I've made a test kernel build with drm_panic enabled (and VT_CONSOLE disabled):

https://koji.fedoraproject.org/koji/taskinfo?taskID=120544794

I've backported a few patches, that are not in v6.10, like:
short panic description:
https://patchwork.freedesktop.org/series/135356/
kmsg panic_screen:
https://patchwork.freedesktop.org/series/134286/
draft nouveau support (tested on 1650X, might be garbage on other GPU):
https://patchwork.freedesktop.org/series/133963/
And also virtio-gpu support, so you can test it easily on a VM.

To install the test kernel, download the rpms kernel, kernel-core, kernel-modules, kernel-modules-core, kernel-modules-extra, and install them with dnf.
It's a Fedora rawhide kernel, but can be installed on F40.

i915, amdgpu, and nvidia are not yet supported, so you need to blacklist them, in order to use simpledrm, if you want to see the panic screen.

To trigger a kernel panic, if you don't fear to crash your machine do this (as root):
echo c > /proc/sysrq_trigger

There is also a debug interface (assuming card0 and plane0):
echo 1 > /sys/kernel/debug/dri/0/drm_panic_plane_0

This will cause some flickering, because it will redraw only 1 of the 2 buffers (most of the time you have double-buffering), and may leak the framebuffer, but allows to see the panic screen without crashing.

You can also test the kmsg panic screen, to get the same debug info as before with:
echo -n kmsg > /sys/module/drm/parameters/panic_screen

Best regards,

--

Jocelyn

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