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 17:51:17 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	"David P. Reed" <dpreed@...d.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Rene Herman <rene.herman@...il.com>,
	"H. Peter Anvin" <hpa@...or.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>
Subject: Re: [PATCH] x86_64: fix problems due to use of "outb" to port 80 on
 some AMD64x2 laptops, etc.

> a minor concern, but I did also point out that using an unused port 
> causes the bus to be tied up for a microsecond or two, which matters on 
> a fast SMP machine.

And I did point out I'd found locking cases that may be relying upon this

> I also note that curent machines like the problem machine have ACPI, and 
> maybe those would be the ones that vendors might start to define port 80 
> to mean something. As I noted, it /seems/ to be only when ACPI is turned 

Port 0x80 means debug. You appear to have a laptop with some kind of
buggy firmware that wants a BIOS update. Everyone use 0x80 for debug -
its in the chipset hardware quite often.

> My belief is that my machine has some device that is responding to port 
> 80 by doing something.  And that something requires some other program 
> to "service" port 80 in some way.  But it sure would be nice to know.   
> I can't personally sand off the top of the chipset to put probes into it 
> - so my normal approach of putting a logic analyzer on the bus doesn't work.

Almost certainly a SMI trap.

> PS: If I have time, I may try to build Rene's port 80 test for Windows 
> and run it under WinXP on this machine 

That would be very interesting.

Alan
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