There's a closed pull request on the void-packages repository

linux5.4: Add first support for RK3399 boards
https://github.com/void-linux/void-packages/pull/20391

Description:
This adds built-in configuration for RK808 Power Management System, RK3x
I2C, as well as rockhip's MMC controller driver in order to be able to
boot RK3399 boards on SD card. This also adds module for thermal sensor,
PCIe, USB and EMMC.

This has been tested on Nanopi-m4 board.