Comment # 53 on bug 1177428 from Karl Mistelberger

(In reply to Takashi Iwai from comment #51)
> Please test just a simple update of kernel-firmware-amdgpu package from:
>  
> http://download.opensuse.org/repositories/home:/tiwai:/test:/fw-fix/
> openSUSE_Factory/noarch/kernel-firmware-amdgpu-20201005-336.1.noarch.rpm

I reverted to broken firmware first by running zypper dup. Then I ran:

The following package is going to be upgraded:
  kernel-firmware-amdgpu

The following package is going to change vendor:
kernel-firmware-amdgpu
  openSUSE -> obs://build.opensuse.org/home:tiwai

1 package to upgrade, 1 to change vendor.
Overall download size: 7.6 MiB. Already cached: 0 B. No additional space will
be used or freed after the operation.
Continue? [y/n/v/...? shows all options] (y): Retrieving package
kernel-firmware-amdgpu-20201005-336.1.noarch (1/1),   7.6 MiB (  7.6 MiB
unpacked)

Boot now works.