pwm-pca9685: Fix several driver bugs

Problems:
- When duty_ns == period_ns, the full OFF bit was not cleared and the
  PWM output of the PCA9685 stayed off.
- When duty_ns == period_ns and the catch-all channel was used, the
  ALL_LED_OFF_L register was not cleared.
- The full ON bit was not cleared when setting the OFF time, therefore
  the exact OFF time was ignored when setting a duty_ns < period_ns

Solution: Clear both OFF registers when setting full ON and clear the
full ON bit when changing the OFF registers.

Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Clemens Gruber <clemens.gruber@pqgruber.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-pca9685.c

@@ -85,6 +85,22 @@ static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 	}
 
 	if (duty_ns == period_ns) {
+		/* Clear both OFF registers */
+		if (pwm->hwpwm >= PCA9685_MAXCHAN)
+			reg = PCA9685_ALL_LED_OFF_L;
+		else
+			reg = LED_N_OFF_L(pwm->hwpwm);
+
+		regmap_write(pca->regmap, reg, 0x0);
+
+		if (pwm->hwpwm >= PCA9685_MAXCHAN)
+			reg = PCA9685_ALL_LED_OFF_H;
+		else
+			reg = LED_N_OFF_H(pwm->hwpwm);
+
+		regmap_write(pca->regmap, reg, 0x0);
+
+		/* Set the full ON bit */
 		if (pwm->hwpwm >= PCA9685_MAXCHAN)
 			reg = PCA9685_ALL_LED_ON_H;
 		else
@@ -112,6 +128,14 @@ static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 
 	regmap_write(pca->regmap, reg, ((int)duty >> 8) & 0xf);
 
+	/* Clear the full ON bit, otherwise the set OFF time has no effect */
+	if (pwm->hwpwm >= PCA9685_MAXCHAN)
+		reg = PCA9685_ALL_LED_ON_H;
+	else
+		reg = LED_N_ON_H(pwm->hwpwm);
+
+	regmap_write(pca->regmap, reg, 0);
+
 	return 0;
 }