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

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Date:	Sun, 30 Dec 2007 17:28:53 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	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


* Andi Kleen <andi@...stfloor.org> wrote:

> > > 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.

do you remember which old systems/chipsets were affected by this 
problem? We had many - meanwhile fixed - PIC related problems, maybe 
it's a red herring and the delay just papered it over.

	Ingo
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