Arch Linux

Description:
For several months I've had issues where GDM fails to start on boot. Finally I got around to debugging this issue, which turns out to be a known upstream bug: https://gitlab.gnome.org/GNOME/gdm/issues/103

Other distros (Ubuntu and Gentoo at least) contain a kludge to solve this: https://gitweb.gentoo.org/repo/gentoo.git/tree/gnome-base/gdm/files/gdm-CanGraphical-wait.patch
(Commit: https://gitweb.gentoo.org/repo/gentoo.git/commit?id=85ea6bed8c994eae9891af1a2fba0e99aa1c3031 )

The mechanism of this workaround is following:

/*
* Workaround for LP: #1794280.
*
* That bug is because the DRM device isn't ready by the time GDM tries to
* start wayland/X.
* This is a script to add to ExecStartPre of gdm.service. It does the
* following:
*
* 1. Enumerate drm devices from udev, looking for a DRM master. If found,
* exit.
* 2. Connect to the 'uevent' signal of gudev, watching for the same to be
* added. Again exit if any are found.
* 3. If, after 10 seconds, we haven't seen anything, try to proceed anyway as
* a failsafe.
*/

Additional info:
* package version(s)
gdm 3.34.1-1
* config and/or log files etc.
Failure with GDM: https://gist.github.com/intgr/a7eee474994e8a845405a7466ac2ebc2
Success with LightDM: https://gist.github.com/intgr/dc3e9ae46be8f78b48e0bc0402139608
* link to upstream bug report, if any
https://gitlab.gnome.org/GNOME/gdm/issues/103

Possible workarounds:
* Many users in forums are recommending "early KMS" to fix GDM issues: https://wiki.archlinux.org/index.php/Kernel_mode_setting#Early_KMS_start