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

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Date:	Sat, 15 Dec 2007 12:25:20 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Rene Herman <rene.herman@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, "David P. Reed" <dpreed@...d.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Rene Herman <rene.herman@...access.nl>,
	Pavel Machek <pavel@....cz>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] x86_64: fix problems due to use of "outb" to port 80
 on some AMD64x2 laptops, etc.

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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