Re: [PATCH 2/4] ArmPlatformPkg/SP805WatchdogDxe: switch to interrupt mode

[Thomas Abraham <thomas.abraham@arm.com>]

Hi Ard,

On Tue, Dec 18, 2018 at 9:59 PM Ard Biesheuvel
<ard.biesheuvel@linaro.org> wrote:
>
> On Tue, 18 Dec 2018 at 14:39, Leif Lindholm <leif.lindholm@linaro.org> wrote:
> >
> > On Tue, Dec 18, 2018 at 02:10:12PM +0100, Ard Biesheuvel wrote:
> > > The SP805 watchdog driver doesn't implement the PI watchdog protocol
> > > fully, but always simply resets the system if the watchdog time runs
> > > out.
> > >
> > > However, the hardware does support the intended usage model, as long
> > > as the SP805 is wired up correctly. So let's implement interrupt based
> > > mode involving a handler that is registered by the DXE core and invoked
> > > when the watchdog runs out. In the interrupt handler, we invoke the
> > > notify function if one was registered, or call the ResetSystem()
> > > runtime service otherwise (as per the UEFI spec)
> >
> > The only question mark from my end is - what happens when the
> > interrupt isn't wired up correctly? Would it be worth to bail out and
> > refuse to register the driver if PcdSP805WatchdogInterrupt is set to
> > 0?
> >
> > Thomas?
> >
>
> I have left the code in place that enables the hard reset, but the
> timeout is double the programmed value (since the countdown timer is
> restarted on an interrupt, and the hard reset is generated when it
> reaches zero the second time)
>
> This should cover both the miswired interrupt scenario, and the
> scenario where ResetSystem() (or the handler) gets stuck and never
> returns.

Yes, this would suffice. But the system would reset after twice the
amount of time than programmed, which probably is okay.

-Thomas.

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