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

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Message-ID: <4777DB4E.9080105@keyaccess.nl>
Date:	Sun, 30 Dec 2007 18:54:22 +0100
From:	Rene Herman <rene.herman@...access.nl>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	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 30-12-07 18:06, Ingo Molnar wrote:

> * Rene Herman <rene.herman@...access.nl> wrote:

>> Real ISA systems will also generally respond faster to it than the 
>> unused port (this thing actually has an ISA bus but not VGA on it 
>> ofcourse) which means that "a perfect delay register" it is not. But 
>> yes, I have an actual Am386DX-40 with ISA VGA up and running which 
>> also doesn't care either way, about the ones in misc_32.c or anywhere 
>> else for that matter.
> 
> yeah - and that's typical of most _p() use: most of them are totally 
> bogus, but the global existence of the delay was used as a "it _might_ 
> break system" boogey-man against replacing it.

No delaying at all does break a few systems.

> so _IF_ we do any delay in x86 platform drivers, we at most do a delay 
> on the order of the round-trip latency to the same piece of hardware we 
> are handling.

Given that part of the problem is 2 MHz devices on a 8 MHz bus, you can't do 
this generally.

Rene.
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