Comment 2 for bug 1412730

Investigated the issue some more.
Seems that EDID is not always given by the monitor when asked by the OS, for instance via "Detect Monitors" via gui or via xrandr via command line.
The workaround with xorg.conf I have abandoned. It wasnt working great too. Still a lot of time X was detecting resolutions again resulting in garbled screens or non active screen, however it stayed at the right resolution.

I managed to extract the edid for U2415 (256 byte), which i have attached.
Parse-edid has issues reading the extension block, but in Xorg.0.log I never saw issues reading the edid when it was available from the monitor.
My current workaround is by using kernel commandline parameter drm_kms_helper.edid_firmware=DP-1:edid/U2415.edid
This seems to work well.