drm/panel: lvds: Add support for the power-supply property

A significant number of panels need to power up a regulator in order to
operate properly. Add support for the power-supply property to enable and
disable such a regulator whenever needed.
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/0c0819bdf88fa948188df95e57a10820a8a4548d.1513854122.git-series.maxime.ripard@free-electrons.com

drivers/gpu/drm/panel/panel-lvds.c

@@ -17,6 +17,7 @@
 #include <linux/module.h>
 #include <linux/of_platform.h>
 #include <linux/platform_device.h>
+#include <linux/regulator/consumer.h>
 #include <linux/slab.h>
 
 #include <drm/drmP.h>
@@ -39,6 +40,7 @@ struct panel_lvds {
 	bool data_mirror;
 
 	struct backlight_device *backlight;
+	struct regulator *supply;
 
 	struct gpio_desc *enable_gpio;
 	struct gpio_desc *reset_gpio;
@@ -69,6 +71,9 @@ static int panel_lvds_unprepare(struct drm_panel *panel)
 	if (lvds->enable_gpio)
 		gpiod_set_value_cansleep(lvds->enable_gpio, 0);
 
+	if (lvds->supply)
+		regulator_disable(lvds->supply);
+
 	return 0;
 }
 
@@ -76,6 +81,17 @@ static int panel_lvds_prepare(struct drm_panel *panel)
 {
 	struct panel_lvds *lvds = to_panel_lvds(panel);
 
+	if (lvds->supply) {
+		int err;
+
+		err = regulator_enable(lvds->supply);
+		if (err < 0) {
+			dev_err(lvds->dev, "failed to enable supply: %d\n",
+				err);
+			return err;
+		}
+	}
+
 	if (lvds->enable_gpio)
 		gpiod_set_value_cansleep(lvds->enable_gpio, 1);
 
@@ -196,6 +212,13 @@ static int panel_lvds_probe(struct platform_device *pdev)
 	if (ret < 0)
 		return ret;
 
+	lvds->supply = devm_regulator_get_optional(lvds->dev, "power");
+	if (IS_ERR(lvds->supply)) {
+		ret = PTR_ERR(lvds->supply);
+		dev_err(lvds->dev, "failed to request regulator: %d\n", ret);
+		return ret;
+	}
+
 	/* Get GPIOs and backlight controller. */
 	lvds->enable_gpio = devm_gpiod_get_optional(lvds->dev, "enable",
 						     GPIOD_OUT_LOW);