regulator: core: Add regulator_sync_voltage_rdev()

Some NVIDIA Tegra devices use a CPU soft-reset method for the reboot and
in this case we need to restore the coupled voltages to the state that is
suitable for hardware during boot. Add new regulator_sync_voltage_rdev()
helper which is needed by regulator drivers in order to sync voltage of
a coupled regulators.
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/regulator/core.c

@@ -4105,6 +4105,29 @@ int regulator_set_voltage_time_sel(struct regulator_dev *rdev,
 }
 EXPORT_SYMBOL_GPL(regulator_set_voltage_time_sel);
 
+int regulator_sync_voltage_rdev(struct regulator_dev *rdev)
+{
+	int ret;
+
+	regulator_lock(rdev);
+
+	if (!rdev->desc->ops->set_voltage &&
+	    !rdev->desc->ops->set_voltage_sel) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	/* balance only, if regulator is coupled */
+	if (rdev->coupling_desc.n_coupled > 1)
+		ret = regulator_balance_voltage(rdev, PM_SUSPEND_ON);
+	else
+		ret = -EOPNOTSUPP;
+
+out:
+	regulator_unlock(rdev);
+	return ret;
+}
+
 /**
  * regulator_sync_voltage - re-apply last regulator output voltage
  * @regulator: regulator source

include/linux/regulator/driver.h

@@ -540,6 +540,7 @@ int regulator_set_current_limit_regmap(struct regulator_dev *rdev,
 int regulator_get_current_limit_regmap(struct regulator_dev *rdev);
 void *regulator_get_init_drvdata(struct regulator_init_data *reg_init_data);
 int regulator_set_ramp_delay_regmap(struct regulator_dev *rdev, int ramp_delay);
+int regulator_sync_voltage_rdev(struct regulator_dev *rdev);
 
 /*
  * Helper functions intended to be used by regulator drivers prior registering