regulator: Add API to re-apply voltage to hardware

When cooperating with an external control source the regulator setup
may be changed underneath the API. Currently consumers can just redo
the regulator_set_voltage() to restore a previously set configuration
but provide an explicit API for doing this as optimsations in the
regulator_set_voltage() implementation will shortly prevent that.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>

drivers/regulator/core.c

@@ -1727,6 +1727,53 @@ out:
 }
 EXPORT_SYMBOL_GPL(regulator_set_voltage);
 
+/**
+ * regulator_sync_voltage - re-apply last regulator output voltage
+ * @regulator: regulator source
+ *
+ * Re-apply the last configured voltage.  This is intended to be used
+ * where some external control source the consumer is cooperating with
+ * has caused the configured voltage to change.
+ */
+int regulator_sync_voltage(struct regulator *regulator)
+{
+	struct regulator_dev *rdev = regulator->rdev;
+	int ret, min_uV, max_uV;
+
+	mutex_lock(&rdev->mutex);
+
+	if (!rdev->desc->ops->set_voltage &&
+	    !rdev->desc->ops->set_voltage_sel) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	/* This is only going to work if we've had a voltage configured. */
+	if (!regulator->min_uV && !regulator->max_uV) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	min_uV = regulator->min_uV;
+	max_uV = regulator->max_uV;
+
+	/* This should be a paranoia check... */
+	ret = regulator_check_voltage(rdev, &min_uV, &max_uV);
+	if (ret < 0)
+		goto out;
+
+	ret = regulator_check_consumers(rdev, &min_uV, &max_uV);
+	if (ret < 0)
+		goto out;
+
+	ret = _regulator_do_set_voltage(rdev, min_uV, max_uV);
+
+out:
+	mutex_unlock(&rdev->mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(regulator_sync_voltage);
+
 static int _regulator_get_voltage(struct regulator_dev *rdev)
 {
 	int sel;

include/linux/regulator/consumer.h

@@ -154,6 +154,7 @@ int regulator_is_supported_voltage(struct regulator *regulator,
 				   int min_uV, int max_uV);
 int regulator_set_voltage(struct regulator *regulator, int min_uV, int max_uV);
 int regulator_get_voltage(struct regulator *regulator);
+int regulator_sync_voltage(struct regulator *regulator);
 int regulator_set_current_limit(struct regulator *regulator,
 			       int min_uA, int max_uA);
 int regulator_get_current_limit(struct regulator *regulator);