Hi, I'm also affected by this issue. I have a horrible samsung TV which I use as monitor in my desktop that doesn't send correct EDIDs (it simply doesn't send any EDID). I was working OK with kernel 4.13. Today I have upgraded to 4.15.0-2 and TV is showing mode setting not supported, so the option is not recognized (I've tested with drm_kms_helper.edid_firmware and drm.edid_firmware with no luck). I'm configured grub to use the old kernel for the moment.