1 files changed, 39 insertions, 13 deletions

diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
index d5b647e6be78..4a07315b0744 100644
--- a/drivers/pwm/pwm-sifive.c
+++ b/drivers/pwm/pwm-sifive.c
@@ -4,11 +4,28 @@
  * For SiFive's PWM IP block documentation please refer Chapter 14 of
  * Reference Manual : https://static.dev.sifive.com/FU540-C000-v1.0.pdf
  *
+ * PWM output inversion: According to the SiFive Reference manual
+ * the output of each comparator is high whenever the value of pwms is
+ * greater than or equal to the corresponding pwmcmpX[Reference Manual].
+ *
+ * Figure 29 in the same manual shows that the pwmcmpXcenter bit is
+ * hard-tied to 0 (XNOR), which effectively inverts the comparison so that
+ * the output goes HIGH when  `pwms < pwmcmpX`.
+ *
+ * In other words, each pwmcmp register actually defines the **inactive**
+ * (low) period of the pulse, not the active time exactly opposite to what
+ * the documentation text implies.
+ *
+ * To compensate, this driver always **inverts** the duty value when reading
+ * or writing pwmcmp registers , so that users interact with a conventional
+ * **active-high** PWM interface.
+ *
+ *
  * Limitations:
  * - When changing both duty cycle and period, we cannot prevent in
  *   software that the output might produce a period with mixed
  *   settings (new period length and old duty cycle).
- * - The hardware cannot generate a 100% duty cycle.
+ * - The hardware cannot generate a 0% duty cycle.
  * - The hardware generates only inverted output.
  */
 #include <linux/clk.h>
@@ -101,7 +118,7 @@ static void pwm_sifive_update_clock(struct pwm_sifive_ddata *ddata,
 
 	/* As scale <= 15 the shift operation cannot overflow. */
 	num = (unsigned long long)NSEC_PER_SEC << (PWM_SIFIVE_CMPWIDTH + scale);
-	ddata->real_period = div64_ul(num, rate);
+	ddata->real_period = DIV_ROUND_UP_ULL(num, rate);
 	dev_dbg(ddata->parent,
 		"New real_period = %u ns\n", ddata->real_period);
 }
@@ -110,9 +127,14 @@ 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));
+	/*
+	 * PWM hardware uses 'inactive' counts in pwmcmp, so invert to get actual duty.
+	 * Here, 'inactive' is the low time and we compute duty as max_count - inactive.
+	 */
+	duty = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - inactive;
 
 	state->enabled = duty > 0;
 
@@ -121,9 +143,9 @@ static int pwm_sifive_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
 		state->enabled = false;
 
 	state->period = ddata->real_period;
-	state->duty_cycle =
-		(u64)duty * ddata->real_period >> PWM_SIFIVE_CMPWIDTH;
-	state->polarity = PWM_POLARITY_INVERSED;
+	state->duty_cycle = DIV_ROUND_UP_ULL((u64)duty * ddata->real_period,
+					     (1U << PWM_SIFIVE_CMPWIDTH));
+	state->polarity = PWM_POLARITY_NORMAL;
 
 	return 0;
 }
@@ -137,9 +159,10 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	unsigned long long num;
 	bool enabled;
 	int ret = 0;
-	u32 frac;
+	u64 frac;
+	u32 inactive;
 
-	if (state->polarity != PWM_POLARITY_INVERSED)
+	if (state->polarity != PWM_POLARITY_NORMAL)
 		return -EINVAL;
 
 	cur_state = pwm->state;
@@ -156,9 +179,12 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	 * consecutively
 	 */
 	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);
+	frac = num;
+	do_div(frac, state->period);
+	/* The hardware cannot generate a 0% duty cycle */
+	frac = min(frac, (u64)(1U << PWM_SIFIVE_CMPWIDTH) - 1);
+	/* pwmcmp register must be loaded with the inactive(invert the duty) */
+	inactive = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - frac;
 
 	mutex_lock(&ddata->lock);
 	if (state->period != ddata->approx_period) {
@@ -190,7 +216,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 		}
 	}
 
-	writel(frac, ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm));
+	writel(inactive, ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm));
 
 	if (!state->enabled)
 		clk_disable(ddata->clk);