DDC Input Source Control implementation on latest LG displays

[DervexDev]

This question might be a bit off topic, but do you mind sharing how you managed to make DDC Input Source Control work on the latest LG displays?

I recently bought an LG UltraGear 34GS95QE-B display, and it seems to use alternative DDC values. I'm writing my own tool in Rust to extend the functionality of my KVM, and I'm unable to change the input source to DisplayPort1. Setting VCP feature 0x60 to 0xD0 (208) doesn't work. I tested all 0-255 values, and only 0x1 and 0x2 made the screen black for half a second, but nothing more.

But this configuration somehow works perfectly fine in BetterDisplay Pro:

I was also thinking of using the CLI integration, but I need this to run on Windows as well.

[waydabber]

Sure, m1ddc has this feature as well, here is the source code (note: it's using Objective-C, not Swift):

https://github.com/waydabber/m1ddc

[DervexDev]

Hey, I've already checked this tool out and unfortunately, it doesn't work for me. Here is what I did:

m1ddc display list

# Output:
# [1] LG ULTRAGEAR+ (F0DB7A7E-6804-4F3B-8687-200C7CBCE0C8)
# [2] LC27G5xT (48D766BF-A3F7-4D70-9574-6347F69C9DE1)

m1ddc display F0DB7A7E-6804-4F3B-8687-200C7CBCE0C8 set input-alt 208

# Output:
# 208

And nothing happens. Am I doing something wrong? The LG display is connected using the built-in HDMI port but that shouldn't be the issue as I have an M2 Pro chip and it works in BetterDisplay Pro anyway. Also other m1ddc commands like set volume work just fine.

[waydabber]

Hmm. Honestly, I am not sure (I don't have an LG display that needs input-alt at hand to test) - the command seems fine.

Anyway, the simply difference is that for input select some LG displays expect the command to be sent with data address 0x50 instead of 0x51. All else is the same. :)

[DervexDev]

Hey, I located the issue and here is the PR that fixes it: waydabber/m1ddc#52

[waydabber]

Nice @DervexDev - thank you!