Regulator: add suspend-finish API for regulator core.

The regulator core had suspend-prepare that turns off the regulators
when entering a system-wide suspend. However, it did not have
suspend-finish that pairs with suspend-prepare and the regulator core
has assumed that the regulator devices and their drivers support
autonomous recover at resume.

This patch adds regulator_suspend_finish that pairs with the
previously-existed regulator_suspend_prepare. The function
regulator_suspend_finish turns on the regulators that have always_on set
or positive use_count so that we can reset the regulator states
appropriately at resume.

In regulator_suspend_finish, if has_full_constraints, it disables
unnecessary regulators.

Signed-off-by: MyungJoo Ham <[e-mail]>
Signed-off-by: Kyungmin Park <[e-mail]>
Acked-by: Mark Brown <[e-mail]>
--
Updates
v3
comments corrected (Thanks to Igor)
v2
disable unnecessary regulators (Thanks to Mark)
Signed-off-by: Liam Girdwood <[e-mail]>

drivers/regulator/core.c

···
 EXPORT_SYMBOL_GPL(regulator_suspend_prepare);
 
 /**
+ * regulator_suspend_finish - resume regulators from system wide suspend
+ *
+ * Turn on regulators that might be turned off by regulator_suspend_prepare
+ * and that should be turned on according to the regulators properties.
+ */
+int regulator_suspend_finish(void)
+{
+	struct regulator_dev *rdev;
+	int ret = 0, error;
+
+	mutex_lock(&regulator_list_mutex);
+	list_for_each_entry(rdev, &regulator_list, list) {
+		struct regulator_ops *ops = rdev->desc->ops;
+
+		mutex_lock(&rdev->mutex);
+		if ((rdev->use_count > 0  || rdev->constraints->always_on) &&
+				ops->enable) {
+			error = ops->enable(rdev);
+			if (error)
+				ret = error;
+		} else {
+			if (!has_full_constraints)
+				goto unlock;
+			if (!ops->disable)
+				goto unlock;
+			if (ops->is_enabled && !ops->is_enabled(rdev))
+				goto unlock;
+
+			error = ops->disable(rdev);
+			if (error)
+				ret = error;
+		}
+unlock:
+		mutex_unlock(&rdev->mutex);
+	}
+	mutex_unlock(&regulator_list_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(regulator_suspend_finish);
+
+/**
  * regulator_has_full_constraints - the system has fully specified constraints
  *
  * Calling this function will cause the regulator API to disable all

include/linux/regulator/machine.h

···
 };
 
 int regulator_suspend_prepare(suspend_state_t state);
+int regulator_suspend_finish(void);
 
 #ifdef CONFIG_REGULATOR
 void regulator_has_full_constraints(void);