Message-ID: <477AAD7B.5040405@zytor.com>
Date: Tue, 01 Jan 2008 13:15:39 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Alan Cox <alan@lxorguk.ukuu.org.uk>
CC: "David P. Reed" <dpreed@reed.com>, Rene Herman <rene.herman@gmail.com>,
       Ingo Molnar <mingo@elte.hu>, Paul Rolland <rol@as2917.net>,
       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>	<20071217212509.5edaa372@the-village.bc.nu>	<477A634C.8040000@reed.com> <20080101161557.3ce2d5f8@the-village.bc.nu>
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Alan Cox wrote:
>> 80 makes me suspicious.)   That might mean that the freeze happens only
>> when certain values are written, or when they are written closely in
>> time to some other action - being used to communicate something to the
>> SMM code).   If there is some race in when Linux's port 80 writes happen
>> that happen to change the meaning of a request to the hardware or to
>> SMM, then we could be rarely stepping on
> 
> That does imply some muppet 'extended' the debug interface for power
> management on your laptop. Also pretty much proves that for such systems
> we do have to move from port 0x80 to another delay approach.
> 
> Ingo - the fact that so many ISA bus devices need _p to mean "ISA bus
> clocks" says to me we should keep the _p port 0x80 using variant for old
> systems/device combinations (eg ISA ethernet cards) which won't show up
> in any problem system (we know this from 15 odd years of testing), but
> stop using it for PCI and embedded devices on modern systems.
> 

I have mentioned this before... I think writing zero to port 0xf0 would 
be an acceptable pause interface (to the extent where we need an I/O 
port) except on 386 with 387 present; on those systems we can fall back 
to 0x80.

	-hpa
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