I just noticed a two-part blog series from 3 authors on OpenPOWER security and Trusted Boot. Including a bit of comparision of Trusted Boot -vs- Secure Boot.
OpenPOWER secure and trusted boot,
Part 1: Using trusted boot on IBM OpenPOWER servers
By Dave Heller, Tim Block
Updated April 26, 2019 | Published February 17, 2017
https://developer.ibm.com/technologies/linux/articles/trusted-boot-openpower
OpenPower secure and trusted boot,
Part 2: Protecting system firmware with OpenPOWER secure boot
By Dave Heller, Nageswara Sastry
Updated April 29, 2019 | Published February 23, 2019
https://developer.ibm.com/technologies/linux/articles/protect-system-firmware-openpower
Firmware Security 