How to add a new platform?

I HAVE read Docs: Adding new platform support carefully, but I still got many questions:

  1. I have got 01-architecture.patch, 02-includes.patch and 03-drivers.patch, but I don't know what to do next. And additionally, the patches are terribly huge that the biggest one 03-drivers.patch consumes 200MB+

  2. I found the existing targets usually have a folder like patched-4.x but the patches in it are usually tiny fix, instead of big patches generated above.

  3. Why existing targets don't exist a patch like 01-architecture.patch? Is it because their kernel has merged into mainline?

I am trying supporting a rockchip arm64 board. The kernel and U-boot sources can easily get, as well as the DTS files. I think it would be easy to port it to OpenWrt.

I guess the docs above is too old, so could anyone tell me roughly steps?