regulator: core: provide fixed voltage in desc for single voltage rail

If given rail has the single voltage (n_voltages = 1) then provide the
rail voltage through regulator descriptor so that core can use this
value for finding voltage.

This will avoid the implementation of the callback for get_voltage() or
list_voltage() callback on regulator driver.
Signed-off-by: NLaxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: NMark Brown <broonie@linaro.org>

drivers/regulator/core.c

@@ -2489,6 +2489,8 @@ static int _regulator_get_voltage(struct regulator_dev *rdev)
 		ret = rdev->desc->ops->get_voltage(rdev);
 	} else if (rdev->desc->ops->list_voltage) {
 		ret = rdev->desc->ops->list_voltage(rdev, 0);
+	} else if (rdev->desc->fixed_uV && (rdev->desc->n_voltages == 1)) {
+		ret = rdev->desc->fixed_uV;
 	} else {
 		return -EINVAL;
 	}
@@ -3170,7 +3172,8 @@ static int add_regulator_attributes(struct regulator_dev *rdev)
 	/* some attributes need specific methods to be displayed */
 	if ((ops->get_voltage && ops->get_voltage(rdev) >= 0) ||
 	    (ops->get_voltage_sel && ops->get_voltage_sel(rdev) >= 0) ||
-	    (ops->list_voltage && ops->list_voltage(rdev, 0) >= 0)) {
+	    (ops->list_voltage && ops->list_voltage(rdev, 0) >= 0) ||
+		(rdev->desc->fixed_uV && (rdev->desc->n_voltages == 1))) {
 		status = device_create_file(dev, &dev_attr_microvolts);
 		if (status < 0)
 			return status;

include/linux/regulator/driver.h

@@ -207,6 +207,7 @@ enum regulator_type {
  * @min_uV: Voltage given by the lowest selector (if linear mapping)
  * @uV_step: Voltage increase with each selector (if linear mapping)
  * @linear_min_sel: Minimal selector for starting linear mapping
+ * @fixed_uV: Fixed voltage of rails.
  * @ramp_delay: Time to settle down after voltage change (unit: uV/us)
  * @volt_table: Voltage mapping table (if table based mapping)
  *
@@ -239,6 +240,7 @@ struct regulator_desc {
 	unsigned int min_uV;
 	unsigned int uV_step;
 	unsigned int linear_min_sel;
+	int fixed_uV;
 	unsigned int ramp_delay;
 
 	const struct regulator_linear_range *linear_ranges;