kernel update and amdgpu breaks X

[rvj]

In a recent system update, the kernel went from vmlinuz-6.6.74-gentoo to vmlinuz-6.12.16-gentoo. In the process, wayland / X has broken (although rc-status reports that display-manager is running). The new kernel boots into a default VT1 terminal; VT7 shows a black screen with a blinking underscore.

Booting with the older kernel on the otherwise identical updated system provides a fully functioning display-manager / sddm.

(Also, a different computer with similar setup but different graphics chip upgraded with no problems.)

One detail of this setup that is most likely relevant: IrEFInd is the boot manager, and this requires EFI framebuffer support to be able to display later portions of the boot process, loaded directly into the kernel as a firmware blob, not loaded as a module. All dozen amdgpu/renoir_* blobs have been included. For older versions of the kernel, this worked as required.

To help diagnose, I ran startx and recorded the Xorg startup log, comparing the performance using the fully functional older kernel and the problematic new kernel. Both logs give comparable output, until the newer kernel ends with

[ 48.197] (EE) Device(s) detected, but none match those in the config file.
[ 48.197] (EE)
Fatal server error:
[ 48.197] (EE) no screens found(EE)
[ 48.197] (EE)
Please consult the The X.Org Foundation support at http://wiki.x.org for help.
[ 48.197] (EE) Please also check the log file at "/home/rvj/.local/share/xorg/Xorg.0.log" for additional information.
[ 48.197] (EE)
[ 48.199] (EE) Server terminated with error (1). Closing log file.

whereas the older kernel continues with

[ 24.695] (II) FBDEV(0): Creating default Display subsection in Screen section
"Default Screen Section" for depth/fbbpp 24/32
[ 24.695] (==) FBDEV(0): Depth 24, (==) framebuffer bpp 32
[ 24.695] (==) FBDEV(0): RGB weight 888
[ 24.695] (==) FBDEV(0): Default visual is TrueColor
[ 24.695] (==) FBDEV(0): Using gamma correction (1.0, 1.0, 1.0)
[ 24.695] (II) FBDEV(0): hardware: EFI VGA (video memory: 8100kB)
etc.

Here is the successful Xorg log with the older kernel: https://bpa.st/L5XQ

Here is the failed Xorg log with the newer kernel: https://bpa.st/6VDA

Please advise … any further diagnostics, or files to the posted?

Thanks!