Public bug reported: Title: SDDM HiDPI Scaling Fails on Upgraded Kubuntu [24.10/25.04] with Intel Iris Xe, All Configuration Methods Ineffective
1. System Environment Operating System: Kubuntu [Version approx. 24.10/25.04, kernel approx. 6.x] Upgrade History: System was progressively upgraded from Kubuntu 22.04 LTS. Desktop Environment: KDE Plasma [Version approx. 6.x] running on Wayland (for the user session). Display Manager (SDDM): Version shipped with the OS, built against Qt 6. Hardware: CPU/GPU: Intel Corporation Alder Lake-P GT2 [Iris Xe Graphics] (rev 0c) Display: 15-inch Laptop, 2560x1600 native resolution. User Goal: Achieve 175% scaling (168 DPI) on the SDDM login screen. 2. Problem Description The SDDM greeter UI elements (text, login box, etc.) are rendered at a native 100% scale, making them unreadably small on the HiDPI display. The user's Plasma Wayland session after login scales correctly to 175% as configured in KDE System Settings. The issue is strictly confined to the pre-login SDDM environment. 3. Diagnostic and Troubleshooting History A comprehensive series of standard and advanced configuration methods were attempted to resolve the issue. All methods failed. Attempt 1: Wayland Native Scaling (Failed) Action: An environment variable was set for the SDDM service via a systemd drop-in file (sudo systemctl edit sddm): Environment="QT_SCREEN_SCALE_FACTORS=1.75". Verification: Inspection of the running sddm process environment via /proc/<PID>/environ confirmed that the variable was successfully received by the process. Outcome: The UI remained unscaled. Further testing revealed that any third-party (likely Qt 5-based) themes caused a white screen crash, confirming the greeter is running on a Qt 6 stack and that the default Breeze theme is the only compatible option. This suggests a bug within the SDDM Breeze theme for Qt 6, where it ignores the scaling factor. Attempt 2: X11 Greeter with Command-Line DPI (Failed) Action: The greeter was forced to X11 mode by setting DisplayServer=x11 in /etc/sddm.conf. The DPI was set via ServerArguments=-nolisten tcp -dpi 168 in /etc/sddm.conf.d/hidpi.conf. Outcome: The setting was ignored. The UI remained unscaled. Attempt 3: X11 Greeter with Modular Xorg Configuration (Failed) Action: A high-priority Xorg configuration file was created at /etc/X11/xorg.conf.d/20-monitor-hidpi.conf. This file used the DisplaySize property (calculated as 387 242 mm for the 2560x1600 display) to force a DPI of 168 for the specific monitor (eDP-1). Outcome: The setting was ignored. The UI remained unscaled. Attempt 4: X11 Greeter with Monolithic Xorg Configuration (Failed) Action: As a final measure, a single, authoritative /etc/X11/xorg.conf was created, explicitly defining Device (with "modesetting" driver), Monitor (with DisplaySize), and Screen sections, leaving no room for ambiguity. Outcome: This highest-priority configuration method was also completely ignored by the X server spawned by SDDM. 4. Final Analysis & Conclusion The system is behaving in a non-standard manner, as it ignores all documented methods for HiDPI configuration for the SDDM greeter. Since the configuration files were verified to be correct and all standard approaches have been exhausted, this is not a user configuration error. The evidence points to a system-level bug likely located in the interaction between SDDM, the Xorg server, and the Intel Mesa (modesetting) driver on this specific hardware generation (Alder Lake) and software stack. The X server process launched by SDDM fails to respect its own configuration files when running as the greeter. This detailed report can be submitted to the official bug trackers for Kubuntu, KDE, or even the freedesktop.org Xorg project for further investigation by developers. my E-mail:[email protected] ProblemType: Bug DistroRelease: Ubuntu 25.04 Package: sddm 0.21.0+git20241213.4a9aa2e-1ubuntu2 ProcVersionSignature: Ubuntu 6.14.0-28.28-generic 6.14.8 Uname: Linux 6.14.0-28-generic x86_64 ApportVersion: 2.32.0-0ubuntu5.3 Architecture: amd64 CasperMD5CheckResult: pass CurrentDesktop: KDE Date: Sun Aug 17 00:40:05 2025 InstallationDate: Installed on 2022-09-26 (1055 days ago) InstallationMedia: Kubuntu 22.04.1 LTS "Jammy Jellyfish" - Release amd64 (20220809.1) SourcePackage: sddm UpgradeStatus: Upgraded to plucky on 2025-05-31 (77 days ago) ** Affects: sddm (Ubuntu) Importance: Undecided Status: New ** Tags: amd64 apport-bug plucky wayland-session -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2120761 Title: SDDM HiDPI Scaling Fails on Intel Alder Lake (Iris Xe) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/sddm/+bug/2120761/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
