Landing with the Linux 4.5 kernel will be the next-generation media controller support. This "next-gen MC" work is the result of one year of development and enables media controller support at the DVB subsystem, improves the media controller to support other types of V4L devices like radio and TV devices and to extend the media controller functionality so it can be used by other subsystems (DVB / ALSA / IIO). A new ioctl is presented as part of this next-generation support for exposing it to user-space, but for the Linux 4.5 kernel that code is disabled until Linux 4.6 rolls around to ensure the ioctl is in good shape.
There's a lot of code involved as part of this new media controller support. I'm still working on digging up more details and learning about it, so for now just stop by this pull request for the bits shared by Mauro Carvalho Chehab.