linux-kernel - Re: HPET : Legacy Routing Replacement Enable

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Date:	Fri, 27 Oct 2006 07:57:08 +0200
From:	Vojtech Pavlik <vojtech@...e.cz>
To:	Andi Kleen <ak@....de>
Cc:	Om Narasimhan <om.turyx@...il.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	linux-kernel@...r.kernel.org, randy.dunlap@...cle.com,
	clemens@...isch.de, bob.picco@...com
Subject: Re: HPET : Legacy Routing Replacement Enable - 3rd try.

On Fri, Oct 27, 2006 at 04:42:38AM +0200, Andi Kleen wrote:

> On Wed, Oct 25, 2006 at 02:20:22PM -0700, Om Narasimhan wrote:
> > I tested against five different bioses (some with 8132, some with
> > CK-804 ..etc) and I observed three different patterns.
> > 
> > 1. HW is LRR capable, HPET ACPI it is 1, timer interrupt is on INT2.
> > Before the fix: Linux cannot get timer interrupts on INT0, goes for ACPI 
> > timer.
> 
> What ACPI timer?  I don't think we have any fallback for int 0.
> 
> Not sure what you mean with INT2. Pin2 on ioapic 0 perhaps?
> 
> > After the fix : Works fine. This is according to hpet spec.
> 
> On what exact motherboard was that?
> 
> > 
> > To handle case 3, I removed all references to acpi_hpet_lrr, explained
> > this case in the code and decided to solely rely on the command line
> > parameter for LRR capability. Rational for this approach is ,
> 
> This means the systems which you said fixes this would need the command
> line parameter to work? 
> 
> > 1. At present, there are not many BIOSes which implement LRR (correctly)
> > 2. People would see the bootup message (MP-BIOS bug...) if LRR is
> > enabled and no timer interrupt on INT0. They can pass the hpet_lrr=1
> > to make everything work fine.
> > Is it the right approach?
> 
> Generally we try to work everywhere without command line parameter
> unless something is terminally broken. 

JFYI: The new per-cpu timekeeping code doesn't need the HPET legacy bit,
thus not replacing IRQ0 (PIT) and IRQ13 (RTC). It still can do that, but
will work just as well without it.

-- 
Vojtech Pavlik
Director SuSE Labs
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