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@diehl.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>

drivers/leds/leds-pwm.c

@@ -17,10 +17,12 @@
 #include <linux/err.h>
 #include <linux/pwm.h>
 #include <linux/slab.h>
+#include "leds.h"
 
 struct led_pwm {
 	const char	*name;
 	u8		active_low;
+	u8		default_state;
 	unsigned int	max_brightness;
 };
 
@@ -77,7 +79,38 @@ 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 */
+	switch (led->default_state) {
+	case LEDS_DEFSTATE_KEEP:
+		pwm_get_state(led_data->pwm, &led_data->pwmstate);
+		if (led_data->pwmstate.period)
+			break;
+		led->default_state = LEDS_DEFSTATE_OFF;
+		dev_warn(dev,
+			"failed to read period for %s, default to off",
+			led->name);
+		fallthrough;
+	default:
+		pwm_init_state(led_data->pwm, &led_data->pwmstate);
+		break;
+	}
+
+	/* set brightness */
+	switch (led->default_state) {
+	case LEDS_DEFSTATE_ON:
+		led_data->cdev.brightness = led->max_brightness;
+		break;
+	case LEDS_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;
+		}
+		break;
+	}
 
 	ret = devm_led_classdev_register_ext(dev, &led_data->cdev, &init_data);
 	if (ret) {
@@ -86,11 +119,13 @@ 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_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++;
@@ -120,6 +155,8 @@ static int led_pwm_create_fwnode(struct device *dev, struct led_pwm_priv *priv)
 		fwnode_property_read_u32(fwnode, "max-brightness",
 					 &led.max_brightness);
 
+		led.default_state = led_init_default_state_get(fwnode);
+
 		ret = led_pwm_add(dev, priv, &led, fwnode);
 		if (ret)
 			goto err_child_out;