USB C DP Alt Mode external monitor

Question

I just bought a new dell XPS 13 for work and everything is working smoothly except the external monitor and it's pretty annoying to be tied to the small 13 inch display

I bought an usb C to HDMI cable with thunderbolt 3 support, tested it with my phone and it works on my hdmi screen

but when I plug my laptop I have no signal message

when I run lspci -tv with the display plugged, I got :

+-1c.4-[03-6d]----00.0-[04-6d]--+-00.0-[05]-- | +-01.0-[06-38]-- | +-02.0-[39]----00.0 Intel Corporation JHL6540 Thunderbolt 3 USB Controller (C step) [Alpine Ridge 4C 2016] | -04.0-[3a-6d]--

when I run xrandr -q I have

Screen 0: minimum 320 x 200, current 3840 x 2160, maximum 8192 x 8192 eDP-1 connected primary 3840x2160+0+0 (normal left inverted right x axis y axis) 294mm x 165mm

DP-1 disconnected (normal left inverted right x axis y axis)

DP-2 disconnected (normal left inverted right x axis y axis)

any clue on how to get external display working ?

Answer 1

From your Amazon link in the comments, you appear to have a DP Alt Mode cable, which essentially uses USB C Port for DisplayPort protocol output, which would make use of your regular video card. I believe (but am not positive) that on a Dell XPS 13, that should be an Intel driver. It should, at any rate, show up as one of your DP*-devices, but is not.

Based on that, you might see if this answer from AskUbuntu is helpful. Another debugging steps you could take care:

• See whether it works in Windows; if it doesn't, it's perhaps not supported at all.
• Try booting up with the DisplayPort already connected, to see if it's a life detection issue.

You could also try using a DisplayLink cable, which would have different drivers. In general when you Google this, if I were you, I'd search for Ubuntu (on which Elementary is based) and "DP Alt Mode", which is what your cable uses.