Messages in this thread |  | | | Date | Fri, 14 Dec 2007 18:20:04 -0800 | | From | "H. Peter Anvin" <> | | Subject | Re: [PATCH] x86_64: fix problems due to use of "outb" to port 80 on some AMD64x2 laptops, etc. | |
David P. Reed wrote:
>
> I believe (though no one seems to have confirming documentation from the
> chipset or motherboard vendor) that port 80 is actually functional for
> some unknown function on these machines. (They do respond to "in"
> instructions faster than a bus cycle abort does - more evidence).
>
This is normal. IN from port 0x80 is used by the DMA address map chip.
As far as I understand, there are other laptops with the same chipset
which don't have this problem, so it's likely either a motherboard or
firmware issue. My guess is that they probably let debugging code out
in the field (trap port 0x80 in SMM, and then try to output it on some
debugging bus.)
-hpa
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