Is the Raspberry Pi truly open-source?

[bob prohaska]

Broadcom released what is claimed to be documentation of the GPU for the Raspberry Pi in
http://www.broadcom.com/docs/support/videocore/VideoCoreIV-AG100-R.pdf

Is it useful to developers of opensource software? The referring document is at
https://rpiplayground.wordpress.com/2014/05/03/hacking-the-gpu-for-fun-and-profit-pt-1/

Both seem informative, but I'm not a programmer and can't tell. Neither document seems 
prominent in the archives.

Thanks for reading!

bob prohaska