The main development site and GIT repository for Digital TV drivers is https://linuxtv.org.
The DVB mailing list linux-dvb is hosted at vger. Please see http://vger.kernel.org/vger-lists.html#linux-media for details.
The media subsystem Wiki is hosted at https://linuxtv.org/wiki/. There, you'll find lots of information, from both development and usage of media boards. Please check it before asking newbie questions on the mailing list or IRC channels.
The API documentation is documented at the Kernel tree. You can find it in both html and pdf formats, together with other useful documentation at:
You may also find useful material at https://linuxtv.org/downloads/.
In order to get the needed firmware for some drivers to work, there's a script at the kernel tree, at scripts/get_dvb_firmware.