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    SubjectRe: A question concerning time outs and possible lost interrupts

    On Mon, 14 Sep 1998, Gerard Roudier wrote:

    > 1 - Read the Interrupt Status Register (ISTAT)
    > If completion interrupt (INTFLY)
    > 2 - Write the ISTAT to clear the interrupt condition.
    > 3 - Reread the ISTAT. This read will ensure that PCI posted writes
    > that may have occured between (1) and (2) are flushed and that the
    > Interrupt condition is actually cleared.
    > (This seems overcommitting, but hopefully it is not)
    > 4 - Scan the completion queue.
    >
    > Between (1) and (2) the controller may have written to memory some
    > completion data and these transactions may be posted.
    > The write to the ISTAT (2) may also be posted.
    > (3) ensures that all this stuff will be actually visible by the
    > corresponding parts at the moment the completion queue is scanned
    > by the C code.

    just out of curiousity, does the problem remain if the NCR driver is
    booted in non-ioremapped mode? in/out is slower but much more conservative
    and this should exclude lots of cache invalidation/chipset posted write
    bug possibilities.

    -- mingo


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