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Re: Add NULL power handler to x86/ipmi(4)

On Sat, 17 Jul 2010, David Young wrote:

ipmi(4) should probably not suspend if its watchdog timer is active.

Would it be sufficient for ipmi(4) to refuse to suspend (return
false from the suspend method) if the watchdog is active?

Yes.  I think that's the right thing to do for now.

This is actually fairly easy to do.

Or should it make some sort of effort to disable the watchdog, and
attempt to reenable the watchdog during the subsequent resume?

That defeats the purpose of a watchdog timer, at least for my purposes.
This is a local policy choice that should probably not be hard-coded.
Maybe we need additional watchdog modes?

1 Watchdog countdown stops during suspension, restarts after

Probably a bit more difficult than #3 below, and it assumes that the remaining time is available.

2 Watchdog keeps counting down during suspend (we'll wake periodically
 to tickle it)

This might be rather tricky. Depending on the type of suspend, the time for a wake-up to occur could be faily long and/or variable. And there might not even be a way for the system to schedule its own wake event.

3 Watchdog prevents suspension

As I indicated, this is fairly easy to do, simply check if the w-dog is armed or not.

The attached patch provides an ipmi_suspend() method to implement #3. But I suspect that this is really a more generic watchdog capability, and it should be implemented for the entire class of watchdogs rather than only for ipmi(4)?


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Index: ipmi.c
RCS file: /cvsroot/src/sys/arch/x86/x86/ipmi.c,v
retrieving revision 1.46
diff -u -p -r1.46 ipmi.c
--- ipmi.c      10 Apr 2010 19:02:39 -0000      1.46
+++ ipmi.c      17 Jul 2010 02:40:27 -0000
@@ -225,6 +225,8 @@ int ipmi_sensor_status(struct ipmi_softc
 int     add_child_sensors(struct ipmi_softc *, uint8_t *, int, int, int,
     int, int, int, const char *);
+bool   ipmi_suspend(device_t, const pmf_qual_t *);
 struct ipmi_if kcs_if = {
@@ -1934,6 +1936,10 @@ ipmi_thread(void *cookie)
        sc->sc_wdog.smw_tickle = ipmi_watchdog_tickle;
+       /* Set up a power handler so we can possibly sleep */
+       if (!pmf_device_register(self, ipmi_suspend, NULL))
+                aprint_error_dev(self, "couldn't establish a power handler\n");
        while (sc->sc_thread_running) {
@@ -2093,3 +2099,14 @@ ipmi_dotickle(struct ipmi_softc *sc)
                    device_xname(sc->sc_dev), rc);
+ipmi_suspend(device_t dev, const pmf_qual_t *qual)
+       struct ipmi_softc *sc = device_private(dev);
+       /* Don't allow suspend if watchdog is armed */
+       if ((sc->sc_wdog.smw_mode & WDOG_MODE_MASK) != WDOG_MODE_DISARMED)
+               return false;
+       return true;

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