regulator: pwm-regulator: Simplify voltage to duty-cycle call

If we reverse some of the logic and change the formula used,
we can simplify the function greatly.

It is intentional that this function is supplied and then re-worked
within the same patch-set.  The submission in the previous patch is
the tried and tested (i.e. in real releases) method written by ST.
This patch contains a simplification provided later.  It looks and
performs better, but doesn't have the same time-under-test that the
original method does.  The idea is that we keep some history in
order to provide an easy way back i.e. revert.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/pwm-regulator.c

@@ -93,26 +93,13 @@ static int pwm_regulator_list_voltage(struct regulator_dev *rdev,
 /**
  * Continuous voltage call-backs
  */
-static int pwm_voltage_to_duty_cycle(struct regulator_dev *rdev,
-					int volt_mV)
+static int pwm_voltage_to_duty_cycle(struct regulator_dev *rdev, int req_uV)
 {
-	struct pwm_regulator_data *drvdata = rdev_get_drvdata(rdev);
-	int min_mV = rdev->constraints->min_uV / 1000;
-	int max_mV = rdev->constraints->max_uV / 1000;
-	int max_duty_cycle = drvdata->max_duty_cycle;
-	int vdiff = min_mV - max_mV;
-	int pwm_code;
-	int tmp;
-
-	tmp = ((max_duty_cycle - min_mV) * max_duty_cycle) / vdiff;
-	pwm_code = ((tmp + max_duty_cycle) * volt_mV) / vdiff;
-
-	if (pwm_code < 0)
-		pwm_code = 0;
-	if (pwm_code > max_duty_cycle)
-		pwm_code = max_duty_cycle;
-
-	return pwm_code * 100 / max_duty_cycle;
+	int min_uV = rdev->constraints->min_uV;
+	int max_uV = rdev->constraints->max_uV;
+	int diff = max_uV - min_uV;
+
+	return 100 - ((((req_uV * 100) - (min_uV * 100)) / diff));
 }
 
 static int pwm_regulator_get_voltage(struct regulator_dev *rdev)
@@ -131,7 +118,7 @@ static int pwm_regulator_set_voltage(struct regulator_dev *rdev,
 	int duty_cycle;
 	int ret;
 
-	duty_cycle = pwm_voltage_to_duty_cycle(rdev, min_uV / 1000);
+	duty_cycle = pwm_voltage_to_duty_cycle(rdev, min_uV);
 
 	ret = pwm_config(drvdata->pwm,
 			 (drvdata->pwm->period / 100) * duty_cycle,