drm: Skip __drm_mode_set_config_internal() on atomic drivers

Everything (apart from the actual ->set_config() call)
__drm_mode_set_config_internal() does is now useless on
atomic drivers. So let's just skip all the foreplay.

v2: Use drm_drv_uses_atomic_modeset() (Daniel)
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180705190010.19836-1-ville.syrjala@linux.intel.com

drivers/gpu/drm/drm_crtc.c

@@ -461,6 +461,8 @@ static int __drm_mode_set_config_internal(struct drm_mode_set *set,
 	struct drm_crtc *tmp;
 	int ret;
 
+	WARN_ON(drm_drv_uses_atomic_modeset(crtc->dev));
+
 	/*
 	 * NOTE: ->set_config can also disable other crtcs (if we steal all
 	 * connectors from it), hence we need to refcount the fbs across all
@@ -478,10 +480,8 @@ static int __drm_mode_set_config_internal(struct drm_mode_set *set,
 	if (ret == 0) {
 		struct drm_plane *plane = crtc->primary;
 
-		if (!plane->state) {
-			plane->crtc = fb ? crtc : NULL;
-			plane->fb = fb;
-		}
+		plane->crtc = fb ? crtc : NULL;
+		plane->fb = fb;
 	}
 
 	drm_for_each_crtc(tmp, crtc->dev) {
@@ -496,6 +496,7 @@ static int __drm_mode_set_config_internal(struct drm_mode_set *set,
 
 	return ret;
 }
+
 /**
  * drm_mode_set_config_internal - helper to call &drm_mode_config_funcs.set_config
  * @set: modeset config to set
@@ -740,7 +741,11 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 	set.connectors = connector_set;
 	set.num_connectors = crtc_req->count_connectors;
 	set.fb = fb;
-	ret = __drm_mode_set_config_internal(&set, &ctx);
+
+	if (drm_drv_uses_atomic_modeset(dev))
+		ret = crtc->funcs->set_config(&set, &ctx);
+	else
+		ret = __drm_mode_set_config_internal(&set, &ctx);
 
 out:
 	if (fb)