I installed a Radeon WX 3100 a few days ago on my buster system. It failed to bring up the X server. I installed the proprietary drivers from AMD's site, but still no dice. Just for fun I tried to boot the previous kernel 4.19.0-8 and the system worked fine.
I have install the amd-graphics-firmware from buster backports version 20190717-2. Also installed xserver-xorg-video-amdgpu version 18.1.99+git20190207-1. I have reconfigured the kernel and ran update-initramfs. Also purged the amdgpu xorg driver and reinstalled. Any ideas on how to get the system to run X with the 4.19.0-9 kernel. log snippet from xorg log on 4.19.0-9 - failed [ 60.114] (II) systemd-logind: logind integration requires -keeptty and -keeptty was not provided, disabling logind integration [ 60.116] (--) PCI:*(1@0:0:0) 1002:6985:103c:0b0e rev 0, Mem @ 0xe0000000/268435456, 0xf0000000/2097152, 0xf7e00000/262144, I/O @ 0x0000e000/256, BIOS @ 0x????????/131072 [ 60.116] (II) LoadModule: "glx" [ 60.116] (II) Loading /usr/lib/xorg/modules/extensions/libglx.so [ 60.116] (II) Module glx: vendor="X.Org Foundation" [ 60.116] compiled for 1.20.4, module version = 1.0.0 [ 60.116] ABI class: X.Org Server Extension, version 10.0 [ 60.116] (==) Matched ati as autoconfigured driver 0 drm is not loaded and amdgpu is not matched log snippet from xorg log on 4.19.0-8 - worked OK [ 54.191] (II) systemd-logind: logind integration requires -keeptty and -keeptty was not provided, disabling logind integration [ 54.191] (II) xfree86: Adding drm device (/dev/dri/card0) [ 54.203] (--) PCI:*(1@0:0:0) 1002:6985:103c:0b0e rev 0, Mem @ 0xe0000000/268435456, 0xf0000000/2097152, 0xf7e00000/262144, I/O @ 0x0000e000/256, BIOS @ 0x????????/131072 [ 54.204] (II) LoadModule: "glx" [ 54.240] (II) Loading /usr/lib/xorg/modules/extensions/libglx.so [ 54.500] (II) Module glx: vendor="X.Org Foundation" [ 54.500] compiled for 1.20.4, module version = 1.0.0 [ 54.500] ABI class: X.Org Server Extension, version 10.0 [ 54.500] (II) Applying OutputClass "AMDgpu" to /dev/dri/card0 [ 54.500] loading driver: amdgpu [ 54.500] (==) Matched amdgpu as autoconfigured driver 0 [ 54.500] (==) Matched ati as autoconfigured driver 1 thanks