drm/i915: Add new helper to return current attached encoder for connector

For introducing splitted encoder/connector structure, this helper will return
connector's attached encoder when needed.
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/intel_display.c

@@ -4982,6 +4982,31 @@ struct drm_encoder *intel_best_encoder(struct drm_connector *connector)
 	return &intel_encoder->enc;
 }
 
+/*
+ * Return which encoder is currently attached for connector.
+ */
+struct drm_encoder *intel_attached_encoder (struct drm_connector *connector)
+{
+	struct drm_mode_object *obj;
+	struct drm_encoder *encoder;
+	int i;
+
+	for (i = 0; i < DRM_CONNECTOR_MAX_ENCODER; i++) {
+		if (connector->encoder_ids[i] == 0)
+			break;
+
+		obj = drm_mode_object_find(connector->dev,
+                                           connector->encoder_ids[i],
+                                           DRM_MODE_OBJECT_ENCODER);
+		if (!obj)
+			continue;
+
+		encoder = obj_to_encoder(obj);
+		return encoder;
+	}
+	return NULL;
+}
+
 /*
  * set vga decode state - true == enable VGA decode
  */

drivers/gpu/drm/i915/intel_drv.h

@@ -190,6 +190,7 @@ extern void intel_encoder_prepare (struct drm_encoder *encoder);
 extern void intel_encoder_commit (struct drm_encoder *encoder);
 
 extern struct drm_encoder *intel_best_encoder(struct drm_connector *connector);
+extern struct drm_encoder *intel_attached_encoder(struct drm_connector *connector);
 
 extern struct drm_display_mode *intel_crtc_mode_get(struct drm_device *dev,
 						    struct drm_crtc *crtc);