linux-kernel - Re: [GEODE] Geode GX/LX watchdog timer (was 2.6.24-rc8 hangs at mfgpt-timer)

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Date:	Sun, 20 Jan 2008 15:16:03 -0500
From:	lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
To:	Jordan Crouse <jordan.crouse@....com>
Cc:	Arnd Hannemann <hannemann@...informatik.rwth-aachen.de>,
	Andres Salomon <dilinger@...ued.net>, marc.jones@....com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	wim@...ana.be
Subject: Re: [GEODE] Geode GX/LX watchdog timer (was 2.6.24-rc8 hangs at mfgpt-timer)

On Fri, Jan 18, 2008 at 06:06:24PM -0700, Jordan Crouse wrote:
> As promised, a watchdog driver for the Geode GX/LX processors is attached.
> I basically just ported the previous patch forward to 2.6.24.
> 
> I also have good news or bad news depending on your perspective.  I wanted
> to test this against 2.6.24, and OLPC is stuck at an older kernel version,
> so I had to test this with coreboot (LinuxBIOS) on another Geode 
> platform.  Like all BIOSen execpt for the OLPC firmware, coreboot uses
> VSA (SMM handler) which consumes all the timers.

Hmm, the Geode LX platform I work with uses VSA/SMM and I have had no
problems using timer 2 for a watchdog.  Some of the timers are certainly
already setup by something in the BIOS, but quite a few are not in use.
The board I am using is the compulab iGLX module.  I did have to mangle
together a watchdog driver myself some time ago since there wasn't one
for the Geode LX at the time.

Of course I haven't gone past 2.6.18 kernel for now (I am tracking
Debian stable for the most part), so I have no idea if something in a
newer kernel breaks things.

> So I used the magical MSR and surprise! - the timer tick hung.  
> I compiled out the timer tick, and tested the watchdog timer instead,
> and it worked fine on timer 0.  So I don't think the MFGPTs themselves
> have anything to do with this problem, but I do think it might be 
> related to VSA and possibly interrupts too.  I'm going to invoke the
> strong BIOS fu of our LinuxBIOS / BIOS expert Marc Jones, and see what
> he comes up with.
> 
> I don't know how much of a hassle it would be for Andres to get a 2.6.24
> kernel running on the OLPC to make sure that this isn't a regression
> in the timer tick code (I suspect it isn't a regression, but you never
> know).  I also think that it would probably be in our best interest to
> default CONFIG_GEODE_MFGPT_TIMER to 'n' until we get this figured
> out.  Since most BIOSen don't have timers available, that shouldn't affect
> too many people.
> 
> So, anyway, enjoy the watchdog timer - I hope it meets everybody's
> expectations for the 2.6.25 kernel.

--
Len Sorensen
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