Troubleshoot USB-C Librem 14

I got a BenQ EW2780U 27" 4K monitor. I also got a Cygnett USB-C 3.1 cable. Using a HDMI cable, the screen and audio is automatically working.

The monitor says it supports USB-C Power Delivery 60W, DisplayPort Alt Mode and Data, but plugging it into my Librem 14 (PureOS and PureBoot v18) nothing works. Neither the monitor or laptop detects anything, no power or screen. I don’t have any other USB-C devices to test.

How do I go about checking if the laptop is seeing anything?

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Are you using the correct USB-C port? Only one of the USB-C ports does altmode (video).

Use lsusb -v (before and after connecting something to the USB-C port) to see whether the laptop is seeing anything.

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I’m also trying to use USB-C for video. I see nothing in display manager, and I’m assuming I have the correct port in use of the two available. Bus 2 seems like the right one to be on (Device 7 is the display port adapter I wish to use

klaus@librem14:~$ sudo lsusb
Bus 002 Device 003: ID 05e3:0749 Genesys Logic, Inc. SD Card Reader and Writer
Bus 002 Device 007: ID 17e9:600c DisplayLink Plugable USBC-6950UE
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 003: ID 316d:4c4b Purism, SPC Librem Key
Bus 001 Device 010: ID 24f0:0140 Metadot Das Keyboard 4
Bus 001 Device 009: ID 046d:c24a Logitech, Inc. G600 Gaming Mouse
Bus 001 Device 008: ID 10d5:1234 Uni Class Technology Co., Ltd
Bus 001 Device 007: ID 05e3:0608 Genesys Logic, Inc. Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Let me know what you think, thanks!

I would put that to the test.

If this doesn’t work out-of-the-box, you probably are going to need output from lsusb -v but you may be better off also specifying -s in order to limit the amount of output i.e. lsusb -v -s2:7 but before that I would also look in the system log / journal to see what messages are appearing when you connect the dock and/or also the monitor.

The internet doesn’t seem to think much of the combination of Linux and DisplayLink. (You could ask DisplayLink what the current state of play would be expected to be with Linux. I note that Amazon simply says, for that product, “Linux not supported”.) You haven’t explicitly said what distro you are using.

If it were me, I would be trying a simple USB-C DP video altmode to HDMI adapter (assuming your monitor has an HDMI input). If that works then you might get more adventurous and try a dock.

PS I just saw your other topic. If you literally have two external monitors and neither has HDMI support at all (i.e. only DP) then

“trying a simple USB-C DP video altmode to HDMI adapter (assuming your monitor has an HDMI input)”

needs to read

“trying a simple USB-C DP video altmode to DP adapter”. (and then you would need to find an HDMI to DP adapter for the other monitor.)

I think this is your problem here. I don’t believe DisplayLink is supported, at least without some sort of special driver. I tried on mine with a simpe USB-C to DP cable and it worked correctly. You may need some special drivers such as https://www.displaylink.com/downloads/file?d=68

Good luck!

That was the idea I needed! The device is validated as working, when installing the manufactures Ubuntu based drivers. My OS is Puros 10 beta, on the L14 laptop. I am driving dual DP monitors on the USB-C port, and also have support for the ethernet device on the DisplayLink hardware as well. All vetted and attested to as passing :wink:

Thanks for the idea, much appreciated.

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When I’m running sudo lsusb, I’m getting the following output.

preetham@priyatham:~$ sudo lsusb
Bus 002 Device 002: ID 05e3:0749 Genesys Logic, Inc. SD Card Reader and Writer
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 007: ID 0bda:5450 Realtek Semiconductor Corp. BillBoard Device
Bus 001 Device 005: ID 046d:c534 Logitech, Inc. Unifying Receiver
Bus 001 Device 006: ID 04ca:300d Lite-On Technology Corp. Atheros AR3012 Bluetooth
Bus 001 Device 003: ID 0bda:5830 Realtek Semiconductor Corp. USB2.0 camera
Bus 001 Device 002: ID 046d:c534 Logitech, Inc. Unifying Receiver
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

The output:
Bus 001 Device 007: ID 0bda:5450 Realtek Semiconductor Corp. BillBoard Device represents the type-C cable that I connected. Nothing is showing up saying “No signal detected” on my newly bought BENQ EW3270U 4K 32 inch monitor. I used the type-C to type-C cable which was given in the monitor package. I used it on Macbook air and it’s working. Is the type-C cable output for display working in Ibrem 14?

Only the right side (next to power plug) USB-C port supports USB PD and DP Alt over USB. DP alt mode has been bit iffy and even if you happen to have 2 certified devices it is possible those wont work together for unknown reasons.

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I did connect earlier to this port also but din worked. But now yesss it worked for me when connected to the USB-C near to power plug :grinning:. I used the same USB-C to USB-C cable provided within the monitor package. Whereas, I observed a behavior that the librem 14 laptop switches off as soon as I connect the USB-C to the DP. As I switched on it started working. Can you explain that if you figured out why is it happening. And, thank you so much for your reply which solved my issue :blush:.

Great that it worked for you. My cable must be the problem as nothing is being registered on either end. Now I need to buy one online as it seems no stores have fully compliant cables.

There is, apparently, such a thing as “wrong orientation” when using USB-C cables. It would be worth it to try turning them over and/or switching ends (if both ends are USB-C).

It din work at first go to me also. Try multiple times by removing and inserting at the time laptop is ON and OFF and switch ON by keeping the cable plugged in. If still not working, try @Gavaudan solution switching the ends again with all variations. If not, then you can buy a new USB-C to USB-C. Also, beware in choosing the cable’s refresh rate as 60 Hz otherwise you’ll experience a lag in video. I found the cable which provided in monitor package has the 60 Hz rate capability.