pwm: jz4740: Make disable operation compatible with TCU2 mode

On the JZ4750 and later SoCs, channel 1 and 2 operate in a different
way (TCU2 mode) as the other channels. If a TCU2 mode counter is
stopped before its PWM functionality is disabled, the output is not
guaranteed to return to the initial level.
Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-jz4740.c

@@ -71,9 +71,15 @@ static void jz4740_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
 {
 	uint32_t ctrl = jz4740_timer_get_ctrl(pwm->hwpwm);
 
+	/* Disable PWM output.
+	 * In TCU2 mode (channel 1/2 on JZ4750+), this must be done before the
+	 * counter is stopped, while in TCU1 mode the order does not matter.
+	 */
 	ctrl &= ~JZ_TIMER_CTRL_PWM_ENABLE;
-	jz4740_timer_disable(pwm->hwpwm);
 	jz4740_timer_set_ctrl(pwm->hwpwm, ctrl);
+
+	/* Stop counter */
+	jz4740_timer_disable(pwm->hwpwm);
 }
 
 static int jz4740_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,