[Skiboot] [PATCH 3/3] ipmi/wdt: Add ipmi watchdog timer support

[Alistair Popple]

On Thu, 29 Jan 2015 11:56:33 Benjamin Herrenschmidt wrote:
> On Thu, 2015-01-29 at 08:54 +0800, Jeremy Kerr wrote:
> > Hi Ben,
> > 
> > > Bah, petitboot kernel will start it and that's it, once it's started,
> > > it's started and if we kexec something tat doesn't support it we are
> > > toast anyway
> > 
> > My plan is to have petitboot disable the watchdog timer just before
> > kexec. This way, we don't export this "ABI" beyond the petitboot
> > environment, which we'd have control of anyway.
> > 
> > The OS kernel can re-enable it if necessary, but isn't required to.
> 
> Which means that if it fails to boot, we have no watchdog... I don't
> like this *that* much...
> 
> Can the watchdog be tied to an interrupt from the BMC ? Something we
> know we will react to unless the kernel is dead ?

Yes, there is a pre-timeout interrupt which works. So how about instead of 
requiring the payload OS to disable it we just set a pre-timeout interrupt 
prior to entering the OS? Once we see that interrupt in skiboot we can just 
disable the WDT and then it's up to the payload to do what it wants with the 
WDT through IPMI commands. If we never see the interrupt the WDT will trip and 
the system will reboot.

> Ben.