[PATCH v9 2/3] pwm: sifive: change the PWM algorithm

From: Nylon Chen
Date: Thu Feb 22 2024 - 03:13:24 EST


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]

Co-developed-by: Zong Li <zong.li@xxxxxxxxxx>
Signed-off-by: Zong Li <zong.li@xxxxxxxxxx>
Co-developed-by: Vincent Chen <vincent.chen@xxxxxxxxxx>
Signed-off-by: Vincent Chen <vincent.chen@xxxxxxxxxx>
Signed-off-by: Nylon Chen <nylon.chen@xxxxxxxxxx>
---
drivers/pwm/pwm-sifive.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
index eabddb7c7820..a586cfe4191b 100644
--- a/drivers/pwm/pwm-sifive.c
+++ b/drivers/pwm/pwm-sifive.c
@@ -110,9 +110,10 @@ static int pwm_sifive_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
struct pwm_state *state)
{
struct pwm_sifive_ddata *ddata = pwm_sifive_chip_to_ddata(chip);
- u32 duty, val;
+ u32 duty, val, inactive;

- duty = readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm));
+ inactive = readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm));
+ duty = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - inactive;

state->enabled = duty > 0;

@@ -123,7 +124,7 @@ static int pwm_sifive_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
state->period = ddata->real_period;
state->duty_cycle =
(u64)duty * ddata->real_period >> PWM_SIFIVE_CMPWIDTH;
- state->polarity = PWM_POLARITY_INVERSED;
+ state->polarity = PWM_POLARITY_NORMAL;

return 0;
}
@@ -139,7 +140,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
int ret = 0;
u32 frac;

- if (state->polarity != PWM_POLARITY_INVERSED)
+ if (state->polarity != PWM_POLARITY_NORMAL)
return -EINVAL;

cur_state = pwm->state;
@@ -159,6 +160,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
frac = DIV64_U64_ROUND_CLOSEST(num, state->period);
/* The hardware cannot generate a 100% duty cycle */
frac = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1);
+ frac = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - frac;

mutex_lock(&ddata->lock);
if (state->period != ddata->approx_period) {
--
2.43.0