OpenPower has the entire firmware Apache licensed, see the link. that's WAY more than any Intel/AMD CPU. Even all the secure-boot stuff is open(Apache Licensed).
Joining the foundation gets you the chip blueprints, etc.
For hardware it's like leaps and bounds more open than anything else out there that can compete with it. Could they open up more, of course, but for hardware, it's pretty amazingly open.
https://openpowerfoundation.org/