Subject: Re: bug#76554: Laptop screen blank after kexec reboot

From: Maxim Cournoyer <[email-masked]>
Date: Sat, 26 Apr 2025 22:32:28 +0900

Hi Simon,

Simon Streit <[email-masked]> writes:

> Ludovic Courtès <[email-masked]> writes:
>
>> Oh, worse than what I experienced.
>
> Still more convenient than typing in the password two times.  I first
> thought kexec was not working.  It is an improvement for me already. :)
>
> I just did a reboot with kexec from kexec-tools on an identical machine
> running Debian Bookworm with LUKS encryption:
>
> The screen goes on with a blinking prompt.  The external video is on too
> and can plug it in and out again.
>
> I just tried it manually with kexec from kexec-tools in Guix.  The
> display stayed dark here too and I somehow didn't manage to unlock
> the device.  The HDD-Lamp hinted that something was happening.

So just to make sure I got that right, it works correctly on Debian but
incorrectly (black screen) on Guix System on the *same* hardware?

If correct, that'd probably point to our kernel configuration (or
non-free firmware?  do you you use linux-firmware on Debian and not on
Guix System (through nonguix or the likes)) ?

It'd be interesting to see what happens if you use Linux-libre on your
Debian machine and try the same.  Perhaps attach your Debian's
/proc/config.gz that works so that we can diff with ours for clues.

As another data point: I have the black screen issue when I use 'reboot
--kexec', but in my case it's not the backlight that is too low, the
video signal is completely cut and my external monitor (it's a desktop)
goes into standby.  That's with a modern Ryzen 9 machine and its iGPU
for the video (which sadly requires firmware blobs for 3D acceleration
and hardware video decoding).

-- 
Thanks,
Maxim