Hi guys,
The problem is now solved and I thought I'd share how.
First thing: the resolution. My old screen gave me 2560x1440 when
connected to my old computer yet only 1920x1080 when connected to my new
computer. It turns out that this was unrelated to the graphics driver
issue: this screen allows different max resolutions depending on which
slot is used at its back. Its displayPort 1.2 slot is fine. The other slot
is HDMI 1, capable only of 1920x1080. My new computer only has HDMI
connectivity, not displayPort, whereas I used displayPort on the old one.
Once connected to a newer screen, the new PC gave me 2560x1440 as
expected.
At this stage, if left alone, the new PC would run correctly. But once I
started using it as my main computer, X crashed every 3 hours roughly. I
had installed a recent kernel through the backports. I followed Jörg's
explanations below to get a more complete set of programs from testing,
but this did not improve the stability. Following Felix' advice I had
already added "quiet modprobe.blacklist=radeon" to
GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub . A discussion with
Brave AI led to adding more kernel parameters to this line :
"amdgpu.ppfeaturemask=0xfffd3fff amdgpu.noretry=0". This worked. Now, from
time to time I see X becoming sluggish for about 5 seconds, but it doesn't
crash and returns to normal after that. The computer is fully usable.
Many thanks to all of you who gave me very valuable advice!
Sébastien.
Jörg-Volker Peetz (Thu, 20 Nov 2025):
Hi Sébastien,
change this line in /etc/apt/sources.list :
deb http://deb.debian.org/debian/ trixie main non-free-firmware non-free
contrib
to
deb http://deb.debian.org/debian/ trixie testing main non-free-firmware
non-free contrib
and create /etc/apt/preferences with the following content:
Package: *
Pin: release a=testing
Pin-Priority: 90
I recommend a value below 100 for the Pin-Priority so that the packages of
the backports repository are preferred over those in testing.
Then, command
sudo apt update
which downloads current information about all packages in the configured
repositories (compare Debian Reference Chap. 2.5).
To see which packages are now available and which of them are installed,
command
apt list '~nlinux-image-amd64' --all-versions
More information about the versions and changes of a Debian package can be
found on the web-site https://tracker.debian.org/ .
In order to test the installation, say, of the package linux-image-amd64 from
the testing repository, command
sudo apt -t testing install linux-image-amd64 --simulate
This shows which packages would actually be installed.
If it's o.k. for you to install the proposed packages, repeat the command
without '--simulate'.
Regards,
Jörg.
