I have a new 2-computer KVM switch. Steetek brand off Amazon. Supports 2 DisplayPort monitors per computer so there are a total of 4 DP in and 2 DP out. It's connected to two computers with old AMD GPUs:
Computer #1: OpenSUSE 16.0, kernel 7.3.0. GPU is an old Radeon RX570. Running Xwayland 24.1.6
Computer #2: Fedora 43, kernel 7.2.11. GPU is an old Radeon Pro WX 3200 (RX550-class GPU). Running Xwayland 24.1.13
The KVM is connected to two monitors: a 38" Acer widescreen (3840x1600) and a generic 24" Lenovo-brand (1920x1080). Both (obviously) connected via DisplayPort. Both monitors are old. I think DP1.2 is the most recent protocol supported by them.
(Before I go further, I'll mention that without the KVM, neither computer shows any issues when connected to both monitors simultaneously.)
With the KVM in place, switching from computer #1 to computer #2 is pretty solid.
Switching from computer #2 to computer #1 is dicey. The Lenovo monitor seems fine but the Acer monitor usually goes into a loop where its signal will bounce on and off every 5-10 seconds. When this is happening, the system journal on Computer #1 shows the following:
Oct 20 19:20:35 excelsior kernel: [drm] DM_MST: DP14, 4-lane link detected
Oct 20 19:20:44 excelsior kernel: [drm] DM_MST: stopping TM on aconnector: 00000000bdbcb8d7 [id: 93]
Oct 20 19:20:44 excelsior kernel: [drm] DM_MST: starting TM on aconnector: 00000000bdbcb8d7 [id: 93]
Oct 20 19:20:44 excelsior kernel: [drm] DM_MST: DP14, 4-lane link detected
Oct 20 19:20:58 excelsior kernel: [drm] DM_MST: stopping TM on aconnector: 00000000bdbcb8d7 [id: 93]
Oct 20 19:20:59 excelsior kernel: [drm] DM_MST: starting TM on aconnector: 00000000bdbcb8d7 [id: 93]
Oct 20 19:20:59 excelsior kernel: [drm] DM_MST: DP14, 4-lane link detected
Oct 20 19:21:03 excelsior kernel: [drm] DM_MST: stopping TM on aconnector: 00000000bdbcb8d7 [id: 93]
Oct 20 19:21:04 excelsior kernel: [drm] DM_MST: starting TM on aconnector: 00000000bdbcb8d7 [id: 93]
Oct 20 19:21:04 excelsior kernel: [drm] DM_MST: DP14, 4-lane link detected
Oct 20 19:21:14 excelsior kernel: [drm] DM_MST: stopping TM on aconnector: 00000000bdbcb8d7 [id: 93]
Oct 20 19:21:14 excelsior kernel: [drm] DM_MST: starting TM on aconnector: 00000000bdbcb8d7 [id: 93]
Oct 20 19:21:14 excelsior kernel: [drm] DM_MST: DP14, 4-lane link detected
Connecting Computer #1 directly to the monitors using the same cables has worked for years (literally, since around Covid lockdowns). But I have swapped all 4 cables in that signal path with spares just to see if it might fix things. No change.
I've also swapped Computer #1 and Computer #2 on the KVM switch itself to see if the problem moves to the other set of outputs. It does. The problem follows Computer #1 (the one with the RX570 GPU).
So to recap:
- 2 Linux boxes with old amdgpu GPUs, 2 monitors. Each machine works fine when directly connected to 2 monitors.
- With the KVM switch, computer #2 shows no problems but computer #1 results in one of the monitors blinking out every 5-10 seconds. Log messages show TM starting and stopping.
Any ideas what might be going causing the connection to cycle repeatedly on Computer #1 when the KVM is in the signal path?