Claude review: Add support for PIXPAPER 4.26 monochrome e-ink panel

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

Overall Series Review

Subject: Add support for PIXPAPER 4.26 monochrome e-ink panel
Author: LiangCheng Wang <zaq14760@gmail.com>
Patches: 5
Reviewed: 2026-05-07T13:55:14.683316

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This series adds a DRM tiny driver for the Mayqueen Pixpaper 4.26 monochrome e-ink panel (800x480, SPI). The code is structurally modeled on the existing `pixpaper.c` driver for the original Pixpaper panel, which is sensible. However, there are several issues ranging from a critical Kconfig/code mismatch, to empty enable/disable callbacks, indentation problems, and missing shutdown handling. The driver appears to be for a different e-ink controller family (SSD16xx-style commands like 0x01/0x22/0x24/0x44/0x45 vs. the UC8253-style commands in the original pixpaper.c), so having a separate driver file is reasonable.

**Key concerns:**
1. **Kconfig selects `DRM_GEM_DMA_HELPER` but the driver uses `DRM_GEM_SHMEM_DRIVER_OPS`** — this is a build/link-time mismatch that will either fail to compile or pull in unnecessary code.
2. **Empty CRTC enable/disable callbacks** — no power on/off commands are sent to the panel hardware, unlike the existing pixpaper.c driver.
3. **Missing `.shutdown` callback** on the SPI driver — other tiny drivers provide this for orderly shutdown on reboot.
4. **Indentation errors** in `pixpaper_connector_get_modes()`.
5. **Unnecessary forward declaration** and unusual bare block scope in `atomic_update`.

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