GNOME 42 Mutter Lands Fix For Using The Old "Radeon" Graphics Driver

There have been bug reports recently for those using GNOME Shell 42 whether it be the likes of Ubuntu 22.04 or Fedora (Silverblue) 36 Beta over crashes or blank screens appearing when making use of the Radeon DRM/KMS kernel driver. That older Radeon DRM driver is for pre-GCN 1.2 graphics processors (aside from those on GCN 1.0/1.1 that switch to using the AMDGPU kernel driver with optional module parameters) while now Mutter has landed a fix for this issue.

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.

The Radeon DRM driver for older AMD/ATI GPUs doesn't support KMS modifiers. Now GNOME will properly check for that capability to avoid problems.

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.