modesetting driver adds unwanted video modes and there is no way to remove them
Submitted by Henri Kemppainen
Assigned to Xorg Project Team
Link to original bug (#101249)
Description
If an output is advertised as having a panel fitter (whether enabled or not), the modesetting driver will add [1] a bunch of modes that may or may not be usable, and may not be wanted e.g. because the connected monitor provides panel fitting of its own, with better controls or quality.
The situation is especially dire for people using (recent?) amd cards with external monitors, because the scaling is not enabled by default, and even if you enabled it, it does not actually work [2]. So X ends up using made up modes that do not work, even when your monitor has a perfectly good set of modes already.
[2] https://bugs.freedesktop.org/show_bug.cgi?id=95131
There is an option DefaultModes which could be turned off to prevent the addition of said modes at another layer [3], but the modesetting driver does not respect this option.
https://cgit.freedesktop.org/xorg/xserver/tree/hw/xfree86/modes/xf86Crtc.c#n1675