drm/todo: Add idr_init_base todo

Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180219145708.23523-1-daniel.vetter@ffwll.ch

Documentation/gpu/todo.rst

@@ -212,6 +212,16 @@ probably use drm_fb_helper_fbdev_teardown().
 
 Contact: Maintainer of the driver you plan to convert
 
+idr_init_base()
+---------------
+
+DRM core&drivers uses a lot of idr (integer lookup directories) for mapping
+userspace IDs to internal objects, and in most places ID=0 means NULL and hence
+is never used. Switching to idr_init_base() for these would make the idr more
+efficient.
+
+Contact: Daniel Vetter
+
 Core refactorings
 =================