Add support for Mayqueen Pixpaper e-ink panel

This patch series adds support for the Mayqueen Pixpaper e-ink display panel,
controlled via SPI.

The series includes:
- A new vendor-prefix entry for "mayqueen"
- Device tree binding documentation for the Pixpaper panel
- A DRM tiny driver implementation for the Pixpaper panel
- A MAINTAINERS entry for the Pixpaper DRM driver and binding

The panel supports 122x250 resolution with XRGB8888 format and uses SPI,
along with GPIO lines for reset, busy, and data/command control.

The driver has been tested on:
- Raspberry Pi 2 Model B
with Linux kernel 6.16.

---
Changes in v4:
- Applied BIT() macro for all register bit definitions (per checkpatch)
- Fixed alignment and indentation based on checkpatch suggestions
- Removed unnecessary blank lines after braces
- Fixed universal plane init() call indentation
- Link to v3: https://lore.kernel.org/r/20250721-drm-v3-0-e16c3cee7263@...

Changes in v3:
- MAINTAINERS
    - Added pixpaper-regs.h

- Kconfig
    - Rename config symbol to DRM_PIXPAPER (drop TINYDRM_ prefix).
    - Reordered Kconfig select lines alphabetically.

- Code structure & style
    - Fix include order: move <linux/> headers above <drm/> headers.
    - Removed forward declarations; placed static functions next to usage
    - Switched logging to drm_err()/drm_warn()/drm_dbg() (legacy DRM_ERROR/WARN removed)
    - Remove dev_info() statements.
    - Switched encoder type to DRM_MODE_ENCODER_NONE
    - Moved pixpaper_panel_hw_init() from atomic_enable() to probe() to avoid redundant hardware init.
    - Use helper to_pixpaper_panel() instead of container_of() on crtc.

- Robustness
    - Added timeout + warning in pixpaper_wait_busy() to ensure robustness if BUSY line gets stuck.
    - Introduced struct pixpaper_error_ctx to propagate SPI/GPIO errors

- Clean‑ups
    - Removed drm_plane_enable_fb_damage_clips() (full‑frame updates)
    - Removed noisy info prints; kept drm_dbg() only where helpful
    - Consolidated all magic register values/commands into new
      pixpaper-regs.h with datasheet‑aligned naming

- Memory helpers
    - Driver now uses GEM SHMEM helpers; GEM DMA helpers dropped
      (panel has no bus‑mastering DMA)

- Functionality fixes
    - Rewrote pack_pixels_to_byte() to correctly handle 4-color (B/W/R/Y) layout
      based on expected panel color encoding

- DRM callback safety
    - Add missing drm_dev_enter()/drm_dev_exit() in callbacks.

- Tags added
    - Reviewed-by: Rob Herring <robh@kernel.org> (from v1)
    - Acked-by: Rob Herring <robh@kernel.org> (from v1)
    - Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> (from v2)

- Link to v2: https://lore.kernel.org/r/20250714-drm-v2-0-5d1a2e12796c@...

Changes in v2:
- Reordered patches so that DT bindings come before the driver (suggested by Rob Herring)
- Fixed sparse warning: removed duplicate `.reset` initializer in `pixpaper_plane_funcs`
- Fixed checkpatch issues reported by Media CI:
  - Removed unnecessary blank line before closing brace
  - Moved opening parentheses up to function call lines (e.g., `DRM_WARN(...)`)
  - Fixed alignment of conditionals
  - Fixed `dev_warn(` and `drm_universal_plane_init(` formatting
- Thanks to Rob Herring for ack on vendor-prefix patch
- Link to v1: https://lore.kernel.org/r/20250708-drm-v1-0-45055fdadc8a@...

Thanks to all reviewers for feedback across earlier versions.

Best regards,
LiangCheng Wang
<zaq14760@gmail.com>

---
LiangCheng Wang (2):
      dt-bindings: display: Add Mayqueen Pixpaper e-ink panel
      drm: tiny: Add support for Mayqueen Pixpaper e-ink panel

Wig Cheng (1):
      dt-bindings: vendor-prefixes: Add Mayqueen name

 .../bindings/display/mayqueen,pixpaper.yaml        |  63 ++
 .../devicetree/bindings/vendor-prefixes.yaml       |   2 +
 MAINTAINERS                                        |   7 +
 drivers/gpu/drm/tiny/Kconfig                       |  15 +
 drivers/gpu/drm/tiny/Makefile                      |   1 +
 drivers/gpu/drm/tiny/pixpaper-regs.h               | 428 +++++++++++
 drivers/gpu/drm/tiny/pixpaper.c                    | 789 +++++++++++++++++++++
 7 files changed, 1305 insertions(+)
---
base-commit: 7e161a991ea71e6ec526abc8f40c6852ebe3d946
change-id: 20250708-drm-6021df0715d7

Best regards,
-- 
LiangCheng Wang <zaq14760@gmail.com>