https://bugs.kde.org/show_bug.cgi?id=527571
Bug ID: 527571
Summary: With HDR enabled, switching virtual desktops in
Overview makes the DP monitor lose sync for ~2.5 s on
every switch
Classification: Plasma
Product: kwin
Version First 6.8.1
Reported In:
Platform: CachyOS
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: platform-drm
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: ---
Product: kwin
Component: platform-drm (or: colorcorrection / HDR)
Version: 6.8.1
Summary: With HDR enabled, switching virtual desktops in Overview makes the DP
monitor lose sync for ~2.5 s on every switch
== Steps to reproduce ==
1. Wayland session, a single DisplayPort monitor with HDR enabled in Display
settings (10 bpc, BT2020_RGB).
2. Open Overview (Meta+W).
3. Switch to another virtual desktop from Overview, several times.
== Observed result ==
Every switch blanks the monitor completely for about 2.5–3 s, then the picture
comes back. A phone video shows 6 switches in 30 s and 6 blackouts:
1.8→4.5 s, 5.3→8.3 s, 10.5→13.3 s, 15.8→18.5 s, 20.8→23.5 s, 24.8→27.5 s.
Screenshots taken by KWin itself (spectacle) during the switches look clean, so
the problem is in the signal sent to the monitor, not in KWin's rendering.
== Expected result ==
Desktops switch with no loss of signal.
== Evidence ==
With drm.debug=0x106, each blackout lines up with a short-pulse HPD sent by the
sink, and the DPCD ESI read shows LINK_STATUS_CHANGED:
10:48:16.753 [drm:dp_handle_hpd_rx_irq] Got short pulse HPD on link 0
10:48:16.754 [drm:drm_dp_dpcd_read] AUX 0x02002 -> 41 00 10 02 00 00 00 00 00
00 77 77 01 00
(repeated at 10:48:20.360 and 10:48:23.624, one per switch)
Lanes report OK afterwards (77 77, interlane aligned). No KWin warnings and no
amdgpu errors or resets. The only other log line is a libinput "event
processing lagging behind by 40ms" at the moment of a switch.
== Workaround / notes ==
- Turning HDR off stops it. Turning HDR off and back on also cleared it: after
that, HDR stays on with no blackouts.
- It first appeared after the screen woke from the lock screen (~45 min
idle/lock). A plain DPMS off→on (kscreen-doctor --dpms off/on) with HDR on did
NOT reproduce it afterwards, so the trigger that puts it into the bad state is
unknown.
- Started right after upgrading Plasma 6.8.0 → 6.8.1. Never noticed it on 6.8.0
with the same HDR setup.
- The same upgrade also changed the output's vrrPolicy from Automatic to Never
in kwinoutputconfig.json without user action. That's possibly unrelated, but
worth noting. The blackouts persisted after setting it back to Automatic.
== System ==
CachyOS (Arch-based), kernel 7.2.11-1-cachyos-bore-lto
KWin 6.8.1, Qt 6.12.0, Mesa 26.2.4 (radeonsi, OpenGL ES compositing)
GPU: AMD Radeon RX 6600 (navi23), amdgpu
Monitor: ASUS XG279CNS over DisplayPort, 1920x1080@360 Hz, HDR on (SDR
brightness 400 nits, peak override 400), 10 bpc, VRR Automatic
(Phone video available on request.)
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