[Bug 2173915] Re: linux-hwe-5.15 5.15.0-203.213~20.04.1: i915 DP link training fails with "Timeout waiting for DDI BUF D to get active" on Alder Lake-P [8086:46a6]

** Tags added: kernel-daily-bug -- You received this bug notification because you are subscribed to linux in Ubuntu. Matching subscriptions: Bgg, Bmail, Nb https://bugs.launchpad.net/bugs/2173915 Title: linux-hwe-5.15 5.15.0-203.213~20.04.1: i915 DP link training fails with "Timeout waiting for DDI BUF D to get active" on Alder Lake-P [8086:46a6] Status in linux package in Ubuntu: New Bug description: impact: External DisplayPort / Type-C displays connected to DDI D fail modesetting and link training upon hotplug or EDID resolution switching, preventing external monitors from activating and causing Checkbox monitor/zapper-edid to time out. hardware: - Dell XPS 13 Plus (CID 202112-29761), Intel Core i7-1260P, Intel Alder Lake-P Integrated Graphics [8086:46a6] - HP EliteBook 860 G9 Notebook PC (CID 202201-29867), Intel Core i7-1280P, Intel Alder Lake-P Integrated Graphics [8086:46a6] versions: - fails on: 5.15.0-191.201~20.04.1, 5.15.0-203.213~20.04.1 (Ubuntu 20.04.6 focal ESM) - multiple cycles and builds observed failing identically on both models reproduction: 1. Connect external monitor or Zapper HDMI capture via DP / Type-C (enumerated as card0-DP-1). 2. Trigger an EDID resolution switch (e.g. via edid_cycle.py "$ZAPPER_HOST" switching between 1280x1024, 1920x1080, and 2560x1440). 3. Observe kernel log output: i915 0000:00:02.0: [drm] ERROR Timeout waiting for DDI BUF D to get active i915 0000:00:02.0: [drm] ERROR Link Training Unsuccessful 4. Observe test output: Timed out switching EDID. Timed out after 15s waiting for DP-1 to connect. Connected monitors: ['eDP-1']; with current mode: ['eDP-1']; DRM connected: ['DP-1', 'eDP-1']. analysis: In drivers/gpu/drm/i915/display/intel_ddi.c, intel_wait_ddi_buf_active() polls for DDI_BUF_IS_IDLE to clear on port D. When retraining the link during an EDID resolution change on Alder Lake-P, the DDI buffer idle status fails to clear within the timeout. Consequently, intel_dp_start_link_train fails link training, userspace (GNOME / mutter) cannot configure a mode on DP-1, and only eDP-1 remains active in the graphical session despite DRM reporting DP-1 connected. proposed fix: Investigate DDI buffer activation timeouts and link retraining sequencing for Alder Lake-P (Gen12 / ADL-P) DDI D in drivers/gpu/drm/i915/display/intel_ddi.c, or backport relevant i915 DP link training and retimer fixes from newer upstream and OEM kernels. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2173915/+subscriptions