I've noticed that some system images will start the OrangePi with 4:2:2 output on HDMI instead of 4:4:4. This causes artifacts, especially when there's white text on a red background. What's the interface or method to change this? Does this have to be done via U-Boot or can it be done in userspace?

AFAIK, to get fully working 4:4:4 modes, there is the need to import some "experimental" patches that are floating in the rockchip kernel mailing list.

The patches have been tested a lot by libreelec users on various rockchip platform (32 bit rockchip device like rk322x and rk3288 already have them merge in), but have been judged "too complicated to maintain" for rockchip64 repository.

 

You can see the last attempt here and the previous attempt here, useful to get the points of the discussion.

22 hours ago, jock said:

AFAIK, to get fully working 4:4:4 modes, there is the need to import some "experimental" patches that are floating in the rockchip kernel mailing list.

I found that the official OrangePi images enable 4:4:4 output, but only with the Debian image. The Ubuntu image only has 4:2:2 output. I couldn't figure out how they did this as I couldn't see any difference in the driver config. So it seems they changed something in the code to get it working, possibly something similar to the patch you linked.

@McTurbo OrangPi official images use the vendor kernel 5.10 with various custom patches and drivers. Armbian does not offer vendor kernel anymore because after a while they become old and unmaintained.