Broadcom releases SoC graphics driver source

Well - all the gpu registers are available starting at bus-address at 0x7ec00000 (see page 110 of the document).
Similar to the dma registers being accessible starting from: 0x7e007000 or spi at: 0x7e204000.

So you just have to iomap the range into your process range (kernel/user) and then you can start making use of it by poking values to it.

Actually the arm and vPU both make use of the same memory - so there can be an easy means to communicate between the two via memory access..

The full list of documented/undocumented registers can get found at:
https://github.com/hermanhermitage/videocoreiv/wiki/Regis...
(Note that the gpu registers are not listed yet as they have not been discovered so far...)

This GitHub page contains a lot of other valuable information as well - including an assembler and links to development of other tool chain components...