drm/i915/fbc: make FBC work with fastboot

Move intel_fbc_enable to a place where it is called regardless of the
"modeset" variable, and make sure intel_fbc_enable can be called
multiple times without intel_fbc_disable being called.

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1453210558-7875-20-git-send-email-paulo.r.zanoni@intel.com

drivers/gpu/drm/i915/intel_display.c

@@ -13558,7 +13558,6 @@ static int intel_atomic_commit(struct drm_device *dev,
 		if (modeset && crtc->state->active) {
 			update_scanline_offset(to_intel_crtc(crtc));
 			dev_priv->display.crtc_enable(crtc);
-			intel_fbc_enable(intel_crtc);
 		}
 
 		if (update_pipe) {
@@ -13571,6 +13570,9 @@ static int intel_atomic_commit(struct drm_device *dev,
 		if (!modeset)
 			intel_pre_plane_update(intel_crtc);
 
+		if (crtc->state->active && intel_crtc->atomic.update_fbc)
+			intel_fbc_enable(intel_crtc);
+
 		if (crtc->state->active &&
 		    (crtc->state->planes_changed || update_pipe))
 			drm_atomic_helper_commit_planes_on_crtc(crtc_state);

drivers/gpu/drm/i915/intel_fbc.c

@@ -1084,7 +1084,9 @@ out:
  * @crtc: the CRTC
  *
  * This function checks if the given CRTC was chosen for FBC, then enables it if
- * possible. Notice that it doesn't activate FBC.
+ * possible. Notice that it doesn't activate FBC. It is valid to call
+ * intel_fbc_enable multiple times for the same pipe without an
+ * intel_fbc_disable in the middle, as long as it is deactivated.
  */
 void intel_fbc_enable(struct intel_crtc *crtc)
 {
@@ -1097,7 +1099,11 @@ void intel_fbc_enable(struct intel_crtc *crtc)
 	mutex_lock(&fbc->lock);
 
 	if (fbc->enabled) {
-		WARN_ON(fbc->crtc == crtc);
+		WARN_ON(fbc->crtc == NULL);
+		if (fbc->crtc == crtc) {
+			WARN_ON(!crtc->config->enable_fbc);
+			WARN_ON(fbc->active);
+		}
 		goto out;
 	}