Critical Error (Video Corruption and System Restart) during Transition from Login Screen to User Session on AMD RDNA 3 Hardware

[tudorrobertraul-netizen]

Problem Description:
I am using Linux Mint and have identified a severe video signal synchronization issue during the login process. While this behavior seems to be a broader issue within the Linux ecosystem (having encountered similar issues on other distributions/interfaces like Zorin OS), I am reporting this to the Linux Mint team as LightDM appears to be the specific point of failure in this workflow.

Upon entering the password, one or both monitors exhibit extreme visual noise (static/snow, similar to analog television interference), immediately followed by a full system restart.

System Specifications:

GPU: AMD Radeon RX 7900 GRE

CPU: AMD Ryzen 7 5800X

RAM: 32 GB

OS: Linux Mint 22 (Issue persists on other LightDM-based distributions)

Monitor Configuration:

Primary Monitor (Horizontal): 2560x1440 @ 165Hz

Secondary Monitor (Vertical): 1080x2560 @ 75Hz (Native 2560x1080 rotated 90°)

Technical Analysis:
The issue stems from the fact that LightDM operates under the root user (or a separate system user) and utilizes default display settings—typically 60Hz and standard landscape orientation. At the moment of login, when the amdgpu driver attempts to instantaneously switch from LightDM’s 60Hz profile to the user-defined profile (165Hz and 90° rotation), a major synchronization conflict occurs.

On the AMD RDNA 3 architecture, this abrupt shift in frequency and orientation triggers a driver crash (MCLK switching failure) or a total loss of signal, forcing a hard system restart. I have attempted various manual xrandr scripts, but these prove unstable and often interfere with the boot process.

Proposed Solutions:

Integrate Monitor Settings into "Login Window" (lightdm-settings): It would be extremely beneficial if the LightDM configuration GUI included options to manually set the refresh rate, position, and rotation of monitors. This would allow the login interface to run at the same frequencies as the user session, eliminating the hardware "shock" during hand-off.

Automatic Synchronization: Implement a mechanism where LightDM can automatically inherit the display profile (resolution, Hz, and rotation) from the system-wide Cinnamon settings (cinnamon-monitors.xml). This would ensure a fluid and hardware-safe transition.

This improvement is critical for users with modern hardware, where high refresh rates and vertical display configurations have become industry standards.

[leigh123linux]

Because Cinnamon does not natively bridge user-level monitor profiles (cinnamon-settings display) over to LightDM, you must generate a visual layout and point LightDM to it manually. [2]
The most efficient, visual workaround available on Cinnamon relies on a GUI layout tool and a small configuration edit:

Step 1: Use a Layout GUI to Generate the Script

Instead of writing complex display coordinates by hand, use ARandR, which is a graphical interface for X11 screen arrangements.

1. Open your terminal and install it:

sudo apt install arandr

2. Launch ARandR from your applications menu.
3. Your monitors will appear as blocks. Drag, position, and orient them exactly how you prefer them to look at the login screen.
4. Right-click your intended main monitor and ensure Primary is checked.
5. Click Layout (top menu) $\rightarrow$ Save As.
6. Save the file exactly as lightdm_layout.sh in your default user folder, then close the program. [3]

Step 2: Move and Authorise the Script

LightDM runs under its own system account and cannot access files sitting in your personal home folder. You must relocate it to a system directory.
Run these three commands in your terminal to move the script, make it executable, and verify its content: [4]

sudo mv ~/lightdm_layout.sh /etc/lightdm/lightdm_layout.sh
sudo chmod +x /etc/lightdm/lightdm_layout.sh
cat /etc/lightdm/lightdm_layout.sh

(The cat command will display the file content. It should look like a long line starting with xrandr --output...) [4]

Step 3: Tell LightDM to Execute the Layout

Now, you must instruct LightDM to look at this visual layout file before rendering the login screen. [5]

1. Open the LightDM configuration directory with your text editor:

sudo nano /etc/lightdm/lightdm.conf.d/70-display-setup.conf

(If this file is empty, that is completely fine).
2. Paste the following exact configuration lines inside the file:

[Seat:*]
display-setup-script=/etc/lightdm/lightdm_layout.sh

3. Save and close the editor (Press Ctrl+O, then Enter to save, and Ctrl+X to exit). [3, 6, 7]

Step 4: Test it

Log out or restart your computer. LightDM will catch the display-setup-script directive and force Xorg to stitch the screens together exactly how you drew them in the ARandR GUI before rendering the login prompt. [5, 8]
If you run into issues with fractional scaling (e.g., the login screen text looks microscopic on a 4K display), let me know. We can append a scaling modifier directly into that generated file.

[1] [https://github.com](https://github.com/linuxmint/lightdm-settings/blob/master/usr/lib/lightdm-settings/lightdm-settings)
[2] [https://github.com](linuxmint/cinnamon#2379)
[3] [https://www.linux.org](https://www.linux.org/threads/how-to-change-login-greeter-in-linux-mint-cinnamon-fyi-tuxbot-was-no-help.45428/)
[4] [https://forums.linuxmint.com](https://forums.linuxmint.com/viewtopic.php?t=360800)
[5] [https://www.youtube.com](https://www.youtube.com/watch?v=EMGrXVKqeb4)
[6] [https://forums.linuxmint.com](https://forums.linuxmint.com/viewtopic.php?t=462217)
[7] [https://forums.linuxmint.com](https://forums.linuxmint.com/viewtopic.php?t=360800&start=20)
[8] [https://www.reddit.com](https://www.reddit.com/r/linuxquestions/comments/m19gc7/lightdm_on_2_monitors/)

[leigh123linux]

@clem and the team weren't keen on adding similar in the past.

#21

[tudorrobertraul-netizen]

My apologies for opening multiple issues. It wasn't my intention to be disruptive or cause any stress; I was simply trying to provide more data to help address this crash. I will keep all future updates and information consolidated in this thread. Thank you for your patience.