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

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Date:	Mon, 31 Dec 2007 12:23:44 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Rene Herman <rene.herman@...access.nl>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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 19:14:40 +0100
Rene Herman <rene.herman@...access.nl> wrote:

> On 30-12-07 17:48, Alan Cox wrote:
> 
> > For processors with TSC I think we should aim for 2.6.25 to do this and 
> > to have the major other _p fixups done. I pity whoever does stuff like 
> > the scc drivers but most of the rest isn't too bad.
> 
> I'm by the way looking at drivers/net/wd.c which my 386 uses for its dual 
> mode NE2000/WD8013 clone ISA NIC and while it specifically needs no delay at 
> all it seems, the mixed use of out and outb_p seems to suggest that someone 
> once thought about that. Would you advice sticking in a udelay(2) manually 
> there?

I dug out the reference drivers. The reference drivers use the delay and
the 8390 datasheet confirms it is neccessary.

The Crynwr driver has some interesting things to say

| The National 8390 Chip (NIC) requires 4 bus clocks between successive
| chip selects (National DP8390 Data Sheet Addendum, June 1990)

Also " To establish a minimum delay, an I/O instruction must be used. A
good rule of ; thumb is that ISA I/O instructions take ~1.0 microseconds
and MCA I/O ; instructions take ~0.5 microseconds. Reading the NMI Status
Register (0x61) ; is a good way to pause on all machines."

But all the official drivers use pauses and the manual says they are
needed for correct, reliable behaviour - at least with a genuine 8390.




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