Why can I not change xorg.conf.d "OutputClass" to "Device" for RX560 GPU

I have a: Lenovo Y520-15KIBA *CPU Intel i5* with GPU AMD Radeon RX560 linux kernel 4.20.47-custom (with bloobs of new firmware 1.175) DRM is 3.27.0 also kernel 4.17-generic is in the grub I want to know how and if it is possible to setup a 10-amdgpu.conf file in a manner that my amdgpu is not showing errors like or at least give some glxgears output better than 1 FPS: > dmesg | grep amdgpu [ 1.558902] [drm] amdgpu kernel modesetting enabled. [ 1.559324] amdgpu 0000:01:00.0: enabling device (0000 -> 0003) [ 1.598721] amdgpu 0000:01:00.0: VRAM: 2048M 0x000000F400000000 - 0x000000F47FFFFFFF (2048M used) [ 1.598724] amdgpu 0000:01:00.0: GART: 256M 0x000000FF00000000 - 0x000000FF0FFFFFFF [ 1.598959] [drm] amdgpu: 2048M of VRAM memory ready [ 1.598961] [drm] amdgpu: 3072M of GTT memory ready. [ 1.677073] [drm:dc_create [amdgpu]] *ERROR* DC: Number of connectors is zero! [ 1.923112] [drm] Initialized amdgpu 3.27.0 20150101 for 0000:01:00.0 on minor 1 [ 12.285945] amdgpu 0000:01:00.0: GPU pci config reset > DRI_PRIME=0 | grep -B Vendor: Intel Open Source Technology Center (0x8086) Device: Mesa DRI Intel(R) HD Graphics 630 (Kaby Lake GT2) (0x591b) Version: 18.2.8 > DRI_PRIME=1 | grep -B Vendor: X.Org (0x1002) Device: Radeon RX 560 Series (POLARIS11, DRM 3.27.0, 4.20.17-custom, LLVM 7 Testing my card with > DRI_PRIME=1 glxgears gives me 0.7 (sic!) frames per second and causes system freeze therefore I think the card is not working properly i have tried 2019 April with: - drivers from amd ./amdgpu-install + pro on LMDE3, Linux Mint 19 ubuntu 18.04.1 18.04.2 (amd version 17.40, 18.x and 19.10) (each fresh install) - mesa ppa oibaf Mint 19 Ubunut 18 - mesa ppa miguel Mint 19 (install failed) and Ubuntu 18 - somehow I was able to run mesa 19 on ubuntu 18 did not make a difference in glxgears - custom kernel build 4.20. 5.0.6 5.0.8 5.0.9 LMDE3 - rocm on linux mint19 -I always did a video group usermod *see below - I tried various xorg.confs - various vulkan installs and mesa-opencl-icd * > sudo usermod -a -G video $LOGNAME The standard configuration looks like: > sudo pico /usr/share/X11/xorg.conf.d/10-amdgpu.conf Section "OutputClass" Identifier "AMDgpu" MatchDriver "amdgpu" Driver "amdgpu" EndSection and is working out. Section "Device" is not working out (gives a black screen) and I want to know why. I hope to get better performance, when using **"Device"** and adding it to **"Screen Section"**