Re: [PATCH v2 04/14] drm/solomon: Add DRM driver for Solomon SSD16xx e-paper display controllers

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 27.09.26 um 20:23 schrieb Devarsh Thakkar:
> Add a DRM driver for the Solomon Systech SSD16xx family of e-paper display
> controllers (SSD1680 [4], SSD1673 [3], SSD1681 [5], SSD1683 [1]) based
> e-paper display panels, starting with support for the Gooddisplay
> GDEY042T81 which is 4.2", 400x300 resolution black/white e-paper display
> using SSD1683 controller.
>
> Hardware features supported:
>    - SPI communication with optional D/C GPIO (4-wire mode) or 9-bit SPI
>      with embedded D/C# bit (3-wire mode) command/data signaling
>    - BUSY GPIO polling with configurable timeout
>    - Hardware reset via dedicated reset GPIO
>    - Internal temperature sensor readout
>    - Border waveform control with 10 configurable modes:
>      LUT0-3 (GS transition waveforms), fixed voltage levels (VSS/VSH1/VSL/
>      VSH2), VCOM follow, and HiZ (floating, default)
>    - Deep sleep modes: Mode 1 (RAM retained) and Mode 2 (RAM lost)
>    - Data entry modes for all four orientations
>    - Dual display RAM planes: BW RAM (primary image) and RED RAM
>      (partial refresh baseline / 3-color BWR red pixels)
>
> Refresh modes:
>    Three independently selectable refresh waveforms:
>    - Partial (~300-500 ms): low-latency BW update using RED RAM as
>      waveform transition baseline
>    - Full (~1.5-2 s): complete pixel-cycle reset with temperature-
>      compensated LUT reload
>    - Fast (~1.0-1.5 s): abbreviated waveform using a pre-loaded LUT
>
> Pixel format conversions:
>    The driver accepts all common DRM formats and converts to 1bpp:
>    - R1 (native 1bpp), color formats (XRGB8888),
>    - 3-color BWR: classifies pixels as black, white, or red by dominant
>      channel; writes separate 1bpp BW and RED buffers
>
> Orientation / rotation:
>    - Full 4-way rotation: 0° (landscape), 90° (portrait CW),
>      180° (landscape inverted), 270° (portrait CCW)
>    - Implemented via the Data Entry Mode register — no GPU or memory
>      rotation overhead
>    - Configurable via device tree 'rotation' property
>
> DRM framework integration:
>    - drm_atomic_helper-based modesetting with damage tracking
>    - Single primary plane, CRTC, simple encoder, SPI connector
>    - drm_gem_shmem backend for display buffers
>    - fbdev fallback via drm_fbdev_shmem_setup
>
> Links:
> [1] : https://www.crystalfontz.com/controllers/SolomonSystech/SSD1683
> [2] : https://files.seeedstudio.com/wiki/Other_Display/42-epaper/GDEY042T81.pdf
> [3] : https://www.crystalfontz.com/controllers/SolomonSystech/SSD1673
> [4] : https://www.crystalfontz.com/controllers/SolomonSystech/SSD1680
> [5] : https://www.crystalfontz.com/controllers/SolomonSystech/SSD1681
>
> Signed-off-by: Devarsh Thakkar <devarsht@ti.com>
> ---
>
> Changes from v1:
>    - Converted from drm/tiny/panel-ssd16xx.c to drm/solomon/ssd16xx.c
>    - Reorganized code for better maintainability
>    - Improved hardware abstraction for multi-controller support
>    - Enhanced initialization sequence with better power state management
>    - Switch to using GEM_SHMEM helpers
>    - Refactored data entry mode implementation
>    - Removed drm properties for runtime rotation, border waveforms
>    - Removed module params for each of the drm properties
>    - Improved SPDX license header formatting
>    - Better separation of concerns between hardware and DRM integration
>
>   drivers/gpu/drm/solomon/Kconfig   |   13 +
>   drivers/gpu/drm/solomon/Makefile  |    1 +
>   drivers/gpu/drm/solomon/ssd16xx.c | 1849 +++++++++++++++++++++++++++++
>   3 files changed, 1863 insertions(+)
>   create mode 100644 drivers/gpu/drm/solomon/ssd16xx.c
>
> diff --git a/drivers/gpu/drm/solomon/Kconfig b/drivers/gpu/drm/solomon/Kconfig
> index 400a6cab3a67..de2b14819f81 100644
> --- a/drivers/gpu/drm/solomon/Kconfig
> +++ b/drivers/gpu/drm/solomon/Kconfig
> @@ -30,3 +30,16 @@ config DRM_SSD130X_SPI
>   	  Say Y here if the SSD13xx OLED display is connected via SPI bus.
>   
>   	  If M is selected the module will be called ssd130x-spi.
> +
> +config DRM_SSD16XX
> +	tristate "DRM support for Solomon SSD16xx e-ink display controllers"
> +	depends on DRM && SPI
> +	select DRM_CLIENT_SELECTION
> +	select DRM_KMS_HELPER
> +	select DRM_GEM_SHMEM_HELPER
> +	help
> +	  DRM driver for Solomon SSD16xx family e-paper display controllers
> +	  (SSD1673, SSD1680, SSD1681, SSD1683, SSD1677). Supports panels
> +	  such as the GDEY042T81 4.2" 400x300.
> +
> +	  If M is selected the module will be called ssd16xx.
> diff --git a/drivers/gpu/drm/solomon/Makefile b/drivers/gpu/drm/solomon/Makefile
> index b5fc792257d7..72384620785b 100644
> --- a/drivers/gpu/drm/solomon/Makefile
> +++ b/drivers/gpu/drm/solomon/Makefile
> @@ -1,3 +1,4 @@
>   obj-$(CONFIG_DRM_SSD130X)	+= ssd130x.o
>   obj-$(CONFIG_DRM_SSD130X_I2C)	+= ssd130x-i2c.o
>   obj-$(CONFIG_DRM_SSD130X_SPI)	+= ssd130x-spi.o
> +obj-$(CONFIG_DRM_SSD16XX)	+= ssd16xx.o
> diff --git a/drivers/gpu/drm/solomon/ssd16xx.c b/drivers/gpu/drm/solomon/ssd16xx.c
> new file mode 100644
> index 000000000000..d3af055c6739
> --- /dev/null
> +++ b/drivers/gpu/drm/solomon/ssd16xx.c
> @@ -0,0 +1,1849 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * DRM driver for e-paper display panels using Solomon SSD16xx family controllers
> + *
> + * Copyright (C) 2026 Texas Instruments Incorporated - https://www.ti.com/
> + *
> + * Author: Devarsh Thakkar <devarsht@ti.com>
> + *
> + * References: https://github.com/Lesords/epaper
> + */
> +
> +#include <linux/delay.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/property.h>
> +#include <linux/spi/spi.h>
> +
> +#include <drm/clients/drm_client_setup.h>
> +#include <drm/drm_atomic.h>
> +#include <drm/drm_atomic_helper.h>
> +#include <drm/drm_damage_helper.h>
> +#include <drm/drm_drv.h>
> +#include <drm/drm_encoder.h>
> +#include <drm/drm_fb_helper.h>
> +#include <drm/drm_fbdev_shmem.h>
> +#include <drm/drm_framebuffer.h>
> +#include <drm/drm_gem_atomic_helper.h>
> +#include <drm/drm_gem_framebuffer_helper.h>
> +#include <drm/drm_gem_shmem_helper.h>
> +#include <drm/drm_managed.h>
> +#include <drm/drm_probe_helper.h>
> +#include <drm/drm_print.h>
> +
> +/* -----------------------------------------------------------------------
> + * SSD16xx family common: commands, data values, and bit definitions.
> + * These apply equally to SSD1673, SSD1680, and SSD1683.
> + * -----------------------------------------------------------------------
> + */
> +
> +/* SPI command codes (common) */
> +#define SSD16XX_CMD_DRIVER_OUTPUT_CONTROL		0x01
> +#define SSD16XX_CMD_DATA_ENTRY_MODE			0x11
> +#define SSD16XX_CMD_SW_RESET				0x12
> +#define SSD16XX_CMD_MASTER_ACTIVATION			0x20
> +#define SSD16XX_CMD_DISPLAY_UPDATE_CONTROL1		0x21
> +#define SSD16XX_CMD_DISPLAY_UPDATE_CONTROL2		0x22
> +#define SSD16XX_CMD_WRITE_RAM_BW			0x24
> +#define SSD16XX_CMD_BORDER_WAVEFORM_CONTROL		0x3C
> +#define SSD16XX_CMD_SET_RAM_X_ADDRESS_START_END		0x44
> +#define SSD16XX_CMD_SET_RAM_Y_ADDRESS_START_END		0x45
> +#define SSD16XX_CMD_SET_RAM_X_ADDRESS_COUNTER		0x4E
> +#define SSD16XX_CMD_SET_RAM_Y_ADDRESS_COUNTER		0x4F
> +
> +/*
> + * Data Entry Mode (command 0x11) AM/IDY/IDX bit encoding (common).
> + *
> + * Bit 2 (AM): Address update direction: 0 = X direction, 1 = Y direction
> + * ID[1:0] when AM=0 (X-direction modes, address counter advances in X):
> + *   00 = X decrement, Y decrement   01 = X increment, Y decrement
> + *   10 = X decrement, Y increment   11 = X increment, Y increment (default)
> + *
> + * Rotation to data entry mode mapping (actual implementation uses two modes,
> + * with scan direction controlled via RAM cursor positioning and manual tweaking):
> + *   0°/270° → 0x03 (X++, Y++)   Landscape/Portrait-CW: cursor at (0, 0)
> + *   90°/180° → 0x00 (X--, Y--)  Portrait-CCW/Upside-down: cursor at (max, max)
> + *
> + * The pixel packing in convert_fb_to_1bpp is grouped by physical layout:
> + *   - Portrait (90°/270°): column-major packing, rightmost column first
> + *   - Landscape (0°/180°): row-major packing, top to bottom, left to right
> + * Hardware cursor position and scan mode handle the final orientation.
> + */
> +#define SSD16XX_DATA_ENTRY_XDEC_YDEC		0x00  /* X--, Y-- (X-mode) */
> +#define SSD16XX_DATA_ENTRY_XINC_YINC		0x03  /* X++, Y++ (X-mode, default) */
> +
> +/* POR reset value: GD=0 (G0 first), SM=0 (interlaced), TB=0 (G0->G299) */
> +#define SSD16XX_DRIVER_OUTPUT_CTRL_DEFAULT	0x00
> +
> +/* Display Update Control 1 (0x21) byte 2 default (common) */
> +#define SSD16XX_CTRL1_BYTE2_DEFAULT		0x00
> +
> +/*
> + * Display Update Control 2 (0x22) individual bit definitions (common).
> + * NOTE: BIT(3) is NOT common — see SSD1683_CTRL2_MODE2 in the SSD1683
> + * section below; it has a completely different meaning in SSD1673.
> + */
> +#define SSD16XX_CTRL2_ENABLE_CLK		BIT(7)
> +#define SSD16XX_CTRL2_ENABLE_ANALOG		BIT(6)
> +#define SSD16XX_CTRL2_LOAD_TEMPERATURE		BIT(5)
> +#define SSD16XX_CTRL2_LOAD_LUT			BIT(4)
> +#define SSD16XX_CTRL2_DISPLAY			BIT(2)
> +#define SSD16XX_CTRL2_DISABLE_ANALOG		BIT(1)
> +#define SSD16XX_CTRL2_DISABLE_CLK		BIT(0)
> +
> +#define SSD16XX_SPI_BITS_PER_WORD		8
> +#define SSD16XX_SPI_SPEED_DEFAULT		1000000
> +
> +/* Maximum time to wait for the BUSY pin to deassert after a display update */
> +#define SSD16XX_BUSY_WAIT_TIMEOUT_MS		6000
> +
> +/* -----------------------------------------------------------------------
> + * SSD1683 / SSD1680 specific: commands, data values, and bit definitions.
> + * -----------------------------------------------------------------------
> + */
> +
> +/*
> + * Deep Sleep Mode values (command 0x10).
> + */
> +#define SSD1683_DEEP_SLEEP_MODE_1			0x01  /* RAM retained */
> +#define SSD1683_DEEP_SLEEP_MODE_2			0x03  /* RAM lost (max power) */
> +
> +/*
> + * Temperature Sensor Selection (command 0x18).
> + */
> +#define SSD1683_CMD_TEMPERATURE_SENSOR_CONTROL		0x18
> +#define SSD1683_TEMP_SENSOR_INTERNAL			0x80  /* Bit 7: use internal sensor */
> +
> +/*
> + * Write RED RAM (command 0x26).
> + */
> +#define SSD1683_CMD_WRITE_RAM_RED			0x26
> +
> +/*
> + * Border Waveform Control (command 0x3C) byte values.
> + */
> +#define SSD1683_BORDER_WAVEFORM_LUT0		0x00  /* GS Transition LUT0 (black) */
> +#define SSD1683_BORDER_WAVEFORM_LUT1		0x01  /* GS Transition LUT1 (white) */
> +#define SSD1683_BORDER_WAVEFORM_LUT2		0x02  /* GS Transition LUT2 (black) */
> +#define SSD1683_BORDER_WAVEFORM_LUT3		0x03  /* GS Transition LUT3 (gray) */
> +#define SSD1683_BORDER_WAVEFORM_FIXLVL_VSS	0x40  /* Fix Level VSS (0V, black) */
> +#define SSD1683_BORDER_WAVEFORM_FIXLVL_VSH1	0x50  /* Fix Level VSH1 (+15V, black) */
> +#define SSD1683_BORDER_WAVEFORM_FIXLVL_VSL	0x60  /* Fix Level VSL (-15V, white) */
> +#define SSD1683_BORDER_WAVEFORM_FIXLVL_VSH2	0x70  /* Fix Level VSH2 (+15V alt, black) */
> +#define SSD1683_BORDER_WAVEFORM_VCOM		0x80  /* Follow VCOM (-2V~-3V, preserve) */
> +#define SSD1683_BORDER_WAVEFORM_HIZ		0xC0  /* HiZ (floating, default) */
> +
> +/*
> + * Display Update Control 1 (0x21) byte 1 — RED RAM control.
> + */
> +#define SSD1683_CTRL1_NORMAL			0x00  /* Both BW and RED RAMs enabled */
> +#define SSD1683_CTRL1_BYPASS_RED_RAM		0x40  /* Bypass RED RAM (force RED=0) */
> +
> +/*
> + * Display Update Control 2 (0x22) BIT(3) — "Display Mode 2" (partial/BW).
> + */
> +#define SSD1683_CTRL2_MODE2			BIT(3)
> +
> +/* Composite CTRL2 sequences for each refresh mode */
> +#define SSD1683_CTRL2_FULL_REFRESH (SSD16XX_CTRL2_ENABLE_CLK | \
> +				    SSD16XX_CTRL2_ENABLE_ANALOG | \
> +				    SSD16XX_CTRL2_LOAD_TEMPERATURE | \
> +				    SSD16XX_CTRL2_LOAD_LUT | \
> +				    SSD16XX_CTRL2_DISPLAY | \
> +				    SSD16XX_CTRL2_DISABLE_ANALOG | \
> +				    SSD16XX_CTRL2_DISABLE_CLK)  /* 0xF7, ~1.5-2s */
> +
> +#define SSD1683_CTRL2_FAST_REFRESH (SSD16XX_CTRL2_ENABLE_CLK | \
> +				    SSD16XX_CTRL2_ENABLE_ANALOG | \
> +				    SSD16XX_CTRL2_DISPLAY | \
> +				    SSD16XX_CTRL2_DISABLE_ANALOG | \
> +				    SSD16XX_CTRL2_DISABLE_CLK)  /* 0xC7, ~1.0-1.5s */
> +
> +#define SSD1683_CTRL2_PARTIAL_REFRESH (SSD16XX_CTRL2_ENABLE_CLK | \
> +				       SSD16XX_CTRL2_ENABLE_ANALOG | \
> +				       SSD16XX_CTRL2_LOAD_TEMPERATURE | \
> +				       SSD16XX_CTRL2_LOAD_LUT | \
> +				       SSD1683_CTRL2_MODE2 | \
> +				       SSD16XX_CTRL2_DISPLAY | \
> +				       SSD16XX_CTRL2_DISABLE_ANALOG | \
> +				       SSD16XX_CTRL2_DISABLE_CLK)  /* 0xFF, ~300-500ms */
> +
> +/*
> + * Standalone LUT pre-load sequence (0x91 = ENABLE_CLK | LOAD_LUT | LOAD_TEMPERATURE |
> + *                                          DISABLE_CLK).
> + * Pre-loads the OTP LUT without triggering a display update. Required for
> + * FAST refresh mode (0xC7) which omits LOAD_LUT from each update cycle.
> + */
> +#define SSD1683_CTRL2_LOAD_TEMP_LUT		(SSD16XX_CTRL2_ENABLE_CLK | \
> +						 SSD16XX_CTRL2_LOAD_LUT | \
> +						 SSD16XX_CTRL2_LOAD_TEMPERATURE | \
> +						 SSD16XX_CTRL2_DISABLE_CLK)  /* 0xB1 */
> +
> +enum ssd16xx_controller {
> +	SSD1683 = 1,
> +};
> +
> +enum ssd16xx_model {
> +	GDEY042T81 = 1,
> +};
> +
> +enum ssd16xx_refresh_mode {
> +	SSD16XX_REFRESH_PARTIAL = 0,  /* Partial refresh (~300-500ms) */
> +	SSD16XX_REFRESH_FULL,         /* Full refresh (~1.5-2s) */
> +	SSD16XX_REFRESH_FAST,         /* Fast refresh, skip temp load (~1.0-1.5s) */
> +};
> +
> +enum ssd16xx_color_mode {
> +	SSD16XX_COLOR_MODE_BW = 0,     /* Black/white only; RED RAM always bypassed */
> +	SSD16XX_COLOR_MODE_3COLOR = 1, /* 3-colour BWR; RED RAM used for red pixels */
> +};
> +
> +/* Border waveform enum indices (0-9); mapped to HW bytes via
> + * controller_cfg->border_waveform_table[]
> + */
> +enum ssd16xx_border_waveform {
> +	SSD16XX_BORDER_LUT0 = 0,  /* GS Transition LUT0 (black) */
> +	SSD16XX_BORDER_LUT1,      /* GS Transition LUT1 (white) */
> +	SSD16XX_BORDER_LUT2,      /* GS Transition LUT2 (black) */
> +	SSD16XX_BORDER_LUT3,      /* GS Transition LUT3 (gray) */
> +	SSD16XX_BORDER_VSS,       /* Fix Level VSS (black) */
> +	SSD16XX_BORDER_VSH1,      /* Fix Level VSH1 (black) */
> +	SSD16XX_BORDER_VSL,       /* Fix Level VSL (white) */
> +	SSD16XX_BORDER_VSH2,      /* Fix Level VSH2 (black) */
> +	SSD16XX_BORDER_VCOM,      /* Follow VCOM (preserve) */
> +	SSD16XX_BORDER_HIZ,       /* HiZ (floating, default) */
> +};
> +
> +/* SSD1683/SSD1680 border waveform byte encoding for command 0x3C */
> +static const u8 ssd1683_border_waveform_table[] = {
> +	[SSD16XX_BORDER_LUT0] = SSD1683_BORDER_WAVEFORM_LUT0,
> +	[SSD16XX_BORDER_LUT1] = SSD1683_BORDER_WAVEFORM_LUT1,
> +	[SSD16XX_BORDER_LUT2] = SSD1683_BORDER_WAVEFORM_LUT2,
> +	[SSD16XX_BORDER_LUT3] = SSD1683_BORDER_WAVEFORM_LUT3,
> +	[SSD16XX_BORDER_VSS]  = SSD1683_BORDER_WAVEFORM_FIXLVL_VSS,
> +	[SSD16XX_BORDER_VSH1] = SSD1683_BORDER_WAVEFORM_FIXLVL_VSH1,
> +	[SSD16XX_BORDER_VSL]  = SSD1683_BORDER_WAVEFORM_FIXLVL_VSL,
> +	[SSD16XX_BORDER_VSH2] = SSD1683_BORDER_WAVEFORM_FIXLVL_VSH2,
> +	[SSD16XX_BORDER_VCOM] = SSD1683_BORDER_WAVEFORM_VCOM,
> +	[SSD16XX_BORDER_HIZ]  = SSD1683_BORDER_WAVEFORM_HIZ,
> +};
> +
> +struct ssd16xx_controller_config {
> +	u16 max_width;
> +	u16 max_height;
> +	u8 ram_x_address_bits;
> +	u8 ram_y_address_bits;
> +
> +	/*
> +	 * has_temp_sensor_ctrl: controller supports command 0x18 (Temperature
> +	 * Sensor Selection).  Present in SSD1683/SSD1680; absent in SSD1673
> +	 * which uses command 0x1A (direct temperature write) instead.
> +	 */
> +	bool has_temp_sensor_ctrl;
> +
> +	/*
> +	 * Deep sleep mode byte values for command 0x10.
> +	 *   deep_sleep_mode_level1: lower-power sleep, RAM content retained
> +	 *     (MODE_1 on SSD1683/SSD1680; used for runtime idle / app-close).
> +	 *   deep_sleep_mode_level2: maximum power savings, RAM may be lost
> +	 *     (MODE_2 on SSD1683/SSD1680; used for system suspend).
> +	 * Chips with a single sleep mode set both fields to the same value.
> +	 */
> +	u8 deep_sleep_mode_level1;
> +	u8 deep_sleep_mode_level2;
> +
> +	/*
> +	 * border_waveform_table: chip-specific byte values for the 10 logical
> +	 * border waveform modes (indexed by enum ssd16xx_border_waveform).
> +	 * The encoding of command 0x3C differs between SSD1683/SSD1680 and
> +	 * SSD1673, so each controller provides its own translation table.
> +	 */
> +	const u8 *border_waveform_table;
> +
> +	/*
> +	 * Display Update Control 1 (cmd 0x21) byte 1 values.
> +	 * ctrl1_normal:         both BW and RED RAMs participate in the waveform.
> +	 * ctrl1_bypass_red_ram: RED RAM bypassed; waveform driven from BW RAM only.
> +	 * SSD1673 has no RED RAM so both fields carry the same value.
> +	 */
> +	u8 ctrl1_normal;
> +	u8 ctrl1_bypass_red_ram;
> +
> +	/*
> +	 * Display Update Control 2 (cmd 0x22) composite sequences for each
> +	 * refresh mode (indexed by enum ssd16xx_refresh_mode) and the
> +	 * standalone LUT pre-load sequence used before fast refresh.
> +	 * Values differ between SSD1683/SSD1680 and SSD1673 (MODE2 bit, etc.).
> +	 */
> +	u8 ctrl2_refresh[3];     /* indexed by SSD16XX_REFRESH_PARTIAL/FULL/FAST */
> +	u8 ctrl2_load_temp_lut;  /* standalone LUT pre-load (no display update) */
> +};
> +
> +struct ssd16xx_device_config {
> +	/* Data Entry Mode - controls X/Y increment direction for landscape (0°) */
> +	u8 data_entry_mode;
> +
> +	/* Driver Output Control - third byte (scan direction) */
> +	u8 driver_output_ctrl_byte3;
> +
> +	/* Default refresh mode for this panel */
> +	enum ssd16xx_refresh_mode default_refresh_mode;
> +
> +	/* Default border waveform during clear/init (enum index 0-9) */
> +	enum ssd16xx_border_waveform default_border_waveform_init;
> +
> +	/* Default border waveform during display updates (enum index 0-9) */
> +	enum ssd16xx_border_waveform default_border_waveform_update;
> +
> +	/* Whether to re-send border waveform command before each display update */
> +	bool default_border_refresh_on_every_update;
> +
> +	/*
> +	 * Default refresh-mode-init: -1=disabled, else skip baseline establishment
> +	 * and start directly in this refresh mode.
> +	 */
> +	int default_refresh_mode_init;
> +
> +	/*
> +	 * Whether this panel has a physical red colour plane (3-colour BWR).
> +	 * false: 2-colour black/white only; the RED RAM is always bypassed.
> +	 * true:  3-colour panel; full-refresh writes to the RED RAM so that
> +	 *        red pixels are driven through the red waveform.
> +	 */
> +	bool red_supported;
> +
> +	/*
> +	 * Default colour mode for this panel.
> +	 * For BW-only panels this must be SSD16XX_COLOR_MODE_BW.
> +	 * For BWR panels this can be set to SSD16XX_COLOR_MODE_3COLOR to
> +	 * enable red ink by default;
> +	 */
> +	enum ssd16xx_color_mode default_color_mode;
> +
> +	/* Panel-specific display mode (resolution and physical dimensions) */
> +	const struct drm_display_mode *mode;
> +};
> +
> +struct ssd16xx_device {
> +	struct drm_device drm;
> +
> +	struct drm_plane primary_plane;
> +	struct drm_crtc crtc;
> +	struct drm_encoder encoder;
> +	struct drm_connector connector;
> +
> +	struct spi_device *spi;
> +	struct gpio_desc *reset;
> +	struct gpio_desc *busy;
> +	struct gpio_desc *dc;
> +
> +	enum ssd16xx_model model;
> +	enum ssd16xx_controller controller;
> +	const struct ssd16xx_controller_config *controller_cfg;
> +	const struct ssd16xx_device_config *device_cfg;
> +	struct drm_display_mode *mode;
> +	u32 width;
> +	u32 height;
> +
> +	bool initialized;
> +	bool init_refresh_pending; /* First frame after refresh_mode_init enable */
> +
> +	int orientation; /* Display orientation in degrees: 0/90/180/270 */
> +	enum ssd16xx_refresh_mode refresh_mode; /* Active refresh mode */
> +	enum ssd16xx_color_mode color_mode;     /* Active color mode (BW or 3-color) */
> +	bool fast_lut_pending; /* LUT pre-load needed before next fast refresh */
> +
> +	/* Border waveform (as enum indices) */
> +	int border_waveform_init_idx;   /* Border waveform during clear/init */
> +	int border_waveform_update_idx; /* Border waveform during display updates */
> +	bool border_refresh_on_every_update; /* Re-send border cmd each display update */
> +	bool border_waveform_pending;   /* One-shot: send border cmd on next update */
> +
> +	/* Display control */
> +	int refresh_mode_init; /* -1=disabled, else use this mode for the first frame */
> +
> +	u8  *tx_buf;     /* 1bpp frame buffer (mono + white) */
> +	u8  *tx_red_buf; /* 1bpp red-channel buffer (3-color panels only) */
> +	u16 *tx_buf9;    /* 9-bit SPI expansion buffer (3-wire mode only) */
> +
> +	struct drm_framebuffer *last_fb;        /* Last drawn FB for reinit redraws */
> +};
> +
> +static inline struct ssd16xx_device *to_ssd16xx_device(struct drm_device *drm)
> +{
> +	return container_of(drm, struct ssd16xx_device, drm);
> +}
> +
> +static inline struct ssd16xx_device *crtc_to_ssd16xx_device(struct drm_crtc *crtc)
> +{
> +	return container_of(crtc, struct ssd16xx_device, crtc);
> +}
> +
> +static inline struct ssd16xx_device *plane_to_ssd16xx_device(struct drm_plane *plane)
> +{
> +	return container_of(plane, struct ssd16xx_device, primary_plane);
> +}
> +
> +static const struct ssd16xx_controller_config ssd16xx_controller_configs[] = {
> +	[SSD1683] = {
> +		.max_width = 400,
> +		.max_height = 300,
> +		.ram_x_address_bits = 8,
> +		.ram_y_address_bits = 16,
> +		.has_temp_sensor_ctrl    = true,
> +		.deep_sleep_mode_level1  = SSD1683_DEEP_SLEEP_MODE_1,
> +		.deep_sleep_mode_level2  = SSD1683_DEEP_SLEEP_MODE_2,
> +		.border_waveform_table   = ssd1683_border_waveform_table,
> +		.ctrl1_normal            = SSD1683_CTRL1_NORMAL,
> +		.ctrl1_bypass_red_ram    = SSD1683_CTRL1_BYPASS_RED_RAM,
> +		.ctrl2_refresh = {
> +			[SSD16XX_REFRESH_PARTIAL] = SSD1683_CTRL2_PARTIAL_REFRESH,
> +			[SSD16XX_REFRESH_FULL]    = SSD1683_CTRL2_FULL_REFRESH,
> +			[SSD16XX_REFRESH_FAST]    = SSD1683_CTRL2_FAST_REFRESH,
> +		},
> +		.ctrl2_load_temp_lut     = SSD1683_CTRL2_LOAD_TEMP_LUT,
> +	},
> +};
> +
> +/* GDEY042T81: 4.2" 400x300 panel, 84.8x63.6mm active area */
> +static const struct drm_display_mode gdey042t81_mode = {
> +	DRM_SIMPLE_MODE(400, 300, 85, 64),
> +};
> +
> +static const struct ssd16xx_device_config ssd16xx_device_configs[] = {
> +	[GDEY042T81] = {
> +		.data_entry_mode = SSD16XX_DATA_ENTRY_XINC_YINC,
> +		.driver_output_ctrl_byte3 = SSD16XX_DRIVER_OUTPUT_CTRL_DEFAULT,
> +		.default_refresh_mode = SSD16XX_REFRESH_PARTIAL,
> +		.default_border_waveform_init   = SSD16XX_BORDER_LUT1,
> +		.default_border_waveform_update = SSD16XX_BORDER_VCOM,
> +		.default_border_refresh_on_every_update = true,
> +		.default_refresh_mode_init = SSD16XX_REFRESH_FULL,
> +		.red_supported = false,  /* 2-colour black/white panel */
> +		.default_color_mode = SSD16XX_COLOR_MODE_BW,
> +		.mode = &gdey042t81_mode,
> +	},
> +};
> +
> +static void ssd16xx_wait_for_device(struct ssd16xx_device *device,
> +				    int *err)
> +{
> +	unsigned long timeout_jiffies = jiffies +
> +		msecs_to_jiffies(SSD16XX_BUSY_WAIT_TIMEOUT_MS);
> +	unsigned long start_ms = jiffies_to_msecs(jiffies);
> +	int busy_val;
> +
> +	if (*err)
> +		return;
> +
> +	busy_val = gpiod_get_value_cansleep(device->busy);
> +	drm_dbg(&device->drm, "BUSY initial value: %d\n", busy_val);
> +
> +	while (gpiod_get_value_cansleep(device->busy) == 1) {
> +		if (time_after(jiffies, timeout_jiffies)) {
> +			drm_err(&device->drm, "Busy wait timed out after %lums\n",
> +				jiffies_to_msecs(jiffies) - start_ms);
> +			*err = -ETIMEDOUT;
> +			return;
> +		}
> +		usleep_range(1000, 2000);
> +	}
> +
> +	drm_dbg(&device->drm, "BUSY became ready after %lums\n",
> +		jiffies_to_msecs(jiffies) - start_ms);
> +}
> +
> +static void ssd16xx_spi_sync(struct spi_device *spi, struct spi_message *msg,
> +			     int *err)
> +{
> +	int ret;
> +
> +	if (*err)
> +		return;
> +
> +	ret = spi_sync(spi, msg);
> +	if (ret < 0)
> +		*err = ret;
> +}
> +
> +static void ssd16xx_send_cmd(struct ssd16xx_device *device, u8 cmd,
> +			     int *err)
> +{
> +	u16 word;
> +	struct spi_transfer xfer = {};
> +	struct spi_message msg;
> +
> +	if (*err)
> +		return;
> +
> +	spi_message_init(&msg);
> +	spi_message_add_tail(&xfer, &msg);
> +
> +	if (device->dc) {
> +		/* 4-wire SPI: D/C# GPIO low selects command mode */
> +		xfer.tx_buf = &cmd;
> +		xfer.len = 1;
> +		gpiod_set_value_cansleep(device->dc, 0);
> +	} else {
> +		/*
> +		 * 3-wire SPI (9-bit): bit 8 is the D/C# bit.
> +		 * D/C# = 0 means the following 8 bits are a command.
> +		 */
> +		word = cmd; /* bit 8 = 0 for command */
> +		xfer.tx_buf = &word;
> +		xfer.len = sizeof(u16);
> +		xfer.bits_per_word = 9;
> +	}
> +
> +	ssd16xx_spi_sync(device->spi, &msg, err);
> +}
> +
> +static void ssd16xx_send_data(struct ssd16xx_device *device, u8 data,
> +			      int *err)
> +{
> +	u16 word;
> +	struct spi_transfer xfer = {};
> +	struct spi_message msg;
> +
> +	if (*err)
> +		return;
> +
> +	spi_message_init(&msg);
> +	spi_message_add_tail(&xfer, &msg);
> +
> +	if (device->dc) {
> +		/* 4-wire SPI: D/C# GPIO high selects data mode */
> +		xfer.tx_buf = &data;
> +		xfer.len = 1;
> +		gpiod_set_value_cansleep(device->dc, 1);
> +	} else {
> +		/*
> +		 * 3-wire SPI (9-bit): bit 8 is the D/C# bit.
> +		 * D/C# = 1 means the following 8 bits are data.
> +		 */
> +		word = 0x100 | data;
> +		xfer.tx_buf = &word;
> +		xfer.len = sizeof(u16);
> +		xfer.bits_per_word = 9;
> +	}
> +
> +	ssd16xx_spi_sync(device->spi, &msg, err);
> +}
> +
> +static void ssd16xx_send_x_param(struct ssd16xx_device *device, u16 x,
> +				 int *err)
> +{
> +	if (*err)
> +		return;
> +
> +	if (device->controller_cfg->ram_x_address_bits == 8) {
> +		ssd16xx_send_data(device, (u8)x, err);
> +	} else {
> +		ssd16xx_send_data(device, x & 0xFF, err);
> +		ssd16xx_send_data(device, (x >> 8) & 0xFF, err);
> +	}
> +}
> +
> +static void ssd16xx_send_y_param(struct ssd16xx_device *device, u16 y,
> +				 int *err)
> +{
> +	if (*err)
> +		return;
> +
> +	if (device->controller_cfg->ram_y_address_bits == 8) {
> +		ssd16xx_send_data(device, (u8)y, err);
> +	} else {
> +		ssd16xx_send_data(device, y & 0xFF, err);
> +		ssd16xx_send_data(device, (y >> 8) & 0xFF, err);
> +	}
> +}
> +
> +static void ssd16xx_send_data_bulk(struct ssd16xx_device *device,
> +				   const u8 *data, size_t len,
> +				   int *err)
> +{
> +	struct spi_transfer xfer = {};
> +	struct spi_message msg;
> +
> +	if (*err)
> +		return;
> +
> +	if (!data || !len)
> +		return;
> +
> +	spi_message_init(&msg);
> +	spi_message_add_tail(&xfer, &msg);
> +
> +	if (device->dc) {
> +		/* 4-wire SPI: D/C# GPIO high selects data mode */
> +		xfer.tx_buf = data;
> +		xfer.len = len;
> +		gpiod_set_value_cansleep(device->dc, 1);
> +		ssd16xx_spi_sync(device->spi, &msg, err);
> +	} else {
> +		/* 3-wire (9-bit): expand u8 → u16 with D/C#=1 in bit 8. */
> +		size_t i;
> +		u16 *buf = device->tx_buf9;
> +
> +		for (i = 0; i < len; i++)
> +			buf[i] = 0x100 | data[i];
> +
> +		xfer.tx_buf = buf;
> +		xfer.len = len * sizeof(u16);
> +		xfer.bits_per_word = 9;
> +		ssd16xx_spi_sync(device->spi, &msg, err);
> +	}
> +}
> +
> +static void ssd16xx_display_update(struct ssd16xx_device *device,
> +				   u8 ctrl1_byte1, u8 ctrl1_byte2, u8 ctrl2_mode,
> +				   int *err)
> +{
> +	if (*err)
> +		return;
> +
> +	drm_dbg(&device->drm,
> +		"display_update: Setting ctrl1=0x%02x,0x%02x mode=0x%02x\n",
> +		ctrl1_byte1, ctrl1_byte2, ctrl2_mode);
> +
> +	ssd16xx_send_cmd(device, SSD16XX_CMD_DISPLAY_UPDATE_CONTROL1, err);
> +	ssd16xx_send_data(device, ctrl1_byte1, err);
> +	ssd16xx_send_data(device, ctrl1_byte2, err);
> +
> +	ssd16xx_send_cmd(device, SSD16XX_CMD_DISPLAY_UPDATE_CONTROL2, err);
> +	ssd16xx_send_data(device, ctrl2_mode, err);
> +	ssd16xx_send_cmd(device, SSD16XX_CMD_MASTER_ACTIVATION, err);
> +
> +	drm_dbg(&device->drm,
> +		"display_update: Master activation sent, waiting...\n");
> +
> +	ssd16xx_wait_for_device(device, err);
> +}
> +
> +static void ssd16xx_hw_reset(struct ssd16xx_device *device)
> +{
> +	gpiod_set_value_cansleep(device->reset, 1);
> +	usleep_range(10000, 11000);
> +	gpiod_set_value_cansleep(device->reset, 0);
> +	usleep_range(10000, 11000);
> +}
> +
> +/*
> + * ssd16xx_preload_fast_lut() - pre-load the OTP LUT for fast refresh mode.
> + *
> + * Fast refresh (CTRL2 = 0xC7) omits the LOAD_LUT step on every update to save
> + * time.  It relies on the LUT being loaded upfront via this standalone sequence
> + * (CTRL2 = 0xB1: ENABLE_CLK | LOAD_LUT | SSD16XX_CTRL2_LOAD_TEMPERATURE | DISABLE_CLK,
> + *  no display update).
> + *
> + * Must be called when:
> + *   a) hw_init runs with refresh_mode == FAST, and
> + *   b) switching to fast refresh from a mode that did not leave a valid Mode1
> + *      LUT in the controller (i.e. previous mode was not FULL refresh, which
> + *      carries LOAD_LUT in its own CTRL2 sequence).
> + */
> +static int ssd16xx_preload_fast_lut(struct ssd16xx_device *device)
> +{
> +	int err = 0;
> +
> +	ssd16xx_send_cmd(device, SSD16XX_CMD_DISPLAY_UPDATE_CONTROL1, &err);
> +	ssd16xx_send_data(device, device->controller_cfg->ctrl1_bypass_red_ram, &err);
> +	ssd16xx_send_data(device, SSD16XX_CTRL1_BYTE2_DEFAULT, &err);
> +
> +	ssd16xx_send_cmd(device, SSD16XX_CMD_DISPLAY_UPDATE_CONTROL2, &err);
> +	ssd16xx_send_data(device, device->controller_cfg->ctrl2_load_temp_lut, &err);
> +
> +	ssd16xx_send_cmd(device, SSD16XX_CMD_MASTER_ACTIVATION, &err);
> +	ssd16xx_wait_for_device(device, &err);
> +
> +	return err;
> +}
> +
> +static int ssd16xx_hw_init(struct ssd16xx_device *device)
> +{
> +	int err = 0;
> +	u8 data_entry_mode;
> +	/*
> +	 * Driver Output Control MUX ratio = (gate lines - 1).
> +	 * Use the actual device height, not the controller maximum —
> +	 * a smaller device must only drive its own gate lines.
> +	 */
> +
> +	ssd16xx_hw_reset(device);
> +
> +	/* Software reset */
> +	ssd16xx_send_cmd(device, SSD16XX_CMD_SW_RESET, &err);
> +	ssd16xx_wait_for_device(device, &err);
> +
> +	/* Driver output control (0x01): MUX ratio and scan direction. */
> +	ssd16xx_send_cmd(device, SSD16XX_CMD_DRIVER_OUTPUT_CONTROL, &err);
> +	ssd16xx_send_y_param(device, device->height - 1, &err);
> +	ssd16xx_send_data(device, device->device_cfg->driver_output_ctrl_byte3, &err);
> +
> +	/* Internal temperature sensor (SSD1683/SSD1680 only; not present in SSD1673) */
> +	if (device->controller_cfg->has_temp_sensor_ctrl) {
> +		ssd16xx_send_cmd(device, SSD1683_CMD_TEMPERATURE_SENSOR_CONTROL, &err);
> +		ssd16xx_send_data(device, SSD1683_TEMP_SENSOR_INTERNAL, &err);
> +	}
> +
> +	/*
> +	 * For FAST refresh mode, pre-load the LUT once here during initialization.
> +	 * FAST mode ctrl2 (0xC7) omits LOAD_LUT on every update for speed, so the
> +	 * LUT must be loaded upfront. FULL (0xF7) and PARTIAL (0xFF) load LUT on
> +	 * every update, so no preload is needed for those modes.
> +	 */
> +	if (device->refresh_mode == SSD16XX_REFRESH_FAST) {
> +		ssd16xx_send_cmd(device, SSD16XX_CMD_DISPLAY_UPDATE_CONTROL1, &err);
> +		ssd16xx_send_data(device, device->controller_cfg->ctrl1_bypass_red_ram, &err);
> +		ssd16xx_send_data(device, SSD16XX_CTRL1_BYTE2_DEFAULT, &err);
> +
> +		ssd16xx_send_cmd(device, SSD16XX_CMD_DISPLAY_UPDATE_CONTROL2, &err);
> +		ssd16xx_send_data(device, device->controller_cfg->ctrl2_load_temp_lut, &err);
> +
> +		ssd16xx_send_cmd(device, SSD16XX_CMD_MASTER_ACTIVATION, &err);
> +		ssd16xx_wait_for_device(device, &err);
> +	}
> +
> +	/*
> +	 * Set Data Entry Mode (0x11) based on orientation.  This controls
> +	 * how the RAM address counter auto-advances after each byte write.
> +	 *
> +	 * Implementation uses two data entry modes:
> +	 *   - 90°/180° use XDEC_YDEC (0x00): X--, Y-- with cursor at (max, max)
> +	 *   - 0°/270° use XINC_YINC (0x03): X++, Y++ with cursor at (0, 0)
> +	 *
> +	 * The convert_fb_to_1bpp packing is grouped by physical layout:
> +	 *   - Portrait orientations (90°/270°): column-major packing
> +	 *   - Landscape orientations (0°/180°): row-major packing
> +	 *
> +	 * Final scan direction and image orientation are controlled by the
> +	 * combination of data entry mode and RAM cursor position set in fb_dirty.
> +	 *
> +	 * The RAM address window and cursor are NOT set here; fb_dirty
> +	 * always programmes them (with the correct end-before-start order
> +	 * for decrement modes) immediately before writing frame data.
> +	 */
> +	switch (device->orientation) {
> +	case 90:
> +	case 180:
> +		data_entry_mode = SSD16XX_DATA_ENTRY_XDEC_YDEC;
> +		break;
> +	default: /* 0°/270° */
> +		data_entry_mode = SSD16XX_DATA_ENTRY_XINC_YINC;
> +		break;
> +	}
> +
> +	ssd16xx_send_cmd(device, SSD16XX_CMD_DATA_ENTRY_MODE, &err);
> +	ssd16xx_send_data(device, data_entry_mode, &err);
> +	drm_dbg(&device->drm, "hw_init: orientation=%u° data_entry=0x%02x\n",
> +		device->orientation, data_entry_mode);
> +
> +	ssd16xx_wait_for_device(device, &err);
> +
> +	if (err)
> +		drm_err(&device->drm, "Hardware initialization failed: %d\n", err);
> +
> +	return err;
> +}
> +
> +/*
> + * ssd16xx_pixel_luma() - return ITU-R BT.601 luminance (0-255) for one pixel.
> + *
> + * Currently only XRGB8888 is supported.  The function is retained as a named
> + * helper to make it straightforward to add further formats in the future.
> + * R1 is never passed here — it is already 1bpp and handled directly by callers.
> + */
> +static u8 ssd16xx_pixel_luma(struct iosys_map *src,
> +			     struct drm_framebuffer *fb,
> +			     unsigned int x, unsigned int y)
> +{
> +	u32 *line = (u32 *)(src->vaddr + y * fb->pitches[0]);
> +	u32 px = line[x];
> +	u8 r = (px >> 16) & 0xFF, g = (px >> 8) & 0xFF, b = px & 0xFF;
> +
> +	return (u8)((299u * r + 587u * g + 114u * b) / 1000u);
> +}
> +
> +/*
> + * ssd16xx_pixel_is_white() - test whether an XRGB8888 or R1 pixel is white.
> + *
> + * For XRGB8888: ITU-R BT.601 luminance > 127 maps to white.
> + * For R1: the pixel's bit value directly encodes white (1) or black (0).
> + */
> +static bool ssd16xx_pixel_is_white(struct iosys_map *src,
> +				   struct drm_framebuffer *fb,
> +				   unsigned int x, unsigned int y)
> +{
> +	if (fb->format->format == DRM_FORMAT_R1) {
> +		u8 *line = (u8 *)(src->vaddr + y * fb->pitches[0]);
> +
> +		return !!(line[x / 8] & (1 << (7 - (x % 8))));
> +	}
> +	return ssd16xx_pixel_luma(src, fb, x, y) > 127;
> +}
> +
> +/*
> + * ssd16xx_pixel_is_red() - test whether an XRGB8888 pixel is dominated by red.
> + *
> + * Returns true when red exceeds 50% intensity and is strictly greater than
> + * both green and blue (dominant red hue). R1 carries no colour information
> + * and always returns false.
> + */
> +static bool ssd16xx_pixel_is_red(struct iosys_map *src,
> +				 struct drm_framebuffer *fb,
> +				 unsigned int x, unsigned int y)
> +{
> +	u32 *line;
> +	u32 px;
> +	u8 r, g, b;
> +
> +	if (fb->format->format != DRM_FORMAT_XRGB8888)
> +		return false;
> +
> +	line = (u32 *)(src->vaddr + y * fb->pitches[0]);
> +	px = line[x];
> +	r = (px >> 16) & 0xFF;
> +	g = (px >> 8) & 0xFF;
> +	b = px & 0xFF;
> +
> +	return r > 127 && r > g && r > b;
> +}
> +
> +/*
> + * ssd16xx_convert_fb_to_3color() - split a framebuffer into BW and RED planes.
> + * @bw_dst:  output buffer for the black/white RAM plane (1=white, 0=black)
> + * @red_dst: output buffer for the red RAM plane        (1=red,   0=not red)
> + *
> + * Supports XRGB8888 and R1 formats.
> + *
> + * XRGB8888: pixels with a dominant red channel (r > 127 && r > g && r > b)
> + * map to red ink; remaining pixels threshold to white/black via BT.601 luma.
> + *
> + * R1 on a 3-color panel: the 1-bits are interpreted as red ink on a white
> + * background.  BW RAM is set to all-white and RED RAM receives the R1 data
> + * directly (1=red, 0=no red).  This matches the behaviour of a user who
> + * explicitly selects color_mode=3-color and submits a 1-bit mask to place
> + * red ink.
> + */
> +static void ssd16xx_convert_fb_to_3color(u8 *bw_dst, u8 *red_dst,
> +					 struct iosys_map *src,
> +					 struct drm_framebuffer *fb,
> +					 struct drm_rect *rect)
> +{
> +	unsigned int x, y;
> +	u8 bw_byte = 0, red_byte = 0;
> +	unsigned int bit_pos = 0;
> +	unsigned int dst_idx = 0;
> +
> +	if (fb->format->format == DRM_FORMAT_R1) {
> +		unsigned int src_pitch = fb->pitches[0];
> +		unsigned int width_bytes = drm_rect_width(rect) / 8;
> +		unsigned int data_size = width_bytes * drm_rect_height(rect);
> +
> +		/* White background — no black pixels, only red ink shows */
> +		memset(bw_dst, 0xFF, data_size);
> +		/* RED RAM: copy R1 data directly (1=red ink, 0=no red) */
> +		for (y = rect->y1; y < rect->y2; y++) {
> +			u8 *line = src->vaddr + y * src_pitch + (rect->x1 / 8);
> +
> +			memcpy(red_dst + dst_idx, line, width_bytes);
> +			dst_idx += width_bytes;
> +		}
> +		return;
> +	}
> +
> +	/* XRGB8888 */
> +	for (y = rect->y1; y < rect->y2; y++) {
> +		for (x = rect->x1; x < rect->x2; x++) {
> +			bool is_red = ssd16xx_pixel_is_red(src, fb, x, y);
> +
> +			if (is_red)
> +				red_byte |= (1 << (7 - bit_pos));
> +			else if (ssd16xx_pixel_is_white(src, fb, x, y))
> +				bw_byte |= (1 << (7 - bit_pos));
> +			if (++bit_pos == 8) {
> +				bw_dst[dst_idx] = bw_byte;
> +				red_dst[dst_idx] = red_byte;
> +				dst_idx++;
> +				bw_byte = 0;
> +				red_byte = 0;
> +				bit_pos = 0;
> +			}
> +		}
> +		if (bit_pos > 0) {
> +			bw_dst[dst_idx] = bw_byte;
> +			red_dst[dst_idx] = red_byte;
> +			dst_idx++;
> +			bw_byte = 0;
> +			red_byte = 0;
> +			bit_pos = 0;
> +		}
> +	}
> +}
> +
> +/*
> + * Convert framebuffer to 1-bit monochrome for e-paper display.
> + *
> + * Supports XRGB8888 (thresholded via ITU-R BT.601 luma at 127) and R1
> + * (native 1bpp, zero-copy fast path for aligned landscape frames).
> + *
> + * Output layout:
> + *   0°/180°  landscape: row-major, left-to-right, top-to-bottom
> + *   90°/270° CW portrait: column-major, rightmost column first
> + */
> +static void ssd16xx_convert_fb_to_1bpp(u8 *dst, struct iosys_map *src,
> +				       struct drm_framebuffer *fb,
> +				       struct drm_rect *rect,
> +				       unsigned int orientation)
> +{
> +	u32 format = fb->format->format;
> +	int x, y;
> +	u8 byte = 0;
> +	unsigned int bit_pos = 0;
> +	unsigned int dst_idx = 0;
> +
> +	/* Use fixed threshold of 127 for grayscale to monochrome conversion. */
> +	drm_dbg(fb->dev,
> +		"convert_1bpp: fmt=%p4cc rect=(%d,%d)-(%d,%d) orient=%u° path=%s\n",
> +		&fb->format->format,
> +		rect->x1, rect->y1, rect->x2, rect->y2,
> +		orientation,
> +		(format == DRM_FORMAT_R1 && orientation == 0 && rect->x1 % 8 == 0) ? "R1-fast" :
> +		(orientation == 90 || orientation == 270) ? "portrait" : "landscape");
> +
> +	/*
> +	 * R1 fast path: 0° landscape with byte-aligned rect.
> +	 * R1 is already 1bpp so landscape rows map directly to output bytes via
> +	 * memcpy — no per-pixel computation needed.  rect->x1 must be a
> +	 * multiple of 8 so that (rect->x1 / 8) gives the correct byte offset;
> +	 * if not, the generic pixel-by-pixel loop below handles non-aligned
> +	 * rects safely.
> +	 */
> +	if (format == DRM_FORMAT_R1 && orientation == 0 && rect->x1 % 8 == 0) {
> +		unsigned int src_pitch = fb->pitches[0];
> +		unsigned int width_bytes = drm_rect_width(rect) / 8;
> +
> +		for (y = rect->y1; y < rect->y2; y++) {
> +			u8 *src_line = src->vaddr + y * src_pitch + (rect->x1 / 8);
> +
> +			memcpy(dst + dst_idx, src_line, width_bytes);
> +			dst_idx += width_bytes;
> +		}
> +		return;
> +	}
> +
> +	switch (orientation) {
> +	case 90:
> +	case 270:
> +		/*
> +		 * Portrait (90° or 270°): column-major packing.
> +		 * Each portrait source column becomes one physical RAM row.
> +		 * The data entry mode and cursor position control scan direction.
> +		 */
> +		for (x = rect->x2 - 1; x >= (int)rect->x1; x--) {
> +			for (y = rect->y1; y < rect->y2; y++) {
> +				if (ssd16xx_pixel_is_white(src, fb, x, y))
> +					byte |= (1 << (7 - bit_pos));
> +				if (++bit_pos == 8) {
> +					dst[dst_idx++] = byte;
> +					byte = 0;
> +					bit_pos = 0;
> +				}
> +			}
> +			if (bit_pos > 0) {
> +				dst[dst_idx++] = byte;
> +				byte = 0;
> +				bit_pos = 0;
> +			}
> +		}
> +		break;
> +
> +	case 0:
> +	case 180:
> +	default:
> +		/*
> +		 * Landscape (0° or 180°): row-major packing.
> +		 * Each landscape source row becomes one physical RAM row.
> +		 * The data entry mode and cursor position control scan direction.
> +		 */
> +		for (y = rect->y1; y < rect->y2; y++) {
> +			for (x = rect->x1; x < rect->x2; x++) {
> +				if (ssd16xx_pixel_is_white(src, fb, x, y))
> +					byte |= (1 << (7 - bit_pos));
> +				if (++bit_pos == 8) {
> +					dst[dst_idx++] = byte;
> +					byte = 0;
> +					bit_pos = 0;
> +				}
> +			}
> +			if (bit_pos > 0) {
> +				dst[dst_idx++] = byte;
> +				byte = 0;
> +				bit_pos = 0;
> +			}
> +		}
> +		break;
> +	}
> +}
> +
> +static int ssd16xx_fb_dirty(struct drm_framebuffer *fb, struct drm_rect *rect,
> +			    struct ssd16xx_device *device,
> +			    const struct iosys_map *src_map)
> +{
> +	const u8 *ctrl2_tbl = device->controller_cfg->ctrl2_refresh;
> +	struct iosys_map map = *src_map;
> +	int err = 0;
> +	unsigned int data_size = (device->width * device->height) / 8;
> +	u8 *mono_buffer = NULL;
> +	u8 *red_buffer = NULL;
> +	u16 ram_x_start, ram_x_end, ram_y_start, ram_y_end;
> +
> +	/*
> +	 * Process full display area.  The rect for convert_fb_to_1bpp uses
> +	 * the framebuffer (logical) dimensions - the pixel iteration walks
> +	 * the source fb coordinate space. RAM window registers below use
> +	 * the physical panel dimensions (device->width/height).
> +	 */
> +	rect->x1 = 0;
> +	rect->y1 = 0;
> +	rect->x2 = fb->width;
> +	rect->y2 = fb->height;
> +
> +	drm_dbg(&device->drm,
> +		"fb_dirty: fb=%dx%d, refresh_mode=%d, orientation=%d\n",
> +		fb->width, fb->height, device->refresh_mode, device->orientation);
> +
> +	mono_buffer = device->tx_buf;
> +	memset(mono_buffer, 0, data_size);
> +
> +	/* 3-colour FULL/FAST: populate red channel. */
> +	if (device->color_mode == SSD16XX_COLOR_MODE_3COLOR &&
> +	    (device->refresh_mode == SSD16XX_REFRESH_FULL ||
> +	     device->refresh_mode == SSD16XX_REFRESH_FAST)) {
> +		red_buffer = device->tx_red_buf;
> +		memset(red_buffer, 0, data_size);
> +	}
> +
> +	/*
> +	 * R1 format interpretation depends on color_mode:
> +	 *
> +	 *   color_mode = 3-color (red_buffer != NULL):
> +	 *     R1 bits are treated as red ink — 1 = red pixel on a white
> +	 *     background, 0 = no red.  This allows applications to submit a
> +	 *     1-bit mask to place red ink on a BWR panel.
> +	 *     Handled by the R1 path in ssd16xx_convert_fb_to_3color().
> +	 *
> +	 *   color_mode = BW (red_buffer == NULL):
> +	 *     R1 bits are treated as luma — 1 = white, 0 = black.
> +	 *     Handled by the native fast path in ssd16xx_convert_fb_to_1bpp().
> +	 */
> +	if (red_buffer)
> +		ssd16xx_convert_fb_to_3color(mono_buffer, red_buffer, &map, fb, rect);
> +	else
> +		ssd16xx_convert_fb_to_1bpp(mono_buffer, &map, fb, rect, device->orientation);
> +
> +	drm_dbg(&device->drm,
> +		"fb_dirty: mono[0..3]=0x%02x 0x%02x 0x%02x 0x%02x (data_size=%u)\n",
> +		mono_buffer[0], mono_buffer[1], mono_buffer[2], mono_buffer[3],
> +		data_size);
> +
> +	/* Set RAM window and cursor for current orientation. */
> +	ram_x_start = 0;
> +	/*
> +	 * X end depends on the controller's addressing model:
> +	 *   Byte-addressed (ram_x_address_bits == 8, e.g. SSD1683):
> +	 *     XEnd = device_width/8 - 1  (byte offset into RAM row)
> +	 *   Pixel-addressed (ram_x_address_bits != 8, e.g. SSD1677):
> +	 *     XEnd = device_width - 1    (direct pixel index)
> +	 * The model is controller-specific; the value is device-specific.
> +	 */
> +	if (device->controller_cfg->ram_x_address_bits == 8)
> +		ram_x_end = (device->width / 8) - 1;
> +	else
> +		ram_x_end = device->width - 1;
> +	ram_y_start = 0;
> +	ram_y_end = device->height - 1;
> +
> +	switch (device->orientation) {
> +	case 90:
> +	case 180:
> +		/* 90°/180°: XDEC_YDEC mode, send end-before-start; cursor at (max, max). */
> +		ssd16xx_send_cmd(device, SSD16XX_CMD_SET_RAM_X_ADDRESS_START_END, &err);
> +		ssd16xx_send_x_param(device, ram_x_end, &err);
> +		ssd16xx_send_x_param(device, ram_x_start, &err);
> +
> +		ssd16xx_send_cmd(device, SSD16XX_CMD_SET_RAM_Y_ADDRESS_START_END, &err);
> +		ssd16xx_send_y_param(device, ram_y_end, &err);
> +		ssd16xx_send_y_param(device, ram_y_start, &err);
> +
> +		ssd16xx_send_cmd(device, SSD16XX_CMD_SET_RAM_X_ADDRESS_COUNTER, &err);
> +		ssd16xx_send_x_param(device, ram_x_end, &err);
> +
> +		ssd16xx_send_cmd(device, SSD16XX_CMD_SET_RAM_Y_ADDRESS_COUNTER, &err);
> +		ssd16xx_send_y_param(device, ram_y_end, &err);
> +		break;
> +
> +	default: /* 0°/270° */
> +		/* 0°/270°: XINC_YINC mode, cursor at (0, 0). */
> +		ssd16xx_send_cmd(device, SSD16XX_CMD_SET_RAM_X_ADDRESS_START_END, &err);
> +		ssd16xx_send_x_param(device, ram_x_start, &err);
> +		ssd16xx_send_x_param(device, ram_x_end, &err);
> +
> +		ssd16xx_send_cmd(device, SSD16XX_CMD_SET_RAM_Y_ADDRESS_START_END, &err);
> +		ssd16xx_send_y_param(device, ram_y_start, &err);
> +		ssd16xx_send_y_param(device, ram_y_end, &err);
> +
> +		ssd16xx_send_cmd(device, SSD16XX_CMD_SET_RAM_X_ADDRESS_COUNTER, &err);
> +		ssd16xx_send_x_param(device, ram_x_start, &err);
> +
> +		ssd16xx_send_cmd(device, SSD16XX_CMD_SET_RAM_Y_ADDRESS_COUNTER, &err);
> +		ssd16xx_send_y_param(device, ram_y_start, &err);
> +		break;
> +	}
> +
> +	ssd16xx_send_cmd(device, SSD16XX_CMD_WRITE_RAM_BW, &err);
> +	ssd16xx_send_data_bulk(device, mono_buffer, data_size, &err);
> +
> +	/* Re-send border waveform when: every-update mode, init frame
> +	 */
> +	drm_dbg(&device->drm,
> +		"fb_dirty: border check: every_update=%d init_pending=%d border_pending=%d idx=%d hw=0x%02x\n",
> +		device->border_refresh_on_every_update, device->init_refresh_pending,
> +		device->border_waveform_pending, device->border_waveform_update_idx,
> +		device->controller_cfg->border_waveform_table[device->border_waveform_update_idx]);
> +	if (device->border_refresh_on_every_update || device->init_refresh_pending ||
> +	    device->border_waveform_pending) {
> +		u8 idx = device->border_waveform_update_idx;
> +		u8 border = device->controller_cfg->border_waveform_table[idx];
> +
> +		drm_dbg(&device->drm, "fb_dirty: Sending border waveform: 0x%02x\n",
> +			border);
> +		ssd16xx_send_cmd(device, SSD16XX_CMD_BORDER_WAVEFORM_CONTROL, &err);
> +		ssd16xx_send_data(device, border, &err);
> +		device->border_waveform_pending = false;
> +	}
> +
> +	switch (device->refresh_mode) {
> +	case SSD16XX_REFRESH_FULL:
> +		/*
> +		 * BW full refresh: write RED RAM BEFORE display_update
> +		 * to avoid a post-BUSY write timing issue on some
> +		 * controller revisions that silently corrupts RED RAM.
> +		 * RED RAM is then bypassed (CTRL1_BYPASS_RED_RAM) so
> +		 * stale RED RAM content does not affect the output.
> +		 */
> +		ssd16xx_send_cmd(device, SSD1683_CMD_WRITE_RAM_RED, &err);
> +		if (red_buffer) {
> +			/* 3-colour: write red channel before activating */
> +			ssd16xx_send_data_bulk(device, red_buffer, data_size, &err);
> +			ssd16xx_display_update(device, device->controller_cfg->ctrl1_normal,
> +					       SSD16XX_CTRL1_BYTE2_DEFAULT,
> +					       ctrl2_tbl[SSD16XX_REFRESH_FULL], &err);
> +		} else {
> +			ssd16xx_send_data_bulk(device, mono_buffer, data_size, &err);
> +			ssd16xx_display_update(device, device->controller_cfg->ctrl1_bypass_red_ram,
> +					       SSD16XX_CTRL1_BYTE2_DEFAULT,
> +					       ctrl2_tbl[SSD16XX_REFRESH_FULL], &err);
> +		}
> +		break;
> +	case SSD16XX_REFRESH_FAST:
> +		/*
> +		 * Fast refresh: LUT pre-loaded during hw_init; BYPASS_RED_RAM
> +		 * so RED RAM does not affect the current output.
> +		 * Write RED RAM BEFORE display_update (same reasoning as FULL)
> +		 * so it holds the just-displayed frame as a valid reference for
> +		 * any subsequent PARTIAL refresh.
> +		 */
> +
> +		ssd16xx_send_cmd(device, SSD1683_CMD_WRITE_RAM_RED, &err);
> +		if (red_buffer) {
> +			/* 3-colour: write red channel before activating */
> +			ssd16xx_send_data_bulk(device, red_buffer, data_size, &err);
> +			ssd16xx_display_update(device, device->controller_cfg->ctrl1_normal,
> +					       SSD16XX_CTRL1_BYTE2_DEFAULT,
> +					       ctrl2_tbl[SSD16XX_REFRESH_FAST], &err);
> +		} else {
> +			ssd16xx_send_data_bulk(device, mono_buffer, data_size, &err);
> +			ssd16xx_display_update(device, device->controller_cfg->ctrl1_bypass_red_ram,
> +					       SSD16XX_CTRL1_BYTE2_DEFAULT,
> +					       ctrl2_tbl[SSD16XX_REFRESH_FAST], &err);
> +		}
> +		break;
> +	case SSD16XX_REFRESH_PARTIAL:
> +	default:
> +		/*
> +		 * Partial refresh: both RAMs used for transition waveforms.
> +		 * RED RAM must hold the PREVIOUS frame (= current display
> +		 * content) so the controller can compute pixel transitions.
> +		 * Write RED RAM AFTER display_update so it captures the
> +		 * just-displayed frame as the reference for the next partial.
> +		 */
> +		drm_dbg(&device->drm,
> +			"fb_dirty: partial pre-update: mono[0]=0x%02x (BW=new, RED=prev)\n",
> +			mono_buffer[0]);
> +		ssd16xx_display_update(device, device->controller_cfg->ctrl1_normal,
> +				       SSD16XX_CTRL1_BYTE2_DEFAULT,
> +				       ctrl2_tbl[SSD16XX_REFRESH_PARTIAL], &err);
> +		ssd16xx_send_cmd(device, SSD1683_CMD_WRITE_RAM_RED, &err);
> +		ssd16xx_send_data_bulk(device, mono_buffer, data_size, &err);
> +		drm_dbg(&device->drm,
> +			"fb_dirty: partial post-update: wrote RED baseline mono[0]=0x%02x\n",
> +			mono_buffer[0]);
> +		break;
> +	}
> +
> +	return err;
> +}
> +
> +/* -----------------------------------------------------------------------------
> + * Plane Functions
> + */
> +
> +static void ssd16xx_plane_destroy(struct drm_plane *plane)
> +{
> +	drm_plane_cleanup(plane);
> +}
> +
> +static const struct drm_plane_funcs ssd16xx_plane_funcs = {
> +	.update_plane = drm_atomic_helper_update_plane,
> +	.disable_plane = drm_atomic_helper_disable_plane,
> +	.destroy = ssd16xx_plane_destroy,
> +	DRM_GEM_SHADOW_PLANE_FUNCS,
> +};
> +
> +static int ssd16xx_plane_atomic_check(struct drm_plane *plane,
> +				      struct drm_atomic_commit *state)
> +{
> +	struct drm_plane_state *new_plane_state =
> +		drm_atomic_get_new_plane_state(state, plane);
> +	struct drm_crtc_state *crtc_state;
> +
> +	if (!new_plane_state->crtc)
> +		return 0;
> +
> +	crtc_state = drm_atomic_get_new_crtc_state(state, new_plane_state->crtc);
> +
> +	return drm_atomic_helper_check_plane_state(new_plane_state, crtc_state,
> +						   DRM_PLANE_NO_SCALING,
> +						   DRM_PLANE_NO_SCALING,
> +						   false, false);
> +}
> +
> +static void ssd16xx_plane_atomic_update(struct drm_plane *plane,
> +					struct drm_atomic_commit *state)
> +{
> +	struct drm_plane_state *old_state = drm_atomic_get_old_plane_state(state, plane);
> +	struct drm_plane_state *new_state = drm_atomic_get_new_plane_state(state, plane);
> +	struct drm_shadow_plane_state *shadow_state = to_drm_shadow_plane_state(new_state);
> +	struct ssd16xx_device *device = plane_to_ssd16xx_device(plane);
> +	enum ssd16xx_refresh_mode saved_mode;
> +	u8 saved_border_waveform_idx;
> +	struct drm_framebuffer *fb = new_state->fb;
> +	struct drm_rect rect;
> +	int ret;
> +

The atomic_update function is missing drm_dev_enter() and drm_dev exit().

Your driver also needs lock the gem buffer with 
drm_gem_fb_begin_cpu_access() and drm_gem_fb_end_cpu_access() whenever 
you read its data. See [1] for an example. Otherwise a concurrent 
exporter could write into the memory.

[1] 
https://elixir.bootlin.com/linux/v7.2.8/source/drivers/gpu/drm/ast/ast_cursor.c#L198


> +	drm_dbg(&device->drm, "plane_atomic_update: fb=%p, initialized=%d\n",
> +		fb, device->initialized);
> +
> +	if (!fb || !device->initialized)
> +		return;

Your driver should have initialized HW long before it comes here.

> +
> +	if (!drm_atomic_helper_damage_merged(old_state, new_state, &rect)) {
> +		rect.x1 = 0;
> +		rect.y1 = 0;
> +		rect.x2 = fb->width;
> +		rect.y2 = fb->height;
> +		drm_dbg(&device->drm, "plane_atomic_update: no damage, using full screen\n");
> +	}

The correct pattern is:

   if (damage_merged()) {
     // do screen update.
   }

your driver is not allowed to setup its own rectangles and update those 
instead.


> +
> +	drm_dbg(&device->drm, "plane_atomic_update: calling fb_dirty rect=(%d,%d)-(%d,%d)\n",
> +		rect.x1, rect.y1, rect.x2, rect.y2);
> +	/*
> +	 * When refresh_mode_init was set, use the specified mode for this first
> +	 * frame only, then restore the user-configured refresh_mode so
> +	 * subsequent updates continue with the configured mode.
> +	 */
> +	saved_mode = device->refresh_mode;
> +	saved_border_waveform_idx = device->border_waveform_update_idx;
> +	if (device->init_refresh_pending) {
> +		device->refresh_mode = device->refresh_mode_init;
> +		device->border_waveform_update_idx = device->border_waveform_init_idx;
> +	}
> +
> +	/*
> +	 * Fast refresh (0xC7) omits LOAD_LUT on every update cycle and relies
> +	 * on the LUT being pre-loaded upfront.  The property setter arms
> +	 * fast_lut_pending whenever the user switches into fast mode.  Consume
> +	 * the flag here (once) before the first fast-refresh frame so the
> +	 * controller's LUT is in the correct state.
> +	 */
> +	if (device->fast_lut_pending) {
> +		ret = ssd16xx_preload_fast_lut(device);
> +		if (ret) {
> +			drm_err(&device->drm,
> +				"plane_atomic_update: fast LUT preload failed: %d\n", ret);
> +		}
> +
> +		device->fast_lut_pending = false;
> +	}
> +
> +	ret = ssd16xx_fb_dirty(fb, &rect, device, &shadow_state->data[0]);
> +	if (ret)
> +		drm_err(&device->drm, "plane_atomic_update: display update failed: %d\n", ret);
> +	else
> +		device->last_fb = fb;
> +
> +	device->refresh_mode = saved_mode;
> +	device->border_waveform_update_idx = saved_border_waveform_idx;
> +
> +	/*
> +	 * If this was the init frame (which used border_waveform_init_idx
> +	 * inside fb_dirty), arm border_waveform_pending so the normal
> +	 * (non-init) border value is sent at the start of the next update.
> +	 */
> +	if (device->init_refresh_pending) {
> +		device->init_refresh_pending = false;
> +		device->border_waveform_pending = true;
> +	}
> +}
> +
> +static const struct drm_plane_helper_funcs ssd16xx_plane_helper_funcs = {
> +	DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
> +	.atomic_check = ssd16xx_plane_atomic_check,
> +	.atomic_update = ssd16xx_plane_atomic_update,
> +};
> +
> +/* -----------------------------------------------------------------------------
> + * CRTC Functions
> + */
> +
> +static void ssd16xx_crtc_destroy(struct drm_crtc *crtc)
> +{
> +	drm_crtc_cleanup(crtc);
> +}

No need for this wrapper AFAICT.

> +
> +static const struct drm_crtc_funcs ssd16xx_crtc_funcs = {
> +	.atomic_create_state = drm_atomic_helper_crtc_create_state,
> +	.destroy = ssd16xx_crtc_destroy,
> +	.set_config = drm_atomic_helper_set_config,
> +	.page_flip = drm_atomic_helper_page_flip,
> +	.atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,
> +	.atomic_destroy_state = drm_atomic_helper_crtc_destroy_state,
> +};
> +
> +static enum drm_mode_status ssd16xx_crtc_mode_valid(struct drm_crtc *crtc,
> +						    const struct drm_display_mode *mode)
> +{
> +	struct ssd16xx_device *device = crtc_to_ssd16xx_device(crtc);
> +
> +	/* Accept only our device's native mode (landscape or portrait) */
> +	if ((mode->hdisplay == device->mode->hdisplay &&
> +	     mode->vdisplay == device->mode->vdisplay) ||
> +	    (mode->hdisplay == device->mode->vdisplay &&
> +	     mode->vdisplay == device->mode->hdisplay))
> +		return MODE_OK;
> +
> +	return MODE_BAD;
> +}
> +
> +static int ssd16xx_crtc_atomic_check(struct drm_crtc *crtc,
> +				     struct drm_atomic_commit *state)
> +{
> +	return 0;

Since the CRTC and primary plane need to move in sync, here's a good 
place to test that with drm_atomic_helper_check_crtc_primary_plane(). 
See [2] for an example.

[2] 
https://elixir.bootlin.com/linux/v7.2.8/source/drivers/gpu/drm/sysfb/drm_sysfb_modeset.c#L496


> +}
> +
> +static void ssd16xx_crtc_atomic_disable(struct drm_crtc *crtc,
> +					struct drm_atomic_commit *state)
> +{
> +	struct ssd16xx_device *device = crtc_to_ssd16xx_device(crtc);
> +	int idx;
> +
> +	if (!drm_dev_enter(&device->drm, &idx))
> +		return;
> +
> +	drm_dev_exit(idx);
> +}

No need for this helper AFAICT.

> +
> +static void ssd16xx_crtc_atomic_enable(struct drm_crtc *crtc,
> +				       struct drm_atomic_commit *state)
> +{
> +	struct ssd16xx_device *device = crtc_to_ssd16xx_device(crtc);
> +	int ret, idx;
> +
> +	if (!drm_dev_enter(&device->drm, &idx))
> +		return;
> +
> +	drm_dbg(&device->drm, "atomic_enable: %dx%d orientation=%u°\n",
> +		device->width, device->height, device->orientation);
> +
> +	ret = ssd16xx_hw_init(device);
> +	if (ret) {
> +		drm_err(&device->drm, "crtc_atomic_enable: HW init failed: %d\n", ret);
> +		goto out;
> +	}
> +	device->initialized = true;

This is also problematic. The driver should have initialized the device 
hardware when probing it.  If this fails, probe need to fail with an 
error.  There should then not be a modesetting pipeline at all.

> +
> +	/*
> +	 * If refresh_mode_init is set, arm init_refresh_pending so
> +	 * plane_atomic_update uses the specified mode for the first frame
> +	 * then restores the user-configured or device default refresh_mode.
> +	 */
> +	if (device->refresh_mode_init >= 0) {
> +		drm_dbg(&device->drm,
> +			"atomic_enable: refresh_mode_init=%d, using for first frame\n",
> +			device->refresh_mode_init);
> +		device->init_refresh_pending = true;
> +	}
> +
> +out:
> +	drm_dev_exit(idx);
> +}
> +
> +/*
> + * Re-initialize hardware and redraw the current framebuffer when the
> + * display orientation changes at runtime
> + */
> +static void ssd16xx_crtc_atomic_flush(struct drm_crtc *crtc,
> +				      struct drm_atomic_commit *state)
> +{
> +	struct ssd16xx_device *device = crtc_to_ssd16xx_device(crtc);
> +	struct drm_framebuffer *fb;
> +	struct drm_rect full;
> +	int ret, idx;
> +
> +	if (!device->initialized)
> +		return;
> +
> +	if (!drm_dev_enter(&device->drm, &idx))
> +		return;
> +
> +	drm_dbg(&device->drm, "atomic_flush: reinit, orientation=%u°\n",
> +		device->orientation);
> +
> +	ret = ssd16xx_hw_init(device);
> +	if (ret) {
> +		drm_err(&device->drm, "Orientation re-init failed: %d\n", ret);
> +		goto out;
> +	}

Another one of those HW inits. IIRC there are many more of them.

> +
> +	fb = device->primary_plane.state ? device->primary_plane.state->fb
> +					: device->last_fb;
> +	if (fb) {
> +		struct drm_gem_object *obj = drm_gem_fb_get_obj(fb, 0);
> +		struct iosys_map map;
> +
> +		full.x1 = 0;
> +		full.y1 = 0;
> +		full.x2 = fb->width;
> +		full.y2 = fb->height;
> +
> +		ret = drm_gem_vmap(obj, &map);
> +		if (!ret) {
> +			ret = ssd16xx_fb_dirty(fb, &full, device, &map);
> +			drm_gem_vunmap(obj, &map);
> +		}

Screen pixel updates belong in the plane's atomic_update.

> +		if (ret)
> +			drm_err(&device->drm, "atomic_flush: display update failed: %d\n", ret);
> +		else
> +			device->last_fb = fb;
> +	}
> +
> +out:
> +	drm_dev_exit(idx);
> +}
> +
> +static const struct drm_crtc_helper_funcs ssd16xx_crtc_helper_funcs = {
> +	.mode_valid     = ssd16xx_crtc_mode_valid,
> +	.atomic_check   = ssd16xx_crtc_atomic_check,
> +	.atomic_disable = ssd16xx_crtc_atomic_disable,
> +	.atomic_enable  = ssd16xx_crtc_atomic_enable,
> +	.atomic_flush   = ssd16xx_crtc_atomic_flush,
> +};
> +
> +/* -----------------------------------------------------------------------------
> + * Connector Functions
> + */
> +
> +static int ssd16xx_connector_get_modes(struct drm_connector *connector)
> +{
> +	struct ssd16xx_device *device = to_ssd16xx_device(connector->dev);
> +	bool mode_is_portrait = (device->mode->hdisplay < device->mode->vdisplay);
> +	bool orient_is_portrait = (device->orientation == 90 || device->orientation == 270);
> +
> +	drm_dbg(&device->drm,
> +		"connector_get_modes: orientation=%u° mode=%ux%u mode_portrait=%d orient_portrait=%d\n",
> +		device->orientation, device->mode->hdisplay, device->mode->vdisplay,
> +		mode_is_portrait, orient_is_portrait);
> +
> +	/* For portrait, swap dimensions so clients see logical size. */
> +	if (mode_is_portrait != orient_is_portrait) {
> +		struct drm_display_mode *mode;
> +
> +		mode = drm_mode_duplicate(&device->drm, device->mode);
> +		if (!mode)
> +			return 0;
> +		swap(mode->hdisplay, mode->vdisplay);
> +		swap(mode->hsync_start, mode->vsync_start);
> +		swap(mode->hsync_end, mode->vsync_end);
> +		swap(mode->htotal, mode->vtotal);
> +		swap(mode->width_mm, mode->height_mm);
> +		mode->type |= DRM_MODE_TYPE_PREFERRED;
> +		drm_mode_set_name(mode);
> +		drm_mode_probed_add(connector, mode);
> +		return 1;
> +	}
> +
> +	return drm_connector_helper_get_modes_fixed(connector, device->mode);
> +}
> +
> +static const struct drm_connector_helper_funcs ssd16xx_connector_helper_funcs = {
> +	.get_modes = ssd16xx_connector_get_modes,
> +};
> +
> +static const struct drm_connector_funcs ssd16xx_connector_funcs = {
> +	.reset = drm_atomic_helper_connector_reset,
> +	.fill_modes = drm_helper_probe_single_connector_modes,
> +	.destroy = drm_connector_cleanup,
> +	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
> +	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
> +};
> +
> +static const u32 ssd16xx_formats[] = {
> +	DRM_FORMAT_XRGB8888,  /* 32-bit RGB with padding (preferred) */
> +	DRM_FORMAT_R1,        /* 1-bit monochrome (native, zero-copy path) */
> +};
> +
> +DEFINE_DRM_GEM_FOPS(ssd16xx_fops);
> +
> +/*
> + * ssd16xx_drm_master_set - arm init refresh when a new master takes control.
> + */
> +static void ssd16xx_drm_master_set(struct drm_device *drm,
> +				   struct drm_file *file, bool from_open)
> +{
> +	struct ssd16xx_device *device = to_ssd16xx_device(drm);
> +
> +	if (device->refresh_mode_init >= 0)
> +		device->init_refresh_pending = true;
> +}
> +
> +/*
> + * ssd16xx_drm_master_drop - clear display and disarm init refresh when the
> + * master client exits.
> + */
> +static void ssd16xx_drm_master_drop(struct drm_device *drm,
> +				    struct drm_file *file)
> +{
> +	struct ssd16xx_device *device = to_ssd16xx_device(drm);
> +
> +	device->init_refresh_pending = false;
> +}
> +
> +static struct drm_driver ssd16xx_drm_driver = {
> +	.driver_features = DRIVER_GEM | DRIVER_MODESET | DRIVER_ATOMIC,
> +	.fops = &ssd16xx_fops,
> +	.name = "ssd16xx",
> +	.desc = "DRM driver for SSD16xx e-paper controller family",
> +	.major = 1,
> +	.minor = 0,
> +	.master_set  = ssd16xx_drm_master_set,
> +	.master_drop = ssd16xx_drm_master_drop,
> +	DRM_GEM_SHMEM_DRIVER_OPS,
> +	DRM_FBDEV_SHMEM_DRIVER_OPS,
> +};
> +
> +static const struct drm_mode_config_funcs ssd16xx_mode_config_funcs = {
> +	.fb_create = drm_gem_fb_create_with_dirty,
> +	.atomic_check = drm_atomic_helper_check,
> +	.atomic_commit = drm_atomic_helper_commit,
> +};
> +
> +/*
> + * Use the RPM commit-tail variant so that drm_atomic_helper_commit_modeset_enables
> + * (which calls crtc_atomic_enable) runs before drm_atomic_helper_commit_planes.
> + * Without this, the standard commit_tail calls commit_planes before
> + * modeset_enables, so plane_atomic_update would see initialized == false on the
> + * first commit and silently drop the frame.
> + */
> +static const struct drm_mode_config_helper_funcs ssd16xx_mode_config_helper_funcs = {
> +	.atomic_commit_tail = drm_atomic_helper_commit_tail_rpm,
> +};
> +
> +static int ssd16xx_alloc_tx_bufs(struct ssd16xx_device *device)
> +{
> +	/*
> +	 * Allocate for the actual physical panel size (width × height are
> +	 * always the physical dimensions, never swapped for orientation).
> +	 */
> +	size_t frame_size = DIV_ROUND_UP(device->width * device->height, 8);
> +
> +	device->tx_buf = drmm_kmalloc(&device->drm, frame_size, GFP_KERNEL);
> +	if (!device->tx_buf)
> +		return -ENOMEM;
> +
> +	if (device->device_cfg->red_supported) {
> +		device->tx_red_buf = drmm_kmalloc(&device->drm, frame_size, GFP_KERNEL);
> +		if (!device->tx_red_buf)
> +			return -ENOMEM;
> +	}
> +
> +	if (!device->dc) {
> +		device->tx_buf9 = drmm_kmalloc_array(&device->drm, frame_size,
> +						     sizeof(u16), GFP_KERNEL);
> +		if (!device->tx_buf9)
> +			return -ENOMEM;
> +	}
> +
> +	return 0;
> +}
> +
> +static int ssd16xx_probe(struct spi_device *spi)
> +{
> +	struct device *dev = &spi->dev;
> +	struct ssd16xx_device *device;
> +	struct drm_device *drm;
> +	const struct spi_device_id *spi_id;
> +	struct drm_display_mode *mode;
> +	const void *match;
> +	enum ssd16xx_model model;
> +	u32 dt_rotation = 0;
> +	int ret;
> +
> +	match = device_get_match_data(dev);
> +	if (match) {
> +		model = (enum ssd16xx_model)(uintptr_t)match;
> +	} else {
> +		spi_id = spi_get_device_id(spi);
> +		model = (enum ssd16xx_model)spi_id->driver_data;
> +	}
> +
> +	device = devm_drm_dev_alloc(dev, &ssd16xx_drm_driver,
> +				    struct ssd16xx_device, drm);
> +	if (IS_ERR(device))
> +		return PTR_ERR(device);
> +
> +	drm = &device->drm;
> +	device->spi = spi;
> +	device->model = model;
> +	spi_set_drvdata(spi, device);
> +
> +	spi->mode = SPI_MODE_0;
> +	spi->bits_per_word = SSD16XX_SPI_BITS_PER_WORD;
> +
> +	if (!spi->max_speed_hz) {
> +		drm_warn(drm, "spi-max-frequency not specified, using %u Hz\n",
> +			 SSD16XX_SPI_SPEED_DEFAULT);
> +		spi->max_speed_hz = SSD16XX_SPI_SPEED_DEFAULT;
> +	}
> +
> +	ret = spi_setup(spi);
> +	if (ret < 0) {
> +		drm_err(drm, "SPI setup failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	switch (model) {
> +	case GDEY042T81:
> +		device->controller = SSD1683;
> +		break;
> +	default:
> +		drm_err(drm, "Unknown panel model: %d\n", model);
> +		return -EINVAL;
> +	}
> +
> +	if (device->controller >= ARRAY_SIZE(ssd16xx_controller_configs) ||
> +	    !ssd16xx_controller_configs[device->controller].max_width)
> +		return -EINVAL;
> +	device->controller_cfg = &ssd16xx_controller_configs[device->controller];
> +
> +	if (model >= ARRAY_SIZE(ssd16xx_device_configs))
> +		return -EINVAL;
> +	device->device_cfg = &ssd16xx_device_configs[model];
> +
> +	mode = devm_kmemdup(dev, device->device_cfg->mode,
> +			    sizeof(*device->device_cfg->mode), GFP_KERNEL);
> +	if (!mode)
> +		return -ENOMEM;
> +
> +	device->refresh_mode = device->device_cfg->default_refresh_mode;
> +	device->color_mode   = device->device_cfg->default_color_mode;
> +	device->border_waveform_init_idx   = device->device_cfg->default_border_waveform_init;
> +	device->border_waveform_update_idx = device->device_cfg->default_border_waveform_update;
> +	device->border_refresh_on_every_update =
> +		device->device_cfg->default_border_refresh_on_every_update;
> +	device->refresh_mode_init = device->device_cfg->default_refresh_mode_init;
> +
> +	/* Parse "rotation" DT property; swap mode dimensions for portrait. */
> +	device_property_read_u32(dev, "rotation", &dt_rotation);
> +	if (dt_rotation != 0 && dt_rotation != 90 && dt_rotation != 180 && dt_rotation != 270) {
> +		drm_warn(drm, "Invalid DT rotation %u, defaulting to 0°\n", dt_rotation);
> +		dt_rotation = 0;
> +	}
> +	device->orientation = dt_rotation;
> +
> +	device->width = mode->hdisplay;
> +	device->height = mode->vdisplay;
> +
> +	drm_dbg(drm, "Using %s orientation (%u°, physical %ux%u)\n",
> +		(device->orientation == 90 || device->orientation == 270) ?
> +		 "portrait" : "landscape", device->orientation, device->width, device->height);
> +
> +	/* Swap mode dimensions for portrait so clients see logical size. */
> +	if (device->orientation == 90 || device->orientation == 270) {
> +		swap(mode->hdisplay, mode->vdisplay);
> +		swap(mode->hsync_start, mode->vsync_start);
> +		swap(mode->hsync_end, mode->vsync_end);
> +		swap(mode->htotal, mode->vtotal);
> +		swap(mode->width_mm, mode->height_mm);
> +		drm_dbg(drm, "Mode dimensions swapped for portrait: %ux%u\n",
> +			mode->hdisplay, mode->vdisplay);
> +	} else {
> +		drm_dbg(drm, "Mode dimensions unchanged: %ux%u\n",
> +			mode->hdisplay, mode->vdisplay);
> +	}
> +	device->mode = mode;
> +
> +	/* Validate panel dimensions against controller hardware limits. */
> +	if (device->width > device->controller_cfg->max_width ||
> +	    device->height > device->controller_cfg->max_height) {
> +		drm_err(drm, "panel %ux%u exceeds controller max %ux%u\n",
> +			device->width, device->height,
> +			device->controller_cfg->max_width,
> +			device->controller_cfg->max_height);
> +		return -EINVAL;
> +	}
> +
> +	/*
> +	 * For byte-addressed X (SSD1683, ram_x_address_bits == 8), each X
> +	 * address covers 8 pixels.  The panel width must be a multiple of 8
> +	 * so that (width/8 - 1) gives the correct byte-aligned window end.
> +	 */
> +	if (device->controller_cfg->ram_x_address_bits == 8 &&
> +	    device->width % 8 != 0) {
> +		drm_err(drm, "panel width %u not a multiple of 8 required for byte-addressed X controller)\n",
> +			device->width);
> +		return -EINVAL;
> +	}
> +
> +	/* Acquire GPIOs. */
> +	device->reset = devm_gpiod_get(dev, "reset", GPIOD_OUT_HIGH);
> +	if (IS_ERR(device->reset))
> +		return dev_err_probe(dev, PTR_ERR(device->reset), "Failed to get RESET GPIO\n");
> +
> +	device->busy = devm_gpiod_get(dev, "busy", GPIOD_IN);
> +	if (IS_ERR(device->busy))
> +		return dev_err_probe(dev, PTR_ERR(device->busy), "Failed to get BUSY GPIO\n");
> +
> +	device->dc = devm_gpiod_get_optional(dev, "dc", GPIOD_OUT_LOW);
> +	if (IS_ERR(device->dc))
> +		return dev_err_probe(dev, PTR_ERR(device->dc), "Failed to get DC GPIO\n");
> +	if (!device->dc) {
> +		if (!spi_is_bpw_supported(spi, 9))
> +			return dev_err_probe(dev, -EINVAL,
> +					     "3-wire SPI mode requires 9-bit word support\n");
> +		drm_dbg(drm, "dc-gpios not specified, using 3-wire (9-bit) SPI mode\n");
> +	}
> +
> +	ret = ssd16xx_alloc_tx_bufs(device);
> +	if (ret)
> +		return ret;
> +
> +	ssd16xx_hw_reset(device);
> +
> +	ret = drmm_mode_config_init(drm);
> +	if (ret)
> +		return ret;
> +
> +	drm->mode_config.funcs = &ssd16xx_mode_config_funcs;
> +	drm->mode_config.helper_private = &ssd16xx_mode_config_helper_funcs;
> +	drm->mode_config.min_width = min(device->width, device->height);
> +	drm->mode_config.max_width = max(device->width, device->height);
> +	drm->mode_config.min_height = min(device->width, device->height);
> +	drm->mode_config.max_height = max(device->width, device->height);
> +
> +	drm_connector_helper_add(&device->connector, &ssd16xx_connector_helper_funcs);
> +	ret = drm_connector_init(drm, &device->connector, &ssd16xx_connector_funcs,
> +				 DRM_MODE_CONNECTOR_SPI);
> +	if (ret)
> +		return ret;
> +
> +	ret = drm_universal_plane_init(drm, &device->primary_plane, 0,
> +				       &ssd16xx_plane_funcs,
> +				       ssd16xx_formats, ARRAY_SIZE(ssd16xx_formats),
> +				       NULL, DRM_PLANE_TYPE_PRIMARY, NULL);
> +	if (ret)
> +		return ret;
> +	drm_plane_helper_add(&device->primary_plane, &ssd16xx_plane_helper_funcs);
> +	drm_plane_enable_fb_damage_clips(&device->primary_plane);
> +
> +	ret = drm_crtc_init_with_planes(drm, &device->crtc, &device->primary_plane,
> +					NULL, &ssd16xx_crtc_funcs, NULL);
> +	if (ret)
> +		return ret;
> +	drm_crtc_helper_add(&device->crtc, &ssd16xx_crtc_helper_funcs);
> +
> +	ret = drmm_encoder_init(drm, &device->encoder, NULL, DRM_MODE_ENCODER_NONE, NULL);
> +	if (ret)
> +		return ret;
> +	device->encoder.possible_crtcs = drm_crtc_mask(&device->crtc);
> +
> +	ret = drm_connector_attach_encoder(&device->connector, &device->encoder);
> +	if (ret)
> +		return ret;
> +
> +	drm_mode_config_reset(drm);
> +
> +	ret = drm_dev_register(drm, 0);
> +	if (ret)
> +		return ret;
> +
> +	drm_dbg(drm, "SSD16xx e-paper display initialized (%dx%d, %d° rotation)\n",
> +		device->width, device->height, device->orientation);
> +
> +	drm_client_setup(drm, NULL);
> +
> +	return 0;
> +}
> +
> +static void ssd16xx_remove(struct spi_device *spi)
> +{
> +	struct ssd16xx_device *device = spi_get_drvdata(spi);
> +
> +	drm_dev_unplug(&device->drm);
> +	drm_atomic_helper_shutdown(&device->drm);
> +}
> +
> +static void ssd16xx_shutdown(struct spi_device *spi)
> +{
> +	struct ssd16xx_device *device = spi_get_drvdata(spi);
> +
> +	drm_atomic_helper_shutdown(&device->drm);
> +}
> +
> +static const struct of_device_id ssd16xx_of_match[] = {
> +	{ .compatible = "gooddisplay,gdey042t81", .data = (void *)GDEY042T81 },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, ssd16xx_of_match);
> +
> +static const struct spi_device_id ssd16xx_id[] = {
> +	{ "gdey042t81", GDEY042T81 },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(spi, ssd16xx_id);
> +
> +static struct spi_driver ssd16xx_spi_driver = {
> +	.driver = {
> +		.name = "ssd16xx",
> +		.of_match_table = ssd16xx_of_match,
> +	},
> +	.probe = ssd16xx_probe,
> +	.remove = ssd16xx_remove,
> +	.shutdown = ssd16xx_shutdown,
> +	.id_table = ssd16xx_id,
> +};
> +module_spi_driver(ssd16xx_spi_driver);
> +
> +MODULE_AUTHOR("Devarsh Thakkar <devarsht@ti.com>");
> +MODULE_DESCRIPTION("DRM driver for Solomon SSD16xx e-paper display controller family");
> +MODULE_LICENSE("GPL");

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Stefan Gaiser, Jochen Jaser, Abhinav Puri, (HRB 36809, AG Nürnberg)