It's not VC4 GPU, which is fully documented and fairly open. The bootloader runs on VPU, for which the reverse engineering is the only option, because there wer

It's not VC4 GPU, which is fully documented and fairly open. The bootloader runs on VPU, for which the reverse engineering is the only option, because there were no resources for doing anything sane with the official internal docs, when I checked last time. And Broadcom does not even own a compiler for this ISA. So, people had been officially encouraged to reverse engineer it.