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

["H. Peter Anvin" <hpa@zytor.com>]

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