Re: [PATCH v3 2/2] watchdog: fix w83627hf_wdt clear timeout expired

[Guenter Roeck]

On Wed, Apr 03, 2013 at 08:50:26AM -0700, Guenter Roeck wrote:
> On Wed, Apr 03, 2013 at 08:06:59AM -0700, Tony Chung wrote:
> > On Tue, Apr 2, 2013 at 9:21 PM, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > 
> > >
> > >
> > > What is the exact chip type in your system ? I want to have a look into the
> > > datasheet; maybe I can find out how it can trigger without causing a reset.
> > 
> > Winbond 83627HF chip
> > 

Followup: what chip revision ?

Revision G or later have a new configuration bit, bit 3 of CR E7 on logical
device A.

SELWDTORST. Watch Dog Timer Reset Control.
= 0 is reset by LPC_RST.
= 1 is reset by PWR_OK.

I could imagine that the WDT logic is never correctly initialized in your
system, which might explain the behavior. If so, your code is indeed
correct (or the best I could come up with too), as we would have to ensure
that the wdt subsystem is initialized correctly by writing into all its registers.

Given that, I would suggest to re-submit the patch with a different explanation
(we don't know if the wdt really started running, all we know is that the
expired bit is set), and I'll give it an Acked-by. Something along the line of 

"Observed that the Watchdog Timer Status bit can be set when the driver is
 loaded. Reset it during initialization. The time-out value must be set to 0
 explicitly in this case to prevent an immediate reset".

Thanks,
Guenter

> > I believe BIOS has watchdog disabled otherwise it would have reboot the box.
> > However, the timer just start counting.
> > 
> > Comparing to ipmi_watchdog, you can do this:
> > modprobe ipmi_watchdog ... start_now=0 ...action=<>  nowayout=1
> > 
> > So it is possible to load the driver without start counting.
> > 
> That is a different driver, though. you don't have the start_now option here.
> 
> > Notice it is an else, so t is actually 0 already (i.e. expired or
> > never start running):
> 
> Still no idea why that would cause the system to reboot when you reset
> the trigger without setting t to 0 again (or why the system doesn't reset
> in the first place if the watchdog already triggered).
> 
> I am not really sure what the best approach is here, so let's leave it
> up to the maintainer to decide which way to go.
> 
> Thanks,
> Guenter
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