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Date: Tue, 11 Dec 2007 09:05:06 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: "David P. Reed" <dpreed@reed.com>
CC: Rene Herman <rene.herman@keyaccess.nl>, Paul Rolland <rol@as2917.net>,
       David Newall <david@davidnewall.com>, Krzysztof Halasa <khc@pm.waw.pl>,
       Pavel Machek <pavel@ucw.cz>, Andi Kleen <andi@firstfloor.org>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>, linux-kernel@vger.kernel.org,
       Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
       rol@witbe.net
Subject: Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64
 with MCP51 laptops
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David P. Reed wrote:
> I do remind all that 0x80 is a BIOS-specific standard, and is per BIOS - 
> other ports have been used in the history of the IBM PC family by some 
> vendors, and some machines have used it for DMA port mapping!!

Correction: ALL machines use it for DMA port mapping.  The port is 
assigned to the legacy DMA controller, but performs no operation. 
That's what makes it safe to write (NOT read!)

	-hpa