[PATCH v4 2/3] pwm: loongson: Reset the counters before enabling PWM

[Keguang Zhang via B4 Relay]

From: Keguang Zhang <keguang.zhang@xxxxxxxxx>

The PWM controller may retain its initial hardware state when the driver
binds. Reset the counters before enabling to ensure that the PWM starts
from a known state.

Fixes: 2b62c89448dd ("pwm: Add Loongson PWM controller support")
Fixes: 0de9b836a3bc ("pwm: loongson: Reload PWM configuration through counter reset")
Cc: stable@xxxxxxxxxxxxxxx
Suggested-by: Uwe Kleine-König <ukleinek@xxxxxxxxxx>
Signed-off-by: Keguang Zhang <keguang.zhang@xxxxxxxxx>
---
 drivers/pwm/pwm-loongson.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/pwm/pwm-loongson.c b/drivers/pwm/pwm-loongson.c
index 7af5d4ce1060..977d867bdb8a 100644
--- a/drivers/pwm/pwm-loongson.c
+++ b/drivers/pwm/pwm-loongson.c
@@ -110,6 +110,14 @@ static int pwm_loongson_enable(struct pwm_chip *chip, struct pwm_device *pwm)
 	struct pwm_loongson_ddata *ddata = to_pwm_loongson_ddata(chip);
 
 	val = pwm_loongson_readl(ddata, LOONGSON_PWM_REG_CTRL);
+
+	/*
+	 * Ensure that the values of LOW and PERIOD are sampled into
+	 * the shadow register when the hardware starts running.
+	 */
+	if (!(val & LOONGSON_PWM_CTRL_REG_RST))
+		pwm_loongson_writel(ddata, val | LOONGSON_PWM_CTRL_REG_RST, LOONGSON_PWM_REG_CTRL);
+
 	val &= ~LOONGSON_PWM_CTRL_REG_RST;
 	val |= LOONGSON_PWM_CTRL_REG_EN;
 	pwm_loongson_writel(ddata, val, LOONGSON_PWM_REG_CTRL);

-- 
2.43.0