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

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Date:	Tue, 01 Jan 2008 13:15:39 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	"David P. Reed" <dpreed@...d.com>,
	Rene Herman <rene.herman@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Paul Rolland <rol@...917.net>,
	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.

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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