Is there support for USB C DP alt mode via Thunderbolt?
from cralder@lemmy.world to linux@lemmy.ml on 13 Jan 17:58
https://lemmy.world/post/24236377

Does Linux support this? I am trying to connect my laptop to a monitor via USB C. The laptop has two Thunderbolt ports and the monitor has support for USB C DP alt mode. I have tested the same setup on my work laptop (windows 11) and it works fine but my laptop running arch does not work. My laptop detects the monitor correctly so it shows up in the KDE plasma display configuration but the monitor is not getting any input. As far as I could tell this is supported in the kernel. Am I wrong? Am I missing some important package?

#linux

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Kidplayer_666@lemm.ee on 13 Jan 18:05 next collapse

What’s the model, just for starters

cralder@lemmy.world on 13 Jan 18:22 collapse

Right sorry forgot to mention that. The laptop is an Asus Vivobook S14 K3402Z (not the OLED one in case that matters). The monitor is a Philips Evnia 49M2C8900

Veraxis@lemmy.world on 13 Jan 18:14 next collapse

Do you have the bolt and plasma-thunderbolt packages installed? I believe I had to do that to use a thunderbolt SSD enclosure/docks with my laptop. I am not sure about DP alt mode, though.

cralder@lemmy.world on 13 Jan 18:23 collapse

Yes those are both installed

lime@feddit.nu on 13 Jan 18:30 next collapse

do you have evdi installed? and if not, does it work when you reboot with the cable connected?

wiki.archlinux.org/title/DisplayLink

cralder@lemmy.world on 13 Jan 18:48 collapse

No I don’t have that installed. Isn’t DisplayLink something completely different?

Rebooting while connected sorta worked, but not really. When I logged in the laptop monitor went black and the external monitor was black with a white underscore at the top left as if a terminal was open. So that’s something I guess but I could not use my computer at all in this state.

lime@feddit.nu on 13 Jan 19:00 next collapse

yeah displaylink is sort of a streaming feature, but evdi is a kernel module that makes the kernel aware of multiple monitors over usb (among other things), it’s required for display plug-n-play over usb in my experience.

progandy@feddit.org on 14 Jan 17:06 collapse

It is not required for the displayport alternate mode of usb-c.

It is an alternative with limited performance that is built on top of usb and does not require hardware support on the PC side.

lime@feddit.nu on 14 Jan 18:26 collapse

good to know, i’ve never managed to get it working without. what’s the recommended approach then?

progandy@feddit.org on 15 Jan 07:52 collapse

If your monitor/docking station/adapter and the computer support the DP Alternate mode, then you should use that, it should be supported directly by the kernel. Problems may occur if the port is connected to the dedicated graphics and you use the internal graphics card. In my experience it worked perfectly so I do not know any good troubleshooting steps.

lime@feddit.nu on 15 Jan 08:36 collapse

then, maybe it was added to the kernel after i first tried it and i’ve been working with old assumptions.

lime@feddit.nu on 13 Jan 19:04 collapse

also that behavior is interesting because it means the display is detected and the computer is drawing to it but something in your environment is unstable. check the system log for previous boot to see what screwed up.

BritishJ@lemmy.world on 13 Jan 22:25 next collapse

Works fine. I use it on my XPS 13 daily with Fedora 41

Zamundaaa@discuss.tchncs.de on 13 Jan 22:53 next collapse

My laptop detects the monitor correctly so it shows up in the KDE plasma display configuration but the monitor is not getting any input.

So the system thinks it’s enabled? Can you move the mouse cursor to it?

cralder@lemmy.world on 14 Jan 05:10 collapse

Exactly. No I can’t move my mouse to the external monitor.

Zamundaaa@discuss.tchncs.de on 20 Jan 00:05 collapse

No I can’t move my mouse to the external monitor.

Do you mean that it stays on the internal display, or that it doesn’t show up on the external one?

Or to ask it differently, can you move a window where the monitor should be?

cralder@lemmy.world on 20 Jan 04:50 collapse

The mouse stays on the internal display.

Zamundaaa@discuss.tchncs.de on 20 Jan 17:01 collapse

Okay, then the driver doesn’t allow Plasma to turn it on for some reason. You can report that at gitlab.freedesktop.org/drm/i915/kernel/-/issues, maybe someone from Intel can help.

mvirts@lemmy.world on 15 Jan 08:35 next collapse

What does dmesg say when you plug it in?

cralder@lemmy.world on 15 Jan 16:50 collapse 

[  930.571238] usb 3-4: new high-speed USB device number 21 using xhci_hcd
[  930.706640] usb 3-4: New USB device found, idVendor=2109, idProduct=2817, bcdDevice= 7.74
[  930.706652] usb 3-4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[  930.706655] usb 3-4: Product: USB2.0 Hub             
[  930.706658] usb 3-4: Manufacturer: VIA Labs, Inc.         
[  930.706661] usb 3-4: SerialNumber: 000000000
[  930.709490] hub 3-4:1.0: USB hub found
[  930.709697] hub 3-4:1.0: 5 ports detected
[  931.438189] usb 3-4.4: new high-speed USB device number 22 using xhci_hcd
[  931.583868] usb 3-4.4: New USB device found, idVendor=2109, idProduct=2211, bcdDevice= 5.84
[  931.583877] usb 3-4.4: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[  931.583879] usb 3-4.4: Product: USB2.0 Hub             
[  931.583881] usb 3-4.4: Manufacturer: VIA Labs, Inc.         
[  931.585386] hub 3-4.4:1.0: USB hub found
[  931.585580] hub 3-4.4:1.0: 4 ports detected
[  932.100980] usb 3-4.5: new high-speed USB device number 23 using xhci_hcd
[  932.183614] usb 3-4.5: New USB device found, idVendor=2109, idProduct=8884, bcdDevice= 0.01
[  932.183624] usb 3-4.5: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[  932.183626] usb 3-4.5: Product: USB Billboard Device   
[  932.183629] usb 3-4.5: Manufacturer: VIA Labs, Inc.         
[  932.183630] usb 3-4.5: SerialNumber: 0000000000000001
[  932.634461] usb 3-4.4.1: new full-speed USB device number 24 using xhci_hcd
[  932.830091] usb 3-4.4.1: New USB device found, idVendor=1038, idProduct=12ad, bcdDevice= 1.19
[  932.830109] usb 3-4.4.1: New USB device strings: Mfr=4, Product=5, SerialNumber=0
[  932.830115] usb 3-4.4.1: Product: SteelSeries Arctis 7
[  932.830120] usb 3-4.4.1: Manufacturer: SteelSeries 
[  933.230162] input: SteelSeries  SteelSeries Arctis 7 Consumer Control as /devices/pci0000:00/0000:00:14.0/usb3/3-4/3-4.4/3-4.4.1/3-4.4.1:1.5/0003:1038:12AD.0004/input/input17
[  933.281660] input: SteelSeries  SteelSeries Arctis 7 as /devices/pci0000:00/0000:00:14.0/usb3/3-4/3-4.4/3-4.4.1/3-4.4.1:1.5/0003:1038:12AD.0004/input/input19
[  933.282589] hid-generic 0003:1038:12AD.0004: input,hiddev96,hidraw1: USB HID v1.11 Device [SteelSeries  SteelSeries Arctis 7] on usb-0000:00:14.0-4.4.1/input5
[  933.411058] usb 3-4.4.2: new full-speed USB device number 25 using xhci_hcd
[  933.545758] usb 3-4.4.2: New USB device found, idVendor=0cf2, idProduct=b201, bcdDevice= 1.00
[  933.545764] usb 3-4.4.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[  933.545766] usb 3-4.4.2: Product: 6K7732
[  933.545767] usb 3-4.4.2: Manufacturer: ENE
[  933.545768] usb 3-4.4.2: SerialNumber: 6243168002
[  933.551282] hid-generic 0003:0CF2:B201.0005: hiddev97,hidraw2: USB HID v1.11 Device [ENE 6K7732] on usb-0000:00:14.0-4.4.2/input1
mvirts@lemmy.world on 15 Jan 17:44 collapse

This is a stupid question, but you are powering the monitor externally, right?

cralder@lemmy.world on 15 Jan 19:45 collapse

Yes

rodbiren@midwest.social on 15 Jan 10:21 next collapse

It has to do with muxing for the dGPU. I have bashed my head against this what seems like endlessly. My suggestion is that you should enable only dedicated gpu mode in your bios. That has worked for me. It kind of sucks because you feel like you are leaving performance on the table, but I have found nothing that works properly on any DE in any configuration.

At the end of the day it is basically a hardware issue, and for your specific hardware it will not work. I’m my limited opinion.

cralder@lemmy.world on 15 Jan 16:31 collapse

This laptop has no dedicated gpu

rodbiren@midwest.social on 15 Jan 16:43 collapse

Well crap

serenissi@lemmy.world on 15 Jan 12:51 collapse

Works ootb on fedora kde wayland.

Is your usb c dp connected to a gpu other than the one the compositor running on? Does the screen show in display settings? Setting different configurations and refresh rate works?