regulator: core: Only increment use_count when enable_count changes

The use_count of a regulator should only be incremented when the
enable_count changes from 0 to 1. Similarly, the use_count should
only be decremented when the enable_count changes from 1 to 0.

In the previous implementation, use_count was sometimes decremented
to 0 when some consumer called unbalanced disable,
leading to unexpected disable even the regulator is enabled by
other consumers. With this change, the use_count accurately reflects
the number of users which the regulator is enabled.

This should make things more robust in the case where a consumer does
leak references.

Signed-off-by: Rui Zhang <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/regulator/core.c

···
 		/* Fallthrough on positive return values - already enabled */
 	}
 
-	rdev->use_count++;
+	if (regulator->enable_count == 1)
+		rdev->use_count++;
 
 	return 0;
 
···
 
 	lockdep_assert_held_once(&rdev->mutex.base);
 
-	if (WARN(rdev->use_count <= 0,
+	if (WARN(regulator->enable_count == 0,
 		 "unbalanced disables for %s\n", rdev_get_name(rdev)))
 		return -EIO;
 
-	/* are we the last user and permitted to disable ? */
-	if (rdev->use_count == 1 &&
-	    (rdev->constraints && !rdev->constraints->always_on)) {
+	if (regulator->enable_count == 1) {
+	/* disabling last enable_count from this regulator */
+		/* are we the last user and permitted to disable ? */
+		if (rdev->use_count == 1 &&
+		    (rdev->constraints && !rdev->constraints->always_on)) {
 
-		/* we are last user */
-		if (regulator_ops_is_valid(rdev, REGULATOR_CHANGE_STATUS)) {
-			ret = _notifier_call_chain(rdev,
-						   REGULATOR_EVENT_PRE_DISABLE,
-						   NULL);
-			if (ret & NOTIFY_STOP_MASK)
-				return -EINVAL;
+			/* we are last user */
+			if (regulator_ops_is_valid(rdev, REGULATOR_CHANGE_STATUS)) {
+				ret = _notifier_call_chain(rdev,
+							   REGULATOR_EVENT_PRE_DISABLE,
+							   NULL);
+				if (ret & NOTIFY_STOP_MASK)
+					return -EINVAL;
 
-			ret = _regulator_do_disable(rdev);
-			if (ret < 0) {
-				rdev_err(rdev, "failed to disable: %pe\n", ERR_PTR(ret));
-				_notifier_call_chain(rdev,
-						REGULATOR_EVENT_ABORT_DISABLE,
+				ret = _regulator_do_disable(rdev);
+				if (ret < 0) {
+					rdev_err(rdev, "failed to disable: %pe\n", ERR_PTR(ret));
+					_notifier_call_chain(rdev,
+							REGULATOR_EVENT_ABORT_DISABLE,
+							NULL);
+					return ret;
+				}
+				_notifier_call_chain(rdev, REGULATOR_EVENT_DISABLE,
 						NULL);
-				return ret;
 			}
-			_notifier_call_chain(rdev, REGULATOR_EVENT_DISABLE,
-					NULL);
-		}
 
-		rdev->use_count = 0;
-	} else if (rdev->use_count > 1) {
-		rdev->use_count--;
+			rdev->use_count = 0;
+		} else if (rdev->use_count > 1) {
+			rdev->use_count--;
+		}
 	}
 
 	if (ret == 0)