https://bugs.kde.org/show_bug.cgi?id=476018
Bug ID: 476018
Summary: Fake refresh rates when using adaptive sync (VRR)
Classification: Plasma
Product: KScreen
Version: 5.27.8
Platform: Archlinux
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: common
Assignee: kscreen-bugs-n...@kde.org
Reporter: mequer...@gmail.com
Target Milestone: ---
SUMMARY
When using a monitor with adaptive sync / variable refresh rate, extra fake
refresh rates get automatically added to the "Refresh rate" list in "Display
Configuration". For example, my monitor has refresh rates of 240, 165, 144,
120, and 60 Hz at its native resolution. Only these refresh rates can be found
in its EDID and are also the only ones listed in Windows 10. But in KDE/Plasma
the following refresh rates are listed: 240, 165, 144, 120, 96, 72, 60, 50, and
48 Hz. So fake refresh rates of 96, 72, 50, and 48 Hz are added. When I select
96 or 72 Hz, the monitors refresh rate does change to 96 or 72 Hz, but VRR
stops working even though "Adaptive sync" is still set to "Automatic". When I
select 50 or 48 Hz, the image becomes completely distorted. Even worse, the
real refresh rate of 120 Hz gets overwritten by a fake 120 Hz so adaptive sync
doesn't even work when I select 120 Hz. I have to run `kscreen-doctor -o`, look
for the other 120 Hz, and apply it by running `kscreen-doctor
output.DP-1.mode.5`. Both the real and the fake 120 Hz options look identical
in the output of kscreen-doctor, so I have to try both to see which one is fake
and which is real. Another indication that some of the listed refresh rates are
fake is that after applying 120 Hz, I can apply 96 or 72 Hz without the monitor
go black for a few seconds. The new fake refresh rate gets "applied"
immediately with no delay/blanking whatsoever. Changing from a real refresh
rate to a different real refresh rate always causes the monitor to black for a
few seconds (just like in Windows 10).
STEPS TO REPRODUCE
1. Connect high refresh-rate monitor with adaptive sync / VRR
2. Notice fake refresh rates added in Display Configuration
3. Try to use a fake refresh rate
4. VRR stops working or the image becomes distorted
OBSERVED RESULT
Extra fake refresh rates and/or real refresh rates that get overwritten by fake
refresh rates.
EXPECTED RESULT
No fake refresh rates listed and no real refresh rates overwritten by fake
refresh rates. If fake refresh rates must be added, it should be clear that
they're not real and that VRR doesn't work with them, and real refresh rates
should never be overwritten by a fake one. It would also be helpful if the
output of `kscreen-doctor -o` would distinguish between fake and real refresh
rates.
SOFTWARE/OS VERSIONS
Linux: 6.5.8
KDE Plasma Version: 5.27.8
KDE Frameworks Version: 5.111.0
Qt Version: 5.15.11
ADDITIONAL INFORMATION
GPU: AMD RX 6650XT, using amdgpu drivers.
This may be related to AMD's FreeSync Video mode, but I think it should be
disabled as `/sys/module/amdgpu/parameters/freesync_video` defaults to 0.
Here's some more info on that:
https://www.phoronix.com/news/AMDGPU-FS-Video-Default-PS.
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