L1KVM DP 1.4 Not Working With Hackintosh

I’ve got a niche-of-all-niches problem with the Level1Techs KVM.

The Problem: Display Port Works WIthout KVM, Does Not Work With

  • Using Level1Techs DP cables throughout
  • Hackintosh specs: Vanilla guide created Opencore bootloader Hackintosh. Running a Coffee Lake 10400 CPU with proper framebuffer patching

What Happens With KVM

  • The monitor is still detected
  • There is very, very bad flickering (more black than screen)

KVM Works with Linux

The same setup works fine under Linux (Fedora), so I suspect it is some unholy combination of a Hackintosh + the KVM that is causing this issue - exactly the sort of ultra-niche edge-case I was hoping to get help with on the L1 forums.

Any ideas on why this might be the case? Do I need to get a DP repeater to boost the signal strength? I don’t have cables that are any shorter than the Level1Techs cables.

It could be DPCP or HDCP is being interrupted. Apple always assumes a device is HDCP compliant unless it’s told otherwise. You may need to find a way to tell the OS that it’s not HDCP/DPCP compliant.

Thanks for the tip. Do you have any idea how I could begin to do that?

You may have to use native HDMI if it’s going to be picky about HDCP. In my experience, this happens with Active DP adapters converting to HDMI because of either a lack of amperage or bad HDCP sync.

Hmm… I’m actually using display port. iGPU DP port -> KVM -> monitor. I’m really hoping that I’ll be able to use the KVM (since it works so well under Linux), but if it’s irresolvable (or not easily resolved), then that’s kind of a deal breaker for me

The level1techs repeater will very very likely fix this for you.

The iGPU has a drive strength driver option that apple, in infinite wisdom, sets to low power mode always. If you can find it, you can change it. AMDGPUs have a gui option for it in windows, but I’m not sure what the hack/mac equivalent is.

This is very low signal-to-noise ratio, which is probably because Apple’s iGPU driver has configured the DP port for low-power mode, like as if it is an embedded display (embedded display port).

The KVM is pretty stupid, tbh. It doesn’t have a repeater and doesn’t mess with the signal other than the signal loss you get through a couple of connectors and the extra cable length. Because there is no built-in repeater whats happening is PC -> cable + connector + connector + cable -> display vs PC -> Cable -> Display … quite a few more opportunities for SnR loss. High quality Dp1.4 cables, that are short, if you can get non-fake ones, will probably also help but some people don’t have good luck finding cables and frustrate easily.

But mostly it’s not really a KVM thing, just KVM exposes undesirable things. Likely a 12 foot DP cable would behave the same way sans KVM since that’s a closer equivalent than just one cable between hackintosh iGPU and display.

hey, wait a sec? The L1 cables are only DP1.2… this is with the DP1.4 KVM? You probably would be okay with shorter DP1.4 cables, the SnR on the 1.4KVM is much much tighter than the 1.2KVM.

Huh, this could explain why a Active DP to HDMI was failing on a MacBook Air I had access to. I wonder if the fix you mentioned will get a Club3D DP 1.2 to HDMI 2.0b active converter working with a MacBook Air 2015 to output 4K 60p.

Yes I realize your repeater has a HDMI output, this is for science.

I got some of those, and the answer was no, macs are weird, and stingy with power. L1 adapter is externally powered specifically because of this hair-graying maddening nonsense.

I meant using the repeater, not changing the power setting for the DP port in OSX.

@wendell Sorry to resurrect this, and I want to correct an error: This was with the Display Port 1.2KVM (specifically the 4 port model).

I had mostly given up on this because as you say, Apple is weird. But I had recently replaced my Viotek Monitor with a LG 83A monitor (great IPS panel, nicer colours compared to VA). Whereas previously only the hack using an iGPU was experiencing problems, now even the one using and AMD GPU was experiencing trouble also.

I caved and bought one of the L1T DP Repeaters and tried using it. It works (as in, display is now showing), but now I have a new problem. I’m not sure what sort of unholy combination of niche cases I’m using to stress the repeater in such a way, but I’m getting ghosting - on both macOS and Linux (RHEL)

At first I thought it was just plain flickering (at around once a second), but after I saw the RHEL logo showing through on my macOS desktop, I thought I would have no choice but to come here begging for help.

For future me (and anyone else looking), the solution to this was to disable DP 1.4 in the options of the LG 83A monitor, which allowed the use of the monitor on multiple GPU’s (Intel iGPU, RX 570) without the need for a repeater. The repeater is still good stuff though!

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