Public bug reported:
Hi there! I have a Lenovo Carbon X1 and I use an external HP Z27 4K
monitor. I have the monitor connected to the Lenovo laptop using a HDMI
cable. I also have the same monitor connected to a Dell desktop computer
using a DP cable.
I can change the selected input on the monitor from HDMI (laptop) to DP
(desktop). The problem is that when I change it back, both the external
monitor AND the laptop screen flicker as if I had physically plugged in
the monitor.
Checking dmesg, I'm getting the following messages:
```
[616849.330989] [drm:drm_dp_dual_mode_detect [drm_kms_helper]] *ERROR*
Unexpected DP dual mode adaptor ID 50
[616853.593595] [drm:drm_dp_dual_mode_detect [drm_kms_helper]] *ERROR*
Unexpected DP dual mode adaptor ID 50
```
Sometimes I get back my desktop, but more often then not the external
monitor is stuck as 1920*1080 and I have to use `autorandr` to fix that.
```
lsb_release -rd
Description: Ubuntu 21.04
Release: 21.04
```
```
uname -a
Linux my-laptop 5.11.0-22-generic #23-Ubuntu SMP Thu Jun 17 00:34:23 UTC 2021
x86_64 x86_64 x86_64 GNU/Linux
```
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Attachment added: "version.log"
https://bugs.launchpad.net/bugs/1936868/+attachment/5511963/+files/version.log
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https://bugs.launchpad.net/bugs/1936868
Title:
monitor flickers when input is changed back
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