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Shapeshifter

Member

Registered: 2008-03-11

Posts: 230

[Solved] Display via USB-C/DisplayPort only works if connected at boot

Hi.

I'm connecting an LG 34UC87-B display to a Dell XPS 7390 2-in-1 via a very short USB-C to DisplayPort cable.

If I do a cold boot with the display already connected, it works perfectly in both framebuffer and X (full resolution and framerate). It's recognized as connected to DP-1 and I can also enable, disable and control it via xrandr:

DP-1 connected 3440x1440+3840+0 (normal left inverted right x axis y axis) 800mm x 335mm
   3440x1440     59.97*+  49.99    29.99
 (...)

In all other instances, it doesn't work at all. Not even in Windows.

If I boot and then plug in the display, I get these messages in dmesg:

[ 6593.621822] usb usb2-port1: Cannot enable. Maybe the USB cable is bad?
[ 6597.681753] usb usb2-port1: Cannot enable. Maybe the USB cable is bad?
[ 6597.681815] usb usb2-port1: attempt power cycle
[ 6602.055111] usb usb2-port1: Cannot enable. Maybe the USB cable is bad?
[ 6606.114729] usb usb2-port1: Cannot enable. Maybe the USB cable is bad?
[ 6606.114793] usb usb2-port1: unable to enumerate USB device

If I booted with the monitor connected and then disconnect/reconnect it, there are no messages in dmesg at all. However, in xrandr, it then shows up as DP-4:

DP-4 disconnected (normal left inverted right x axis y axis)
  3440x1440 (0xb4) 319.750MHz +HSync -VSync
        h: width  3440 start 3488 end 3520 total 3600 skew    0 clock  88.82KHz
        v: height 1440 start 1443 end 1453 total 1481           clock  59.97Hz

But I can't enable it or do anything with it.

The laptop firmware and everything should be up to date (done via the Dell tool in Windows). The BIOS is also up to date.

I tested the cable on a different laptop/screen combo and it worked fine.

I'm stumped. Because it works perfectly in one particular condition, and not at all otherwise...

I'm assuming a firmware bug that can only be fixed by Dell. Any ideas?

Last edited by Shapeshifter (2020-01-24 16:57:28)

bigicecream

Member

Registered: 2020-01-23

Posts: 3

Re: [Solved] Display via USB-C/DisplayPort only works if connected at boot

I face the same problem

Shapeshifter

Member

Registered: 2008-03-11

Posts: 230

Re: [Solved] Display via USB-C/DisplayPort only works if connected at boot

I got another cable and it works perfectly fine.

FYI:
The bad cable (which worked with a different laptop and screen but not mine) is a "Value" cheap brand, model 11.99.5845
The good cable is a Club 3D, model CAC-1517

Guess it makes a difference...

Last edited by Shapeshifter (2020-01-24 16:58:04)

fasseg

Member

Registered: 2020-02-05

Posts: 1

Re: [Solved] Display via USB-C/DisplayPort only works if connected at boot

I found that with the cheap cable I am using hot plugging works when I replug the cable at the display end instead of the usb-c end.

Last edited by fasseg (2020-02-05 14:36:51)