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    SubjectRe: [PATCH] x86: provide a DMI based port 0x80 I/O delay override.
    David P. Reed wrote:
    > Alan, thank you for the pointers. I have been doing variations on this
    > testing theme for a while - I get intrigued by a good debugging
    > challenge, and after all it's my machine...
    > Two relevant new data points, and then some more suggestions:
    > 1. It appears to be a real port. SMI traps are not happening in the
    > normal outb to 80. Hundreds of them execute perfectly with the expected
    > instruction counts. If I can trace the particular event that creates
    > the hard freeze (getting really creative, here) and stop before the
    > freeze disables the entire computer, I will. That may be an SMI, or
    > perhaps any other kind of interrupt or exception. Maybe someone knows
    > how to safely trace through an impending SMI while doing printk's or
    > something?
    > 2. It appears to be the standard POST diagnostic port. On a whim, I
    > disassembled my DSDT code, and studied it more closely. It turns out
    > that there are a bunch of "Store(..., DBUG)" instructions scattered
    > throughout, and when you look at what DBUG is defined as, it is defined
    > as an IO Port at IO address DBGP, which is a 1-byte value = 0x80. So
    > the ACPI BIOS thinks it has something to do with debugging. There's a
    > little strangeness here, however, because the value sent to the port
    > occasionally has something to do with arguments to the ACPI operations
    > relating to sleep and wakeup ... could just be that those arguments are
    > distinctive.

    Dumb question: if you change your iodelay function so it always writes
    zero to port 0x80, does it start working?


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