linux-kernel - [RFC PATCH 4/4] pwm: sun4i: Delay after writing the period

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Date:   Tue, 17 Mar 2020 16:59:06 +0100
From:   Pascal Roeleven <dev@...calroeleven.nl>
To:     Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        linux-pwm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Cc:     linux-sunxi@...glegroups.com,
        Pascal Roeleven <dev@...calroeleven.nl>
Subject: [RFC PATCH 4/4] pwm: sun4i: Delay after writing the period

When disabling, ensure the period write is complete before continuing.
This fixes an issue on some devices when the write isn't complete before
the panel is turned off but the clock gate is still on.

Signed-off-by: Pascal Roeleven <dev@...calroeleven.nl>
---
 drivers/pwm/pwm-sun4i.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c
index a11d00f96..75250fd4c 100644
--- a/drivers/pwm/pwm-sun4i.c
+++ b/drivers/pwm/pwm-sun4i.c
@@ -299,6 +299,10 @@ static int sun4i_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	sun4i_pwm_writel(sun4i_pwm, val, PWM_CH_PRD(pwm->hwpwm));
 	next_period = jiffies + usecs_to_jiffies(cstate.period / 1000 + 1);
 
+	/* When disabling, make sure the period register is written first */
+	if (!state->enabled && cstate.enabled)
+		sun4i_pwm_wait(next_period);
+
 	if (state->polarity != PWM_POLARITY_NORMAL)
 		ctrl &= ~BIT_CH(PWM_ACT_STATE, pwm->hwpwm);
 	else
@@ -320,6 +324,7 @@ static int sun4i_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 		return 0;
 
 	/* We need a full period to elapse before disabling the channel. */
+	next_period = jiffies + usecs_to_jiffies(cstate.period / 1000 + 1);
 	sun4i_pwm_wait(next_period);
 
 	spin_lock(&sun4i_pwm->ctrl_lock);
-- 
2.20.1