Upgraded to U-Boot v2020.10rc4 and removed console-ttyS2,1500000 from extlinux.conf but still no HDMI video when UART0 is not connected.
Will try again when U-Boot v2020.10 becomes available, also worth noting USB3 is not recognised. I think the dtb-file which comes with u-boot might be the culprit.
Edit:
It turns out that the dtb-file provided by U-Boot is incomplete or they turnoff HDMI output.
As a workaround one can extract a working dtb-file from ArchLinuxARM-aarch64-latest.tar.gz provided by https://archlinuxarm.org/platforms/armv8...hip/rock64 with the added benefit of USB3 fully working, downside is NO HDMI-Audio and the screen flickers a lot when any Desktop Environment is running, in Terminal it is just fine.
Will try again when U-Boot v2020.10 becomes available, also worth noting USB3 is not recognised. I think the dtb-file which comes with u-boot might be the culprit.
Edit:
It turns out that the dtb-file provided by U-Boot is incomplete or they turnoff HDMI output.
As a workaround one can extract a working dtb-file from ArchLinuxARM-aarch64-latest.tar.gz provided by https://archlinuxarm.org/platforms/armv8...hip/rock64 with the added benefit of USB3 fully working, downside is NO HDMI-Audio and the screen flickers a lot when any Desktop Environment is running, in Terminal it is just fine.