Overview
Upgrade of Oracle Grid Infrastructure is needed in case your database is RAC database and you wish to upgrade it to a higher version. Furthermore, the upgrade is done in completely online fashion for the database, since each node is patched individually and thus the database remains online.
Upgrade 12.1.0.2 -> 12.2.0.1
Upgrade 12.2.0.1 -> 12.2.0.2
As soon as I have time :)