regulator: Add settling time for non-linear voltage transition

Some regulators (some PWM regulators) have the voltage transition
non-linear i.e. exponentially. On such cases, the settling time
for voltage transition can not be presented in the voltage-ramp-delay.

Add new property for non-linear voltage transition and handle this
in getting the voltage settling time.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/core.c

@@ -2753,6 +2753,8 @@ static int _regulator_set_voltage_time(struct regulator_dev *rdev,
 		ramp_delay = rdev->constraints->ramp_delay;
 	else if (rdev->desc->ramp_delay)
 		ramp_delay = rdev->desc->ramp_delay;
+	else if (rdev->constraints->settling_time)
+		return rdev->constraints->settling_time;
 
 	if (ramp_delay == 0) {
 		rdev_dbg(rdev, "ramp_delay not set\n");

drivers/regulator/of_regulator.c

@@ -86,6 +86,10 @@ static void of_get_regulation_constraints(struct device_node *np,
 			constraints->ramp_disable = true;
 	}
 
+	ret = of_property_read_u32(np, "regulator-settling-time-us", &pval);
+	if (!ret)
+		constraints->settling_time = pval;
+
 	ret = of_property_read_u32(np, "regulator-enable-ramp-delay", &pval);
 	if (!ret)
 		constraints->enable_time = pval;

include/linux/regulator/machine.h

@@ -108,6 +108,8 @@ struct regulator_state {
  * @initial_state: Suspend state to set by default.
  * @initial_mode: Mode to set at startup.
  * @ramp_delay: Time to settle down after voltage change (unit: uV/us)
+ * @settling_time: Time to settle down after voltage change when voltage
+ *		   change is non-linear (unit: microseconds).
  * @active_discharge: Enable/disable active discharge. The enum
  *		      regulator_active_discharge values are used for
  *		      initialisation.
@@ -149,6 +151,7 @@ struct regulation_constraints {
 	unsigned int initial_mode;
 
 	unsigned int ramp_delay;
+	unsigned int settling_time;
 	unsigned int enable_time;
 
 	unsigned int active_discharge;