Add DRM driver for Solomon SSD16xx e-paper display controllers

This series adds a DRM driver for the Solomon Systech SSD16xx family of e-paper display controllers (SSD1673, SSD1680, SSD1681, SSD1683), starting with support for the Gooddisplay GDEY042T81, a 4.2" 400×300 black-and-white e-paper panel driven by the SSD1683 controller.

The driver is designed and architected keeping the bi-stable nature and low-power requirements of epaper display based systems in mind along with having adequate flexibility to support varying use-case requirements for the e-paper display use-cases.

The driver integrates with the DRM atomic modesetting framework and supports:

- SPI communication in both 4-wire mode (separate D/C GPIO) and 3-wire mode (9-bit SPI with embedded D/C# bit)
- Full 4-way rotation via the Data Entry Mode register, with no GPU or memory-copy overhead
- Three independently selectable refresh waveforms: partial (~300–500 ms),

    full (~1.5–2 s), and fast (~1.0–1.5 s)

- 3-colour BWR pixel classification for panels with a red RAM plane
- Pixel format support: XRGB8888 (color path) and R1 (native 1bpp, zero-copy path)
- Runtime PM with configurable autosuspend: the controller enters Mode 1 deep sleep (RAM retained) after an idle timeout, waking transparently on the next frame update
- System suspend/resume: switches to Mode 2 deep sleep (maximum power savings) on system suspend and rebuilds the pipeline on resume
- Runtime-configurable DRM plane properties for refresh mode, colour mode, and session control (clear-on-init/close/disable, init-refresh waveform); rotation is set at probe time from a device tree property, and border waveform uses a fixed per-panel default

Changes from v2 [6]:

Bindings:
- Rename the binding file to solomon,ssd1683.yaml to match an actual compatible, and shape the compatible as oneOf so the SSD1677 patch only adds a branch
- Reference panel-common.yaml and use the common 'rotation' property instead of a local one that said "clockwise"
- Add spi-3wire and document that omitting dc-gpios selects 3-wire mode

Driver core (base patch):
- Keep lazy hardware initialization: ssd16xx_hw_init() is deferred to

    crtc_atomic_enable(); probe() performs only a GPIO reset. Follows
    the precedent of repaper.c and ssd130x.c

- Add drm_dev_enter()/drm_dev_exit() to plane_atomic_update
- Wrap the framebuffer read in drm_gem_fb_begin/end_cpu_access()
- Skip the update when drm_atomic_helper_damage_merged() reports no damage instead of making up a full-screen rectangle
- Remove ssd16xx_crtc_atomic_flush() and last_fb; the orientation is static so flush did a full hardware re-init and a second redraw on every commit, and last_fb had no remaining users
- Use drm_crtc_cleanup() directly as the CRTC .destroy callback
- Call drm_atomic_helper_check_crtc_primary_plane() from CRTC atomic_check
- Send SPI data from a DMA-safe buffer in struct ssd16xx_device instead of the stack
- Read XRGB8888 pixels with le32_to_cpup()
- Size the transfer buffers per row, as the packing code does
- Make Kconfig depend on MMU
- GDEY042T81: use the HIZ border waveform for updates and do not refresh the border on every update, to avoid border flicker

Session management (clear_on_init/close/disable):
- Split display_cleared_on_deinit into cleared_on_disable and cleared_on_close. A single flag made a clear on disable suppress the clear on close and was never re-armed on re-enable
- Reset the RAM window before clearing and size the clear buffer per row
- In 3-colour mode clear the red RAM to 0x00 (no red) instead of writing the all-white buffer to it, which would paint the panel red

Power management:
- Check for damage before taking the runtime PM reference, so the panel is not woken up when there is nothing to draw
- Put the panel to sleep in remove() with pm_runtime_force_suspend(), independent of clear_on_disable
- Return the error from pm_runtime_force_suspend() in system suspend
- Do not clear ->initialized again in system resume; force_resume() already re-initializes the hardware
- Do not fail runtime suspend if the deep sleep command fails, as that would block all later resumes

Plane properties:
- Reject 3-color mode together with partial refresh in the plane atomic_check, as partial refresh does not update the red channel
- Only create the color_mode property on panels with a red plane instead of exposing a property with a single possible value
- Add a mutex serializing the session state and panel access between atomic commits and master_set()/master_drop(); master_drop() can run concurrently with a nonblocking commit (e.g. on DROP_MASTER) and both drive the SPI bus with the same transfer buffers
- Sync the session properties from the new plane state in atomic_enable as well, since it runs before plane_atomic_update and used the values of the previous commit

MAINTAINERS / platform integration:
- Follow the rename of the binding file to solomon,ssd1683.yaml
- Add the GDEY042T81 EVM overlay to the MAINTAINERS file list
- Drop PixPaper reference from the MAINTAINERS commit message (not

    in v3)

- DTS overlay: fix the BUSY pin name in the comments (pad 0x00b8 is GPMC0_CLK, not GPMC0_AD0), use GPIO_ACTIVE_HIGH for the fet-sel gpio-hog, fix SPDX separator to uppercase OR per SPDX-2.1, mark [DO_NOT_MERGE] (for driver review context only)

Changes from v1[0]:
- Restructured into 14 modular patches covering bindings, driver core, features, and platform integration (was 6 patches in v1)
- Added comprehensive device-tree bindings support for vendor prefixes and SSD16xx controller configurations
- Refactored driver architecture from drm/tiny panel driver to drm/solomon bridge driver
- Switch to using GEM_SHMEM helpers
- Refactored data entry mode implementation
- Removed runtime-configurable rotation/border-waveform DRM properties and their module params; rotation is now set via device tree, and border waveform now uses an enhanced fixed per-panel default
- Added support for Solomon SSD1677 controller variant
- Improved session management with plane properties
- Added comprehensive power management support
- Support for panels with reversed RAM X order
- Dropped RGB888, RGB565, R8, NV12, NV16, YUYV, and UYVY format support; driver now only exposes XRGB8888 and R1

[0]: [V1 patch series]
https://lore.kernel.org/all/[email protected]/

[1]: [Development Branch]
https://github.com/devarsht/linux-next/tree/epaper_v3_final_4

[2]: [Test Suite]
https://github.com/devarsht/linux-next/tree/epaper_v3_final_4/tests_27sept_new8

[3]: [Test Logs]
https://github.com/devarsht/linux-next/tree/epaper_v3_final_4/tests_27sept_new8/logs

[4]: [Test Results]
https://github.com/devarsht/linux-next/tree/epaper_v3_final_4/tests_27sept_new8/results

[5]: [Result Summary]
https://github.com/devarsht/linux-next/blob/epaper_v3_final_4/tests_27sept_new8/results/run_all*.summary

[6]: [V2 Patch]
https://lore.kernel.org/all/[email protected]/

Devarsh Thakkar (13):
dt-bindings: vendor-prefixes: Add Dalian Good Display Co., Ltd.
dt-bindings: display: Add Solomon SSD16xx e-paper controller
dt-bindings: display: solomon,ssd16xx: Add Solomon SSD1677 controller drm/solomon: Add DRM driver for Solomon SSD16xx e-paper display
controllers
drm/solomon: ssd16xx: Add clear_on_init/close/disable session
management
drm/solomon: ssd16xx: Add support for Solomon SSD1677 controller drm/solomon: ssd16xx: Add power management support drm/solomon: ssd16xx: Expose refresh mode as plane property drm/solomon: ssd16xx: Expose color mode as plane property drm/solomon: ssd16xx: Expose session management as plane properties
MAINTAINERS: Add entry for Solomon SSD16xx DRM driver
arm64: defconfig: Enable DRM_SSD16XX for AM62L3 EVM
arm64: dts: ti: [DO_NOT_MERGE] Add AM62L3 EVM overlay for GDEY042T81
e-paper display

LiangCheng Wang (1):
drm/solomon: ssd16xx: support panels whose RAM X order is reversed

 .../bindings/display/solomon,ssd1683.yaml     |   86 +
 .../devicetree/bindings/vendor-prefixes.yaml  |    2 +
 MAINTAINERS                                   |    9 +
 arch/arm64/boot/dts/ti/Makefile               |    6 +
 .../ti/k3-am62l3-evm-epaper-gdey042t81.dtso   |   96 +
 arch/arm64/configs/defconfig                  |    1 +
 drivers/gpu/drm/solomon/Kconfig               |   13 +
 drivers/gpu/drm/solomon/Makefile              |    1 +
 drivers/gpu/drm/solomon/ssd16xx.c             | 2659 +++++++++++++++++
 9 files changed, 2873 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/solomon,ssd1683.yaml
 create mode 100644 arch/arm64/boot/dts/ti/k3-am62l3-evm-epaper-gdey042t81.dtso
 create mode 100644 drivers/gpu/drm/solomon/ssd16xx.c

2.39.1