Re: SP805 driver

[Udit Kumar <udit.kumar@nxp.com>]

> -----Original Message-----
> From: Leif Lindholm <leif.lindholm@linaro.org>
> Sent: Tuesday, December 18, 2018 2:56 PM


> 
> On Tue, Dec 18, 2018 at 05:20:59AM +0000, Udit Kumar wrote:
> > Thanks for note Leif,
> >
> > I am trying to understand this behavior  of specification.
> >
> > >"If no handler has been registered, or the registered handler
> > >returns, then the system will be reset by calling the Runtime Service
> > >ResetSystem()."
> > I believe,  this handler needs to be called by wdt driver after wdt is
> > expired. Meaning , we want wdt to work without resetting the system.
> > Therefore a mask is needed with wdt, which will prevent to reset the
> > system.   I see it working, at least for SP805, because of PMU mask
> > bits.
> 
> Yes, if the WDT can be configured to generate an interrupt instead of a
> hardware reset, it can be used to implement this protocol.

Here I am just thinking of one condition , some application started the wdt
and CPU got stuck somewhere in ISR routine, 
Now this wdt is expired. We will end up in hang system. 
I agree doing reset in graceful manner is always great, but In this case, resetting the 
as it is, will be more useful. 

Thought ? 
 
> > Also ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdogDxe.c has this
> limitation.
> > I haven’t read spec of this wdt.  I hope there should a mask around.
> 
> No, the situation for the GenericWatchdogDxe is not as dire.
> 
> Correct: it does not permit registering software handlers (which perhaps we
> should do something about, but is ... acceptable).
> 
> _But_, it still conforms to the above text; when the timer expires, it resets the
> system by calling the ResetSystem() service. It does not directly force a
> hardware reset.

Hmm, this does partly by calling  ResetSystem(), however this does not 
Allow to install handler in WatchdogRegisterHandler.

> The severe problem is not the lack of the ability to register the software handler
> (which does remove much of the utility), but the removal of reset control from
> the system firmware.
> 
> > Coming back to hardware, which does not have mask around wdt, how to
> > implement this feature.
> 
> Simple - you can't.
> 
> You can absolutely implement exactly the functionality you have today, with
> minimal changes to the protocol - it just should not be registered as an
> implementation of EFI_WATCHDOG_TIMER_ARCH_PROTOCOL.

I believe,  EFI_WATCHDOG_TIMER_ARCH_PROTOCOL is must 
Are you suggesting to EFI_WATCHDOG_TIMER_ARCH_PROTOCOL from MdeModulePkg
and hook platform specific code with this.
Or simply register EFI_WATCHDOG_TIMER_ARCH_PROTOCOL with dummy functions.

> Then your platform code can invoke this custom protocol as needed.
 
> Regards,
> 
> Leif