amdgpu requires firmware installed

[Vuk Vasiljevic <vukv93@gmail.com>]

Hello,

I have a problem with AMDGPU driver after an update from stretch to buster.
On startup no X server is started (but can be later on by calling startx),
and following error appears in the log.

[    1.311354] [drm] amdgpu kernel modesetting enabled.
[    1.311464] [drm:amdgpu_pci_probe [amdgpu]] *ERROR* amdgpu requires 
firmware installed

While on stretch, I have installed some proprietary parts of AMDGPU-PRO,
and only removed it after the update. Can this be the cause of error,
and if so, can it be fixed?

amdgpu module appears not to be loaded, but not used.

$ lsmod | grep amdgpu
amdgpu               3416064  0
chash                  16384  1 amdgpu
gpu_sched              28672  1 amdgpu
i2c_algo_bit           16384  1 amdgpu
ttm                   126976  1 amdgpu
drm_kms_helper        200704  1 amdgpu
drm                   483328  4 gpu_sched,drm_kms_helper,amdgpu,ttm


I have following firmware packages installed and up to date.

firmware-amd-graphics
firmware-linux
firmware-linux-free
firmware-linux-nonfree


Some system info:

$ uname -a
Linux optimus 4.19.0-5-amd64 #1 SMP Debian 4.19.37-5 (2019-06-19) x86_64 
GNU/Linux

$ glxinfo|egrep "string"
server glx vendor string: SGI
server glx version string: 1.4
client glx vendor string: Mesa Project and SGI
client glx version string: 1.4
OpenGL vendor string: VMware, Inc.
OpenGL renderer string: llvmpipe (LLVM 7.0, 128 bits)
OpenGL core profile version string: 3.3 (Core Profile) Mesa 18.3.6
OpenGL core profile shading language version string: 3.30
OpenGL version string: 3.1 Mesa 18.3.6
OpenGL shading language version string: 1.40
OpenGL ES profile version string: OpenGL ES 3.0 Mesa 18.3.6
OpenGL ES profile shading language version string: OpenGL ES GLSL ES 3.00


Please tell me if any additional logs or other info is needed.

Thanks in advance,
Vuk