diff --git a/nouveau/private.h b/nouveau/private.h
index 55fe57d8..dcc23d16 100644
--- a/nouveau/private.h
+++ b/nouveau/private.h
@@ -11,6 +11,10 @@
 
 #include "nouveau.h"
 
+/*
+ * 0x00000001 dump all pushbuffers
+ * 0x80000000 if compiled with SIMULATE return -EINVAL for all pb submissions
+ */
 drm_private extern uint32_t nouveau_debug;
 drm_private extern FILE *nouveau_out;
 #define dbg_on(lvl) (nouveau_debug & (1 << lvl))