pwm: Restore initial state if a legacy callback fails

It is not entirely accurate to go back to the initial state after e.g.
.enable() failed, as .config() still modified the hardware, but this same
inconsistency exists for drivers that implement .apply().
Signed-off-by: NUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: NThierry Reding <thierry.reding@gmail.com>

drivers/pwm/core.c

@@ -526,10 +526,8 @@ static int pwm_apply_legacy(struct pwm_chip *chip, struct pwm_device *pwm,
 			    const struct pwm_state *state)
 {
 	int err;
+	struct pwm_state initial_state = pwm->state;
 
-	/*
-	 * FIXME: restore the initial state in case of error.
-	 */
 	if (state->polarity != pwm->state.polarity) {
 		if (!chip->ops->set_polarity)
 			return -EINVAL;
@@ -550,7 +548,7 @@ static int pwm_apply_legacy(struct pwm_chip *chip, struct pwm_device *pwm,
 
 		err = chip->ops->set_polarity(chip, pwm, state->polarity);
 		if (err)
-			return err;
+			goto rollback;
 
 		pwm->state.polarity = state->polarity;
 	}
@@ -573,7 +571,7 @@ static int pwm_apply_legacy(struct pwm_chip *chip, struct pwm_device *pwm,
 				state->duty_cycle,
 				state->period);
 	if (err)
-		return err;
+		goto rollback;
 
 	pwm->state.period = state->period;
 	pwm->state.duty_cycle = state->duty_cycle;
@@ -581,10 +579,14 @@ static int pwm_apply_legacy(struct pwm_chip *chip, struct pwm_device *pwm,
 	if (!pwm->state.enabled) {
 		err = chip->ops->enable(chip, pwm);
 		if (err)
-			return err;
+			goto rollback;
 	}
 
 	return 0;
+
+rollback:
+	pwm->state = initial_state;
+	return err;
 }
 
 /**