Claude review: drm/i915/display: All patches to make PREEMPT_RT work on i915 + xe.

[Claude Code Review Bot <claude-review@example.com>]

Overall Series Review

Subject: drm/i915/display: All patches to make PREEMPT_RT work on i915 + xe.
Author: Maarten Lankhorst <dev@lankhorst.se>
Patches: 31
Reviewed: 2026-03-11T13:21:17.008561

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This is v7 of a 26-patch series to make the i915 (and xe) display driver work with PREEMPT_RT kernels. The core strategy is sound: instead of converting all vblank-related spinlocks to raw spinlocks, the series introduces a 2-stage arming mechanism for vblank events and vblank work, so that the critical section with interrupts disabled only needs to perform a simple `WRITE_ONCE()` rather than acquire sleeping locks.

The series covers:
1. **DRM core changes** (patches 1-2): 2-stage vblank work/event arming
2. **Display critical section rework** (patches 3-7): Converting i915 display to use the new 2-stage mechanism, removing locks from the vblank evade critical section
3. **RT-specific fixes** (patches 8-18): `_fw` register access variants, lock conversions, RT-aware busy loops
4. **Selftests/config** (patches 19-26): Selftest fixes, removing `!PREEMPT_RT` dependency, CI hacks

**Strengths:** The overall approach of 2-stage arming is elegant and avoids a massive raw spinlock conversion. Many individual fixes (LPE audio, execlists locking, GUC busy loop) are well-motivated with lockdep splats.

**Concerns:**
- Patches 24-25 are clearly FOR-CI/debug patches that should not be merged. Patch 24 force-enables PREEMPT_RT and removes the vblank evade debug config. Patch 25 bumps lockdep stack trace limits as a CI workaround.
- Patch 21 has a TODO in its commit message, suggesting unfinished work.
- Several patches lack Signed-off-by chains or commit message body (patch 19).
- The mbox ordering doesn't match the patch numbering, which may cause confusion.

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