Message-ID: <4766D443.6040805@zytor.com>
Date: Mon, 17 Dec 2007 11:55:47 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
User-Agent: Thunderbird 2.0.0.9 (X11/20071115)
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To: "David P. Reed" <dpreed@reed.com>
CC: Rene Herman <rene.herman@gmail.com>, Ingo Molnar <mingo@elte.hu>,
       Paul Rolland <rol@as2917.net>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Pavel Machek <pavel@ucw.cz>, Thomas Gleixner <tglx@linutronix.de>,
       linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
       rol@witbe.net
Subject: Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override.
References: <4762C551.5070003@zytor.com> <20071214210652.GB28793@elf.ucw.cz> <4763001A.1070102@zytor.com> <20071214232955.545ab809@the-village.bc.nu> <20071215080831.404cdb32@tux.DEF.witbe.net> <47638C8C.2090604@gmail.com> <476438B4.2020600@zytor.com> <476462BE.3030701@gmail.com> <4764687D.6080609@zytor.com> <476524DB.7020806@gmail.com> <20071216152250.GA21245@elte.hu> <4765D43E.1010800@gmail.com> <4765D95C.4010404@zytor.com> <4765DCB0.8030901@gmail.com> <4765EE7F.80002@zytor.com> <47667366.7010405@gmail.com> <4766AE88.4080904@zytor.com> <4766D175.7040807@reed.com>
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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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