I am working on cross compiling the kernel at https://github.com/raspberrypi/linux/tree/rpi-4.19.y-rt .
It is my understanding that TiejunChina maintains this repo with all the appropriate patches.
However, I have run into a few problems:
1.) When compiling on Ubuntu 18.04 LTS, the modules_install doesn't create the files. I can fix this by cross-compiling on Debian 10.
2.) After booting the system, both the Ethernet & USB ports are not active.
Is there anyone out there that has successfully patched 4.19? If so, which version & did you patch it from PREEMPT_RT itself or using the Repo Tiejun manages?