pwm-backlight: Add power supply support

Backlights require a power supply to work properly. This commit adds a
regulator to power up and power down the backlight.

Signed-off-by: Thierry Reding <[e-mail]>

Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt

···
       last value in the array represents a 100% duty cycle (brightest).
   - default-brightness-level: the default brightness level (index into the
       array defined by the "brightness-levels" property)
+  - power-supply: regulator for supply voltage
 
 Optional properties:
   - pwm-names: a list of names for the PWM devices specified in the
···
 		brightness-levels = <0 4 8 16 32 64 128 255>;
 		default-brightness-level = <6>;
 
+		power-supply = <&vdd_bl_reg>;
 		enable-gpios = <&gpio 58 0>;
 	};

drivers/video/backlight/pwm_bl.c

···
 #include <linux/err.h>
 #include <linux/pwm.h>
 #include <linux/pwm_backlight.h>
+#include <linux/regulator/consumer.h>
 #include <linux/slab.h>
 
 struct pwm_bl_data {
···
 	unsigned int		lth_brightness;
 	unsigned int		*levels;
 	bool			enabled;
+	struct regulator	*power_supply;
 	int			enable_gpio;
 	unsigned long		enable_gpio_flags;
 	int			(*notify)(struct device *,
···
 
 	pwm_config(pb->pwm, duty_cycle, pb->period);
 
+	err = regulator_enable(pb->power_supply);
+	if (err < 0)
+		dev_err(pb->dev, "failed to enable power supply\n");
+
 	if (gpio_is_valid(pb->enable_gpio)) {
 		if (pb->enable_gpio_flags & PWM_BACKLIGHT_GPIO_ACTIVE_LOW)
 			gpio_set_value(pb->enable_gpio, 0);
···
 			gpio_set_value(pb->enable_gpio, 0);
 	}
 
+	regulator_disable(pb->power_supply);
 	pb->enabled = false;
 }
 
···
 				pb->enable_gpio, ret);
 			goto err_alloc;
 		}
+	}
+
+	pb->power_supply = devm_regulator_get(&pdev->dev, "power");
+	if (IS_ERR(pb->power_supply)) {
+		ret = PTR_ERR(pb->power_supply);
+		goto err_gpio;
 	}
 
 	pb->pwm = devm_pwm_get(&pdev->dev, NULL);