[PATCH 2/2] watchdog: add watchdog behavior configuration

[Michael Walle]

Am 2020-09-26 14:44, schrieb Tom Rini:
[..]
>> If we want to have a hardware based watchdog in the UEFI context, we
>> need a U-Boot internal API by which we can enable and disable a 
>> hardware
>> watchdog with an arbitrary duration (>> 5 min) with 1 second 
>> resolution.
>> Then our implementation of SetWatchdogTimer() could call into this 
>> API.
> 
> Thanks for excerpting from the UEFI spec where it talks about a
> "watchdog" at all.  It's clear from these excerpts that the spec simply
> does not talk about a hardware watchdog at all and is using the term in
> one of its other meanings.  Which means that we need to figure out and
> document something nominally sane so at least it's not a surprise to 
> the
> user.
> 
> Michael, what driver under drivers/watchdog/ is your platform using
> exactly?  Thanks!

In its current form (i.e. basic BSP support) it uses the sp805_wdt.c;
which is a nice to have, but the real watchdog is an external device.
There is no support in U-Boot for it yet, but I'm planning to add it
and thus I need the CONFIG_WDT ;)

Currently this external watchdog is disabled (there are non-volatile
configuration bits on the board and one bit is for disabling this
watchdog at startup). Otherwise it would always activate the board's
failsafe mode because it isn't triggered by U-Boot.

And yes, this watchdog also have a lock bit, once set, you cannot
deactivate it anymore (although you can change the timeout period
in a given range).

Because at the moment there is no driver for this watchdog yet (it
is a custom one), my newest version of my "basic board support for
Kontron sl28" has the CONFIG_WDT deactivated. I prefer having a
usable bootefi to have support for the SoC internal watchdog.

-michael