Cirrus Logic have released an update on their sources (https://github.com/CirrusLogic/rpi-linux/wiki/Building-the-code#install-the-kernel-modules-and-dtb-file-on-the-raspberry-pi) for the Raspberry Pi kernel.
For musicians trying to get the older Raspberry Pi boards (only A+ and B+) running in realtime mode like described here I provide an inofficial package for this kernel including all realtime patches. More info about this can be found on http://wiki.linuxaudio.org/wiki/raspberrypi.
The package contains a precompiled realtime kernel and the necessary libs/firmware files including the overlays provided by Cirrus Logic and can be downloaded here.
Instructions for installing the files can be found in the README.txt
This version of the kernel supports mmap which is needed for jack/jackd2 and a lot of other things to work.
A realtime example can be found here: https://blog.georgmill.de/2015/03/28/waveboard-with-arduino/