[PATCH v3 2/2] pwm: sifive: change the PWM controlled LED algorithm

[Nylon Chen]

The `frac` variable represents the pulse inactive time, and the result of
this algorithm is the pulse active time. Therefore, we must reverse the
result.

The reference is SiFive FU740-C000 Manual[0]

Link: https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b16acba_fu740-c000-manual-v1p6.pdf [0]

Acked-by: Conor Dooley <conor.dooley at microchip.com>
Reviewed-by: Conor Dooley <conor.dooley at microchip.com>
Signed-off-by: Nylon Chen <nylon.chen at sifive.com>
Signed-off-by: Vincent Chen <vincent.chen at sifive.com>
---
 drivers/pwm/pwm-sifive.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
index 393a4b97fc19..d5d5f36da297 100644
--- a/drivers/pwm/pwm-sifive.c
+++ b/drivers/pwm/pwm-sifive.c
@@ -132,13 +132,13 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 {
 	struct pwm_sifive_ddata *ddata = pwm_sifive_chip_to_ddata(chip);
 	struct pwm_state cur_state;
-	unsigned int duty_cycle;
+	unsigned int duty_cycle, period;
 	unsigned long long num;
 	bool enabled;
 	int ret = 0;
 	u32 frac;
 
-	if (state->polarity != PWM_POLARITY_INVERSED)
+	if (state->polarity != PWM_POLARITY_NORMAL && state->polarity != PWM_POLARITY_INVERSED)
 		return -EINVAL;
 
 	cur_state = pwm->state;
@@ -154,10 +154,13 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	 * calculating the register values first and then writing them
 	 * consecutively
 	 */
+	period = max(state->period, ddata->approx_period);
 	num = (u64)duty_cycle * (1U << PWM_SIFIVE_CMPWIDTH);
 	frac = DIV64_U64_ROUND_CLOSEST(num, state->period);
-	/* The hardware cannot generate a 100% duty cycle */
 	frac = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1);
+	/* The hardware cannot generate a 100% duty cycle */
+	frac = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - frac;
+
 
 	mutex_lock(&ddata->lock);
 	if (state->period != ddata->approx_period) {
-- 
2.40.0