[PATCH] pwm: mediatek: support inverted polarity

[Lorenz Brun]

According to the MT7986 Reference Manual the Mediatek  PWM controller
doesn't appear to have support for inverted polarity.

This implements the same solution as in pwm-meson and just inverts the
duty cycle instead, which results in the same outcome.

Signed-off-by: Lorenz Brun <lorenz at brun.one>
---
 drivers/pwm/pwm-mediatek.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/pwm/pwm-mediatek.c b/drivers/pwm/pwm-mediatek.c
index 5b5eeaff35da..6f4a54c8299f 100644
--- a/drivers/pwm/pwm-mediatek.c
+++ b/drivers/pwm/pwm-mediatek.c
@@ -202,9 +202,7 @@ static int pwm_mediatek_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 			      const struct pwm_state *state)
 {
 	int err;
-
-	if (state->polarity != PWM_POLARITY_NORMAL)
-		return -EINVAL;
+	u64 duty_cycle;
 
 	if (!state->enabled) {
 		if (pwm->state.enabled)
@@ -213,7 +211,14 @@ static int pwm_mediatek_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 		return 0;
 	}
 
-	err = pwm_mediatek_config(pwm->chip, pwm, state->duty_cycle, state->period);
+	// According to the MT7986 Reference Manual the peripheral does not
+	// appear to have the capability to invert the output. Instead just
+	// invert the duty cycle.
+	duty_cycle = state->duty_cycle;
+	if (state->polarity == PWM_POLARITY_INVERSED)
+		duty_cycle = state->period - state->duty_cycle;
+
+	err = pwm_mediatek_config(pwm->chip, pwm, duty_cycle, state->period);
 	if (err)
 		return err;
 
-- 
2.39.1