Dual Monitor not booting with Kernel 6.8?

[2Fast4]

Hi all,
I've upgraded to Kubuntu 24.04. With the initial 6.5 (?) Kernel I had no problems but after upgrading to the 6.8 series the computer no longer reaches the login screen if both monitors are on.

1. Both Monitors on: I see the Grub boot menu, after selecting to boot Kubuntu 6.8.* I only get black screens. Switching one or both Monitors off/on again will not change the situation.
2. Only on Monitor switched on: Kubuntu boots normaly, I get to the login screen. If I switch the second Monitor on now it stays black. If I login the second Monitor works normaly (Desktop gets extended). The second Monitor also works as intended if I switch it on after login.

I think it has to do with the Kernel (?) update to 6.8. In the first update to 6.8 I could still select the 6.5 in the extended boot options in the GRUB menu and this worked as expected (both Monitors show the login screen after booting).

I've the following HW setup:

-AMD Radeon RX 5700 XT
-Two Displayport cables
-Aten KVM Switch
-Two Displayport cables
-Monitors 1&2

I've not installed any dedicated drivers for the graphics card. I have a workaround so it's maybe not a critical problem, but still annoying. I've used the above setup for ~ 2 years previously without this issue.

[claydoh]

The 6.5 kernel is from the previous release.

I've not installed any dedicated drivers for the graphics card.

You won't need any, the open driver/mesa is the best choice.

How does it work without the KVM switch, if that isn't too much of a pita?
Which specific model?
Did you need any driver or configuration for the switch at all?

[2Fast4]

You won't need any, the open driver/mesa is the best choice.

It was also my understanding that no driver is needed. Good to hear that this is at least not wrong :-)

How does it work without the KVM switch, if that isn't too much of a pita?
Which specific model?
Did you need any driver or configuration for the switch at all?

The KVM switch is an ATEN CS1942DP. No driver needed and no configuration. I assume the Computer is not even really aware it's not connected directly to the monitors (maybe outside of some displayport protocol things, which are probably handled on the hardware level?).

But I'll try cutting out of the loop and report back later.