GNOME 42 Mutter Lands Fix For Using The Old "Radeon" Graphics Driver
The crashes at start-up or blank screens appearing for those on the older Radeon DRM driver should now be fixed with the latest Git code and work out to point releases too. This is just if using that older Radeon DRM driver and not the newer AMDGPU DRM/KMS kernel driver.
The issue turned out to be Mutter trying to make use of KMS buffer modifiers even with the Radeon kernel driver not supporting them (DRM_CAP_ADDFB2_MODIFIERS).
Mutter previously disabled KMS modifiers for the Radeon driver using blacklisting with a udev rule but then (accidentally?) dropped the modifiers udev blacklisting when the Nouveau and AMDGPU rules were cleared. The fix merged this past week is actually checking for the DRM_CAP_ADDFB2_MODIFIERS capability and disabling KMS modifiers usage if that cap isn't exposed and thereby avoiding driver-specific blacklisting/whitelisting.
So in turn this fix has been merged and should make the older ATI/AMD Radeon graphics cards happy with GNOME 42.
If you are experiencing a crash at start-up or blank screen issue with the Radeon kernel driver on GNOME, a workaround as well is using the MUTTER_DEBUG_USE_KMS_MODIFIERS=0 environment variable to manually disable modifiers.