ARM client program boot architecture

Is there a written spec or description of how a boot program (u-boot, UEFI, hypervisor) boots an OS on ARM platforms?

ePAPR-type device trees are used to describe a platform, but what about the type of information in sections 5.3, 5.4 and 5.5 of the ePAPR: -initial mapped areas -state of MMU at the point the boot program transfers control to the OS, initial MMU mappings -initial state of registers -mechanisms to start secondary CPUs-- e.g. spin table

Besides reading code is this stuff written down anywhere? ...for both ARM v7 and ARM v8.

Thanks, Stuart Yoder