linux-kernel - Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64 with MCP51 laptops

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Date:	Tue, 11 Dec 2007 09:05:06 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"David P. Reed" <dpreed@...d.com>
CC:	Rene Herman <rene.herman@...access.nl>,
	Paul Rolland <rol@...917.net>,
	David Newall <david@...idnewall.com>,
	Krzysztof Halasa <khc@...waw.pl>, Pavel Machek <pavel@....cz>,
	Andi Kleen <andi@...stfloor.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, rol@...be.net
Subject: Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64
 with MCP51 laptops

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
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