[U-Boot] Watchdog support for ppc4xx

[Detlev Zundel <dzu@denx.de>]

Hi Wolfgang,

> Dear Stefan Roese,
>
> In message <201005201355.01964.sr@denx.de> you wrote:
>> 
>> > Also I would like to determine in u-boot if a
>> > reset was caused by the watchdog timer using the TSR WRS field.  If it
>> > was reset by the watchdog we will boot into a failsafe partition to
>> > protect against system update errors.
>> > 
>> > Has anyone done something like this?
>> 
>> Such a detection is not implemented for PPC4xx. Not sure if it's implemented 
>> for any other architecture.
>
> I think lwmon5 performs such checking; eventually this is buryied
> somewhere in the POST code.

Well, at least I know that for mpc5121 we read the reser status register
at boot and copy it to global data
(arch/powerpc/cpu/mpc512x/cpu_init.c:64).  The value is also output in
the U-Boot prompt (arch/powerpc/cpu/mpc512x/cpu.c:68) which is a nice
thing IMHO.

Checking a "git grep reset_status" one can see that something similar is
done for other PowerPC cpus as well, so I'd suggest reusing this method
for ppc4xx and providing a mechanism to access this information from a
script.

Cheers
  Detlev

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