This device doesn't fully work with mainline Kernel yet.

As amazingfate (the Armbian dev for this device) clearly stated on the forum: cellular and camera are not working, only display, touch, wifi, and bluetooth are functional—so it won't replace your phone OS for calls and texts

Can confirm. S905X5M is a different beast than the S905X. If there's interest, I can start another thread with an image and status, once this is somewhat more stable. Currently booting, but not without some debug console interaction on power up. In the meantime, code's up at https://github.com/tparys/build/tree/odroidc5 if anyone wants to go poking

Hello, I hope you don't have any problem. Maybe me and my brother have defective or more unstable helios64 than you. Only thing I can say that Prahal share here the specifics files rk3399-kobol-helios64.dtb-6.XX.xx-L2-hs400-opp in this forum since two years ago my helios64 and my brother's helios64 work stable only with it. I back to 6.12.58 Kernel with rk3399-kobol-helios64.dtb-6.12.xx-L2-hs400-opp file and freeze firmware/kernel with armbian-config.

I am having issues with eMMC detection… The kernel does not detect the eMMC, but apparently U-Boot does. Attached are images.