[RESPONDED] Flaky dual 4K60 over TB (Arch Linux) - How to analyze?

I have gotten dual 4K60 display outputs to work over TB, using the following procedure:

  1. Plug TB dock in, with one screen attached
  2. Attach the Framework HDMI card to a downstream TB port
  3. Dual 4K60

If instead, I plug the dock in with both screens attached, one of them reliably ends up at 30 fps refresh rate.

I’m looking to understand how this allocation takes place in the various parts of the Linux kernel, also if and how I can influence this behaviour.

Pointers to relevant documentation are most welcome. Currently running Kernel 6.2.13-arch1-1

Wayland or X?

Let’s see what we can do here.

  • Wayland or X?
  • Which display(s) brand/model?
  • Which Dock brand/model?
  • 11th or 12th gen Framework?

Thanks for picking this up!

  • Wayland, using sway, output config below
  • 2 x Samsung LU28R55
  • CalDigit TS4
  • 12th gen i7-1260P

Previous setup with a MacBook Pro
Both screens connected via DisplayPort, one using a USB-C to DisplayPort cable made by CalDigit. Said cable worked at 60fps then, but doesn’t do that with the Framework so far.

Current setup
One screen via DP cable from the dock, one via HDMI on a Framework HDMI Expansion Card (which I understand is using DP Alt Mode). Both are downstream of the TS4.

Sway Output Config

### Output configuration
# Default wallpaper (more resolutions are available in /usr/share/backgrounds/sway/)
output * bg /home/leo/bg/SuperBIT_tarantula.png fill
# Example configuration:
#   output HDMI-A-1 resolution 1920x1080 position 1920,0
# You can get the names of your outputs by running: swaymsg -t get_outputs

# Built-In Screen
output eDP-1 scale 2 pos 0 1080 adaptive_sync on
#output eDP-1 disable

# Left
output DP-3 mode 3840x2160@60Hz pos 0 0 scale 2

# Right
output DP-4 mode 3840x2160@60Hz pos 1920 0 scale 2