Display Sometimes Missing Resolution/Refresh/Bitrate Options

[proactivematter]

Hello,

I have an Asus Zenscreen MB16QHG (Portable Monitor) which runs native 2560x1600 @ 120hz 10Bits. However, sometimes it behaves weirdly when the system wakes up, showing as being capable of many fewer resolutions at lower refresh rates and lower bit depths. Not even the native settings remain available in this circumstance - which is unfortunately how the system sees it 90% of the time.

In an attempt to diagnose what is happening, I used BDT to export the EDID data at a time when the monitor was running correctly and also when it was running incorrectly. However the Base64 is the same in both cases and the exported .bin files also only differ in terms of the current resolution / mode. Everything else appears to be the same.

Now, I do have something unique going on with my setup. The chain looks like the following:

Macbook Pro 16 M1 Max
Rextron DisplayPort 1.4 KVM (PAAG-ET3124B)
Rextron DisplayPort 1.2 to USB-C DP-Alt Converter (VCPUC-60)
Asus Zenscreen (MB16QHG)

Since the Asus Display only has USB-C DP Alt Ports, "DP 1.2 to USB-C DP-Alt Converter" adds power to the Full Sized DP signal coming from the KVM to make it compatible.

I would like to note that I also have a Windows 11 Machine connected to this KVM and that the Asus never behaves oddly / missing options on that system. This is a Mac-exclusive issue.

For what it's worth, the DP-Alt converter is advertised as being fully compatible with all displays as well as both Mac and Windows systems. I have reached out to the manufacturer and am waiting to hear back, but I thought I'd ask here because waydabber is a display wizard and might have some insight as to why this is happening and why the EDIDs are the same.

Happy to provide any additional files / details - let me know.

Thanks.

[waydabber]

Do you have this issue when the KVM is not in the mix? If it's a wake issue, you can try using the "Reinitialize on wake" feature which tries to reconnect the display after a wake - this might help with the setup. Alternatively only looking at the kernel logs might help you figure out what is going on and how things are negotiated.

[proactivematter]

I feel like kernel logs would offer the most insight here. Do you have any guidance as in where to access those? Is it through the "Console" app?

In regards to investigating the chain, I would also like to understand whether the issue originates from the USB-C to DP Converter or the KVM, but since this only happens on my Macbook, I would need to convert the full sized DP Port BACK to USB-C in order to be able to remove the KVM from the chain. I'm considering purchasing an adapter for this purpose, but again I'm more inclined to check the Kernel logs for now. If I remove both the converter and the KVM from the chain (straight USB-C to USB-C connection) then the issue does not happen, of course.

Thank you so much for your help.

[proactivematter]

So I checked some of the logs. I'm not sure what keywords to use or what to look out for, but I see clearly that Link Training is falling to HBR1 sometimes... not sure if there's other information that may point as to why.