[PATCH v3 3/4] pwm: imx27: verify decreasing PWM FIFO av value

[Leif Middelschulte <leif.middelschulte@gmail.com>]

Avoid unnecessary sleeps as adviced[0], if the FIFO cannot be emptied.

[0] https://lore.kernel.org/lkml/20230310174517.rb7xxrougkse2lrc@pengutronix.de/T/#ec9560c1f613d9c0d7b77d72ad9051768812f80db

Signed-off-by: Leif Middelschulte <Leif.Middelschulte@gmail.com>
---
 drivers/pwm/pwm-imx27.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/pwm/pwm-imx27.c b/drivers/pwm/pwm-imx27.c
index c2a1e2030072..9673e809d212 100644
--- a/drivers/pwm/pwm-imx27.c
+++ b/drivers/pwm/pwm-imx27.c
@@ -126,7 +126,7 @@ static int pwm_imx27_wait_fifo_empty(struct pwm_chip *chip,
 	struct device *dev = chip->dev;
 	unsigned int period_ms = DIV_ROUND_UP_ULL(pwm->state.period, NSEC_PER_MSEC);
 	int tries = MX3_PWM_FIFOAV_EMPTY_LOOP;
-	int fifoav;
+	int fifoav, previous_fifoav = INT_MAX;
 	u32 sr;
 
 	while (tries--) {
@@ -134,6 +134,10 @@ static int pwm_imx27_wait_fifo_empty(struct pwm_chip *chip,
 		fifoav = FIELD_GET(MX3_PWMSR_FIFOAV, sr);
 		if (fifoav == MX3_PWMSR_FIFOAV_EMPTY)
 			return;
+		/* if the FIFO value does not decrease, there is another problem */
+		if (previous_fifoav == fifoav)
+			break;
+		previous_fifoav = fifoav;
 		msleep(period_ms);
 	}
 	dev_warn(dev, "FIFO has been refilled concurrently\n");
-- 
2.39.2 (Apple Git-143)