Question KVM woes: mixing HDMI and DisplayPort

[SAmalathion]

Problem: DP-only KVM switch connection uncertainty with multiple displays and computers that don't all support DP.

There are two displays:

* Primary: Acer Predator X25 bmiiprzx 24.5". 1080p native up to 360hz. DisplayPort 1.4 // 2xHDMI 2.0
* Secondary: Some generic old LG 24.5". 1080p native up to 60hz. HDMI // also has VGA support (lul).

There are two computers:

* My personal machine with 1xHDMI 2.1 // 3x DisplayPort 1.4 -- used for gaming, so this is the one I want to make sure I get max performance on.
* A macbook with an HDMI port on it but no DisplayPort. Used for work only. It would be nice to have high refresh rate here but not critical.

The goal: Connect both displays to both computers using a KVM switch. Without thinking this all the way through, I got this one: https://www.amazon.com/gp/product/B0C2TDC5LQ

So, this KVM switch I got supports DisplayPort. That's good, since I believe I need DisplayPort to get max refresh rate at native res on the primary monitor. But now I'm realizing I have a bit of a clusterfuck situation with the different interfaces.

Is it feasible to use adapters or something in this situation? Or am I just screwed without a KVM switch that supports both? (If yes, is there such a thing?)

 

[VirtualLarry]

Or am I just screwed without a KVM switch that supports both?

You are screwed. Measure twice before cutting.

 

[SAmalathion]

Really? I see HDMI<->DisplayPort adapters and cables. Wouldn't that be viable?

 

[VirtualLarry]

No, you see displayport output to HDMI display. Those cables are not bi-directional.

 

[VirtualLarry]

You'll have to look for an "active" HDMI output to Displayport display converter for your macbook, and pray that the whole contraption works together properly.

 

[SAmalathion]

I appreciate you taking the time to explain this. Just to make sure I follow, is this what you're suggesting?

 

[VirtualLarry]

yeah, that's what I'm suggesting

Edit: My bad, I was assuming it was a 2x2 matrix switch. If this is a more traditional uni-display KVM, then no, what you want isn't possible.
Sorry.

 

[Brainonska511]

How old is this Macbook? Does it only have 1x HDMI? Can it output via another method as well?

One option, that might be a bit more involved when you want to switch (ie, needing to press 2 buttons), but may be operationally easier to implement (this also assumes the Macbook can support 2 external displays):
1) Get a USB switch for your peripherals (keyboard/mouse) (costs ~$20)
2) Hook the Acer up to the desktop with DP and HDMI to the MacBook
3) Hook the LG up to a cheap HDMI switch, connect HDMI switch to each of the computers (I've used this to "add" an HDMI port to a TV)
>>Ditch step 3 if the Macbook can't support 2 external monitors (and just hook the LG directly up to the desktop with the HDMI)

 

[SAmalathion]

Alright, I got a HDMI->DP adapter and a DP->HDMI cable and hooked everything up like in the diagram.

Bizarrely (to me), everything works except that the secondary monitor is not detected by either machine. Switching between machines works fine, the primary display works fine, but the secondary display doesn't get any signal and doesn't show up in display options / xrandr. What might I be doing wrong there? Is it possible I somehow got the "wrong" DP->HDMI cable? https://www.amazon.com/dp/B07ZQ7K6S1

 

[SAmalathion]

Is it unrealistic to expect this to work with mixed refresh rates off one output cable from each machine?

 

[Velgen]

I am not aware of any KVMs that support multiple displays over a single cable. Does the Macbook not support Displayport over USB-C?

KVMs can be rather picky about cables in theory that cable SHOULD work, but maybe it needs an active adapter like this one https://www.amazon.com/dp/B077JB28KM?th=1

 

[Red Squirrel]

For KVMs I really try to stick with native connections as much as I can as introducing adapters just adds variables to the mix to cause problems. At home I have 2 KVMs, They are TESmart HDMI. So I made sure that my entire cabling is HDMI for both PCs. Finding a GPU with 2 HDMI ports was weirdly hard though... seems everything is DP now. Suppose if I was to do it over I would get the DP version of the KVM and do DP for everything. DP has a much shorter max cable length though... I think that's why I ended up going HDMI. My8 PCs are in the server room and I have 25 foot cables coming to the office.

For my work machine though, everything is DP, so I use DP to HDMI adapters going to the KVMs. That took a bit of trial and error to get going, some adapters would just refuse to work, or flicker, or do weird crap. Also need to watch out, as some adapters don't support 4k.

But yes be aware of the signal direction when using adapters as most of them are active, as in, they have actual circuitry inside that does conversion, so they are directional.

Oh, and for me I actually had to set both refresh rates to 50hz, for some reason 60hz causes the 2nd monitor to flicker. If I use different rates, when I drag a window across both monitors it looks really weird. So I try to stick to same rate across the board.