Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override.
- From: "H. Peter Anvin" <hpa@xxxxxxxxx>
- Date: Tue, 01 Jan 2008 13:16:49 -0800
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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