Check this "See MIPS Run" book on porting Linux to MIPS [1]. Since MIPS has becomes RISC-V, it will be an excellent reference to Linux on RISC-V platform [2].

[1]https://www.amazon.com/Morgan-Kaufmann-Computer-Architecture...

[2]https://www.eejournal.com/article/wait-what-mips-becomes-ris...