linux-kernel - [PATCH v5 2/3] leds: pwm: add support for default-state device property

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Date:   Tue, 21 Apr 2020 13:09:14 +0000
From:   Denis Osterland-Heim <denis.osterland@...hl.com>
To:     "dmurphy@...com" <dmurphy@...com>, "pavel@....cz" <pavel@....cz>,
        "jacek.anaszewski@...il.com" <jacek.anaszewski@...il.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Denis Osterland-Heim" <denis.osterland@...hl.com>,
        "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: [PATCH v5 2/3] leds: pwm: add support for default-state device
 property

This patch adds support for "default-state" devicetree property, which
allows to defer pwm init to first use of led.

This allows to configure the PWM early in bootloader to let the LED
blink until an application in Linux userspace sets something different.

Signed-off-by: Denis Osterland-Heim <Denis.Osterland@...hl.com>
---
 drivers/leds/leds-pwm.c | 54 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 48 insertions(+), 6 deletions(-)

diff --git a/drivers/leds/leds-pwm.c b/drivers/leds/leds-pwm.c
index ef7b91bd2064..7b199c151768 100644
--- a/drivers/leds/leds-pwm.c
+++ b/drivers/leds/leds-pwm.c
@@ -18,10 +18,15 @@
 #include <linux/pwm.h>
 #include <linux/slab.h>
 
+#define LEDS_PWM_DEFSTATE_OFF	0
+#define LEDS_PWM_DEFSTATE_ON	1
+#define LEDS_PWM_DEFSTATE_KEEP	2
+
 struct led_pwm {
 	const char	*name;
 	const char	*default_trigger;
 	u8		active_low;
+	u8		default_state;
 	unsigned int	max_brightness;
 };
 
@@ -88,7 +93,30 @@ static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv,
 
 	led_data->cdev.brightness_set_blocking = led_pwm_set;
 
-	pwm_init_state(led_data->pwm, &led_data->pwmstate);
+	/* init PWM state */
+	if (led->default_state == LEDS_PWM_DEFSTATE_KEEP) {
+		pwm_get_state(led_data->pwm, &led_data->pwmstate);
+		if (!led_data->pwmstate.period) {
+			led->default_state = LEDS_PWM_DEFSTATE_OFF;
+			dev_warn(dev,
+				"failed to read period for %s, default to off",
+				led->name);
+		}
+	}
+	if (led->default_state != LEDS_PWM_DEFSTATE_KEEP)
+		pwm_init_state(led_data->pwm, &led_data->pwmstate);
+
+	/* set brightness */
+	if (led->default_state == LEDS_PWM_DEFSTATE_ON)
+		led_data->cdev.brightness = led->max_brightness;
+	else if (led->default_state == LEDS_PWM_DEFSTATE_KEEP) {
+		uint64_t brightness;
+
+		brightness = led->max_brightness;
+		brightness *= led_data->pwmstate.duty_cycle;
+		do_div(brightness, led_data->pwmstate.period);
+		led_data->cdev.brightness = brightness;
+	}
 
 	ret = devm_led_classdev_register(dev, &led_data->cdev);
 	if (ret) {
@@ -97,11 +125,13 @@ static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv,
 		return ret;
 	}
 
-	ret = led_pwm_set(&led_data->cdev, led_data->cdev.brightness);
-	if (ret) {
-		dev_err(dev, "failed to set led PWM value for %s: %d",
-			led->name, ret);
-		return ret;
+	if (led->default_state != LEDS_PWM_DEFSTATE_KEEP) {
+		ret = led_pwm_set(&led_data->cdev, led_data->cdev.brightness);
+		if (ret) {
+			dev_err(dev, "failed to set led PWM value for %s: %d",
+				led->name, ret);
+			return ret;
+		}
 	}
 
 	priv->num_leds++;
@@ -117,6 +147,8 @@ static int led_pwm_create_fwnode(struct device *dev, struct led_pwm_priv *priv)
 	memset(&led, 0, sizeof(led));
 
 	device_for_each_child_node(dev, fwnode) {
+		const char *state = NULL;
+
 		ret = fwnode_property_read_string(fwnode, "label", &led.name);
 		if (ret && is_of_node(fwnode))
 			led.name = to_of_node(fwnode)->name;
@@ -134,6 +166,16 @@ static int led_pwm_create_fwnode(struct device *dev, struct led_pwm_priv *priv)
 		fwnode_property_read_u32(fwnode, "max-brightness",
 					 &led.max_brightness);
 
+		if (!fwnode_property_read_string(fwnode, "default-state",
+						 &state)) {
+			if (!strcmp(state, "keep"))
+				led.default_state = LEDS_PWM_DEFSTATE_KEEP;
+			else if (!strcmp(state, "on"))
+				led.default_state = LEDS_PWM_DEFSTATE_ON;
+			else
+				led.default_state = LEDS_PWM_DEFSTATE_OFF;
+		}
+
 		ret = led_pwm_add(dev, priv, &led, fwnode);
 		if (ret) {
 			fwnode_handle_put(fwnode);
-- 
2.26.2



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