[U-Boot] [PATCH] at91: Don't initialize watchdog if CONFIG_SYS_WDTC_WDMR_VAL is undefined

[Alexander Stein <alexander.stein@systec-electronic.com>]

Dear Wolfgang Denk,

Am Donnerstag, 22. Juli 2010, 09:09:12 schrieb Wolfgang Denk:
> > Well, my problem is, that CONFIG_SYS_WDTC_WDMR_VAL is used to program the
> > internal watchdog. But this watchdog can only be programmed once until a
> > reset occurs. So there is no possibility for linux to reprogram it.
> 
> This is normal. Any watchdog that is worth the name will behave
> similar.

Well, I encountered several watchdog which start only after the first trigger.

> > So, if CONFIG_SYS_WDTC_WDMR_VAL is not defined and the watchdog is not
> > programed using my patch, the watchdog still runs with default settings
> > (timeout of 16s). So a user may choose to trigger the watchdog from
> > u-boot (define CONFIG_AT91SAM9_WATCHDOG and CONFIG_HW_WATCHDOG) or let
> > it run silently. To summarize, CONFIG_SYS_WDTC_WDMR_VAL is not needed to
> > use CONFIG_AT91SAM9_WATCHDOG and CONFIG_HW_WATCHDOG.
> 
> Then the subject is misleading - it suggests you do not initialize /
> let run the watchdog at all if CONFIG_SYS_WDTC_WDMR_VAL is undefined.

Ok, maybe the subject need some rework.

> I think we should make sure that everything is in a sane and
> consistent state - if CONFIG_HW_WATCHDOG (and
> CONFIG_AT91SAM9_WATCHDOG) are set, this indicates that U-Boot is
> supposed to use the watchdog, which in turn means they should
> initialize it.

Of course, if CONFIG_HW_WATCHDOG and CONFIG_AT91SAM9_WATCHDOG is set, u-boot 
should use/trigger the watchdog. But (re-)programming the watchdog on AT91 is 
not _always_ necessary. Without programming (using CONFIG_SYS_WDTC_WDMR_VAL), 
the watchdog just runs with default settings, allowing e.g. Linux to reprogram 
it later.
This patch allows to program the watchdog from u-boot, if wanted, but also 
allows to reprogram it later from Linux. While triggering the watchdog from u-
boot itself does still work, wrt. the default watchdog settings.

Best regards,
Alexander Stein