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

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Message-ID: <478EF4C9.8030406@davidnewall.com>
Date:	Thu, 17 Jan 2008 16:55:13 +1030
From:	David Newall <davidn@...idnewall.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	"David P. Reed" <dpreed@...d.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Rene Herman <rene.herman@...access.nl>,
	Zachary Amsden <zach@...are.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Christer Weinigel <christer@...nigel.se>,
	Ondrej Zary <linux@...nbow-software.org>,
	Bodo Eggert <7eggert@....de>, 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 <rol@...be.net>
Subject: Re: Re: [PATCH] x86: provide a DMI based port 0x80
 I/O delay override.

Alan Cox wrote:
>> If the hardware required an intermediate junk I/O, that would be a
>> reason to do one, but it doesn't, does it?  It requires a delay.  It's
>> written thus in all of the application notes.
>>     
>
> And the only instruction that is synchronized to the bus in question is
> an I/O instruction.
>   

This is a timing issue, isn't it?  How are we synchronising, other than
by delaying for a (bus-dependant) period?  The characteristics of each
bus are known so a number can be assigned for "one bus cycle", without
having to use the bus.



>> Wrong again.  Of course one knows how long the delay should be.  The bus
>> speed is known. 
>>     
>
> Wrong again. ISA bus speed is neither defined precisely, nor visible in a
> system portable fashion.
>   

You say, "system portable," but I think you mean, "automatically
determined."  We don't have to define this value automatically, if
that's so hard to do.  We can use a tunable kernel-parameter.

> I'm so glad you have nothing better to do than troll

I'm not trolling.  You know this is true because many people perceive
this to be a problem.  I'm working on fixing it.  Not all Linux problems
are solvable by diving into code, and there is anecdotal evidence to
believe this one has big performance considerations.  I don't understand
why you are opposed to even talking about it.


> if you
> actually wrote code I'd be worried it might get into something people
> used.

Speaking of writing code: I remember working on a bluetooth Oops. 
Lacking the hardware, I went to you for advice on how to get it before
someone for testing.  You never replied.
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