Mainline U-Boot & Kernel support?

So both the Linux Kernel & U-Boot now have files (linux/arch/arm64/boot/dts/amlogic/meson-sm1-bananapi-m5.dts and u-boot/configs/bananapi-m5_defconfig) which suggest support for the board to me.

I’ve been trying to build + flash an image from mainline w/ a procedure based on the scripts in the bsp, but haven’t been able to get anything booting.

Can anyone suggest a guide/docs/video/anything to look at for this? I’m new to the world of SBCs.