Xorg cannot set screen resolution for external monitor(4K ThinkVision P27u)
Setting external monitor's resolution will always result in failure, and fallback to the original resolution.
I filed a bug to i915 first.
I try to set external monitor's resolution in the following two ways:
The external monitors will flash several times.
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xrandr --output
Able to switch to the target resolution, but soon it will go back to the original one.
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UI gnome-control-center display
Able to switch to the target resolution, but soon it will go back to the original one. If I click the "Keep Changes" before the reverting, it will stay in the correct resolution. The "Keep Changes" timer is not hitting 0, but it do revert the resolution change.
Something else
Switch display mode from join display to mirror, will also fail, to me I think they are of the same reason.
I use the udev rules to call xrandr --output on hotplug, then setting the resolution on the UI can work properly.
I am a newbie in the display tech stack, why does the resolution change will go through hotplugs? I did not find any error or warnings in the journalctl output.
I do not know where is the root cause, but I am still trying to locate it.