[PATCH v2 5/5] pwm: imx27: wait till the duty cycle is applied

[Marco Felsch]

Currently the driver don't check if the new state was applied or not.
This can cause glitches on the output pin if the new state disables the
PWM. In this case the PWM clocks are disabled before the new duty cycle
value gets applied.

The fix is to wait till the desired duty cycle was applied.

Signed-off-by: Marco Felsch <m.felsch at pengutronix.de>
---
v2:
- new patch

 drivers/pwm/pwm-imx27.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drivers/pwm/pwm-imx27.c b/drivers/pwm/pwm-imx27.c
index 07c6a263a39c..ffa00bcd81da 100644
--- a/drivers/pwm/pwm-imx27.c
+++ b/drivers/pwm/pwm-imx27.c
@@ -222,6 +222,26 @@ static int pwm_imx27_get_fifo_slot(struct pwm_chip *chip,
 	return fifoav;
 }
 
+static int pwm_imx27_wait_till_applied(struct pwm_chip *chip,
+				       struct pwm_device *pwm)
+{
+	unsigned int attempts = 4;
+	unsigned int period_ms;
+	int busy_slots;
+
+	do {
+		busy_slots = pwm_imx27_get_fifo_slot(chip, pwm);
+		if (busy_slots == 0)
+			return 0;
+
+		period_ms = DIV_ROUND_UP(pwm_get_period(pwm),
+					 NSEC_PER_MSEC);
+		msleep(period_ms);
+	} while (attempts--);
+
+	return -ETIMEDOUT;
+}
+
 static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 			   const struct pwm_state *state)
 {
@@ -277,6 +297,11 @@ static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 		writel(duty_cycles, imx->mmio_base + MX3_PWMSAR);
 	else
 		writel(0, imx->mmio_base + MX3_PWMSAR);
+
+	ret = pwm_imx27_wait_till_applied(chip, pwm);
+	if (ret)
+		goto out;
+
 	writel(period_cycles, imx->mmio_base + MX3_PWMPR);
 
 	/*
-- 
2.20.1