backlight: pwm_bl: Re-add driver internal enabled tracking

Commit e6bcca0 ("backlight: pwm_bl: Switch to using "atomic" PWM API")
removed the driver internal enabled tracking in favor of simply checking
the pwm state.

This can lead to issues as all of gpio-, regulator- and pwm-state are used
to determine the initial state and the bootloader or kernel can leave them
in an inconsistent state at boot.

In my case on rk3399-kevin, the pwm backlight is build as module and the
kernel disables the supply regulator as unused while keeping the pwm running
thus pwm_bl calling pwm_backlight_power_off() during probe and creating an
unmatched regulator-disable call, as it never got enabled from the pwm-bl
before.

To prevent these consistency issues, reintroduce the driver-internal
tracking of the enabled state.

Fixes: e6bcca0 ("backlight: pwm_bl: Switch to using "atomic" PWM API")
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>

Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/video/backlight/pwm_bl.c

@@ -30,6 +30,7 @@ struct pwm_bl_data {
 	struct device		*dev;
 	unsigned int		lth_brightness;
 	unsigned int		*levels;
+	bool			enabled;
 	struct regulator	*power_supply;
 	struct gpio_desc	*enable_gpio;
 	unsigned int		scale;
@@ -50,7 +51,7 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb)
 	int err;
 
 	pwm_get_state(pb->pwm, &state);
-	if (state.enabled)
+	if (pb->enabled)
 		return;
 
 	err = regulator_enable(pb->power_supply);
@@ -65,14 +66,16 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb)
 
 	if (pb->enable_gpio)
 		gpiod_set_value_cansleep(pb->enable_gpio, 1);
+
+	pb->enabled = true;
 }
 
 static void pwm_backlight_power_off(struct pwm_bl_data *pb)
 {
 	struct pwm_state state;
 
 	pwm_get_state(pb->pwm, &state);
-	if (!state.enabled)
+	if (!pb->enabled)
 		return;
 
 	if (pb->enable_gpio)
@@ -86,6 +89,7 @@ static void pwm_backlight_power_off(struct pwm_bl_data *pb)
 	pwm_apply_state(pb->pwm, &state);
 
 	regulator_disable(pb->power_supply);
+	pb->enabled = false;
 }
 
 static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness)
@@ -483,6 +487,7 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 	pb->check_fb = data->check_fb;
 	pb->exit = data->exit;
 	pb->dev = &pdev->dev;
+	pb->enabled = false;
 	pb->post_pwm_on_delay = data->post_pwm_on_delay;
 	pb->pwm_off_delay = data->pwm_off_delay;