SRU for Q - https://lists.ubuntu.com/archives/kernel- team/2026-March/166266.html
** Description changed: [Impact] HP and Dell systems with Intel Panther Lake-H (PTL-H) CPU and eDP panel configured for Panel Replay suffer a permanent black screen after logout from the desktop. Only a hard reboot restores the display. [Fix] Remove the two erroneous register writes from intel_alpm_disable() so that only the actual enable bits (ALPM_CTL_ALPM_ENABLE and ALPM_CTL_LOBF_ENABLE) are cleared on disable. PORT_ALPM_CTL is no longer touched during the disable path, and ALPM_CTL_ALPM_AUX_LESS_ENABLE is left intact for the subsequent intel_alpm_configure() call during link training. The fix is in linux-next as of 2026-02-27: 008304c9ae75c772d3460040de56e12112cdf5e6 drm/i915/alpm: ALPM disable fixes In mainline b7.0-rc2 - eb4a7139e9737 drm/i915/alpm: ALPM disable fixes + eb4a7139e9737 drm/i915/alpm: ALPM disable fixes Patchwork: https://patchwork.freedesktop.org/patch/704253/ [Test Plan] Requires Intel PTL-H system with a Panel Replay + DSC eDP panel (DISPLAY_VER = 20). Click logout button from the top-right menu and then the GDM shows up. [Where problems could occur] - It may break Intel i915/xe display driver Panel Replay and PSR functionality on PTL-class hardware (DISPLAY_VER >= 20). - If the fix incorrectly omits a necessary cleanup step in intel_alpm_disable(), the ALPM hardware state might not be properly quiesced before subsequent link training, potentially causing Panel Replay or PSR2 to fail to enable at all (black screen at boot or first modeset rather than only on resume). It could also manifest as display corruption, link training failures, or AUX communication errors logged in dmesg on affected hardware. - The change is confined to the DISPLAY_VER >= 20 code path; older hardware is not affected. + The change modifies the ALPM disable path in the Intel i915 display driver, which + is exercised whenever PSR2 or Panel Replay is active on eDP panels. + If the removal of the PORT_ALPM_CTL write is incorrect (i.e., if some hardware + requires it to be cleared at disable time), ALPM may fail to disable properly, + leaving the link in a low-power state that prevents display from recovering. This + would manifest as a black screen or display not coming back after suspend/resume. + Similarly, if removing the ALPM_CTL_ALPM_AUX_LESS_ENABLE clear has unintended + side effects on some panel configurations, the ALPM mode (AUX-Less vs AUX-Wake) + could be stuck in the wrong state, causing link training failures or display + flicker on affected eDP panels. + The fix is reviewed by Intel display maintainers (Reviewed-by: Michał Grzelak), + reducing regression risk, but panels with non-standard ALPM implementations may + behave differently. [Other Info] Remaining open issue: a ~20-second GDM login delay after logout (unrelated to ALPM) is tracked upstream at https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/7497 and is outside the scope of this SRU. ** Description changed: [Impact] HP and Dell systems with Intel Panther Lake-H (PTL-H) CPU and eDP panel configured for Panel Replay suffer a permanent black screen after logout from the desktop. Only a hard reboot restores the display. [Fix] - Remove the two erroneous register writes from intel_alpm_disable() so that only the actual - enable bits (ALPM_CTL_ALPM_ENABLE and ALPM_CTL_LOBF_ENABLE) are cleared on disable. - PORT_ALPM_CTL is no longer touched during the disable path, and ALPM_CTL_ALPM_AUX_LESS_ENABLE - is left intact for the subsequent intel_alpm_configure() call during link training. + Fix the intel_alpm_disable() function in drivers/gpu/drm/i915/display/intel_alpm.c: + 1. Remove the PORT_ALPM_CTL write from intel_alpm_disable() — this register + must only be written before link training, not during disable. + 2. Stop clearing ALPM_CTL_ALPM_AUX_LESS_ENABLE in intel_alpm_disable() — this + bit is about mode switching (AUX-Less vs AUX-Wake), not ALPM enable/disable. + The fix is in linux-next as of 2026-02-27: 008304c9ae75c772d3460040de56e12112cdf5e6 drm/i915/alpm: ALPM disable fixes In mainline b7.0-rc2 eb4a7139e9737 drm/i915/alpm: ALPM disable fixes Patchwork: https://patchwork.freedesktop.org/patch/704253/ [Test Plan] - Requires Intel PTL-H system with a Panel Replay + DSC eDP panel (DISPLAY_VER = 20). + Requires a system with Intel integrated graphics and an eDP panel that supports + Panel Replay (typically recent Intel platforms with Panel Replay-capable eDP displays). + Click logout button from the top-right menu and then the GDM shows up. [Where problems could occur] The change modifies the ALPM disable path in the Intel i915 display driver, which is exercised whenever PSR2 or Panel Replay is active on eDP panels. If the removal of the PORT_ALPM_CTL write is incorrect (i.e., if some hardware requires it to be cleared at disable time), ALPM may fail to disable properly, leaving the link in a low-power state that prevents display from recovering. This would manifest as a black screen or display not coming back after suspend/resume. Similarly, if removing the ALPM_CTL_ALPM_AUX_LESS_ENABLE clear has unintended side effects on some panel configurations, the ALPM mode (AUX-Less vs AUX-Wake) could be stuck in the wrong state, causing link training failures or display flicker on affected eDP panels. The fix is reviewed by Intel display maintainers (Reviewed-by: Michał Grzelak), reducing regression risk, but panels with non-standard ALPM implementations may behave differently. [Other Info] Remaining open issue: a ~20-second GDM login delay after logout (unrelated to ALPM) is tracked upstream at https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/7497 and is outside the scope of this SRU. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2143100 Title: Got black screen after clicked logout button To manage notifications about this bug go to: https://bugs.launchpad.net/hwe-next/+bug/2143100/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
