Are there any KVM switches that do Displayport well (i.e. where switching between inputs does not look like a display disconnect to the PC)?
I'm still using HDMI because I like to share my home multi-monitor setup between my personal machine and my work laptop, and the KVM switches are able to fool the PCs into thinking the monitor are always connected. Years ago I tried a Displayport switch, but it could not -- I assume because if the greater sophistication of the Displayport protocol.
The magic words you're looking for are "EDID emulation". The KVM will continue to send the EDID data from the monitor even after you've switched away, which will fix that issue.
It's relatively uncommon and not always implemented super well, but it's a requirement for any DP KVM to be not super annoying IMO.
There was one particular KVM brand that was supposed to do it well whose name is escaping me now :/. I was looking at buying one in ~ May 2020 for obvious reasons, but they were on super-backorder (also for obvious reasons), so I never got around to it. IIRC they were about $500 for a 4 input/2 output version, so not cheap.
I use one, so I can confirm they work extremely well, subject to some caveats:
* The total cable length is important, both between the host / KVM and the KVM / monitor, as well as any daisy chained displays you have. I had to use certified cables to get everything working reliably with my setup.
* There's a weird interaction with BIOS power on. The boot display drivers I have freak out if they aren't the active display and fail. I solve this by switching the KVM before I turn the computer on. After everything is booted into an OS, it works fine to switch.
* Power supply quality is important. I had some issues before I made sure the power supply was reliable.
KVM switches are just inherently difficult little devices. I haven't had issues since I got it working though.
>There's a weird interaction with BIOS power on. The boot display drivers I have freak out if they aren't the active display and fail. I solve this by switching the KVM before I turn the computer on. After everything is booted into an OS, it works fine to switch.
Do you have an AMD GPU by any chance? I have the level1tech 2-head DP 1.4 KVM, with an AMD RX 560 on a Linux host, and after updating to kernel 6.4 recently my computer now boots fine without a monitor attached.
I had a similar issue where a display had to be _on_ and _connected_ (i.e: active on the KVM) at boot time, or the GPU wouldn't work at all. I could get in via SSH, so I tried various amdgpu recovery options, poking the device to reset it, reloading the kernel modules, etc., and never had any luck. I just lived with the quirk. It was problematic because if you left home with the KVM selected on the Windows guest, and needed to reboot the Linux host remotely, you'd come home to a non-functional Linux desktop.
I have a similar issue with a Nvidia 1080Ti on my old desktop. It's related to the UEFI deciding if the iGPU or the Nvidia GPU should be primary and to disable the iGPU or if the iGPU should stay enabled.
Alternatively, you may have been thinking about ConnectPro. I ordered a kvm from them around the same timeframe and it was delayed quite a bit from backorder. (Though, they also did a major UI change, so might not be able to tell either).
Two thumbs down for connect pro. I ordered their top of the line 4 computer, 2 monitor DisplayPort KVM and it took months to arrive. I could not cycle between inputs using the buttons. They were more like a suggestion to use that signal path; I would constantly need to power cycle the kvm, monitors, or both.
I ended up ditching it on eBay at a significant loss for a $30 usb switch and just switch monitor inputs manually. Far cheaper solution and way less fussy.
I had the same issue with this device. I ended up writing some code that you could run on a machine to operate the switching via the RS232 port: https://github.com/timgws/kvm-switch/
Bonus for adding 'glide and switch' functionality, so you can move the mouse to the edge of the screen and it would jump the input to the next display in your layout. It's like a hardware version of Synergy.
Very finicky device, but if you don't touch it - and you don't use any of the shortcuts - it works.
Neat! I used to use ShareMouse (pay-ware, if you want more than two machines tied together) for this, because setting it up and keeping it working are so easy compared to whatever version of Synergy existed at the time.
Synergy made me manually configure my monitors by dragging little boxes around in a window, would frequently refuse to connect, would spontaneously disconnect, and repeatedly mangled my config such that I had to keep manually configuring it over again.
With ShareMouse, it was "open a copy of it on each machine, slide mouse in direction of next machine, then optionally enable encryption (to prevent other users' instances of ShareMouse from being able to attach)".
I should also add that their customer support was totally worthless. They promised me a firmware update, and stopped responding after I confirmed my firmware version - the process to get that value was already quite arcane, so ultimately I felt like they never really had any intention of helping and were simply stalling me out.
None of them are perfect, but I've heard good things about the DP switch from Level1techs. The thing is, all of them are a little tricky, but they mostly differ in how quirky they are, and I suspect the reason why people like the Level1techs DP switch is that they seem to at least try to alleviate some of the issues DP switches tend to get into.
The startech one I have is alright... But Apple computers absolutely hate it and frequently refuse to display, and sometimes Windows gets stuck and USB devices stop working. Strangely enough... Linux doesn't ever have any problems with either display or input. A rare win, but fine by me.
The Level1Techs KVM switches are rebranded Startech switches with 'dumber' firmwares whose dumbness affords better compatibility with niche DisplayPort features.
I have a bunch of them and I like them pretty well, but getting a bunch of computers all plugged in turns out to be a bit of a nightmare, especially when you need some long-ish cable runs or you are daisy-chaining devices (e.g., multiple KVM switches, adding USB hubs or Thunderbolt docks, etc.).
The Level1Techs KVM switches don't meet GP's criterion for hotplugging behavior, unfortunately. Switching between devices is just an unplug and replug for them.
Like you, I've found that macOS and Windows don't handle hotplugging monitors well, but Linux desktops (in my case, KDE Plasma) consistently do the right thing and don't require a repeater to lie to them about monitors always being plugged in.
FWIW, I don't get the 'Apple computers just refuse to work' issue with any of my L1T KVMs.
> The Level1Techs KVM switches are rebranded Startech switches with 'dumber' firmwares whose dumbness affords better compatibility with niche DisplayPort features.
Rextron [1] is the actual ODM. They don't do any direct to consumer sales, though. That's why L1 / Startech / other "brands" sell them on amazon and the like.
Last I spoke with the L1 guy, they were still having some issues with the high speed USB-C switching chips on the 1x4 "all USB-C" model that he's got a wait-list for.
> FWIW, I don't get the 'Apple computers just refuse to work' issue with any of my L1T KVMs.
My work intel macbook worked great on it for like a year once I got a high quality usb-c -> displayport cable, but an os update borked it... though it's definitely the mac that's the problem as it also has problems sometimes with just strait to the monitor too (on the other hand 49" ultrawide is pushing the bandwidth near it's limits).
My personal arm macbook has always worked great on it with even a crappy usb-c -> displayport
my windows desktop also always worked great on it.
> on the other hand 49" ultrawide is pushing the bandwidth near it's limits
One of the things I've learned too late is that using DisplayPort (and maybe HDMI, idk) anywhere near its bandwidth limits is not worth it for me. Having to think about cable run lengths as well as cable quality and peripheral quirks and internal Thunderbolt dock bandwidth allocation and so on and so on just fucking sucks.
It'll probably take until the next/latest (2.1) generation of DisplayPort propagates before using multiple monitors with specs similar to my current ones (high refresh rate and HDR, but not even HiDPI) isn't painful, cumbersome, and finicky.
I probably won't be able to use them by then anyway. Ugh.
I had much more serious problems with a StarTech DP KVM and Macs. My Macbook would hang and crash-reboot. Both on the initial plug-in and on switching inputs.
Everything else seemed to handle it fine with Linux being especially unphased, as usual.
I got their 10gbps displayport switch to use with switching a single monitor between a Windows desktop PC and an M1 MacBook Pro. I have a 4k@144hz monitor and can get the full framerate and resolution with this setup. I've never had any problems, would highly recommend.
It's gotten better in the last year or so with Windows 10 but it'll still sometimes just fall apart when the display configuration changes, which is something that just never happened for any reason with HDMI/DVI.
The new Dell 6K has kvm (and PiP) functionality across its inputs, and it does appear from my modest use of this feature so far, that it works as you would want (ie it still thinks the display is connected, even when not showing that input)
I would prefer that with 1 display but I have 2 Dell 6Ks
and it's kind of annoying if I want to have them each on a different PC. (I use a usb switch to switch my peripherals between displays)
Can you explain why this is beneficial? I have a mac laptop and pc desktop at home that i switch between depending on whatever I need to do. By triggering a disconnect, it means all my mac windows that are on the main monitor will zip back over to the laptop so they're still reachable if i need to access them with the trackpad and integrated keyboard. When I switch the kvm back to mac all those windows jump back to the main monitor.
Flaky drivers. KVM induced unresponsiveness is pretty much the only reason I ever have to hardboot my computers.
Also, even if the drivers are solid, they take longer to renegotiate with a monitor that was removed and plugged back in compared to one they think was always there, which matters if you switch back and forth frequently.
Lastly, sometimes the OS doesn't put things back they way they were when you plug a monitor back in. If you have a laptop which has a lower resolution display than the external monitor, you'll often return to find all the windows shrunk to fit the laptop display. Not an issue if you run everything full-screen, but annoying if you tile windows.
I had the startech one the siblings have mentioned but that wasn't very good and didn't do EDID emulation correctly. This CKL one [0] has been working really well, and supports USB 3 which is a nice bonus so I can share my webcam. Though sometimes after wake up my macbook forgets about my second monitor (I have an M1 connected to a cable matters thunderbolt dock), my windows machine which has direct DP connections doesn't have the same issue.
Never mind KVM switches, I wish powering off my DP monitor while leaving wall AC power plugged in didn't appear as a display disconnect to the computer.
I don't think I've had a KVM switch work well since VGA+PS/2
They all try to be too smart.
As a matter of fact, I usually use a monitor switch of some sort, then use mechanical USB switches - one for keyboard, one for mouse. That seems to be the only way to get mouse and keyboard to work well (basically just a hardware connection, no smarts)
I'm still using HDMI because I like to share my home multi-monitor setup between my personal machine and my work laptop, and the KVM switches are able to fool the PCs into thinking the monitor are always connected. Years ago I tried a Displayport switch, but it could not -- I assume because if the greater sophistication of the Displayport protocol.