Hang at boot on Dell Inspiron 15

[Demi Marie Obenour <demiobenour@gmail.com>]

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I built a Spectrum OS image using
https://github.com/DemiMarie/spectrum/tree/499323fa448406ec728b1f29a4bca6dc54f5df32.
This is almost the same as Spectrum git main, and I am almost
certain that the differences (visible on GitHub) are not related to
this problem.  Therefore, I'm reporting this as if it were a bug in
Spectrum itself.

The bug is pretty simple: on a Dell Inspiron 15, booting freezes
forever.  The last message from the kernel before it stops is:

amdgpu 0000:03:00.0: [drm] fb0: amdgpudrmfb frame buffer device

This machine has an AMD Ryzen 7000 series CPU with integrated
graphics and a 512GB NVMe drive.  The installation ISO was built by

$ nix build --log-format bar-with-logs --file release/combined --out-link "path to Caddy web root"

with a custom config.nix that I can also share if
needed.  It just specifies the update URL and signing
key, though.  The actual install ISO I built can be found at
<https://test-spectrum-updater.devbydemi.com/demi/spectrum-updates/spectrum-installer.iso>
(no authentication needed).  This was built on (and is hosted by)
a test server I don't particularly trust, so don't mount or boot it
on a machine you care about outside of a VM with no GPU acceleration
or other sandbox holes.

To even install Spectrum, I had to kexec from the existing NixOS
install because the firmware wouldn't boot the image off of the
USB stick.  I presume this is a firmware bug, which would not at all
surprise me.

I'm not sure how to go about diagnosing this.  The hang happens after
s6 gets started, but the boot is so fast that it is hard to tell if
it has switched from the initramfs to the rootfs yet.  In any case,
it seems to happen before Weston gets a chance to produce any output
on screen.  Suggestions welcome!
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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