[RFC PATCH 1/5] watchdog: Add API to trigger reboots

On Fri, May 02, 2014 at 09:29:25PM -0700, Guenter Roeck wrote:

quoted

quoted

+	if (wdd->ops->reboot)
+		wdd_reboot_dev = wdd;
+

Overall, it looks really great, but I guess we can make it a
list. Otherwise, we might end up in a situation where we could not
reboot anymore, like this one for example:
  - a first watchdog is probed, registers a reboot function
  - a second watchdog is probed, registers a reboot function that
    overwrites the first one.
  - then, the second watchdog disappears for some reason, and the
    reboot is set to NULL

I thought about that, but how likely (or unlikely) is that to ever happen ?
So I figured it is not worth the effort, and would just add complexity without
real gain. We could always add the list later if we ever encounter a situation
where two watchdogs in the same system provide a reboot callback.

The A31 we were discussing about in the other thread that doesn't have
a watchdog driver yet has four, identical, watchogs. I'm not really
concerned about the mentionned issue, since they will never be
removed, but the situation might happen with an on-SoC watchdog and an
i2c one (if that even exists).

But yes, right, that can be postponed.

quoted

Or maybe we can just use the start callback, with the min timeout already
registered, and prevent the user to kick the watchdog.

Doesn't always work, unfortunately, even now. The moxart driver causes 
an explicit and immediate reset. Also, some watchdogs don't reset the system
directly but get an interrupt, which then calls the reset handler. Which,
in our case, would call the start callback again, and you would have an endless
loop.

Ok. You have my Acked-by then.

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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