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[TGL+docking] System can't boot up when connect an external monitor

We found the system cannot boot up when connected to an external monitor via Docking on TigerLake platform.

Some clues we found:

  1. Regression:

It's a regression. Revert this commit and the machine boot up successfully. commit dd9e01dfd0ec9b57fb8b1bf5c938d36437d08430 Author: Imre Deak imre.deak@intel.com Date: Mon May 4 10:58:28 2020 +0300 drm/i915/tgl+: Fix interrupt handling for DP AUX transactions BugLink: https://bugs.launchpad.net/bugs/1855399 Unmask/enable AUX interrupts on all ports on TGL+. So far the interrupts worked only on port A, which meant each transaction on other ports took 10ms.

  1. We tried Intel DRM nightly and also Linux kernel 5.9 RC1. Both can reproduce the issue.

[Steps to reproduce]

  1. Power off the laptop.
  2. Connect an external monitor to docking DisplaypPort/HDMI/TypeC-To-HDMI/Type-C-To-DisplayPort port.
  3. Connect docking to laptop via thunderbolt port.
  4. Power on the laptop.

[Expected result] System can boot into OS.

[Actual result] System can't boot into OS.

[Failure rate] 5/5

Asked @cooperch for help.

Edited by Hsiao-Ting Wang
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