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Hello,
I am experiencing an issue with automatic external monitor detection
when connected via a Dell Pro Thunderbolt 4 Dock (SD25TB4) on my Dell
Precision 5490 laptop, running Ubuntu 24.04.2 LTS.
The external monitor (connected via DisplayPort on the dock) is not
automatically detected by the system when the laptop starts or when I
connect the dock with the monitor already plugged in. The xrandr
--listmonitors command initially only lists the laptop's built-in
screen.
However, the external monitor works correctly if, after the system has
booted and the dock is connected, I manually unplug and re-plug ONLY the
DisplayPort cable on the docking station. This action triggers the
detection and activation of the display.
Hardware Information:
Laptop: Dell Precision 5490
Docking Station: Dell Pro Thunderbolt 4 Smart Dock (SD25TB4)
External Monitor: [Brand and Model of the Monitor, if known - ADD THIS
INFORMATION]
Monitor -> Dock Connection: DisplayPort
Laptop -> Dock Connection: Thunderbolt 4 / USB-C
Thunderbolt Dock Identification:
● Dell Thunderbolt 4 Dock
├─ type: peripheral
├─ name: Dell Thunderbolt 4 Dock
├─ vendor: Dell
├─ uuid: [ANONYMIZED_UUID]
├─ generation: USB4
├─ status: authorized
│ ├─ domain: [ANONYMIZED_UUID]
│ ├─ rx speed: 40 Gb/s = 2 lanes * 20 Gb/s
│ ├─ tx speed: 40 Gb/s = 2 lanes * 20 Gb/s
│ └─ authflags: none
├─ authorized: [DATE_ANONYMIZED]
├─ connected: [DATE_ANONYMIZED]
└─ stored: [DATE_ANONYMIZED]
├─ policy: iommu
└─ key: no
(Note: Output shows the dock is authorized and connected).
Software Information:
Linux Distribution: Ubuntu 24.04.2 LTS
Linux Kernel Version: 6.11.0-24-generic
Intel Graphics Driver: i915 (confirmed by lspci)
NVIDIA Graphics Driver: nvidia (proprietary driver, confirmed by lspci)
NVIDIA Driver Version: nvidia-driver-570-open
Optimus Graphics Mode: on-demand (confirmed by prime-select query). Testing
nvidia exclusive mode did not resolve automatic detection at boot.
bolt Version : 0.9.7-1
xrandr Version: 1.5.2
Steps to Reproduce the Bug:
Connect the Dell SD25TB4 docking station to the Dell Precision 5490 laptop
using the Thunderbolt/USB-C cable.
Connect the external monitor to the docking station via DisplayPort.
Boot the laptop into Linux (Ubuntu 24.04.2 LTS).
After the graphical session loads, observe that the external monitor is not
detected (it remains black/in standby).
Open a terminal and run xrandr --listmonitors (it will only list the
internal display).
Expected Behavior:
The external monitor should be automatically detected by the Linux
system at boot or shortly after connecting the docking station and
enabled according to display settings.
Observed Behavior:
The external monitor is not automatically detected at boot or dock
connection.
Workaround:
The issue can be resolved by manually unplugging and re-plugging ONLY
the DisplayPort cable on the docking station after the system has
booted. The monitor is then immediately detected and works.
Additional Diagnostic Information :
❯ lspci -k | grep -A 2 -E "(VGA|3D)"
00:02.0 VGA compatible controller: Intel Corporation Meteor Lake-P [Intel Arc
Graphics] (rev 08)
Subsystem: Dell Meteor Lake-P [Intel Arc Graphics]
Kernel driver in use: i915
--
01:00.0 3D controller: NVIDIA Corporation AD107GLM [RTX 1000 Ada Generation
Laptop GPU] (rev a1)
Subsystem: Dell Device 0cc7
Kernel driver in use: nvidia
Finding regarding dmesg / journalctl logs:
We attempted to capture kernel logs (sudo dmesg -C followed by sudo
dmesg -k or sudo journalctl --since ...) while performing the action of
replugging the DisplayPort cable that makes the display work.
Despite the manual action triggering detection, these logs showed NO
relevant messages or standard display hotplug events related to the drm,
nvidia, i915, thunderbolt, usb4, DP, DisplayPort, EDID, connector, or hotplug
layers at the time of the manual action. This seems to indicates that the
low-level detection event is not being correctly signaled or logged. We dont
really know why.
Output of lsusb : (Shows dock's USB components are detected)
❯ lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 002 Device 002: ID 8087:0b40 Intel Corp. USB3.0 Hub
Bus 002 Device 003: ID 0bda:0480 Realtek Semiconductor Corp. 4-Port USB 3.0 Hub
Bus 002 Device 004: ID 0bda:0485 Realtek Semiconductor Corp. 4-Port USB 3.0 Hub
Bus 002 Device 005: ID 0bda:0481 Realtek Semiconductor Corp. USB3.2 Hub
Bus 002 Device 006: ID 0bda:8156 Realtek Semiconductor Corp. USB 10/100/1G/2.5G
LAN
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 003 Device 003: ID 8086:0b63 Intel Corp. USB Bridge
Bus 003 Device 004: ID 27c6:634c Shenzhen Goodix Technology Co.,Ltd. Goodix
Fingerprint USB Device
Bus 003 Device 006: ID 1d5c:5801 Fresco Logic USB2.0 Hub
Bus 003 Device 007: ID 0bda:5480 Realtek Semiconductor Corp. 4-Port USB 2.0 Hub
Bus 003 Device 008: ID 413c:b0a4 Dell Computer Corp. HID GENERIC DEVICE
Bus 003 Device 009: ID 0bda:5485 Realtek Semiconductor Corp. 4-Port USB 2.0 Hub
Bus 003 Device 010: ID 0bda:5481 Realtek Semiconductor Corp. USB2.1 Hub
Bus 003 Device 011: ID 413c:b0a2 Dell Computer Corp. USB2.0 HID
Bus 003 Device 012: ID 413c:b0a3 Dell Computer Corp. USB2.0 HID
Bus 003 Device 013: ID 413c:b0a5 Dell Computer Corp. VMM8431
Bus 003 Device 014: ID 413c:b06e Dell Computer Corp. K2 DOCK HID
Bus 003 Device 015: ID 413c:b0a1 Dell Computer Corp. HID Device
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Impact:
This bug makes the daily use of the external monitor via the docking
station inconvenient, requiring a manual intervention (unplugging/re-
plugging the DisplayPort cable) with each connection or restart.
** Affects: xorg (Ubuntu)
Importance: Undecided
Status: New
** Tags: bot-comment
--
Failed automatic external monitor detection
https://bugs.launchpad.net/bugs/2109692
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