ACK: [SRU][Q][PATCH 0/1] Got black screen after clicked logout button

[Yufeng Gao]

On 16/3/26 13:39, AceLan Kao wrote:
> From: "Chia-Lin Kao (AceLan)" <acelan.kao at canonical.com>
>
> BugLink: https://bugs.launchpad.net/bugs/2143100
>
> [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]
> 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 v7.0-rc2
>    eb4a7139e9737 drm/i915/alpm: ALPM disable fixes
>
> Patchwork: https://patchwork.freedesktop.org/patch/704253/
>
> [Test Plan]
> 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.
>
> [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.
>
> Jouni Högander (1):
>    drm/i915/alpm: ALPM disable fixes
>
>   drivers/gpu/drm/i915/display/intel_alpm.c | 7 +------
>   1 file changed, 1 insertion(+), 6 deletions(-)
>
> --
> 2.53.0
>
>
Acked-by: Yufeng Gao <yufeng.gao at canonical.com>