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

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Date:	Tue, 1 Jan 2008 21:55:45 +0100
From:	Christer Weinigel <christer@...nigel.se>
To:	Rene Herman <rene.herman@...access.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	"David P. Reed" <dpreed@...d.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Rene Herman <rene.herman@...il.com>,
	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 Tue, 01 Jan 2008 20:59:20 +0100
Rene Herman <rene.herman@...access.nl> wrote:

> On 01-01-08 20:35, Christer Weinigel wrote:
> 
> > On old hardware (or anything with an ISA bus which I'd guess
> > includes the Geode SCx200 SoC which is basically a MediaGX
> > processor, a southbridge and an ISA bus with a Super I/O chip on
> > it) an out to 80h will use exactly one ISA cycle.
> 
> Not to disagree with the point but more like 8 (1 us at 8 MHz). It's
> the timeout property.

Ah, sorry, you're right of course.

> > I'm not sure what Alan meant with his comments about locking, but if
> > changing outb_p to use an udelay means that we have to add locking,
> > that is also going to affect the code size and speed.
> 
> Explained here:
> 
> http://lkml.org/lkml/2007/12/30/136
> 
> However, that's not an argument. Missing locking is a bug, and
> current outb I/O delay use hiding it doesn't change that.

Thanks, I had missed that one.

Regarding Alan's comment:

>For that matter does anyone actually have video cards old enough for us
>to care actually still in use with Linux today ? 

I'm afraid that some PC104 systems may still use ancient video cards.

  /Christer
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