Re: [PATCH] x86_64: fix problems due to use of "outb" to port 80 on some AMD64x2 laptops, etc.
- From: "H. Peter Anvin" <hpa@xxxxxxxxx>
- Date: Fri, 14 Dec 2007 18:20:04 -0800
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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- [PATCH] x86_64: fix problems due to use of "outb" to port 80 on some AMD64x2 laptops, etc.
- From: David P. Reed
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