linux-kernel - [PATCH v2 5/6] pwm: jz4740: Force TCU2 channels to return to their init level

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Date:   Fri,  7 Jun 2019 17:44:09 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     od@...c.me, linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paul Cercueil <paul@...pouillou.net>
Subject: [PATCH v2 5/6] pwm: jz4740: Force TCU2 channels to return to their init level

When the PWM mode of TCU2 channels is disabled, their corresponding pin
does not always return to its initial level. Force this by using a small
trick: we set duty > period, which is an invalid configuration for the
hardware, which then correctly resets the pin to the initial level.

Signed-off-by: Paul Cercueil <paul@...pouillou.net>
---

Notes:
    v2: New patch

 drivers/pwm/pwm-jz4740.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c
index 75254360621c..f901e8a0d33d 100644
--- a/drivers/pwm/pwm-jz4740.c
+++ b/drivers/pwm/pwm-jz4740.c
@@ -63,7 +63,15 @@ 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.
+	/*
+	 * Set duty > period. This trick allows the TCU channels in TCU2 mode to
+	 * properly return to their init level.
+	 */
+	jz4740_timer_set_duty(pwm->hwpwm, 0xffff);
+	jz4740_timer_set_period(pwm->hwpwm, 0x0);
+
+	/*
+	 * 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.
 	 */
-- 
2.21.0.593.g511ec345e18