Bug 2533250

After a Fedora update of ~150 packages including kernel 7.2.5-200.fc44 and 
linux-firmware/amd-gpu-firmware version 20260910, the system becomes nearly 
unusable at boot on an AMD Radeon RX 6500M (Navi 24) laptop:

- The LUKS disk decryption prompt renders corrupted/garbled instead of the 
  normal text interface
- Each keystroke at the LUKS prompt causes the screen to go black for 
  ~30 seconds before responding
- After login, the SDDM/Plasma custom theme fails to load, falling back 
  to default
- A kernel panic was also observed when booting an Ubuntu live USB on the 
  same machine (unrelated OS, same hardware)

journalctl logs from the affected boot show a continuous loop of:

amdgpu 0000:08:00.0: [drm] *ERROR* Error queueing DMUB command: status=2
amdgpu 0000:08:00.0: [drm] *ERROR* dc_dmub_srv_log_diagnostic_data: DMCUB error - collecting diagnostic data
amdgpu 0000:08:00.0: [drm] enabling link 0 failed: 15

This matches the linux-firmware 20260910 changelog, which includes a revert 
of a previous GC 10.3.6 firmware update alongside "DMCUB updates for various 
ASICs" — the same combination reverted upstream in September 2025 
(kernel-firmware-amdgpu PR #26) for similar reasons.

Reproducible: Always

Steps to Reproduce:
1. Update Fedora 44 with linux-firmware/amd-gpu-firmware version 20260910 
   and kernel 7.2.5-200.fc44 on a system with AMD Radeon RX 6500M (Navi 24)
2. Reboot
3. Observe LUKS prompt and subsequent login
Actual Results:
LUKS prompt renders corrupted; screen freezes ~30s per keystroke; SDDM 
custom theme fails to load; journalctl shows continuous DMCUB command 
queueing errors from amdgpu driver.

Expected Results:
Normal LUKS prompt and login, as with kernel 7.2.4-200.fc44 (previous 
version, unaffected).

Additional Information:
Workaround: booting the previous kernel 7.2.4-200.fc44.x86_64 (with the 
prior linux-firmware version) resolves the issue completely.

Hardware: HP Victus by HP Gaming Laptop 15-fb2xxx, AMD Radeon RX 6500M 
(Navi 24). Full lspci -nn output and journalctl excerpt available as 
attachments.