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

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Date:	Mon, 31 Dec 2007 16:29:39 +0100
From:	Christer Weinigel <christer@...nigel.se>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rene Herman <rene.herman@...access.nl>,
	Ingo Molnar <mingo@...e.hu>, dpreed@...d.com,
	Islam Amer <pharon@...il.com>, hpa@...or.com,
	Pavel Machek <pavel@....cz>, Ingo Molnar <mingo@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override

On Sun, 30 Dec 2007 21:13:29 +0000
Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> > But that does't mean that other ports won't have the same timings.
> > Also, it doesn't mean that we really need to have exactly *those*
> > timings.
> 
> For ISA bus you want "at least" those timings. That is an easy case
> anyway - ISA bus boxes, old processors and generally no TSC so we can
> fall back to 0x80 - we know from 15 years experience the problem only
> occurs with recent non ISA systems that have borked firmware.
> 
> Lots of ISA hardware does really need the delays and most of it will
> be on old processors as well naturally enough.

If I recall correctly, the MediaGX/Geode processor does need _p for the
PIT accesses, and that CPU family does have a TSC (even though the TSC
stops at times so is hard to use).  I also seem to remember that the
breakage did not happen very often, but running a system without _p
overnight usually showed one hiccup where a read from the counter got
corrupted.

So unless I'm wrong (which I very well could be, it's been a couple of
years since I was debugging the PIT code on a misbehaving Geode SC1200
based system) there is at least one fairly modern CPU, which is used in
lots of embedded systems, and in active use, which does need the _p.

Just a data point... It's not only ancient systems that need _p.

  /Christer

-- 
"Just how much can I get away with and still go to heaven?"

Christer Weinigel <christer@...nigel.se>  http://www.weinigel.se
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