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

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Date:	Sun, 30 Dec 2007 17:08:17 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rene Herman <rene.herman@...access.nl>, dpreed@...d.com,
	Islam Amer <pharon@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, hpa@...or.com,
	Pavel Machek <pavel@....cz>, Ingo Molnar <mingo@...hat.com>,
	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, Dec 30, 2007 at 02:05:44PM +0100, Ingo Molnar wrote:
> 
> * Andi Kleen <andi@...stfloor.org> wrote:
> 
> > > drivers that then are shown to really need it could use their *own* 
> > > ports.
> > 
> > The i8259 driver uses it and it is known to be needed on some old 
> > chipsets. But it doesn't really have any "own" ports to use afaik.
> 
> we'll solve that via an i8259-specific quirk. That is a lot cleaner and 
> maintainable than the current generic, always-enabled "opt out" 
> port-0x80 quirk.

You mean using pci quirks + udelay? Will be probably challenging to collect
PCI-IDs for that. And there might be old systems needing it without PCI.
They likely won't have DMI either.

In theory you could make it a DMI year cut off of course (and assume old
if no DMI, although that happens occasionally with new systems too); but
that is generally considered ugly.

I don't think it's a big problem to keep delays of some form by default in 8259 --
people who care about performance should be definitely using APIC mode instead.

-Andi
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