Claude review: drm/atomic: introduce PAGE_FLIP_EVENT property

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Overall Series Review

Subject: drm/atomic: introduce PAGE_FLIP_EVENT property
Author: Simon Ser <contact@emersion.fr>
Patches: 3
Reviewed: 2026-06-04T15:29:59.502018

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This is a single patch from Simon Ser that introduces a new `PAGE_FLIP_EVENT` atomic CRTC property, allowing userspace to request page-flip events on a per-CRTC basis rather than the current all-or-nothing `DRM_MODE_PAGE_FLIP_EVENT` flag. The motivation is well-explained and addresses real pain points in compositors (gamescope, libliftoff, wlroots).

The approach is sound and follows established patterns (modeled after `OUT_FENCE_PTR` — always reads as zero, write-only semantic). The implementation is compact and mostly correct, but there is one significant bug around state duplication/reset and a few smaller issues worth discussing.

**Key concern:** The new `page_flip_event_requested` field in `drm_crtc_state` is not cleared in `__drm_atomic_helper_crtc_duplicate_state()`, which means it could carry over from a previous committed state if the memcpy copies a stale `true` value. This is unlike `event`, `async_flip`, and other per-commit fields that are explicitly cleared there.

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