About the upgrade from 9.1P8 to 9.1P12 for 7-mode ==> Cannot be done, no version for 7-mode exists
For the upgrade from 9.1P8 to 9.1 P12 for C-mode you can create a plan using upgrade advisor...
1. Login to support.netapp.com with account that has entitled access to the system running 9.1P8
2. Tools ==> Active IQ
3. On the left there is an arrow (pointing right above), upgrade advisor
4. Give in the serial number of the system and then you can generate the upgrade steps/revert steps....