Date: Sun, 30 Dec 2007 17:28:53 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Andi Kleen <andi@firstfloor.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
       Rene Herman <rene.herman@keyaccess.nl>, dpreed@reed.com,
       Islam Amer <pharon@gmail.com>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
       hpa@zytor.com, Pavel Machek <pavel@ucw.cz>,
       Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
       Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override
Message-ID: <20071230162853.GA32453@elte.hu>
References: <477711DC.5030800@keyaccess.nl> <alpine.LFD.1.00.0712300124440.32517@woody.linux-foundation.org> <20071230124852.GA30836@one.firstfloor.org> <20071230130544.GB16946@elte.hu> <20071230160817.GB32752@one.firstfloor.org>
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* Andi Kleen <andi@firstfloor.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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