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

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Date:	Fri, 27 Oct 2006 09:29:44 +0300
From:	Mika Penttilä <mika.penttila@...umbus.fi>
To:	Vojtech Pavlik <vojtech@...e.cz>
Cc:	Andi Kleen <ak@....de>, 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.

Vojtech Pavlik wrote:
> 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.
>
>   
There seems to be lot of confusion here. Current code isn't using hpet 
as tick source if legacy is not supported. This patch adds 
hpet_lrr_force but it's not clear how it interacts with hpet_use_timer - 
in some places it is hpet_use_timer and some (hpet_use_timer && 
hpet_lrr_force).

The timer is routed to ioapic pin 2 which is irq0 with source override. 
With this patch with hpet_lrr_force=1 timer irq is set to 2 for x86_64 
and 0 for i386, that can't be right?

--Mika


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