xref: /linux/drivers/gpu/drm/sitronix/st7571-i2c.c (revision 1d043d6c00b010c186ad0ddab0a0b9bd648e9bf1)

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Driver for Sitronix ST7571, a 4 level gray scale dot matrix LCD controller
 *
 * Copyright (C) 2025 Marcus Folkesson <marcus.folkesson@gmail.com>
 */

#include <linux/bitfield.h>
#include <linux/delay.h>
#include <linux/gpio/consumer.h>
#include <linux/i2c.h>
#include <linux/module.h>
#include <linux/regmap.h>

#include <drm/clients/drm_client_setup.h>
#include <drm/drm_atomic.h>
#include <drm/drm_atomic_helper.h>
#include <drm/drm_connector.h>
#include <drm/drm_crtc_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_fourcc.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_modeset_helper_vtables.h>
#include <drm/drm_module.h>
#include <drm/drm_plane.h>
#include <drm/drm_probe_helper.h>

#include <video/display_timing.h>
#include <video/of_display_timing.h>

#define ST7571_COMMAND_MODE			(0x00)
#define ST7571_DATA_MODE			(0x40)

/* Normal mode command set */
#define ST7571_DISPLAY_OFF			(0xae)
#define ST7571_DISPLAY_ON			(0xaf)
#define ST7571_OSC_ON				(0xab)
#define ST7571_SET_COLUMN_LSB(c)		(0x00 | FIELD_PREP(GENMASK(3, 0), (c)))
#define ST7571_SET_COLUMN_MSB(c)		(0x10 | FIELD_PREP(GENMASK(2, 0), (c) >> 4))
#define ST7571_SET_COM0_LSB(x)			(FIELD_PREP(GENMASK(6, 0), (x)))
#define ST7571_SET_COM0_MSB			(0x44)
#define ST7571_SET_COM_SCAN_DIR(d)		(0xc0 | FIELD_PREP(GENMASK(3, 3), (d)))
#define ST7571_SET_CONTRAST_LSB(c)		(FIELD_PREP(GENMASK(5, 0), (c)))
#define ST7571_SET_CONTRAST_MSB			(0x81)
#define ST7571_SET_DISPLAY_DUTY_LSB(d)		(FIELD_PREP(GENMASK(7, 0), (d)))
#define ST7571_SET_DISPLAY_DUTY_MSB		(0x48)
#define ST7571_SET_ENTIRE_DISPLAY_ON(p)		(0xa4 | FIELD_PREP(GENMASK(0, 0), (p)))
#define ST7571_SET_LCD_BIAS(b)			(0x50 | FIELD_PREP(GENMASK(2, 0), (b)))
#define ST7571_SET_MODE_LSB(m)			(FIELD_PREP(GENMASK(7, 2), (m)))
#define ST7571_SET_MODE_MSB			(0x38)
#define ST7571_SET_PAGE(p)			(0xb0 | FIELD_PREP(GENMASK(3, 0), (p)))
#define ST7571_SET_POWER(p)			(0x28 | FIELD_PREP(GENMASK(2, 0), (p)))
#define ST7571_SET_REGULATOR_REG(r)		(0x20 | FIELD_PREP(GENMASK(2, 0), (r)))
#define ST7571_SET_REVERSE(r)			(0xa6 | FIELD_PREP(GENMASK(0, 0), (r)))
#define ST7571_SET_SEG_SCAN_DIR(d)		(0xa0 | FIELD_PREP(GENMASK(0, 0), (d)))
#define ST7571_SET_START_LINE_LSB(l)		(FIELD_PREP(GENMASK(6, 0), (l)))
#define ST7571_SET_START_LINE_MSB		(0x40)

/* Extension command set 3 */
#define ST7571_COMMAND_SET_3			(0x7b)
#define ST7571_SET_COLOR_MODE(c)		(0x10 | FIELD_PREP(GENMASK(0, 0), (c)))
#define ST7571_COMMAND_SET_NORMAL		(0x00)

#define ST7571_PAGE_HEIGHT 8

#define DRIVER_NAME "st7571"
#define DRIVER_DESC "ST7571 DRM driver"
#define DRIVER_MAJOR 1
#define DRIVER_MINOR 0

enum st7571_color_mode {
	ST7571_COLOR_MODE_GRAY = 0,
	ST7571_COLOR_MODE_BLACKWHITE = 1,
};

struct st7571_device;

struct st7571_panel_constraints {
	u32 min_nlines;
	u32 max_nlines;
	u32 min_ncols;
	u32 max_ncols;
	bool support_grayscale;
};

struct st7571_panel_data {
	int (*init)(struct st7571_device *st7571);
	struct st7571_panel_constraints constraints;
};

struct st7571_panel_format {
	void (*prepare_buffer)(struct st7571_device *st7571,
			       const struct iosys_map *vmap,
			       struct drm_framebuffer *fb,
			       struct drm_rect *rect,
			       struct drm_format_conv_state *fmtcnv_state);
	int (*update_rect)(struct drm_framebuffer *fb, struct drm_rect *rect);
	enum st7571_color_mode mode;
	const u8 nformats;
	const u32 formats[];
};

struct st7571_device {
	struct drm_device dev;

	struct drm_plane primary_plane;
	struct drm_crtc crtc;
	struct drm_encoder encoder;
	struct drm_connector connector;

	struct drm_display_mode mode;

	const struct st7571_panel_format *pformat;
	const struct st7571_panel_data *pdata;
	struct i2c_client *client;
	struct gpio_desc *reset;
	struct regmap *regmap;

	/*
	 * Depending on the hardware design, the acknowledge signal may be hard to
	 * recognize as a valid logic "0" level.
	 * Therefor, ignore NAK if possible to stay compatible with most hardware designs
	 * and off-the-shelf panels out there.
	 *
	 * From section 6.4 MICROPOCESSOR INTERFACE section in the datasheet:
	 *
	 * "By connecting SDA_OUT to SDA_IN externally, the SDA line becomes fully
	 * I2C interface compatible.
	 * Separating acknowledge-output from serial data
	 * input is advantageous for chip-on-glass (COG) applications. In COG
	 * applications, the ITO resistance and the pull-up resistor will form a
	 * voltage  divider, which affects acknowledge-signal level. Larger ITO
	 * resistance will raise the acknowledged-signal level and system cannot
	 * recognize this level as a valid logic “0” level. By separating SDA_IN from
	 * SDA_OUT, the IC can be used in a mode that ignores the acknowledge-bit.
	 * For applications which check acknowledge-bit, it is necessary to minimize
	 * the ITO resistance of the SDA_OUT trace to guarantee a valid low level."
	 *
	 */
	bool ignore_nak;

	bool grayscale;
	u32 height_mm;
	u32 width_mm;
	u32 startline;
	u32 nlines;
	u32 ncols;
	u32 bpp;

	/* Intermediate buffer in LCD friendly format */
	u8 *hwbuf;

	/* Row of (transformed) pixels ready to be written to the display */
	u8 *row;
};

static inline struct st7571_device *drm_to_st7571(struct drm_device *dev)
{
	return container_of(dev, struct st7571_device, dev);
}

static int st7571_regmap_write(void *context, const void *data, size_t count)
{
	struct i2c_client *client = context;
	struct st7571_device *st7571 = i2c_get_clientdata(client);
	int ret;

	struct i2c_msg msg = {
		.addr = st7571->client->addr,
		.flags = st7571->ignore_nak ? I2C_M_IGNORE_NAK : 0,
		.len = count,
		.buf = (u8 *)data
	};

	ret = i2c_transfer(st7571->client->adapter, &msg, 1);

	/*
	 * Unfortunately, there is no way to check if the transfer failed because of
	 * a NAK or something else as I2C bus drivers use different return values for NAK.
	 *
	 * However, if the transfer fails and ignore_nak is set, we know it is an error.
	 */
	if (ret < 0 && st7571->ignore_nak)
		return ret;

	return 0;
}

/* The st7571 driver does not read registers but regmap expects a .read */
static int st7571_regmap_read(void *context, const void *reg_buf,
			      size_t reg_size, void *val_buf, size_t val_size)
{
	return -EOPNOTSUPP;
}

static int st7571_send_command_list(struct st7571_device *st7571,
				    const u8 *cmd_list, size_t len)
{
	int ret;

	for (int i = 0; i < len; i++) {
		ret = regmap_write(st7571->regmap, ST7571_COMMAND_MODE, cmd_list[i]);
		if (ret < 0)
			return ret;
	}

	return ret;
}

static inline u8 st7571_transform_xy(const char *p, int x, int y)
{
	int xrest = x % 8;
	u8 result = 0;

	/*
	 * Transforms an (x, y) pixel coordinate into a vertical 8-bit
	 * column from the framebuffer. It calculates the corresponding byte in the
	 * framebuffer, extracts the bit at the given x position across 8 consecutive
	 * rows, and packs those bits into a single byte.
	 *
	 * Return an 8-bit value representing a vertical column of pixels.
	 */
	x = x / 8;
	y = (y / 8) * 8;

	for (int i = 0; i < 8; i++) {
		int row_idx = y + i;
		u8 byte = p[row_idx * 16 + x];
		u8 bit = (byte >> xrest) & 1;

		result |= (bit << i);
	}

	return result;
}

static int st7571_set_position(struct st7571_device *st7571, int x, int y)
{
	u8 cmd_list[] = {
		ST7571_SET_COLUMN_LSB(x),
		ST7571_SET_COLUMN_MSB(x),
		ST7571_SET_PAGE(y / ST7571_PAGE_HEIGHT),
	};

	return st7571_send_command_list(st7571, cmd_list, ARRAY_SIZE(cmd_list));
}

static int st7571_fb_clear_screen(struct st7571_device *st7571)
{
	u32 npixels = st7571->ncols * round_up(st7571->nlines, ST7571_PAGE_HEIGHT) * st7571->bpp;
	char pixelvalue = 0x00;

	for (int i = 0; i < npixels; i++)
		regmap_bulk_write(st7571->regmap, ST7571_DATA_MODE, &pixelvalue, 1);

	return 0;
}

static void st7571_prepare_buffer_monochrome(struct st7571_device *st7571,
					     const struct iosys_map *vmap,
					     struct drm_framebuffer *fb,
					     struct drm_rect *rect,
					     struct drm_format_conv_state *fmtcnv_state)
{
	unsigned int dst_pitch;
	struct iosys_map dst;
	u32 size;

	switch (fb->format->format) {
	case DRM_FORMAT_XRGB8888:
		dst_pitch = DIV_ROUND_UP(drm_rect_width(rect), 8);
		iosys_map_set_vaddr(&dst, st7571->hwbuf);

		drm_fb_xrgb8888_to_mono(&dst, &dst_pitch, vmap, fb, rect, fmtcnv_state);
		break;

	case DRM_FORMAT_R1:
		size = (rect->x2 - rect->x1) * (rect->y2 - rect->y1) / 8;
		memcpy(st7571->hwbuf, vmap->vaddr, size);
		break;
	}
}

static void st7571_prepare_buffer_grayscale(struct st7571_device *st7571,
					    const struct iosys_map *vmap,
					    struct drm_framebuffer *fb,
					    struct drm_rect *rect,
					    struct drm_format_conv_state *fmtcnv_state)
{
	u32 size = (rect->x2 - rect->x1) * (rect->y2 - rect->y1) / 8;
	unsigned int dst_pitch;
	struct iosys_map dst;

	switch (fb->format->format) {
	case DRM_FORMAT_XRGB8888: /* Only support XRGB8888 in monochrome mode */
		dst_pitch = DIV_ROUND_UP(drm_rect_width(rect), 8);
		iosys_map_set_vaddr(&dst, st7571->hwbuf);

		drm_fb_xrgb8888_to_mono(&dst, &dst_pitch, vmap, fb, rect, fmtcnv_state);
		break;

	case DRM_FORMAT_R1:
		size = (rect->x2 - rect->x1) * (rect->y2 - rect->y1) / 8;
		memcpy(st7571->hwbuf, vmap->vaddr, size);
		break;

	case DRM_FORMAT_R2:
		size = (rect->x2 - rect->x1) * (rect->y2 - rect->y1) / 4;
		memcpy(st7571->hwbuf, vmap->vaddr, size);
		break;
	};
}

static int st7571_fb_update_rect_monochrome(struct drm_framebuffer *fb, struct drm_rect *rect)
{
	struct st7571_device *st7571 = drm_to_st7571(fb->dev);
	char *row = st7571->row;

	/* Align y to display page boundaries */
	rect->y1 = round_down(rect->y1, ST7571_PAGE_HEIGHT);
	rect->y2 = min_t(unsigned int, round_up(rect->y2, ST7571_PAGE_HEIGHT), st7571->nlines);

	for (int y = rect->y1; y < rect->y2; y += ST7571_PAGE_HEIGHT) {
		for (int x = rect->x1; x < rect->x2; x++)
			row[x] = st7571_transform_xy(st7571->hwbuf, x, y);

		st7571_set_position(st7571, rect->x1, y);

		/* TODO: Investige why we can't write multiple bytes at once */
		for (int x = rect->x1; x < rect->x2; x++)
			regmap_bulk_write(st7571->regmap, ST7571_DATA_MODE, row + x, 1);
	}

	return 0;
}

static int st7571_fb_update_rect_grayscale(struct drm_framebuffer *fb, struct drm_rect *rect)
{
	struct st7571_device *st7571 = drm_to_st7571(fb->dev);
	u32 format = fb->format->format;
	char *row = st7571->row;
	int x1;
	int x2;

	/* Align y to display page boundaries */
	rect->y1 = round_down(rect->y1, ST7571_PAGE_HEIGHT);
	rect->y2 = min_t(unsigned int, round_up(rect->y2, ST7571_PAGE_HEIGHT), st7571->nlines);

	switch (format) {
	case DRM_FORMAT_XRGB8888:
		/* Threated as monochrome (R1) */
		fallthrough;
	case DRM_FORMAT_R1:
		x1 = rect->x1;
		x2 = rect->x2;
		break;
	case DRM_FORMAT_R2:
		x1 = rect->x1 * 2;
		x2 = rect->x2 * 2;
		break;
	}

	for (int y = rect->y1; y < rect->y2; y += ST7571_PAGE_HEIGHT) {
		for (int x = x1; x < x2; x++)
			row[x] = st7571_transform_xy(st7571->hwbuf, x, y);

		st7571_set_position(st7571, rect->x1, y);

		/* TODO: Investige why we can't write multiple bytes at once */
		for (int x = x1; x < x2; x++) {
			regmap_bulk_write(st7571->regmap, ST7571_DATA_MODE, row + x, 1);

			/*
			 * As the display supports grayscale, all pixels must be written as two bits
			 * even if the format is monochrome.
			 *
			 * The bit values maps to the following grayscale:
			 * 0 0 = White
			 * 0 1 = Light gray
			 * 1 0 = Dark gray
			 * 1 1 = Black
			 *
			 * For monochrome formats, write the same value twice to get
			 * either a black or white pixel.
			 */
			if (format == DRM_FORMAT_R1 || format == DRM_FORMAT_XRGB8888)
				regmap_bulk_write(st7571->regmap, ST7571_DATA_MODE, row + x, 1);
		}
	}

	return 0;
}

static int st7571_connector_get_modes(struct drm_connector *conn)
{
	struct st7571_device *st7571 = drm_to_st7571(conn->dev);

	return drm_connector_helper_get_modes_fixed(conn, &st7571->mode);
}

static const struct drm_connector_helper_funcs st7571_connector_helper_funcs = {
	.get_modes = st7571_connector_get_modes,
};

static const struct st7571_panel_format st7571_monochrome = {
	.prepare_buffer = st7571_prepare_buffer_monochrome,
	.update_rect = st7571_fb_update_rect_monochrome,
	.mode = ST7571_COLOR_MODE_BLACKWHITE,
	.formats = {
		DRM_FORMAT_XRGB8888,
		DRM_FORMAT_R1,
	},
	.nformats = 2,
};

static const struct st7571_panel_format st7571_grayscale = {
	.prepare_buffer = st7571_prepare_buffer_grayscale,
	.update_rect = st7571_fb_update_rect_grayscale,
	.mode = ST7571_COLOR_MODE_GRAY,
	.formats = {
		DRM_FORMAT_XRGB8888,
		DRM_FORMAT_R1,
		DRM_FORMAT_R2,
	},
	.nformats = 3,
};

static const u64 st7571_primary_plane_fmtmods[] = {
	DRM_FORMAT_MOD_LINEAR,
	DRM_FORMAT_MOD_INVALID
};

static int st7571_primary_plane_helper_atomic_check(struct drm_plane *plane,
						    struct drm_atomic_state *state)
{
	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(state, plane);
	struct drm_crtc *new_crtc = new_plane_state->crtc;
	struct drm_crtc_state *new_crtc_state = NULL;

	if (new_crtc)
		new_crtc_state = drm_atomic_get_new_crtc_state(state, new_crtc);

	return drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
						   DRM_PLANE_NO_SCALING,
						   DRM_PLANE_NO_SCALING,
						   false, false);
}

static void st7571_primary_plane_helper_atomic_update(struct drm_plane *plane,
						      struct drm_atomic_state *state)
{
	struct drm_plane_state *old_plane_state = drm_atomic_get_old_plane_state(state, plane);
	struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
	struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(plane_state);
	struct drm_framebuffer *fb = plane_state->fb;
	struct drm_atomic_helper_damage_iter iter;
	struct drm_device *dev = plane->dev;
	struct drm_rect damage;
	struct st7571_device *st7571 = drm_to_st7571(plane->dev);
	int ret, idx;

	if (!fb)
		return; /* no framebuffer; plane is disabled */

	ret = drm_gem_fb_begin_cpu_access(fb, DMA_FROM_DEVICE);
	if (ret)
		return;

	if (!drm_dev_enter(dev, &idx))
		goto out_drm_gem_fb_end_cpu_access;

	drm_atomic_helper_damage_iter_init(&iter, old_plane_state, plane_state);
	drm_atomic_for_each_plane_damage(&iter, &damage) {
		st7571->pformat->prepare_buffer(st7571,
						&shadow_plane_state->data[0],
						fb, &damage,
						&shadow_plane_state->fmtcnv_state);

		st7571->pformat->update_rect(fb, &damage);
	}

	drm_dev_exit(idx);

out_drm_gem_fb_end_cpu_access:
	drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);
}

static void st7571_primary_plane_helper_atomic_disable(struct drm_plane *plane,
						       struct drm_atomic_state *state)
{
	struct drm_device *dev = plane->dev;
	struct st7571_device *st7571 = drm_to_st7571(plane->dev);
	int idx;

	if (!drm_dev_enter(dev, &idx))
		return;

	st7571_fb_clear_screen(st7571);
	drm_dev_exit(idx);
}

static const struct drm_plane_helper_funcs st7571_primary_plane_helper_funcs = {
	DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
	.atomic_check = st7571_primary_plane_helper_atomic_check,
	.atomic_update = st7571_primary_plane_helper_atomic_update,
	.atomic_disable = st7571_primary_plane_helper_atomic_disable,
};

static const struct drm_plane_funcs st7571_primary_plane_funcs = {
	.update_plane = drm_atomic_helper_update_plane,
	.disable_plane = drm_atomic_helper_disable_plane,
	.destroy = drm_plane_cleanup,
	DRM_GEM_SHADOW_PLANE_FUNCS,
};

/*
 * CRTC
 */

static enum drm_mode_status st7571_crtc_mode_valid(struct drm_crtc *crtc,
						   const struct drm_display_mode *mode)
{
	struct st7571_device *st7571 = drm_to_st7571(crtc->dev);

	return drm_crtc_helper_mode_valid_fixed(crtc, mode, &st7571->mode);
}

static const struct drm_crtc_helper_funcs st7571_crtc_helper_funcs = {
	.atomic_check = drm_crtc_helper_atomic_check,
	.mode_valid = st7571_crtc_mode_valid,
};

static const struct drm_crtc_funcs st7571_crtc_funcs = {
	.reset = drm_atomic_helper_crtc_reset,
	.destroy = drm_crtc_cleanup,
	.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,
};

/*
 * Encoder
 */

static void st7571_encoder_atomic_enable(struct drm_encoder *encoder,
					 struct drm_atomic_state *state)
{
	struct drm_device *drm = encoder->dev;
	struct st7571_device *st7571 = drm_to_st7571(drm);
	u8 command = ST7571_DISPLAY_ON;
	int ret;

	ret = st7571->pdata->init(st7571);
	if (ret)
		return;

	st7571_send_command_list(st7571, &command, 1);
}

static void st7571_encoder_atomic_disable(struct drm_encoder *encoder,
					  struct drm_atomic_state *state)
{
	struct drm_device *drm = encoder->dev;
	struct st7571_device *st7571 = drm_to_st7571(drm);
	u8 command = ST7571_DISPLAY_OFF;

	st7571_send_command_list(st7571, &command, 1);
}

static const struct drm_encoder_funcs st7571_encoder_funcs = {
	.destroy = drm_encoder_cleanup,

};

static const struct drm_encoder_helper_funcs st7571_encoder_helper_funcs = {
	.atomic_enable = st7571_encoder_atomic_enable,
	.atomic_disable = st7571_encoder_atomic_disable,
};

/*
 * Connector
 */

static const struct drm_connector_funcs st7571_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 struct drm_mode_config_funcs st7571_mode_config_funcs = {
	.fb_create = drm_gem_fb_create_with_dirty,
	.atomic_check = drm_atomic_helper_check,
	.atomic_commit = drm_atomic_helper_commit,
};

static struct drm_display_mode st7571_mode(struct st7571_device *st7571)
{
	struct drm_display_mode mode = {
		DRM_SIMPLE_MODE(st7571->ncols, st7571->nlines,
				st7571->width_mm, st7571->height_mm),
	};

	return mode;
}

static int st7571_mode_config_init(struct st7571_device *st7571)
{
	struct drm_device *dev = &st7571->dev;
	const struct st7571_panel_constraints *constraints = &st7571->pdata->constraints;
	int ret;

	ret = drmm_mode_config_init(dev);
	if (ret)
		return ret;

	dev->mode_config.min_width = constraints->min_ncols;
	dev->mode_config.min_height = constraints->min_nlines;
	dev->mode_config.max_width = constraints->max_ncols;
	dev->mode_config.max_height = constraints->max_nlines;
	dev->mode_config.preferred_depth = 24;
	dev->mode_config.funcs = &st7571_mode_config_funcs;

	return 0;
}

static int st7571_plane_init(struct st7571_device *st7571,
			     const struct st7571_panel_format *pformat)
{
	struct drm_plane *primary_plane = &st7571->primary_plane;
	struct drm_device *dev = &st7571->dev;
	int ret;

	ret = drm_universal_plane_init(dev, primary_plane, 0,
				       &st7571_primary_plane_funcs,
				       pformat->formats,
				       pformat->nformats,
				       st7571_primary_plane_fmtmods,
				       DRM_PLANE_TYPE_PRIMARY, NULL);
	if (ret)
		return ret;

	drm_plane_helper_add(primary_plane, &st7571_primary_plane_helper_funcs);
	drm_plane_enable_fb_damage_clips(primary_plane);

	return 0;
}

static int st7571_crtc_init(struct st7571_device *st7571)
{
	struct drm_plane *primary_plane = &st7571->primary_plane;
	struct drm_crtc *crtc = &st7571->crtc;
	struct drm_device *dev = &st7571->dev;
	int ret;

	ret = drm_crtc_init_with_planes(dev, crtc, primary_plane, NULL,
					&st7571_crtc_funcs, NULL);
	if (ret)
		return ret;

	drm_crtc_helper_add(crtc, &st7571_crtc_helper_funcs);

	return 0;
}

static int st7571_encoder_init(struct st7571_device *st7571)
{
	struct drm_encoder *encoder = &st7571->encoder;
	struct drm_crtc *crtc = &st7571->crtc;
	struct drm_device *dev = &st7571->dev;
	int ret;

	ret = drm_encoder_init(dev, encoder, &st7571_encoder_funcs, DRM_MODE_ENCODER_NONE, NULL);
	if (ret)
		return ret;

	drm_encoder_helper_add(encoder, &st7571_encoder_helper_funcs);

	encoder->possible_crtcs = drm_crtc_mask(crtc);

	return 0;
}

static int st7571_connector_init(struct st7571_device *st7571)
{
	struct drm_connector *connector = &st7571->connector;
	struct drm_encoder *encoder = &st7571->encoder;
	struct drm_device *dev = &st7571->dev;
	int ret;

	ret = drm_connector_init(dev, connector, &st7571_connector_funcs,
				 DRM_MODE_CONNECTOR_Unknown);
	if (ret)
		return ret;

	drm_connector_helper_add(connector, &st7571_connector_helper_funcs);

	return drm_connector_attach_encoder(connector, encoder);
}

DEFINE_DRM_GEM_FOPS(st7571_fops);

static const struct drm_driver st7571_driver = {
	.driver_features = DRIVER_MODESET | DRIVER_GEM | DRIVER_ATOMIC,

	.name		 = DRIVER_NAME,
	.desc		 = DRIVER_DESC,
	.major		 = DRIVER_MAJOR,
	.minor		 = DRIVER_MINOR,

	.fops		 = &st7571_fops,
	DRM_GEM_SHMEM_DRIVER_OPS,
	DRM_FBDEV_SHMEM_DRIVER_OPS,
};

static const struct regmap_bus st7571_regmap_bus = {
	.read = st7571_regmap_read,
	.write = st7571_regmap_write,
};

static const struct regmap_config st7571_regmap_config = {
	.reg_bits = 8,
	.val_bits = 8,
	.use_single_write = true,
};

static int st7571_validate_parameters(struct st7571_device *st7571)
{
	struct device *dev = st7571->dev.dev;
	const struct st7571_panel_constraints *constraints = &st7571->pdata->constraints;

	if (st7571->width_mm  == 0) {
		dev_err(dev, "Invalid panel width\n");
		return -EINVAL;
	}

	if (st7571->height_mm == 0) {
		dev_err(dev, "Invalid panel height\n");
		return -EINVAL;
	}

	if (st7571->nlines < constraints->min_nlines ||
	    st7571->nlines > constraints->max_nlines) {
		dev_err(dev, "Invalid timing configuration.\n");
		return -EINVAL;
	}

	if (st7571->startline + st7571->nlines > constraints->max_nlines) {
		dev_err(dev, "Invalid timing configuration.\n");
		return -EINVAL;
	}

	if (st7571->ncols < constraints->min_ncols ||
	    st7571->ncols > constraints->max_ncols) {
		dev_err(dev, "Invalid timing configuration.\n");
		return -EINVAL;
	}

	if (st7571->grayscale && !constraints->support_grayscale) {
		dev_err(dev, "Grayscale not supported\n");
		return -EINVAL;
	}

	return 0;
}

static int st7571_parse_dt(struct st7571_device *st7571)
{
	struct device *dev = &st7571->client->dev;
	struct device_node *np = dev->of_node;
	struct display_timing dt;
	int ret;

	ret = of_get_display_timing(np, "panel-timing", &dt);
	if (ret) {
		dev_err(dev, "Failed to get display timing from DT\n");
		return ret;
	}

	of_property_read_u32(np, "width-mm", &st7571->width_mm);
	of_property_read_u32(np, "height-mm", &st7571->height_mm);
	st7571->grayscale = of_property_read_bool(np, "sitronix,grayscale");

	if (st7571->grayscale) {
		st7571->pformat = &st7571_grayscale;
		st7571->bpp = 2;
	} else {
		st7571->pformat = &st7571_monochrome;
		st7571->bpp = 1;
	}

	st7571->startline = dt.vfront_porch.typ;
	st7571->nlines = dt.vactive.typ;
	st7571->ncols = dt.hactive.typ;

	st7571->reset = devm_gpiod_get(dev, "reset", GPIOD_OUT_HIGH);
	if (IS_ERR(st7571->reset))
		return PTR_ERR(st7571->reset);

	return 0;
}

static void st7571_reset(struct st7571_device *st7571)
{
	gpiod_set_value_cansleep(st7571->reset, 1);
	fsleep(20);
	gpiod_set_value_cansleep(st7571->reset, 0);
}

static int st7571_lcd_init(struct st7571_device *st7571)
{
	/*
	 * Most of the initialization sequence is taken directly from the
	 * referential initial code in the ST7571 datasheet.
	 */
	u8 commands[] = {
		ST7571_DISPLAY_OFF,

		ST7571_SET_MODE_MSB,
		ST7571_SET_MODE_LSB(0x2e),

		ST7571_SET_SEG_SCAN_DIR(0),
		ST7571_SET_COM_SCAN_DIR(1),

		ST7571_SET_COM0_MSB,
		ST7571_SET_COM0_LSB(0x00),

		ST7571_SET_START_LINE_MSB,
		ST7571_SET_START_LINE_LSB(st7571->startline),

		ST7571_OSC_ON,
		ST7571_SET_REGULATOR_REG(5),
		ST7571_SET_CONTRAST_MSB,
		ST7571_SET_CONTRAST_LSB(0x33),
		ST7571_SET_LCD_BIAS(0x04),
		ST7571_SET_DISPLAY_DUTY_MSB,
		ST7571_SET_DISPLAY_DUTY_LSB(st7571->nlines),

		ST7571_SET_POWER(0x4),	/* Power Control, VC: ON, VR: OFF, VF: OFF */
		ST7571_SET_POWER(0x6),	/* Power Control, VC: ON, VR: ON, VF: OFF */
		ST7571_SET_POWER(0x7),	/* Power Control, VC: ON, VR: ON, VF: ON */

		ST7571_COMMAND_SET_3,
		ST7571_SET_COLOR_MODE(st7571->pformat->mode),
		ST7571_COMMAND_SET_NORMAL,

		ST7571_SET_REVERSE(0),
		ST7571_SET_ENTIRE_DISPLAY_ON(0),
	};

	/* Perform a reset before initializing the controller */
	st7571_reset(st7571);

	return st7571_send_command_list(st7571, commands, ARRAY_SIZE(commands));
}

static int st7571_probe(struct i2c_client *client)
{
	struct st7571_device *st7571;
	struct drm_device *dev;
	int ret;

	st7571 = devm_drm_dev_alloc(&client->dev, &st7571_driver,
				    struct st7571_device, dev);
	if (IS_ERR(st7571))
		return PTR_ERR(st7571);

	dev = &st7571->dev;
	st7571->client = client;
	i2c_set_clientdata(client, st7571);
	st7571->pdata = device_get_match_data(&client->dev);

	ret = st7571_parse_dt(st7571);
	if (ret)
		return ret;

	ret = st7571_validate_parameters(st7571);
	if (ret)
		return ret;

	st7571->mode = st7571_mode(st7571);

	/*
	 * The hardware design could make it hard to detect a NAK on the I2C bus.
	 * If the adapter does not support protocol mangling do
	 * not set the I2C_M_IGNORE_NAK flag at the expense * of possible
	 * cruft in the logs.
	 */
	if (i2c_check_functionality(client->adapter, I2C_FUNC_PROTOCOL_MANGLING))
		st7571->ignore_nak = true;

	st7571->regmap = devm_regmap_init(&client->dev, &st7571_regmap_bus,
					  client, &st7571_regmap_config);
	if (IS_ERR(st7571->regmap)) {
		return dev_err_probe(&client->dev, PTR_ERR(st7571->regmap),
				     "Failed to initialize regmap\n");
	}

	st7571->hwbuf = devm_kzalloc(&client->dev,
				     (st7571->nlines * st7571->ncols * st7571->bpp) / 8,
				     GFP_KERNEL);
	if (!st7571->hwbuf)
		return -ENOMEM;

	st7571->row = devm_kzalloc(&client->dev,
				   (st7571->ncols * st7571->bpp),
				   GFP_KERNEL);
	if (!st7571->row)
		return -ENOMEM;

	ret = st7571_mode_config_init(st7571);
	if (ret)
		return dev_err_probe(&client->dev, ret,
				     "Failed to initialize mode config\n");

	ret = st7571_plane_init(st7571, st7571->pformat);
	if (ret)
		return dev_err_probe(&client->dev, ret,
				     "Failed to initialize primary plane\n");

	ret = st7571_crtc_init(st7571);
	if (ret < 0)
		return dev_err_probe(&client->dev, ret,
				     "Failed to initialize CRTC\n");

	ret = st7571_encoder_init(st7571);
	if (ret < 0)
		return dev_err_probe(&client->dev, ret,
				     "Failed to initialize encoder\n");

	ret = st7571_connector_init(st7571);
	if (ret < 0)
		return dev_err_probe(&client->dev, ret,
				     "Failed to initialize connector\n");

	drm_mode_config_reset(dev);

	ret = drm_dev_register(dev, 0);
	if (ret)
		return dev_err_probe(&client->dev, ret,
				     "Failed to register DRM device\n");

	drm_client_setup(dev, NULL);
	return 0;
}

static void st7571_remove(struct i2c_client *client)
{
	struct st7571_device *st7571 = i2c_get_clientdata(client);

	drm_dev_unplug(&st7571->dev);
}

struct st7571_panel_data st7571_config = {
	.init = st7571_lcd_init,
	.constraints = {
		.min_nlines = 1,
		.max_nlines = 128,
		.min_ncols = 128,
		.max_ncols = 128,
		.support_grayscale = true,
	},
};

static const struct of_device_id st7571_of_match[] = {
	{ .compatible = "sitronix,st7571", .data = &st7571_config },
	{},
};
MODULE_DEVICE_TABLE(of, st7571_of_match);

static const struct i2c_device_id st7571_id[] = {
	{ "st7571", 0 },
	{ }
};
MODULE_DEVICE_TABLE(i2c, st7571_id);

static struct i2c_driver st7571_i2c_driver = {
	.driver = {
		.name = "st7571",
		.of_match_table = st7571_of_match,
	},
	.probe = st7571_probe,
	.remove = st7571_remove,
	.id_table = st7571_id,
};

module_i2c_driver(st7571_i2c_driver);

MODULE_AUTHOR("Marcus Folkesson <marcus.folkesson@gmail.com>");
MODULE_DESCRIPTION("DRM Driver for Sitronix ST7571 LCD controller");
MODULE_LICENSE("GPL");