linux-kernel - [PATCH 1/2] backlight: lp855x: Initialize PWM state on first brightness change

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Date:   Fri, 14 Jul 2023 14:14:39 +0200
From:   Artur Weber <aweber.kernel@...il.com>
To:     Lee Jones <lee@...nel.org>
Cc:     Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Helge Deller <deller@....de>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Artur Weber <aweber.kernel@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org,
        ~postmarketos/upstreaming@...ts.sr.ht
Subject: [PATCH 1/2] backlight: lp855x: Initialize PWM state on first brightness change

As pointed out by Uwe Kleine-König[1], the changes introduced in
commit c1ff7da03e16 ("video: backlight: lp855x: Get PWM for PWM mode
during probe") caused the PWM state set up by the bootloader to be
re-set when the driver is probed. This differs from the behavior from
before that patch, where the PWM state would be initialized on the
first brightness change.

Fix this by moving the PWM state initialization into the PWM control
function. Add a new variable, needs_pwm_init, to the device info struct
to allow us to check whether we need the initialization, or whether it
has already been done.

[1] https://lore.kernel.org/lkml/20230614083953.e4kkweddjz7wztby@pengutronix.de/

Fixes: c1ff7da03e16 ("video: backlight: lp855x: Get PWM for PWM mode during probe")
Signed-off-by: Artur Weber <aweber.kernel@...il.com>
---
 drivers/video/backlight/lp855x_bl.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/drivers/video/backlight/lp855x_bl.c b/drivers/video/backlight/lp855x_bl.c
index 1c9e921bca14..349ec324bc1e 100644
--- a/drivers/video/backlight/lp855x_bl.c
+++ b/drivers/video/backlight/lp855x_bl.c
@@ -71,6 +71,7 @@ struct lp855x {
 	struct device *dev;
 	struct lp855x_platform_data *pdata;
 	struct pwm_device *pwm;
+	bool needs_pwm_init;
 	struct regulator *supply;	/* regulator for VDD input */
 	struct regulator *enable;	/* regulator for EN/VDDIO input */
 };
@@ -220,7 +221,15 @@ static void lp855x_pwm_ctrl(struct lp855x *lp, int br, int max_br)
 {
 	struct pwm_state state;
 
-	pwm_get_state(lp->pwm, &state);
+	if (lp->needs_pwm_init) {
+		pwm_init_state(lp->pwm, &state);
+		/* Legacy platform data compatibility */
+		if (lp->pdata->period_ns > 0)
+			state.period = lp->pdata->period_ns;
+		lp->needs_pwm_init = false;
+	} else {
+		pwm_get_state(lp->pwm, &state);
+	}
 
 	state.duty_cycle = div_u64(br * state.period, max_br);
 	state.enabled = state.duty_cycle;
@@ -387,7 +396,6 @@ static int lp855x_probe(struct i2c_client *cl)
 	const struct i2c_device_id *id = i2c_client_get_device_id(cl);
 	const struct acpi_device_id *acpi_id = NULL;
 	struct device *dev = &cl->dev;
-	struct pwm_state pwmstate;
 	struct lp855x *lp;
 	int ret;
 
@@ -470,15 +478,11 @@ static int lp855x_probe(struct i2c_client *cl)
 		else
 			return dev_err_probe(dev, ret, "getting PWM\n");
 
+		lp->needs_pwm_init = false;
 		lp->mode = REGISTER_BASED;
 		dev_dbg(dev, "mode: register based\n");
 	} else {
-		pwm_init_state(lp->pwm, &pwmstate);
-		/* Legacy platform data compatibility */
-		if (lp->pdata->period_ns > 0)
-			pwmstate.period = lp->pdata->period_ns;
-		pwm_apply_state(lp->pwm, &pwmstate);
-
+		lp->needs_pwm_init = true;
 		lp->mode = PWM_BASED;
 		dev_dbg(dev, "mode: PWM based\n");
 	}
-- 
2.41.0