External monitors not detected via thunderbolt 3 dock in Devuan, but okay in Popos

External monitors not detected via thunderbolt 3 dock in Devuan, but okay in Popos

[trees1010]

Hi everyone,

I hope I have come to the right place, otherwise let me know where I should direct this question/problem.

I have a problem with using external monitors attached to a thunderbolt 3 dock (Dell, WD19TB) that is OS specific.
The two external monitors attached via DisplayPorts to the dock are detected and used automatically by PopOS/Ubuntu 20, Kernel 5.4 (default configuration).
However, Devuan Beowulf (Debian based) with the default or latest 5.8 Kernel does not detect the monitors and so they cannot be used.

The docking station is authorised using the 'bolt' utility (https://gitlab.freedesktop.org/bolt/bolt) for both PopOS and Devuan.

# boltctl
● Dell WD19TB Thunderbolt Dock
   ├─ type:          peripheral
   ├─ name:          WD19TB Thunderbolt Dock
   ├─ vendor:        Dell
   ├─ uuid:          <UUID>
   ├─ generation:    Thunderbolt 3
   ├─ status:        authorized
   │  ├─ domain:     <DOMAIN>
   │  ├─ rx speed:   40 Gb/s = 2 lanes * 20 Gb/s
   │  ├─ tx speed:   40 Gb/s = 2 lanes * 20 Gb/s
   │  └─ authflags:  none
   ├─ authorized:    Wed 07 Oct 2020 09:01:32 UTC
   ├─ connected:     Wed 21 Oct 2020 19:43:20 UTC
   └─ stored:        Wed 07 Oct 2020 08:12:45 UTC
      ├─ policy:     auto
      └─ key:        no

Both popos and devuan detect the thunderbolt dock being connected and the docks own USB hub.
I can attached USB devices, like a USB camera, to the dock and it works in both devaun and popos.

There is nothing obvious in the popos or devuan logs that would
indicate a major difference as to why the monitors don't work in devuan. There are no errors in the devuan logs to
show why it does not detect the monitors (xrandr shows no extra connections from the docking station when plugged in).

Popos Xorg.0.log shows the monitors being attached when the dock is connected to the laptop. Whilst nothing is
logged in Xorg.0.log in the case of devuan.
I can plug external monitors directly to the laptop via mini-dp and HDMI and they are detected and can be used to display an extended desktop.

The only key difference I have found is by using '$ sudo ddcutil interrogate'.

It shows that popos detects the DDC via i2c bus of the two external monitors, whilst devuan does not detect anything.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PopOS with 5.4 kernel:

*** Primary Check 1: Identify video card and driver ***

Obtaining card and driver information from /sys...
Primary video controller at PCI address 0000:00:02.0 (boot_vga flag is set)
Device class: x030000 VGA compatible controller
Vendor: x8086 Intel Corporation
Device: x9b41 UHD Graphics
Subvendor/Subdevice: 8086/2212 Intel Corporation
Driver name: i915
Driver version: Unable to determine
I2C device: i2c-3 name: i915 gmbus dpc
I2C device: i2c-8 name: DPMST
I2C device: i2c-4 name: i915 gmbus misc
I2C device: i2c-2 name: i915 gmbus dpb
I2C device: i2c-9 name: DPMST
I2C device: i2c-5 name: i915 gmbus dpd

<SNIP>

Examining /sys/bus/i2c/devices...
/sys/bus/i2c/devices/i2c-3/name: i915 gmbus dpc
/sys/bus/i2c/devices/i2c-1/name: Synopsys DesignWare I2C adapter
/sys/bus/i2c/devices/i2c-8/name: DPMST
/sys/bus/i2c/devices/i2c-6/name: DPDDC-A
/sys/bus/i2c/devices/i2c-4/name: i915 gmbus misc
/sys/bus/i2c/devices/i2c-2/name: i915 gmbus dpb
/sys/bus/i2c/devices/i2c-0/name: SMBus I801 adapter at efa0
/sys/bus/i2c/devices/i2c-9/name: DPMST
/sys/bus/i2c/devices/i2c-7/name: DPDDC-B
/sys/bus/i2c/devices/i2c-5/name: i915 gmbus dpd

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Devuan with 5.8 kernel:

*** Primary Check 1: Identify video card and driver ***

Obtaining card and driver information from /sys...
Primary video controller at PCI address 0000:00:02.0 (boot_vga flag is set)
Device class: x030000 VGA compatible controller
Vendor: x8086 Intel Corporation
Device: x9b41 UHD Graphics
Subvendor/Subdevice: 8086/2212 Intel Corporation
Driver name: i915
Driver version: Unable to determine
I2C device: i2c-3 name: i915 gmbus dpc
I2C device: i2c-4 name: i915 gmbus misc
I2C device: i2c-2 name: i915 gmbus dpb
I2C device: i2c-5 name: i915 gmbus dpd

<SNIP>

Examining /sys/bus/i2c/devices...
/sys/bus/i2c/devices/i2c-3/name: i915 gmbus dpc
/sys/bus/i2c/devices/0-0050/name: ee1004
(each_i2c_device ) Unexpected /sys/bus/i2c/devices file name: 0-0050
/sys/bus/i2c/devices/i2c-1/name: Synopsys DesignWare I2C adapter
/sys/bus/i2c/devices/i2c-6/name: AUX A/port A
/sys/bus/i2c/devices/i2c-4/name: i915 gmbus misc
/sys/bus/i2c/devices/i2c-2/name: i915 gmbus dpb
/sys/bus/i2c/devices/i2c-0/name: SMBus I801 adapter at efa0
/sys/bus/i2c/devices/i2c-7/name: AUX B/port B
/sys/bus/i2c/devices/i2c-5/name: i915 gmbus dpd

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The kernel Thunderbolt documentation (https://www.kernel.org/doc/html/v5.4/admin-guide/thunderbolt.html) does not show how to
debug problems like this.

Q1. How to turn on debugging in the kernel and/or modules to provide more information about the connection process and why it fails?

Q2. How does the kernel detect DP/HDMI ports through the thunderbolt 3 dock? I.e. What is meant to happen and should be seen in the logs or /sys/bus/i2c/devices, etc?

Q3. Is there any documentation on how the USB/DP/HDMI/Thunderbolt 3/dock system work? Thunderspy.io was the only place I could find decent description of the architecture.

Any advice appreciated.