I don't maintain Rockchip stuff, but I add boards and such to Amlogic frequently, so:
https://github.com/chewitt/linux/commits/amlogic-5.18.y <= my kernel sources
https://github.com/chewitt/u-boot/commits/amlogic-2022.01 <= my u-boot sources
https://github.com/chewitt/LibreELEC.tv/commits/amlogic <= my LE sources
There are lots of previous examples of devices being added in GitHub.