In this setup, the other device connected to the KVM works well with HDMI + Usb-B connection. Video signal, mouse and keyboard are ok. But on the other side, I have an Thinkpad T470S with Linux 5.16 and it's dock.

Fist, I tried with usb-c(T470s) to usb-c(monitor) connection, xrandr couldn't detect the interface.

With Displayport from dock, video signal works but usb-c for inputs don't.(I configured the KVM).

Then I bought and tried with an adapter DisplayPort(dock) to usb-c(monitor DP Alt Mode), the result was the same as in the previous case.

Y tried to activate typec_displayport kernel module unsuccessfully.

Any idea how I can make it work? Thanks.

1 Answer 1


This is a USB-C dock that you are using, correct? Have you tried connecting the laptop to the display by a full featured (as in rated for at least 5 Gbps USB data, and/or rated for Thunderbolt) USB-C to USB-C cable directly to the laptop, as opposed to with the dock in the chain? Every USB-C dock I've seen will not support DP alt-mode on any downstream ports. Possible exceptions would be a Thunderbolt dock, and without knowing the dock feature set or model we can't tell if the dock is compatible with the KVM in the display.

It appears to me the KVM in the display is not working as intended because the dock is splitting out the USB-C from the laptop into the video, USB, and power portions. This is what docks are intended to do. A display with a USB-C port is intended to avoid the need for a separate dock, the display is supposed to be your dock.

A DisplayPort to USB-C cable is only going to carry video, so connecting a display with such a cable will not provide a connection for any USB ports in the display back to the computer.

I've seen displays with a built-in KVM before and they need to be connected directly to the computer by a full featured USB-C cable to provide video, USB data, and power to a laptop. Not all displays with a USB-C connection will provide power to a laptop but this is not unusual either.

I believe you need to choose between using the dock or using the KVM built-in to the display. Both the dock and the display require a USB-C connection with DP alt-mode to work. Both the dock and the display will break out the USB signals from the USB-C port to allow plugging in USB-A devices. There are newly released Thunderbolt/USB-C docks that should work as a USB-C dock (even if the host computer does not support Thunderbolt on USB-C), supporting a DP alt-mode USB-C display and USB-C devices, but that's not a guarantee.

If you are not using a USB-C dock, but something that uses a proprietary dock port, then you need to look in the specifications on the dock on if it supports DP alt-mode on USB-C. Just because the laptop USB-C port supports DP alt-mode does not mean the dock USB-C ports will.

  • The dock doesn't have USB-C port, is the propietary for T470s. I think using the dock in the equation adds a lot of headaches. As the PC supports USB-C for external monitor, this will be my best option. I tried with this, but isn't a full-featured cable (only 480 Mbit/s). I'll try an appropriate one. Thanks for the answer!
    – dlag
    Commented Feb 26, 2022 at 22:08
  • To get video on USB-C you need a cable rated for USB 3.x, USB4, Thunderbolt, or explicitly DP alt-mode. Maybe the display KVM will allow pairing the USB-C with another video port, as opposed to only video on USB-C. That way you could use the cable you have much like the USB-B port on the other computer for USB only and a different port for video. This assumes a lot on the features of the display.
    – MacGuffin
    Commented Mar 2, 2022 at 18:57

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