Message-ID: <47643830.3000302@zytor.com>
Date: Sat, 15 Dec 2007 12:25:20 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Rene Herman <rene.herman@gmail.com>
CC: Ingo Molnar <mingo@elte.hu>, "David P. Reed" <dpreed@reed.com>,
       Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
       Ingo Molnar <mingo@redhat.com>, Rene Herman <rene.herman@keyaccess.nl>,
       Pavel Machek <pavel@ucw.cz>, Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: [PATCH] x86_64: fix problems due to use of "outb" to port 80
 on some AMD64x2 laptops, etc.
References: <1184218962.12353.209.camel@chaos> <46964352.7040301@reed.com> <1184253339.12353.223.camel@chaos> <469697C6.50903@reed.com> <1184274754.12353.254.camel@chaos> <4761F193.7090400@reed.com> <20071214131502.GA14359@elte.hu> <4762C551.5070003@zytor.com> <20071215074358.GD12110@elte.hu> <4763891A.3010004@gmail.com> <20071215132725.GA23166@elte.hu> <4763DE3F.405@gmail.com>
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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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