regulator: lp8755: 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: b59320cc ("regulator: lp8755: new driver for LP8755")
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/lp8755.c

@@ -372,10 +372,13 @@ static irqreturn_t lp8755_irq_handler(int irq, void *data)
 	for (icnt = 0; icnt < LP8755_BUCK_MAX; icnt++)
 		if ((flag0 & (0x4 << icnt))
 		    && (pchip->irqmask & (0x04 << icnt))
-		    && (pchip->rdev[icnt] != NULL))
+		    && (pchip->rdev[icnt] != NULL)) {
+			regulator_lock(pchip->rdev[icnt]);
 			regulator_notifier_call_chain(pchip->rdev[icnt],
 						      LP8755_EVENT_PWR_FAULT,
 						      NULL);
+			regulator_unlock(pchip->rdev[icnt]);
+		}
 
 	/* read flag1 register */
 	ret = lp8755_read(pchip, 0x0E, &flag1);
@@ -389,18 +392,24 @@ static irqreturn_t lp8755_irq_handler(int irq, void *data)
 	/* send OCP event to all regulator devices */
 	if ((flag1 & 0x01) && (pchip->irqmask & 0x01))
 		for (icnt = 0; icnt < LP8755_BUCK_MAX; icnt++)
-			if (pchip->rdev[icnt] != NULL)
+			if (pchip->rdev[icnt] != NULL) {
+				regulator_lock(pchip->rdev[icnt]);
 				regulator_notifier_call_chain(pchip->rdev[icnt],
 							      LP8755_EVENT_OCP,
 							      NULL);
+				regulator_unlock(pchip->rdev[icnt]);
+			}
 
 	/* send OVP event to all regulator devices */
 	if ((flag1 & 0x02) && (pchip->irqmask & 0x02))
 		for (icnt = 0; icnt < LP8755_BUCK_MAX; icnt++)
-			if (pchip->rdev[icnt] != NULL)
+			if (pchip->rdev[icnt] != NULL) {
+				regulator_lock(pchip->rdev[icnt]);
 				regulator_notifier_call_chain(pchip->rdev[icnt],
 							      LP8755_EVENT_OVP,
 							      NULL);
+				regulator_unlock(pchip->rdev[icnt]);
+			}
 	return IRQ_HANDLED;
 
 err_i2c: