[PATCH 1/1] efi_loader: stop watchdogs in ExitBootServices()

[Michael Walle]

>>> Honestly, not really? Some good number of SoCs will start the watchdog
>>> in ROM and these are also the ones that don't allow you to turn it off.
>> 
>> I hope not, that sounds really risky. How would you debug such a platform?
>
> _Every single_ custom piece of industrial (as opposed to consumer-grade)
> hardware I've worked on as a consultant has had an external,
> always-running, gpio-petted watchdog. It's simply just something that
> the hardware designers include, and in some cases that's even due to
> certification requirements. So an always-running, cannot-be-turned-off,
> watchdog is a real thing, in real hardware, and if specs don't account
> for that, well, the spec is just paper, and we can ignore it.

I agree. But on the other hand, you cannot assume or force the OS to
have a watchdog driver in the general case - which is as I understand
it - one goal of EFI.

Obviously, there are watchdogs that can be disabled and some which
cannot. I don't want to argue about the advantages and disadvantages.

For watchdogs which cannot be turned off, we can't really do anything
anyway after the handoff to the OS - except increasing its timeout if
thats possible.

For watchdogs that can be disabled (and are enabled in u-boot of course),
there seems to be two use-cases:
 (1) embedded EFI boot, that is you know exactly what you are booting, i.e.
     self compiled kernel with a watchdog driver
 (2) booting a general OS via EFI, think of a debian boot CD for example.

I agree, that for (1) the watchdog shouldn't be disabled. For (2) you
cannot assume the booting OS has a driver for the watchdog, let it be an
older version of a distribution which just haven't the SoC watchdog driver
enabled or maybe because there is no driver for it at all (yet).

Is there a way, to have the watchdog disabled for case (2) while also
having the possibity to use bootm/booti/bootz and keep the watchdog
enabled? Basically I want the following:

(1) board boots with watchdog enabled
(2) u-boot services watchdog
(3a) booting embedded linux with booti (watchdog enabled) or
(3b) booting generic OS with bootefi (watchdog disabled)

The missing case is booting an embedded linux with bootefi, which
would be nice to have. But I don't really see it as a use-case for
our board.

-michael