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Hardware: lenovo thinkpad e480 laptop (intel+amd hybrid graphics) + lenovo thinkpad usb-c dock + dell u2415 monitor. Bios / dock firmware: latest versions installed

If external monitor is connected to displayport or vga on dock (no HDMI / dvi ports there), I get running bright pixels on monitor, and sometimes monitor just randomly turns off and on (sometimes few times per minute, sometimes few times per hour). Tested on Ubuntu 18.04 / 19.04, got the same result

On Windows 10 I still get running pixels (but almost invisible) when refresh rates are 59/60 for laptop/external displays, and everything works perfectly when refresh rates are 60/60 - so it looks like hardware is OK

On Ubuntu (both 18.04 and 19.04) everything works fine when external monitor is connected to HDMI port on laptop (no displayport there) - so it looks like intel graphics drivers are OK

Tried to:

  • install appropriate displaylink drivers for 18.04 (nothing changes)
  • install appropriate displaylink drivers for 19.04 (nothing changes)
  • install amdgpu drivers (failed, uninstall failed too)
  • change laptop refresh rate (didn't help, but pixels are "running" differently for different rate)
  • set refresh rates 60/60 (didn't work, those are not possible values)
  • set kernel parameter i915.edp_vswing=2 (didn't help)
  • set i915.preliminary_hw_support=1 (didn't help)
  • set intel_idle.max_cstate (to different values, didn't help)
  • use vga_switcheroo to switch to amd graphics card (failed, commands didn't change anything, even in su mode)

How can I fix this issue with dock displayports / vga?

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