I'll ask the main Amlogic u-boot custodian, but an answer might take a while as I know he's currently on vacation.
Thanks for this.
I understand that it may not be a good idea to try moving to 12.x because of less video support due to having to rely on software rendering, but I wanted to give it a try. If power on via HDMI-CEC isn't going to work I'd just assume waiting until I upgrade to a new board.
Hi. I've been using Coreelec 9.2.5 (Leia) with my ODroid for a few years now. I want to upgrade to a newer Kodi and Libreelec 12.2.
My Samsung TV will not power on the Odroid while running Libreelec. It will power it on when I boot with Coreelec. I've gone into the Libreelec settings and confirmed that the CEC settings match what works in Coreelec, but no dice.
Can someone suggest some steps to troubleshoot this, or maybe config file tweaks that are known to be help for this old hardware?
Thanks in advance for any suggestions that you can give. 
Display MoreSwitched to coreelec 9.0.1 simply by putting the coreelec update into the Update folder an then did a reboot.
All Problems gone,
CEC Poweron works
no flashing white bars on the right side of the screen anymore
no sudden stops on live tv or recordings
no skip problems anymore
really satisfied
I also switched to CoreElec 9.0.1 and have working CEC. Everything else seems to work too. Excellent!
I was not able to upgrade by just putting the update in the .update folder. I rebooted and the update process seemed to proceed. There was an error, however, and my odroid failed to boot, so I had to do a full installation and that worked. I restored the backup I created of the .kodi directory and my library was intact. I don't know if I'm going to run into problems in the future by doing it this way but we'll see.
Hopefully this gets fixed in libreelec but it seems I'm now a coreelec user...
This has been reported multiple times over multiple releases. No fix yet.
Someone who reported having the same problems (on the odroid forums) says it works with coreelec 9.0.1. (LibreELEC 9, odroid-c2: device does not get powered on by TV with CEC - ODROID)
I manually upgraded again to LibreELEC 9.0.0 (SHA256: 1dfe766d8a2ec8b2053f2524a80db77b25026aa283409e3d86c8717befcaf5f3). I ran
systemctl stop kodi
mv .kodi kodi.old
rebootThe odroid seemed to power off instead of reboot. I waited for a few minutes in case something was happening even though I saw "no signal" on my TV. After around 5 minutes I unplugged the odroid's power and plugged it back in. LibreELEC booted and I was prompted to set up my device. I configured the CEC adapter and shutdown Kodi from the interface. I turned on the TV. My HDMI input was unchanged (HDMI 3 - Kodi). I switched to "live TV" and back to HDMI 3: the odroid did not power on.
I cycled the power on the odroid again to get it to boot. I logged in via SSH and typed "reboot". I had the same behaviour as before; the odroid seemed to be off and didn't actually reboot.
I tried the current nightly build, LibreELEC-Odroid_C2.arm-9.0-nightly-20190201-974f4cb.img.gz, moved .kodi out of the way and typed "reboot" within SSH. This time the odroid did reboot. I turned the odroid off via Kodi's interface. My TV turned off. I powered the TV back on and this was just like before: the odroid did not power on.
I went back to 8.2.5 (SHA256: 9cc3cb2cb0481753af9b5db105e1a853673150e08fc51a13904fef4ef0798c5d) and CEC is again working with my LG TV and my C2.
debug logs from the nightly build: Debian Pastezone
I manually updated to 9.0 by copying the image file LibreELEC-Odroid_C2.arm-9.0.0.img.gz to /storage/.update and rebooting, as per Update LibreELEC [LibreELEC.wiki]. With 9.0.0 my odroid-c2 is not powered on via CEC when the TV is powered on. I had to unplug the odroid's power supply and plug it back in to get the odroid to boot up.
I downgraded to 8.2.5 by copying LibreELEC-Odroid_C2.aarch64-8.2.5.img.gz to /storage/.update and creating /storage/.update/.nocompat. I then shutdown the odroid, unplugged the power supply, and plugged it back in. LibreELEC was downgraded to 8.2.5. I shut down the odroid which turned the TV off, as it should have. When I turned the TV back on the odroid powered up.
Edit: The same thing was reported at Odroid_C2 8.90.006 no CEC Power on by connected TV - LibreELEC Forum with a beta version.