drm/i915: ensure single initialization and cleanup of backlight device

Backlight cleanup in the eDP connector destroy callback caused the
backlight device to be removed on some systems that first initialized LVDS
and then attempted to initialize eDP. Prevent multiple backlight
initializations, and ensure backlight cleanup is only done once by moving
it to modeset cleanup.

A small wrinkle is the introduced asymmetry in backlight
setup/cleanup. This could be solved by adding refcounting, but it seems
overkill considering that there should only ever be one backlight device.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=55701
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Tested-by: Peter Verthez <peter.verthez@skynet.be>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -9423,6 +9423,9 @@ void intel_modeset_cleanup(struct drm_device *dev)
 	/* flush any delayed tasks or pending work */
 	flush_scheduled_work();
 
+	/* destroy backlight, if any, before the connectors */
+	intel_panel_destroy_backlight(dev);
+
 	drm_mode_config_cleanup(dev);
 
 	intel_cleanup_overlay(dev);

drivers/gpu/drm/i915/intel_dp.c

@@ -2474,17 +2474,14 @@ done:
 static void
 intel_dp_destroy(struct drm_connector *connector)
 {
-	struct drm_device *dev = connector->dev;
 	struct intel_dp *intel_dp = intel_attached_dp(connector);
 	struct intel_connector *intel_connector = to_intel_connector(connector);
 
 	if (!IS_ERR_OR_NULL(intel_connector->edid))
 		kfree(intel_connector->edid);
 
-	if (is_edp(intel_dp)) {
-		intel_panel_destroy_backlight(dev);
+	if (is_edp(intel_dp))
 		intel_panel_fini(&intel_connector->panel);
-	}
 
 	drm_sysfs_connector_remove(connector);
 	drm_connector_cleanup(connector);

drivers/gpu/drm/i915/intel_lvds.c

@@ -631,7 +631,6 @@ static void intel_lvds_destroy(struct drm_connector *connector)
 	if (!IS_ERR_OR_NULL(lvds_connector->base.edid))
 		kfree(lvds_connector->base.edid);
 
-	intel_panel_destroy_backlight(connector->dev);
 	intel_panel_fini(&lvds_connector->base.panel);
 
 	drm_sysfs_connector_remove(connector);

drivers/gpu/drm/i915/intel_panel.c

@@ -428,6 +428,9 @@ int intel_panel_setup_backlight(struct drm_connector *connector)
 
 	intel_panel_init_backlight(dev);
 
+	if (WARN_ON(dev_priv->backlight.device))
+		return -ENODEV;
+
 	memset(&props, 0, sizeof(props));
 	props.type = BACKLIGHT_RAW;
 	props.brightness = dev_priv->backlight.level;
@@ -453,8 +456,10 @@ int intel_panel_setup_backlight(struct drm_connector *connector)
 void intel_panel_destroy_backlight(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	if (dev_priv->backlight.device)
+	if (dev_priv->backlight.device) {
 		backlight_device_unregister(dev_priv->backlight.device);
+		dev_priv->backlight.device = NULL;
+	}
 }
 #else
 int intel_panel_setup_backlight(struct drm_connector *connector)