USB-C to HDMI communication failure about ddcutil HOT 4 OPEN

First, thank you for opening a new issue instead of re-using an old one. Issues frequently get cluttered with what are actually quite different problems/requests etc.

Second, I have to say that I don't have direct experience using a Type-C connector, and looking at documentation online suggests there's a lot of variability in capabilities and implementation. So take what I say here with a grain of salt.

From your output, I see that the video driver is using its DisplayPort interface - that is, it thinks it's communicating with a DisplayPort device. It is not using DP Dual mode, So the DisplayPort -> HDMI conversion is happening in the adapter. Given how inexpensive your adapter is, I would not be surprised to find that it doesn't fully convert the I2C signal between the DP Aux channel and the physical pins used in HDMI.

I see that your monitor has a DP input. I'd try using a Type-C <-> Displayport cable, since that entails no protocol conversion.

from ddcutil.

I see that your monitor has a DP input. I'd try using a Type-C <-> Displayport cable, since that entails no protocol conversion.

Thank you for the response. I got myself a Type-C <-> DP cable, it works!

I also bought a Type-C <-> HDMI cable, to see if that little adapter was part of the problem. But the issue persists unfortunately.

My goal is to have DDC control from both of my PCs to the same screen. (I'm trying to integrate ddcutil on my project, and this would be useful for testing purposes.) With my laptop occupying the single DP port on the monitor, my desktop has to use HDMI, which is fine.

My problem now is that I need to plug a second monitor, which has HDMI ports only, to my desktop. But my desktop GPU has only 1 HDMI input, now used by the first monitor. So, I have to buy a DP <-> HDMI cable if I want to plug the second monitor as well (and keep the laptop connected to my first monitor via DP).

• Now, would ddcutil would work with a DP <-> HDMI conversion?
• It would be ideal in this case if I could use the Type-C <-> HDMI cable on my laptop. Am I out of luck with this issue? Or could this work with a better cable?

For reference, these are the cables I got: HDMI, DP

from ddcutil.

Re the Type-C <-> HDMI cable for the laptop, it would have to include an active, not passive, adapter that properly handles the I2C signals. This might do: https://www.amazon.com/Accell-USB-C-HDMI-Adapter-Thunderbolt/dp/B01K9S0VYM?th=1

As for the desktop, the connection issues are much simpler. First, you could use a DVI <-> HDMI cable. From our perspective, it's just a straight through connection, no signal/protocol conversion needed.

Alternatively, given how recent it is, the 1660ti almost certainly supports Display Port Dual Mode, aka DP++. In that case the card recognizes that it's Displayport connector is actually talking to a HDMI connection on the monitor, and reconfigures itself to treat the DP connector as just a just a physically different kind of HDMI output. In that case any DP<->HDMI cable will do. If it doesn't, then an active DP<->HDMI is needed.

See: DDC Over DisplayPort. I also found this reddit post informative, though the comment stating that the active/passive distinction is irrelevant is misleading. I'm using active/passive in the sense described in the DisplayPort Interoperability Guide. Though it may be the case that some cables/converters marketed as "active" in fact. for our purposes, just passive with some powered electronic circuitry.

Bear in mind that the proprietary Nvidia driver is problematic in its DDC implementation. See Special Nvidia Driver Settings.

from ddcutil.

Thank you for the exhaustive response. The topic of monitor cables is a vast and interesting one it seems.
I think I'll just go for the DP <-> HDMI cable. Might be handy to have around in any case.

from ddcutil.