Bug 506501

Summary: Cannot use both display port and hdmi with different resolution at the same time
Product: [Plasma] kwin Reporter: guillaume.roche
Component: platform-drmAssignee: KWin default assignee <kwin-bugs-null>
Status: RESOLVED UPSTREAM    
Severity: normal CC: xaver.hugl
Priority: NOR    
Version First Reported In: 6.4.1   
Target Milestone: ---   
Platform: Fedora RPMs   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:
Attachments: drm_info output
kscreen-doctor output
drm logs

Description guillaume.roche 2025-07-02 20:14:19 UTC 
SUMMARY

After upgrading from Fedora 41 to 42, my dual display setup no longer works correctly. Only one display can be activated at a time.

Main display is on display port, secondary is on HDMI.

STEPS TO REPRODUCE
1. Use an AMD GPU (Radeon RX580)
2. Plug an UHD (4k) display to its Display Port output
3. Plug another display (1080p) to its HDMI output
4. Open Plasma settings > Display & Monitor
5. Enable both displays at max resolution
6. Apply

OBSERVED RESULT
Secondary display is not enabled
An error appears; "Couldn’t apply display configuration: The driver rejected the output configuration"

EXPECTED RESULT
Secondary display is enabled. No error occurs.

SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 42
KDE Plasma Version: 6.4.1
KDE Frameworks Version: 6.15.0
Qt Version: 6.9.1
Kernel Version: 6.15.4-200.fc42.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 12 × AMD Ryzen 5 1600X Six-Core Processor
Memory: 16 GiB of RAM (15,5 GiB usable)
Graphics Processor: AMD Radeon RX 580 Series

OpenGL vendor string: AMD
OpenGL renderer string: AMD Radeon RX 580 Series (radeonsi, polaris10, ACO, DRM 3.63, 6.15.4-200.fc42.x86_64)
OpenGL core profile version string: 4.6 (Core Profile) Mesa 25.0.7

ADDITIONAL INFORMATION
I can still enable my HDMI output if I disable the Display port output before applying.
I can enable both displays if I set them both to 1080p resolution.
When the error occurs, I see the following log in journalctl:

kwin_wayland[2064]: kwin_wayland_drm: Atomic modeset test failed! Invalid argument
Comment 1 Zamundaaa 2025-07-03 15:46:40 UTC 
With the two displays connected, please attach the output of
> drm_info
> kscreen-doctor -o
and follow https://invent.kde.org/plasma/kwin/-/wikis/Debugging/Debugging-DRM-issues to get a drm debug log of you trying to enable the second display.
Comment 2 guillaume.roche 2025-07-03 20:18:10 UTC 
Created attachment 182909 [details]
drm_info output
Comment 3 guillaume.roche 2025-07-03 20:18:29 UTC 
Created attachment 182910 [details]
kscreen-doctor output
Comment 4 guillaume.roche 2025-07-03 20:20:57 UTC 
Created attachment 182911 [details]
drm logs

Logs taken while reproducing the issue by enabling my hdmi display. Compressed otherwise it exceeded the file size limit.
Comment 5 Zamundaaa 2025-07-04 13:44:20 UTC 
Alright, this is the culprit:
> [  369.622233] amdgpu 0000:08:00.0: [drm:dce112_validate_bandwidth [amdgpu]] dce112_validate_bandwidth: Bandwidth validation failed!
> [  369.622276] amdgpu 0000:08:00.0: [drm:dm_pflip_high_irq [amdgpu]] crtc:0[000000004a242ee5], pflip_stat:AMDGPU_FLIP_NONE, vrr[0]-fp 0
> [  369.622660] amdgpu 0000:08:00.0: [drm:amdgpu_dm_atomic_check [amdgpu]] DC global validation failure: Bandwidth validation failure (BW and Watermark) (13)
> [  369.623082] amdgpu 0000:08:00.0: [drm:amdgpu_dm_atomic_check [amdgpu]] Atomic check failed with err: -22
> [  369.623514] amdgpu 0000:08:00.0: [drm:drm_atomic_check_only] atomic driver check for 00000000d4205289 failed: -22

I'm pretty sure the rx 580 is able to drive 4k + 1080p without any issues. You can report this driver regression at https://gitlab.freedesktop.org/drm/amd/-/issues - and attach the drm_info output and drm debug log there as well.
Comment 6 guillaume.roche 2025-07-10 19:49:43 UTC 
(In reply to Zamundaaa from comment #5)
> Alright, this is the culprit:
> > [  369.622233] amdgpu 0000:08:00.0: [drm:dce112_validate_bandwidth [amdgpu]] dce112_validate_bandwidth: Bandwidth validation failed!
> > [  369.622276] amdgpu 0000:08:00.0: [drm:dm_pflip_high_irq [amdgpu]] crtc:0[000000004a242ee5], pflip_stat:AMDGPU_FLIP_NONE, vrr[0]-fp 0
> > [  369.622660] amdgpu 0000:08:00.0: [drm:amdgpu_dm_atomic_check [amdgpu]] DC global validation failure: Bandwidth validation failure (BW and Watermark) (13)
> > [  369.623082] amdgpu 0000:08:00.0: [drm:amdgpu_dm_atomic_check [amdgpu]] Atomic check failed with err: -22
> > [  369.623514] amdgpu 0000:08:00.0: [drm:drm_atomic_check_only] atomic driver check for 00000000d4205289 failed: -22
> 
> I'm pretty sure the rx 580 is able to drive 4k + 1080p without any issues.
> You can report this driver regression at
> https://gitlab.freedesktop.org/drm/amd/-/issues - and attach the drm_info
> output and drm debug log there as well.

OK, thanks a lot for having a look!