X fails

After setting up Xfce4 and Xorg, I can't run X.

The following test:

# X -config /root/xorg.conf.new

returns:

(II) [KMS] Kernel modesetting enabled.
amdgpu_device_initialize: DRM version is 2.49.0 but this driver is only compatible with 3.x.x.
(EE)
Fatal server error:
(EE) no screens found(EE)
(EE) Please also check the log file at "/var/log/Xorg.0.log" for additional information.

The log file contains:

(EE) AMDGPU(0): amdgpu_device_initialize failed
(EE) Device(s) detected, but none match those in the config file.
(EE) no screen found(EE)

The config file contains in its section "Devices":

Driver "amdgpu"

Any idea what's wrong?