drm/i915: Check for unpin correctness.

If planes are added to the state after the call to
drm_atomic_helper_check_planes planes_changed may not be set
and we will not unpin the old framebuffer. This results in a
pin leak long after the framebuffer is destroyed, so to find
this add some checks when it happens.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1463490484-19540-21-git-send-email-maarten.lankhorst@linux.intel.com
Reviewed-by: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -13371,11 +13371,20 @@ intel_prepare_plane_fb(struct drm_plane *plane,
 	struct intel_plane *intel_plane = to_intel_plane(plane);
 	struct drm_i915_gem_object *obj = intel_fb_obj(fb);
 	struct drm_i915_gem_object *old_obj = intel_fb_obj(plane->state->fb);
+	struct drm_crtc *crtc = new_state->crtc ?: plane->state->crtc;
 	int ret = 0;
 
 	if (!obj && !old_obj)
 		return 0;
 
+	if (WARN_ON(!new_state->state) || WARN_ON(!crtc) ||
+	    WARN_ON(!to_intel_atomic_state(new_state->state)->work[to_intel_crtc(crtc)->pipe])) {
+		if (WARN_ON(old_obj != obj))
+			return -EINVAL;
+
+		return 0;
+	}
+
 	if (old_obj) {
 		struct drm_crtc_state *crtc_state =
 			drm_atomic_get_existing_crtc_state(new_state->state, plane->state->crtc);