Glitchy screen after suspension on an old iMac (Mid-2011)

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After… 31 years using Windows and macOS, I finally decided to enter the world of Linux, specifically with CachyOS and Plasma Wayland. The thing is: I did this on my ancient Mid-2011 iMac.

Here’s the summary of this installation and setup.

Operating System: CachyOS Linux
KDE Plasma Version: 6.5.5
KDE Frameworks Version: 6.22.0
Qt Version: 6.10.2
Kernel Version: 6.18.8-1-cachyos (64-bit)
Graphics Platform: X11
Processors: 4 × Intel® Core™ i5-2400S CPU @ 2.50GHz
Memory: 16 GiB of RAM (15.6 GiB usable)
Graphics Processor 1: AMD TURKS
Graphics Processor 2: Mesa Intel® HD Graphics 2000
Manufacturer: Apple Inc.
Product Name: iMac12,1
System Version: 1.0

It runs smoothly, cleanly, quickly and I loved it… until the moment the computer went to sleep for the first time. Upon waking, the screens — the iMac’s own display and the external monitor — were illegible, completely glitchy, unusable. Everything was still there, I just couldn’t see or use it.

With CTRL+ALT+F4, I managed to get to TTY and from there I was able to restart the display-manager… but the entire session was closed. Applications, everything. It’s as if I had reset the computer.

I then started looking for solutions. I disabled TOSHY, tried forcing the use of radeon.modeset in cmdline and… nothing happened. I even disabled Firefox’s hardware accelerator and nothing happened.

With a tip from a friend, I ended up installing GNOME and it worked perfectly on CachyOS. When suspended, it comes back normally. Same with Mint, which I had installed before but didn’t like as much as CachyOS + KDE Plasma.

Is there anything else I can do to fix this or is KDE Plasma just not meant for me and my computer?

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I can’t speak to an iMac, but I have Plasma 6.5 running on a n ancient Dell XPS from 2008, and although it is slow, it works and your specs look good. Maybe someone with more experience with this kind hardware can help you.

For now, welcome! I hope you get everything working!

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Thanks, Paul! From what I’ve gathered, it seems to be related to the graphics engines working in ways that my graphics cards don’t understand when waking up. But yes, I hope someone with more experience can pinpoint the issue and help me fix it! :slight_smile:

4

Are you using the older radeon kernel driver rather than amdgpu? If

lsmod | grep radeon

returns results then you might try adding radeon.dpm=0 radeon.runpm=0 to GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub and running update-grub.

This works on my iMac 10,1 with Neon although I still often have to switch to a text console and back to the GUI when it wakes using Fn-Ctl-Opt-F3 then Fn-Ctl-Opt-F1 (Ctl-Alt-F3, Ctl-Alt-F1). Plasma 6.6 will come with a new login manager so maybe the issue will go away.

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Well… it didn’t work. I’m using LIMINE, and I updated the boot file as you said, but it didn’t work. After suspension, it wakes all glitchy. This is what I get when I use lsmod | grep radeon:

radeon               2248704  32
drm_suballoc_helper    20480  2 amdgpu,radeon
drm_ttm_helper         16384  2 amdgpu,radeon
ttm                   131072  4 amdgpu,radeon,drm_ttm_helper,i915
i2c_algo_bit           20480  3 amdgpu,radeon,i915
drm_display_helper    282624  3 amdgpu,radeon,i915
drm_exec               16384  2 amdgpu,radeon
video                  81920  3 amdgpu,radeon,i915
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You could try to blacklist the amdgpu module - you don’t need it for TURKS cards.

Since the module parameters I suggested don’t work then you could try playing with the others. That’s what I did to find the combination which worked for my machine. You can list all the module parameters with

systool -vm radeon

It’s part of the sysfsutils package. The Arch wiki is a good resource for the module usage.

I use Wayland as I find it more stable than X11. Your OP references both X11 and Wayland so I’m not sure what you’re using.

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More module parameter info with:

modinfo -p radeon