regulator: pv88090: 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: c90456e3 ("regulator: pv88090: new regulator driver")
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/pv88090-regulator.c

@@ -237,9 +237,11 @@ static irqreturn_t pv88090_irq_handler(int irq, void *data)
 	if (reg_val & PV88090_E_VDD_FLT) {
 		for (i = 0; i < PV88090_MAX_REGULATORS; i++) {
 			if (chip->rdev[i] != NULL) {
+			        regulator_lock(chip->rdev[i]);
 				regulator_notifier_call_chain(chip->rdev[i],
 					REGULATOR_EVENT_UNDER_VOLTAGE,
 					NULL);
+			        regulator_unlock(chip->rdev[i]);
 			}
 		}
 
@@ -254,9 +256,11 @@ static irqreturn_t pv88090_irq_handler(int irq, void *data)
 	if (reg_val & PV88090_E_OVER_TEMP) {
 		for (i = 0; i < PV88090_MAX_REGULATORS; i++) {
 			if (chip->rdev[i] != NULL) {
+			        regulator_lock(chip->rdev[i]);
 				regulator_notifier_call_chain(chip->rdev[i],
 					REGULATOR_EVENT_OVER_TEMP,
 					NULL);
+			        regulator_unlock(chip->rdev[i]);
 			}
 		}