Claude review: Add splash DRM client

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

Overall Series Review

Subject: Add splash DRM client
Author: Francesco Valla <francesco@valla.it>
Patches: 6
Reviewed: 2026-05-16T16:02:57.224131

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This is a v3 RFC series adding a DRM-based splash screen client (3 patches). The concept is sound and addresses a long-standing TODO item. The implementation follows existing DRM client patterns (modeled after `drm_log.c`) and supports three image sources: plain color background, BMP firmware, and EFI BGRT. The Kconfig structure is reasonable and the code is generally well-structured.

However, there are several issues ranging from potential crashes to data integrity bugs that should be addressed before this moves past RFC stage.

**Key concerns:**
1. **Uninitialized thread pointer crash** in unregister path when hotplug never fires.
2. **Out-of-bounds memory read** in BMP pixel blitting (reading 4 bytes from 3-byte pixel data).
3. **Render thread sleep/wake race condition** — the classic `set_current_state` vs `wake_up_process` pattern has a window for lost wakeups.
4. **Tiled display dimension accumulation** looks swapped (hdisplay vs vdisplay).
5. **`modeset_mask` / scanout indexing** is broken — `j` doesn't track scanout indices correctly.

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