Created attachment 140625 [details] [review]
Don't share clk source between DP and other connectors

Hi Paul,
sorry for the previous comment that was a part of the message for another bug.
Anyways, I was able to reproduce a similar issue as yours with 4 connectors
plugged and only 2 would light up.
But in my case it was caused by DP and HDMI sharing the same clock source, but
since you're not using DP I wonder, what could have caused an issue for you.
I'm attaching 3 experimental patches:
1. 0001-drm-amdgpu-display-Don-t-share-clk-source-between-DP-an.patch
   This patch should fix the issue for DP connection with Tonga
2.0001-drm-amdgpu-display-update-clk-for-various-HDMI-color.patch
   Allows programming of HDMI2.0 and later on Tonga
3. 0001-Disable-source-clock-sharing-between-multiple-connec.patch
   Disable clock sharing by an early return 

Can you try if any of them work for you? 
Thanks