drm/panel: simple: Add proper definition for prepare and unprepare

Move out code from enable and disable routines to prepare
and unprepare routines, so that functionality is properly
distributed across all the panel functions.
Signed-off-by: Ajay Kumar <ajaykumar.rs@samsung.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

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

@@ -47,6 +47,7 @@ struct panel_desc {
 
 struct panel_simple {
 	struct drm_panel base;
+	bool prepared;
 	bool enabled;
 
 	const struct panel_desc *desc;
@@ -108,10 +109,6 @@ static int panel_simple_disable(struct drm_panel *panel)
 		backlight_update_status(p->backlight);
 	}
 
-	if (p->enable_gpio)
-		gpiod_set_value_cansleep(p->enable_gpio, 0);
-
-	regulator_disable(p->supply);
 	p->enabled = false;
 
 	return 0;
@@ -119,20 +116,27 @@ static int panel_simple_disable(struct drm_panel *panel)
 
 static int panel_simple_unprepare(struct drm_panel *panel)
 {
-	return 0;
-}
+	struct panel_simple *p = to_panel_simple(panel);
+
+	if (!p->prepared)
+		return 0;
+
+	if (p->enable_gpio)
+		gpiod_set_value_cansleep(p->enable_gpio, 0);
+
+	regulator_disable(p->supply);
+
+	p->prepared = false;
 
-static int panel_simple_prepare(struct drm_panel *panel)
-{
 	return 0;
 }
 
-static int panel_simple_enable(struct drm_panel *panel)
+static int panel_simple_prepare(struct drm_panel *panel)
 {
 	struct panel_simple *p = to_panel_simple(panel);
 	int err;
 
-	if (p->enabled)
+	if (p->prepared)
 		return 0;
 
 	err = regulator_enable(p->supply);
@@ -144,6 +148,18 @@ static int panel_simple_enable(struct drm_panel *panel)
 	if (p->enable_gpio)
 		gpiod_set_value_cansleep(p->enable_gpio, 1);
 
+	p->prepared = true;
+
+	return 0;
+}
+
+static int panel_simple_enable(struct drm_panel *panel)
+{
+	struct panel_simple *p = to_panel_simple(panel);
+
+	if (p->enabled)
+		return 0;
+
 	if (p->backlight) {
 		p->backlight->props.power = FB_BLANK_UNBLANK;
 		backlight_update_status(p->backlight);
@@ -194,6 +210,7 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
 		return -ENOMEM;
 
 	panel->enabled = false;
+	panel->prepared = false;
 	panel->desc = desc;
 
 	panel->supply = devm_regulator_get(dev, "power");