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>

diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c
index a75ff36..2e41ba2 100644 (file)
--- a/drivers/pwm/pwm-jz4740.c
+++ b/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,