regulator: ltc3676: Fix notifier mutex lock warning

The mutex for the regulator_dev must be controlled by the caller of
the regulator_notifier_call_chain(), as described in the comment
for that function.

Failure to mutex lock and unlock surrounding the notifier call results
in a kernel WARN_ON_ONCE() which will dump a backtrace for the
regulator_notifier_call_chain() when that function call is first made.
The mutex can be controlled using the regulator_lock/unlock() API.

Fixes: 37b918a034 ("regulator: Add LTC3676 support")
Suggested-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Signed-off-by: Steve Twiss <stwiss.opensource@diasemi.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/ltc3676.c

@@ -285,17 +285,23 @@ static irqreturn_t ltc3676_isr(int irq, void *dev_id)
 	if (irqstat & LTC3676_IRQSTAT_THERMAL_WARN) {
 		dev_warn(dev, "Over-temperature Warning\n");
 		event = REGULATOR_EVENT_OVER_TEMP;
-		for (i = 0; i < LTC3676_NUM_REGULATORS; i++)
+		for (i = 0; i < LTC3676_NUM_REGULATORS; i++) {
+			regulator_lock(ltc3676->regulators[i]);
 			regulator_notifier_call_chain(ltc3676->regulators[i],
 						      event, NULL);
+			regulator_unlock(ltc3676->regulators[i]);
+		}
 	}
 
 	if (irqstat & LTC3676_IRQSTAT_UNDERVOLT_WARN) {
 		dev_info(dev, "Undervoltage Warning\n");
 		event = REGULATOR_EVENT_UNDER_VOLTAGE;
-		for (i = 0; i < LTC3676_NUM_REGULATORS; i++)
+		for (i = 0; i < LTC3676_NUM_REGULATORS; i++) {
+			regulator_lock(ltc3676->regulators[i]);
 			regulator_notifier_call_chain(ltc3676->regulators[i],
 						      event, NULL);
+			regulator_unlock(ltc3676->regulators[i]);
+		}
 	}
 
 	/* Clear warning condition */