I tried 2 linux distributions aimed at retrogaming. Lakka is based on librelec, it use nouveau driver with kms, but don't display anything on my hdmi TV or a pc monitor. I also tried Recalbox, it's based on buildroot and the problem is exactly the same. You can find all the logs here: https://github.com/libretro/Lakka-LibreELEC/issues/68
Can you try a newer kernel? There was an issue affecting MCP77/79 HDMI outputs that was fixed in 4.10 (commit 7dfee6827780d4228148263545af936d0cae8930 upstream).
I don't know how to update kernel in lakka/librelec, but I'll wait for a new version and I will test that. Thank you!
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