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I'm trying to get an external monitor (LG 43UD79-B) to work via a USB-C connection -- that is, USB-C on the laptop (Dell XPS 13 9370) to USB-C to the monitor, no conversion to Displayport/HDMI/anything else. The connection works with a USB-C to Displayport cable, and when plugging in the USB-C cable the monitor notifies me that there's a new connection, but xrandr doesn't see any new monitor. That said, if I plug in the USB-C to Displayport cable after the USB-C cable, the monitor shows up as DP-2 instead of DP-1, so it seems that xrandr sees something. Manually defining a mode for the new output and forcing xrandr to use that does not work (monitor stays blank). I've tried multiple USB-C cables and all USB-C ports on the laptop, no success. Running latest standard kernel, no special graphics drivers installed. I've tried installing the displaylink service, but that gave me the same result as before.
I haven't been able to find any information on whether a direct USB-C connection for external monitors is supported at all, but I'd appreciate any pointers on how to make this work.
Here's the relevant dmesg output when I plug in the USB-C cable (monitor has 2 USB-A ports and shows up as a hub, external keyboard connected to that).
[ 4650.901756] pci 0000:03:00.0: [8086:15d3] type 01 class 0x060400
[ 4650.901828] pci 0000:03:00.0: enabling Extended Tags
[ 4650.901985] pci 0000:03:00.0: supports D1 D2
[ 4650.901987] pci 0000:03:00.0: PME# supported from D0 D1 D2 D3hot D3cold
[ 4650.902419] pci 0000:04:00.0: [8086:15d3] type 01 class 0x060400
[ 4650.902522] pci 0000:04:00.0: enabling Extended Tags
[ 4650.902622] pci 0000:04:00.0: supports D1 D2
[ 4650.902623] pci 0000:04:00.0: PME# supported from D0 D1 D2 D3hot D3cold
[ 4650.902771] pci 0000:04:01.0: [8086:15d3] type 01 class 0x060400
[ 4650.902843] pci 0000:04:01.0: enabling Extended Tags
[ 4650.902942] pci 0000:04:01.0: supports D1 D2
[ 4650.902943] pci 0000:04:01.0: PME# supported from D0 D1 D2 D3hot D3cold
[ 4650.903084] pci 0000:04:02.0: [8086:15d3] type 01 class 0x060400
[ 4650.903156] pci 0000:04:02.0: enabling Extended Tags
[ 4650.903252] pci 0000:04:02.0: supports D1 D2
[ 4650.903253] pci 0000:04:02.0: PME# supported from D0 D1 D2 D3hot D3cold
[ 4650.903388] pci 0000:04:04.0: [8086:15d3] type 01 class 0x060400
[ 4650.903460] pci 0000:04:04.0: enabling Extended Tags
[ 4650.903558] pci 0000:04:04.0: supports D1 D2
[ 4650.903559] pci 0000:04:04.0: PME# supported from D0 D1 D2 D3hot D3cold
[ 4650.903714] pci 0000:03:00.0: PCI bridge to [bus 04-6d]
[ 4650.903725] pci 0000:03:00.0: bridge window [mem 0xac000000-0xda0fffff]
[ 4650.903732] pci 0000:03:00.0: bridge window [mem 0x60000000-0xa9ffffff 64bit pref]
[ 4650.903786] pci 0000:04:00.0: PCI bridge to [bus 05]
[ 4650.903796] pci 0000:04:00.0: bridge window [mem 0xda000000-0xda0fffff]
[ 4650.903855] pci 0000:04:01.0: PCI bridge to [bus 06-38]
[ 4650.903865] pci 0000:04:01.0: bridge window [mem 0xac000000-0xc3efffff]
[ 4650.903872] pci 0000:04:01.0: bridge window [mem 0x60000000-0x7fffffff 64bit pref]
[ 4650.903958] pci 0000:39:00.0: [8086:15d4] type 00 class 0x0c0330
[ 4650.903997] pci 0000:39:00.0: reg 0x10: [mem 0xc3f00000-0xc3f0ffff]
[ 4650.904081] pci 0000:39:00.0: enabling Extended Tags
[ 4650.904198] pci 0000:39:00.0: supports D1 D2
[ 4650.904199] pci 0000:39:00.0: PME# supported from D0 D1 D2 D3hot D3cold
[ 4650.904266] pci 0000:39:00.0: 8.000 Gb/s available PCIe bandwidth, limited by 2.5 GT/s x4 link at 0000:04:02.0 (capable of 31.504 Gb/s w
ith 8 GT/s x4 link)
[ 4650.904410] pci 0000:04:02.0: PCI bridge to [bus 39]
[ 4650.904420] pci 0000:04:02.0: bridge window [mem 0xc3f00000-0xc3ffffff]
[ 4650.904476] pci 0000:04:04.0: PCI bridge to [bus 3a-6d]
[ 4650.904486] pci 0000:04:04.0: bridge window [mem 0xc4000000-0xd9ffffff]
[ 4650.904492] pci 0000:04:04.0: bridge window [mem 0x80000000-0xa9ffffff 64bit pref]
[ 4650.904524] pci_bus 0000:04: Allocating resources
[ 4650.904545] pci 0000:04:01.0: bridge window [io 0x1000-0x0fff] to [bus 06-38] add_size 1000
[ 4650.904548] pci 0000:04:02.0: bridge window [io 0x1000-0x0fff] to [bus 39] add_size 1000
[ 4650.904550] pci 0000:04:02.0: bridge window [mem 0x00100000-0x000fffff 64bit pref] to [bus 39] add_size 200000 add_align 100000
[ 4650.904552] pci 0000:04:04.0: bridge window [io 0x1000-0x0fff] to [bus 3a-6d] add_size 1000
[ 4650.904554] pci 0000:03:00.0: bridge window [io 0x1000-0x0fff] to [bus 04-6d] add_size 4000
[ 4650.904558] pci 0000:03:00.0: BAR 13: assigned [io 0x2000-0x5fff]
[ 4650.904564] pci 0000:04:02.0: BAR 15: no space for [mem size 0x00200000 64bit pref]
[ 4650.904566] pci 0000:04:02.0: BAR 15: failed to assign [mem size 0x00200000 64bit pref]
[ 4650.904568] pci 0000:04:01.0: BAR 13: assigned [io 0x2000-0x2fff]
[ 4650.904569] pci 0000:04:02.0: BAR 13: assigned [io 0x3000-0x3fff]
[ 4650.904571] pci 0000:04:04.0: BAR 13: assigned [io 0x4000-0x4fff]
[ 4650.904575] pci 0000:04:02.0: BAR 15: no space for [mem size 0x00200000 64bit pref]
[ 4650.904576] pci 0000:04:02.0: BAR 15: failed to assign [mem size 0x00200000 64bit pref]
[ 4650.904578] pci 0000:04:00.0: PCI bridge to [bus 05]
[ 4650.904584] pci 0000:04:00.0: bridge window [mem 0xda000000-0xda0fffff]
[ 4650.904594] pci 0000:04:01.0: PCI bridge to [bus 06-38]
[ 4650.904597] pci 0000:04:01.0: bridge window [io 0x2000-0x2fff]
[ 4650.904602] pci 0000:04:01.0: bridge window [mem 0xac000000-0xc3efffff]
[ 4650.904606] pci 0000:04:01.0: bridge window [mem 0x60000000-0x7fffffff 64bit pref]
[ 4650.904613] pci 0000:04:02.0: PCI bridge to [bus 39]
[ 4650.904616] pci 0000:04:02.0: bridge window [io 0x3000-0x3fff]
[ 4650.904621] pci 0000:04:02.0: bridge window [mem 0xc3f00000-0xc3ffffff]
[ 4650.904631] pci 0000:04:04.0: PCI bridge to [bus 3a-6d]
[ 4650.904633] pci 0000:04:04.0: bridge window [io 0x4000-0x4fff]
[ 4650.904639] pci 0000:04:04.0: bridge window [mem 0xc4000000-0xd9ffffff]
[ 4650.904643] pci 0000:04:04.0: bridge window [mem 0x80000000-0xa9ffffff 64bit pref]
[ 4650.904649] pci 0000:03:00.0: PCI bridge to [bus 04-6d]
[ 4650.904652] pci 0000:03:00.0: bridge window [io 0x2000-0x5fff]
[ 4650.904657] pci 0000:03:00.0: bridge window [mem 0xac000000-0xda0fffff]
[ 4650.904661] pci 0000:03:00.0: bridge window [mem 0x60000000-0xa9ffffff 64bit pref]
[ 4650.904698] pcieport 0000:03:00.0: enabling device (0006 -> 0007)
[ 4650.906213] pcieport 0000:04:01.0: enabling device (0006 -> 0007)
[ 4650.906457] pcieport 0000:04:02.0: enabling device (0006 -> 0007)
[ 4650.906702] pcieport 0000:04:04.0: enabling device (0006 -> 0007)
[ 4650.907242] xhci_hcd 0000:39:00.0: xHCI Host Controller
[ 4650.907250] xhci_hcd 0000:39:00.0: new USB bus registered, assigned bus number 3
[ 4650.908389] xhci_hcd 0000:39:00.0: hcc params 0x200077c1 hci version 0x110 quirks 0x0000000200009810
[ 4650.909655] usb usb3: New USB device found, idVendor=1d6b, idProduct=0002, bcdDevice= 5.04
[ 4650.909657] usb usb3: New USB device strings: Mfr=3, Product=2, SerialNumber=1
[ 4650.909659] usb usb3: Product: xHCI Host Controller
[ 4650.909660] usb usb3: Manufacturer: Linux 5.4.5-arch1-1 xhci-hcd
[ 4650.909662] usb usb3: SerialNumber: 0000:39:00.0
[ 4650.910903] hub 3-0:1.0: USB hub found
[ 4650.910914] hub 3-0:1.0: 2 ports detected
[ 4650.911499] xhci_hcd 0000:39:00.0: xHCI Host Controller
[ 4650.911504] xhci_hcd 0000:39:00.0: new USB bus registered, assigned bus number 4
[ 4650.911508] xhci_hcd 0000:39:00.0: Host supports USB 3.1 Enhanced SuperSpeed
[ 4650.911549] usb usb4: New USB device found, idVendor=1d6b, idProduct=0003, bcdDevice= 5.04
[ 4650.911551] usb usb4: New USB device strings: Mfr=3, Product=2, SerialNumber=1
[ 4650.911553] usb usb4: Product: xHCI Host Controller
[ 4650.911554] usb usb4: Manufacturer: Linux 5.4.5-arch1-1 xhci-hcd
[ 4650.911555] usb usb4: SerialNumber: 0000:39:00.0
[ 4650.911693] hub 4-0:1.0: USB hub found
[ 4650.911703] hub 4-0:1.0: 2 ports detected
[ 4651.111045] pci_bus 0000:04: Allocating resources
[ 4651.111084] pcieport 0000:04:02.0: bridge window [mem 0x00100000-0x000fffff 64bit pref] to [bus 39] add_size 200000 add_align 100000
[ 4651.111092] pcieport 0000:04:02.0: BAR 15: no space for [mem size 0x00200000 64bit pref]
[ 4651.111094] pcieport 0000:04:02.0: BAR 15: failed to assign [mem size 0x00200000 64bit pref]
[ 4651.111097] pcieport 0000:04:02.0: BAR 15: no space for [mem size 0x00200000 64bit pref]
[ 4651.111099] pcieport 0000:04:02.0: BAR 15: failed to assign [mem size 0x00200000 64bit pref]
[ 4651.270389] usb 3-1: new high-speed USB device number 2 using xhci_hcd
[ 4651.425464] usb 3-1: New USB device found, idVendor=0bda, idProduct=5411, bcdDevice= 1.35
[ 4651.425471] usb 3-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[ 4651.425475] usb 3-1: Product: 4-Port USB 2.0 Hub
[ 4651.425478] usb 3-1: Manufacturer: Generic
[ 4651.427099] hub 3-1:1.0: USB hub found
[ 4651.428313] hub 3-1:1.0: 4 ports detected
[ 4651.710405] usb 3-1.1: new full-speed USB device number 3 using xhci_hcd
[ 4651.829092] usb 3-1.1: not running at top speed; connect to a high speed hub
[ 4651.836919] usb 3-1.1: New USB device found, idVendor=0bda, idProduct=5400, bcdDevice= 1.06
[ 4651.836922] usb 3-1.1: New USB device strings: Mfr=17, Product=18, SerialNumber=19
[ 4651.836924] usb 3-1.1: Product: BillBoard Device
[ 4651.836926] usb 3-1.1: Manufacturer: Realtek
[ 4651.836927] usb 3-1.1: SerialNumber: 123456789ABCDEFGH
[ 4651.930358] usb 3-1.3: new low-speed USB device number 4 using xhci_hcd
[ 4652.033896] usb 3-1.3: New USB device found, idVendor=17ef, idProduct=6009, bcdDevice= 1.27
[ 4652.033899] usb 3-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[ 4652.033900] usb 3-1.3: Product: ThinkPad USB Keyboard with TrackPoint
[ 4652.033902] usb 3-1.3: Manufacturer: Lite-On Technology Corp.
[ 4652.043929] input: Lite-On Technology Corp. ThinkPad USB Keyboard with TrackPoint as /devices/pci0000:00/0000:00:1c.4/0000:03:00.0/0000:04:02.0/0000:39:00.0/usb3/3-1/3-1.3/3-1.3:1.0/0003:17EF:6009.0007/input/input43
[ 4652.104529] lenovo 0003:17EF:6009.0007: input,hidraw2: USB HID v1.10 Keyboard [Lite-On Technology Corp. ThinkPad USB Keyboard with TrackPoint] on usb-0000:39:00.0-1.3/input0
[ 4652.112992] input: Lite-On Technology Corp. ThinkPad USB Keyboard with TrackPoint as /devices/pci0000:00/0000:00:1c.4/0000:03:00.0/0000:04:02.0/0000:39:00.0/usb3/3-1/3-1.3/3-1.3:1.1/0003:17EF:6009.0008/input/input44
[ 4652.167698] lenovo 0003:17EF:6009.0008: input,hiddev0,hidraw3: USB HID v1.10 Mouse [Lite-On Technology Corp. ThinkPad USB Keyboard with TrackPoint] on usb-0000:39:00.0-1.3/input1Offline
The monitor has this connection according to google: DisplayPort 1.2, 4 x HDMI, USB-C (DP Alt. Mode)
Note, the important thing here is the info "Alternate Mode".
The question is, has you Dell laptop also "Alternate Mode" in the USB-C ports for sure, in both ports or only in one, which one ?
Also you may try update your bios:
https://www.dell.com/community/XPS/XPS- … -p/7373084
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At least one USB-C port on the laptop supports this (has the DP logo next to it), and I've tried them all. I'm running the latest version of the BIOS.
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It turns out that the problem was the cable -- I shelled out for a more expensive "certified" thunderbolt cable and everything works!
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