all interrupts
    are messages).

    Thus it can perfectly well cope with soft-masking (delayed disable if
    you prefer) and that is compatible with using a fasteoi handler. There
    should be no reason why that wouldn't work for -rt as well.


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