Add a driver for the TI watchdog.

[rpaulo]

Summary

The TI watchdog timer is present on BeagleBone's. Since 2014, U-Boot
has been booting the BeagleBone with the watchdog enabled. We need to
disable it on boot to avoid a spurious reset.
The timer isn't exactly precise, but it will do as a watchdog. This
is also a reflection of the watchdog(9) API.

In the future, we could handle interrupts, but the watchdog(9) API
needs to be a bit smarter before that can happen.

Test Plan

Booted the BBB with a new U-Boot and confirmed it survives more than
one minute.
Used watchdog and watchdog to test the code.

[andrew]

sys/arm/ti/files.ti

22

I think this should be optional, with the above warning in the kernel config.

sys/arm/ti/ti_wdt.c

127

What do these magic numbers mean? Are they just values the user manual says we need to write to the register?

149

This should handle "ti,omap3-wdt" as that is what Linux uses.

[rpaulo]

sys/arm/ti/ti_wdt.c

127

Yes. I suspect it's a sequence to avoid enabling/disabling the watchdog accidentally.

[rpaulo]

Changes based on review comments.

[rpaulo]

Fixing the previous revision.

[rpaulo]

Fixing the compatible string.

[rpaulo]

Closed by commit rS273257 (authored by @rpaulo).

[stas]

head/sys/arm/ti/ti_wdt.c

102 ↗

(On Diff #2040)

Missing blank line. It looks like you're using style(9) like blank lines in ti_wdt_enable(), but not here and not in some other functions.