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5.16 regression with TigerLake-LP GT2: Displayport Alternate Mode Adapter no longer working

Dear Intel devs,

I am using Arch Linux on a Lenovo ThinkPad L14 Gen 2 with Intel TigerLake-LP GT2 (Iris Xe). No dedicated graphics. I'm using an i-tec USB-C 3.1 Dual 4K DP Video Adapter to connect my two NEC MultiSync EA224Wmi LCD displays with a resolution of 1920x1080. As far as the datasheet goes, it's using DisplayPort Alternate Mode.

This setup has been working fine, however with the update to kernel 5.16 (which brought along PXP), the external displays no longer work and remains black, on every boot. Downgrading the kernel back to 5.15.3 and they are back working. I just tried out drm-tip as recommended (commit ad57bf1ff13e), but the issue is still reproducible there, on every boot.

When switching back and forth between 5.15.3 and 5.16+, what I can see has changed:

  • for all kernel versions, the external display only start working when Xorg is started, but not during framebuffer. I guess that's normal?
  • /sys/bus/pci/drivers/i915/0000:00:02.0/drm/card0/ no longer contains card0-DP-5 & card0-DP-6. Also "DP-5" does not show up in the dmesg output of 5.16+
  • module mei_pxp is now loaded, but typec_displayport isn't any longer. However, blacklisting the former and manually loading the latter module doesn't solve the issue
  • switching between xf86-video-intel and modesetting does not make any difference
  • the same adapter works fine with 5.16+ on a different notebook with CometLake-H GT2 UHD Graphics 630, with the same displays

System information:

  • system architecture: x86_64
  • kernel version: 5.15.13-arch1-1 / 5.16.arch1-1 / 5.16.1.arch1 / 5.16.2-arch1-1 / 5.17.0-rc1-gad57bf1ff13e
  • Linux distribution: Arch Linux (rolling)
  • Machine or mother board model: LENOVO ThinkPad L14 Gen 2
  • Display connector: 1 eDP, 2 DP via USB 3.1 Alternate Mode
  • full dmesg with debug information for 3 kernel versions can be found in this gist: https://gist.github.com/mephinet/891abc53cb1a43259c95111bb296049c

If there's anything I can help you with, please let me know! Regards, Philipp

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