Via, you have to hire a few developers or you can give up in the linux marked share. Your closed driver don't work either here. Nobody can take you serious any more and that's bad.
If you are serious then hire luc and a few more devs and let them write in their blogs about what they are working on. Develop your drivers in the public, with a git repository on fd.org. It's clear that releasing documentation is an expensive business and that you don't want to spend much money on this. If it's relly impossible to release specs then only "your" developers can work on your drivers. But that's the only way sucessfull driver development on linux works.