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    SubjectRe: [PATCH] x86: provide a DMI based port 0x80 I/O delay override.

    > 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.

    Maybe someone just left debugging code in production?

    > In thinking about this, I recognize a couple of things. ACPI is telling
    > us something when it declares a reference to port 80 in its code. It's
    > not telling us the function of this port on this machine, but it is
    > telling us that it is being used by the BIOS. This could be a reason
    > to put out a printk warning message... 'warning: port 80 is used by
    > ACPI BIOS - if you are experiencing problems, you might try an alternate
    > means of iodelay.'
    > Second, it seems likely that there are one of two possible reasons that
    > the port 80 writes cause hang/freezes:
    > 1. buffer overflow in such a device.
    > 2. there is some "meaning" to certain byte values being written (the
    > _PTS and _WAK use of arguments that come from callers to store into port
    > 80 makes me suspicious.) That might mean that the freeze happens only
    > when certain values are written, or when they are written closely in
    > time to some other action - being used to communicate something to the

    There's nothing easier than always writing 0 to the 0x80 to check if
    it hangs in such case...?

    (cesky, pictures)

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