Date: Sat, 15 Dec 2007 17:51:17 +0000
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: "David P. Reed" <dpreed@reed.com>
Cc: Ingo Molnar <mingo@elte.hu>, Rene Herman <rene.herman@gmail.com>,
       "H. Peter Anvin" <hpa@zytor.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>
Subject: Re: [PATCH] x86_64: fix problems due to use of "outb" to port 80 on
 some AMD64x2 laptops, etc.
Message-ID: <20071215175117.17e5d5ee@the-village.bc.nu>
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> 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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