Re: [PATCH] x86_64: fix problems due to use of "outb" to port 80on some AMD64x2 laptops, etc.

From: H. Peter Anvin
Date: Sat Dec 15 2007 - 15:26:58 EST


Rene Herman wrote:

It's really going to have to be a known _un_used register and (the write direction of) port 0x80 is used exactly for that reason. Port 0xed is a known "alternate diagnostic port" used by Phoenix BIOSes at least but Peter Anvin reported trouble with that one -- probably for the outb direction but assuming that means something was in fact responding, we'd have the same timing problem.


Yes, for the outbound direction.

I believe we have two "good" options:

1) port 0xed was tested by the current reporter and found to be safe (and provide slow enough timing). If DMI based quirk hacks are available soon enough we can switch 0x80 to 0xed based on it. Are they?

DMI is just a data structure parked in memory, so it should at least be theoretically possible to get to it.

-hpa
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