Broadcom released documentation and driver source code for VideoCore in 2014 so it should be easier to port things to the RPi now: https://en.wikipedia.org/wiki/Free_and_open-source_graphics_...

AFAIK Linux distribution for the RPi still use the closed-source bootloader, which is some commercial RTOS that needs to sit on a FAT partition and runs on the VideoCore chip (!). There is work on a Free Software bootloader: https://github.com/christinaa/rpi-open-firmware