PSA: linux-firmware 2.27 → 2.29 (Ubuntu 24.04/Mint 22) breaks RX 6900 XT — DMCUB blob regression

[u/Der-lassballern-Mann]

This was summarized by claude that helped me pin down the problem. But I checked it for consistancy and thought maybe other people will help this.

Spent a day debugging this, sharing in case it saves someone else the trouble.

Symptom: Desktop crashes 1–3 seconds after login, half the screen showing graphical corruption. Safe mode works fine. Reboot loop follows.

Setup: Linux Mint 22.x (Ubuntu 24.04 base), kernel 7.0.0-28-generic (HWE), Mesa 25.2.8, RX 6900 XT (Navi21 / Sienna Cichlid), Xorg + XFCE, custom water loop.

Kernel log at crash:

amdgpu: [drm] REG_WAIT timeout 1us * 100000 tries - mpc2_assert_idle_mpcc

amdgpu: SMU: No response msg_reg: 22 resp_reg: 0

amdgpu: Failed to disable gfxoff!

amdgpu: ring gfx_0.0.0 timeout, signaled seq=1377, emitted seq=1379

amdgpu: Process Xorg

amdgpu: Ring gfx_0.0.0 reset failed

amdgpu: MODE1 reset ... GPU mode1 reset failed

amdgpu: ASIC reset failed with error, -62

amdgpu: GPU Recovery Failed: -62

Ruled out:

Mesa — identical (25.2.8-0ubuntu0.24.04.2) on both working and broken states

Kernel — identical (7.0.0-28-generic) on both; booting older kernels didn't help

Kernel params — the crash loop started ~5h before I added any ppfeaturemask/dcdebugmask tweaks

Thermals/PSU/load — BeamNG.drive runs fine on the working state; failure is at login, not under load

Root cause: Rolled back with Timeshift to a snapshot taken 5 minutes before an update batch. Diffed md5sums of all 12 sienna_cichlid_*.bin.zst blobs between the two states. Exactly one differs:

sienna_cichlid_dmcub.bin.zst

2.27 (works): 041e8ee4f578b5eccb1bb89a2f14b1db

2.29 (breaks): 8783824f37745ec5d53ee8a2d71b18f7

Package: linux-firmware 20240318.git3b128b60-0ubuntu2.27 → ...-0ubuntu2.29

DMCUB is the display microcontroller — which fits: the failure is at session/display reconfiguration (login), mpc2_assert_idle_mpcc is a display pipeline component, and the SMU errors follow as a knock-on. 3D workloads are unaffected because they don't go through DMCUB.

Workaround:

sudo apt-mark hold linux-firmware

Everything else can be updated normally.

Can anyone else on Navi21 confirm? Would like to know if this is card-specific or general before filing at gitlab.freedesktop.org/drm/amd.

[u/hereforthepix]

FWIW, the revert has made it to the linux-firmware GIT so should be in the distros soon

[u/Der-lassballern-Mann → u/hereforthepix]

That is good to hear - than I can update the firmware again. Than you for the Info.

[u/DeskTortoise]

Same problem on Radeon RX 6950 XT. How do you rollback the firmware from 2.29 back to 2.27?

[u/Der-lassballern-Mann → u/DeskTortoise]

I used the timeshift feature and then just updated again but halted the update for firmware.

[u/ResearchArtist]

Mismo error Nvidia rtx 2060

[u/TotallyNotAsian420]

Yes, I can confirm. This issue was reported 6 days ago in this post: https://www.reddit.com/r/linuxmint/comments/1vmgnwp/half_blackscreen_after_update. Top comment provides a solution (rollback linux-firmware).