[PATCH v2] pwm: mediatek: Fix duty and period setting

[Uwe Kleine-König]

The period generated by the hardware is

	(PWMDWIDTH + 1) << CLKDIV) / freq

according to my tests with a signal analyser and also the documentation.

The current algorithm doesn't consider the `+ 1` part and so configures
slightly too high periods. The same issue exists for the duty cycle
setting. So subtract 1 from both the register values for period and
duty cycle. If period is 0, bail out, if duty_cycle is 0, just disable
the PWM which results in a constant low output.

Note that clk handling is dropped from pwm_mediatek_{en,dis}able to
handle duty_cycle = 0, so the calls in pwm_mediatek_apply() have to be
modified to do clk handling, too.

Fixes: caf065f8fd58 ("pwm: Add MediaTek PWM support")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig at baylibre.com>
---
Hello,

changes since (implicit) v1,
https://lore.kernel.org/linux-pwm/20250710163705.2095418-2-u.kleine-koenig@baylibre.com/:

 - Drop superflous parenthesis from commit log
 - To implement drop the enable register instead of bit 15 in the CON
   register, adapt commit log accordingly.

Best regards
Uwe

 drivers/pwm/pwm-mediatek.c | 76 ++++++++++++++++++++------------------
 1 file changed, 41 insertions(+), 35 deletions(-)

diff --git a/drivers/pwm/pwm-mediatek.c b/drivers/pwm/pwm-mediatek.c
index 6777c511622a..4460bbca2582 100644
--- a/drivers/pwm/pwm-mediatek.c
+++ b/drivers/pwm/pwm-mediatek.c
@@ -121,6 +121,26 @@ static inline void pwm_mediatek_writel(struct pwm_mediatek_chip *chip,
 	writel(value, chip->regs + chip->soc->reg_offset[num] + offset);
 }
 
+static void pwm_mediatek_enable(struct pwm_chip *chip, struct pwm_device *pwm)
+{
+	struct pwm_mediatek_chip *pc = to_pwm_mediatek_chip(chip);
+	u32 value;
+
+	value = readl(pc->regs);
+	value |= BIT(pwm->hwpwm);
+	writel(value, pc->regs);
+}
+
+static void pwm_mediatek_disable(struct pwm_chip *chip, struct pwm_device *pwm)
+{
+	struct pwm_mediatek_chip *pc = to_pwm_mediatek_chip(chip);
+	u32 value;
+
+	value = readl(pc->regs);
+	value &= ~BIT(pwm->hwpwm);
+	writel(value, pc->regs);
+}
+
 static int pwm_mediatek_config(struct pwm_chip *chip, struct pwm_device *pwm,
 			       int duty_ns, int period_ns)
 {
@@ -150,7 +170,10 @@ static int pwm_mediatek_config(struct pwm_chip *chip, struct pwm_device *pwm,
 	do_div(resolution, clk_rate);
 
 	cnt_period = DIV_ROUND_CLOSEST_ULL((u64)period_ns * 1000, resolution);
-	while (cnt_period > 8191) {
+	if (!cnt_period)
+		return -EINVAL;
+
+	while (cnt_period > 8192) {
 		resolution *= 2;
 		clkdiv++;
 		cnt_period = DIV_ROUND_CLOSEST_ULL((u64)period_ns * 1000,
@@ -173,9 +196,16 @@ static int pwm_mediatek_config(struct pwm_chip *chip, struct pwm_device *pwm,
 	}
 
 	cnt_duty = DIV_ROUND_CLOSEST_ULL((u64)duty_ns * 1000, resolution);
+
 	pwm_mediatek_writel(pc, pwm->hwpwm, PWMCON, BIT(15) | clkdiv);
-	pwm_mediatek_writel(pc, pwm->hwpwm, reg_width, cnt_period);
-	pwm_mediatek_writel(pc, pwm->hwpwm, reg_thres, cnt_duty);
+	pwm_mediatek_writel(pc, pwm->hwpwm, reg_width, cnt_period - 1);
+
+	if (cnt_duty) {
+		pwm_mediatek_writel(pc, pwm->hwpwm, reg_thres, cnt_duty - 1);
+		pwm_mediatek_enable(chip, pwm);
+	} else {
+		pwm_mediatek_disable(chip, pwm);
+	}
 
 out:
 	pwm_mediatek_clk_disable(chip, pwm);
@@ -183,35 +213,6 @@ static int pwm_mediatek_config(struct pwm_chip *chip, struct pwm_device *pwm,
 	return ret;
 }
 
-static int pwm_mediatek_enable(struct pwm_chip *chip, struct pwm_device *pwm)
-{
-	struct pwm_mediatek_chip *pc = to_pwm_mediatek_chip(chip);
-	u32 value;
-	int ret;
-
-	ret = pwm_mediatek_clk_enable(chip, pwm);
-	if (ret < 0)
-		return ret;
-
-	value = readl(pc->regs);
-	value |= BIT(pwm->hwpwm);
-	writel(value, pc->regs);
-
-	return 0;
-}
-
-static void pwm_mediatek_disable(struct pwm_chip *chip, struct pwm_device *pwm)
-{
-	struct pwm_mediatek_chip *pc = to_pwm_mediatek_chip(chip);
-	u32 value;
-
-	value = readl(pc->regs);
-	value &= ~BIT(pwm->hwpwm);
-	writel(value, pc->regs);
-
-	pwm_mediatek_clk_disable(chip, pwm);
-}
-
 static int pwm_mediatek_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 			      const struct pwm_state *state)
 {
@@ -221,8 +222,10 @@ static int pwm_mediatek_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 		return -EINVAL;
 
 	if (!state->enabled) {
-		if (pwm->state.enabled)
+		if (pwm->state.enabled) {
 			pwm_mediatek_disable(chip, pwm);
+			pwm_mediatek_clk_disable(chip, pwm);
+		}
 
 		return 0;
 	}
@@ -231,8 +234,11 @@ static int pwm_mediatek_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	if (err)
 		return err;
 
-	if (!pwm->state.enabled)
-		err = pwm_mediatek_enable(chip, pwm);
+	if (!pwm->state.enabled) {
+		err = pwm_mediatek_clk_enable(chip, pwm);
+		if (err < 0)
+			return err;
+	}
 
 	return err;
 }

base-commit: a02b105fe9f2b82cbd13b13a98c2b9ffae4a7c27
-- 
2.50.0