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

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Message-ID: <20071230204650.GA26120@elte.hu>
Date:	Sun, 30 Dec 2007 21:46:50 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Rene Herman <rene.herman@...access.nl>,
	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


* Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> > So the current plan is to go with an io_delay=udelay default in v2.6.25, 
> > to give this a migration window, and io_delay=none in v2.6.26 [and a 
> > complete removal of arch/x86/kernel/io_delay.c], once the _p() uses are 
> > fixed up. This is gradual enough to notice any regressions we care about 
> > and also makes it nicely bisectable and gradual.
> 
> You will break systems if you blindly go around disabling _p delays 
> for ISA and LPC bus devices. The DEC Hinote laptops for example are 
> well known for requiring the correct ISA and other keyboard controller 
> delays. I don't expect anyone to test with a hinote or see it until it 
> hits Debian or similar 'low resource' friendly devices.

well, using io_delay=udelay is not 'blindly disabling'. io_delay=none 
would be the end goal, once all _p() API uses are eliminated by 
transformation. In drivers/ alone that's more than 1000 callsites, so 
it's quite frequently used, and wont go away overnight.

	Ingo
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