a note about the work left to get XP200 shading work

backend/genesys.c

@@ -2971,6 +2971,12 @@ genesys_send_shading_coefficient (Genesys_Device * dev)
   else
     coeff = 0x2000;
  
+  /* for GL646, shading data is planar if REG01_FASTMOD is set and
+   * chunky if not. For now we rely on the fact that we know that
+   * each sensor is used only in one mode. Currently only the CIS_XP200
+   * sets REG01_FASTMOD.
+   */
+
   switch (dev->model->ccd_type)
     {
     case CIS_XP200: