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

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Date:	Mon, 17 Dec 2007 11:55:47 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"David P. Reed" <dpreed@...d.com>
CC:	Rene Herman <rene.herman@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Paul Rolland <rol@...917.net>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Pavel Machek <pavel@....cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	rol@...be.net
Subject: Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override.

David P. Reed wrote:
> H. Peter Anvin wrote:
>> Rene Herman wrote:
>>>
>>> I do not know how universal that is, but _reading_ port 0xf0 might in 
>>> fact be sensible then? And should even work on a 386/387 pair? (I 
>>> have a 386/387 in fact, although I'd need to dig it up).
>>>
>>
>> No.  Someone might have used 0xf0 as a readonly port for other uses.
>>
> As support: port 80 on the reporter's (my) HP dv9000z laptop clearly 
> responds to reads differently than "unused" ports.  In particular, an 
> inb takes 1/2 the elapsed time compared to a read to "known" unused port 
> 0xed - 792 tsc ticks for port 80 compared to about 1450 tsc ticks for 
> port 0xed and other unused ports (tsc at 800 MHz).
> 

Any timings for port 0xf0 (write zero), out of curiosity?

	-hpa
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