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

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Message-ID: <20080102015539.58d80332@weinigel.se>
Date:	Wed, 2 Jan 2008 01:55:39 +0100
From:	Christer Weinigel <christer@...nigel.se>
To:	Rene Herman <rene.herman@...access.nl>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"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.

On Wed, 02 Jan 2008 00:11:54 +0100
Rene Herman <rene.herman@...access.nl> wrote:

> Well, on the PIIX it is and I guess on anything where it's _not_
> fully internal an 0xf0 write wouldn't have any effect on IRQ13...
> 
> When you earlier mentioned this it seemed 0xed switched on DMI would
> be good enough, but well.
> 
> Alan, do you have an opinion on the port 0xf0 write? It should
> probably still be combined with a replacement/deletion for new
> machines due to the bus-locking "bad for real-time" thing you
> mentioned earlier but in the short run it could be a fairly
> low-impact replacement on anything except a 386+387

Both 0xed and 0xf0 are mapped to internal functions on the AMD Elan
SC400 processor.  It is an AMD 486 based system on a chip and since AMD
just knew that it would never have a math coprocessor, they reused the
0xf0-0xf2 range for the PCMCIA controller.  I guess the AMD Elan SC500
will have similar problems.

I seem to recall that back when I was working with the Elan SC400
(sometime around 1998?) there were discussions about finding an
alternate delay port because outb to 0x80 messed up the debug port.  I
think the Elan stopped those discussions because just about every port
on the Elan was reused for some alternate purpose.  

  /Christer
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