linux-kernel - Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override

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Message-ID: <4777BDA5.4050203@keyaccess.nl>
Date:	Sun, 30 Dec 2007 16:47:49 +0100
From:	Rene Herman <rene.herman@...access.nl>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	dpreed@...d.com, Islam Amer <pharon@...il.com>, hpa@...or.com,
	Pavel Machek <pavel@....cz>, Ingo Molnar <mingo@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override

On 30-12-07 16:28, Ingo Molnar wrote:

> Reading from the 0x3cc port does not impact the cursor position update 
> sequence IIRC - i think the vidport is even ignored for the input 
> direction by most hardware, there's a separate input register. The 0x3cc 
> port is a well-defined VGA register which should be unused on non-VGA 
> hardware. (which makes it a perfect delay register in any case)

Hardly. Duron 1300 on AMD756:

rene@...e4:~/src/port80$ su -c ./port80
cycles: out 2400, in 2401
rene@...e4:~/src/port80$ su -c ./port3cc
cycles: out 459, in 394

As stated a few dozen times by now already, port 0x80 is _decidedly_ _non_ 
_random_

Rene.

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