As of the commit

        9a3296bf1cf8d45349b14b31eeb0d81f8b8774fc radeonsi: use SDMA for initial
clearing of DCC/CMASK/HTILE on CIK-VI

, SDDM crashes on start. The same with GDM, though I bisect-tested mostly with
SDDM. The system log says:

        systemd[1]: Started User Manager for UID 996.
        sddm[513]: Greeter session started successfully
        sddm-greeter[584]: Reading from "/usr/share/xsessions/awesome.desktop"
        sddm-greeter[584]: Reading from
"/usr/share/xsessions/enlightenment.desktop"
        sddm-greeter[584]: Reading from
"/usr/share/xsessions/gnome-classic.desktop"
        sddm-greeter[584]: Reading from
"/usr/share/xsessions/gnome-xorg.desktop"
        sddm-greeter[584]: Reading from "/usr/share/xsessions/gnome.desktop"
        sddm-greeter[584]: Reading from
"/usr/share/xsessions/i3-with-shmlog.desktop"
        sddm-greeter[584]: Reading from "/usr/share/xsessions/i3.desktop"
        sddm-greeter[584]: Reading from
"/usr/share/xsessions/plasma-mediacenter.desktop"
        sddm-greeter[584]: Reading from "/usr/share/xsessions/plasma.desktop"
        sddm-greeter[584]: Reading from
"/usr/share/wayland-sessions/gnome.desktop"
        sddm-greeter[584]: Reading from
"/usr/share/wayland-sessions/sway.desktop"
        sddm-greeter[584]: Connected to the daemon.
        sddm[513]: Message received from greeter: Connect
        sddm-greeter[584]: Loading qrc:/theme/Main.qml...
        sddm-greeter[584]: Adding view for "HDMI-0" QRect(0,0 1920x1080)
        systemd[577]: Started D-Bus User Message Bus.
        sddm-greeter[584]: Message received from daemon: Capabilities
        sddm-greeter[584]: Message received from daemon: HostName
        kernel: sddm-greeter[584]: segfault at 0 ip           (null) sp
00007fffbb3c12e8 error 14 in sddm-greeter[400000+8e000]
        systemd[1]: Created slice system-systemd\x2dcoredump.slice.
        systemd[1]: Started Process Core Dump (PID 593/UID 0).
        sddm-helper[575]: [PAM] Closing session
        sddm-helper[575]: pam_unix(sddm-greeter:session): session closed for
user sddm
        sddm-helper[575]: [PAM] Ended.
        sddm[513]: Auth: sddm-helper exited with 11
        sddm[513]: Greeter stopped.
        systemd-logind[481]: Removed session c1.
        systemd[1]: Stopping User Manager for UID 996...
        systemd[577]: Stopped target Default.
        systemd[577]: Stopping D-Bus User Message Bus...
        systemd[577]: Stopped D-Bus User Message Bus.
        systemd[577]: Stopped target Basic System.
        systemd[577]: Stopped target Paths.
        systemd[577]: Stopped target Timers.
        systemd[577]: Stopped target Sockets.
        systemd[577]: Closed Sound System.
        systemd[577]: Closed D-Bus User Message Bus Socket.
        systemd[577]: Reached target Shutdown.
        systemd[577]: Starting Exit the Session...
        systemd[577]: Received SIGRTMIN+24 from PID 597 (kill).
        systemd[578]: pam_unix(systemd-user:session): session closed for user
sddm
        systemd[1]: Stopped User Manager for UID 996.
        systemd[1]: Removed slice User Slice of sddm.
        systemd-coredump[594]: Process 584 (sddm-greeter) of user 996 dumped
core.

                                                                               
                                         Stack trace of thread 584:
                                                                               
                                         #0  0x0000000000000000 n/a (n/a)

GPU: Radeon HD5730 (note, its driver is rather radeon than radeonsi)