https://bugs.freedesktop.org/show_bug.cgi?id=105046
--- Comment #11 from dwagner jb5sgc1n.nya@20mm.eu --- I solved the same problem for me a long time ago by adding a "drm_kms_helper.edid_firmware=edid/my_monitor_model_edid.bin" option to my kernel command line, after saving the EDID blob of my monitor to the given file.
But sure, would be great if such wasn't necessary.