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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?

-hpa


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