[PATCH v2 5.10-stable] gpio: mvebu: fix pwm .get_state period calculation

[PATCH v2 5.10-stable] gpio: mvebu: fix pwm .get_state period calculation

[Baruch Siach]

commit e73b0101ae5124bf7cd3fb5d250302ad2f16a416 upstream.

The period is the sum of on and off values. That is, calculate period as

  ($on + $off) / clkrate

instead of

  $off / clkrate - $on / clkrate

that makes no sense.

Reported-by: Russell King <linux@armlinux.org.uk>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Fixes: 757642f9a584e ("gpio: mvebu: Add limited PWM support")
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
[baruch: backport to kernels <= v5.10]
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
---

This backported patch applies to all kernels between 4.14 and 5.10
(inclusive).

v2:

  * Add a note on backport with another SoB

  * Add Uwe's Reviewed-by tag
---
 drivers/gpio/gpio-mvebu.c | 25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

diff --git a/drivers/gpio/gpio-mvebu.c b/drivers/gpio/gpio-mvebu.c
index 2f245594a90a..ed7c5fc47f52 100644
--- a/drivers/gpio/gpio-mvebu.c
+++ b/drivers/gpio/gpio-mvebu.c
@@ -660,9 +660,8 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip,
 
 	spin_lock_irqsave(&mvpwm->lock, flags);
 
-	val = (unsigned long long)
-		readl_relaxed(mvebu_pwmreg_blink_on_duration(mvpwm));
-	val *= NSEC_PER_SEC;
+	u = readl_relaxed(mvebu_pwmreg_blink_on_duration(mvpwm));
+	val = (unsigned long long) u * NSEC_PER_SEC;
 	do_div(val, mvpwm->clk_rate);
 	if (val > UINT_MAX)
 		state->duty_cycle = UINT_MAX;
@@ -671,21 +670,17 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip,
 	else
 		state->duty_cycle = 1;
 
-	val = (unsigned long long)
-		readl_relaxed(mvebu_pwmreg_blink_off_duration(mvpwm));
+	val = (unsigned long long) u; /* on duration */
+	/* period = on + off duration */
+	val += readl_relaxed(mvebu_pwmreg_blink_off_duration(mvpwm));
 	val *= NSEC_PER_SEC;
 	do_div(val, mvpwm->clk_rate);
-	if (val < state->duty_cycle) {
+	if (val > UINT_MAX)
+		state->period = UINT_MAX;
+	else if (val)
+		state->period = val;
+	else
 		state->period = 1;
-	} else {
-		val -= state->duty_cycle;
-		if (val > UINT_MAX)
-			state->period = UINT_MAX;
-		else if (val)
-			state->period = val;
-		else
-			state->period = 1;
-	}
 
 	regmap_read(mvchip->regs, GPIO_BLINK_EN_OFF + mvchip->offset, &u);
 	if (u)
-- 
2.29.2