[PATCH v2 0/3] Add support for Sitronix ST7571 LCD controller

[PATCH v2 0/3] Add support for Sitronix ST7571 LCD controller

[Marcus Folkesson]

This series add support for the ST7571 LCD Controller.
It is a 4 gray scale dot matrix LCD controller that supports several
interfaces such as SPI, I2C and a 8bit parallell port.

This driver only supports the I2C interface, but all common parts could
easily be put into a common file to be used with other interfaces.
I only have I2C to test with.

The device is a little defiant, it tends to NAK some commands, but all
commands takes effect, hence the I2C_M_IGNORE_NAK flag.

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
---
Changes in v2:
- Reworked pretty much the whole driver to not use obsolete code.
- Use panel and timing bindings to specify resolution and panel size
- Link to v1: https://lore.kernel.org/r/20250402-st7571-v1-0-351d6b9eeb4a@gmail.com

---
Marcus Folkesson (3):
      dt-bindings: display: Add Sitronix ST7571 panel
      drm/st7571-i2c: add support for Sitronix ST7571 LCD controller
      MAINTAINERS: add antry for Sitronix ST7571 LCD controller

 .../bindings/display/sitronix,st7571.yaml          |  73 +++
 MAINTAINERS                                        |   6 +
 drivers/gpu/drm/tiny/Kconfig                       |  11 +
 drivers/gpu/drm/tiny/Makefile                      |   1 +
 drivers/gpu/drm/tiny/st7571-i2c.c                  | 720 +++++++++++++++++++++
 5 files changed, 811 insertions(+)
---
base-commit: 1e26c5e28ca5821a824e90dd359556f5e9e7b89f
change-id: 20250401-st7571-9382b9cfc03f

Best regards,
-- 
Marcus Folkesson <marcus.folkesson@gmail.com>

[PATCH v2 1/3] dt-bindings: display: Add Sitronix ST7571 panel

[Marcus Folkesson]

Sitronix ST7571 is a 4bit gray scale dot matrix LCD controller.

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
---
 .../bindings/display/sitronix,st7571.yaml          | 73 ++++++++++++++++++++++
 1 file changed, 73 insertions(+)

diff --git a/Documentation/devicetree/bindings/display/sitronix,st7571.yaml b/Documentation/devicetree/bindings/display/sitronix,st7571.yaml
new file mode 100644
index 0000000000000000000000000000000000000000..11575b820c59c5ada427fbb6b015c331215c8db6
--- /dev/null
+++ b/Documentation/devicetree/bindings/display/sitronix,st7571.yaml
@@ -0,0 +1,73 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/sitronix,st7571.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Sitronix ST7571 Display Panels
+
+maintainers:
+  - Marcus Folkesson <marcus.folkesson@gmail.com>
+
+description:
+  This binding is for display panels using a Sitronix ST7571 controller in I2C
+  mode.
+
+allOf:
+  - $ref: panel/panel-common.yaml#
+
+properties:
+  compatible:
+    const: sitronix,st7571
+
+  reg: true
+  reset-gpios: true
+  width-mm: true
+  height-mm: true
+
+  panel-timing:
+    $ref: panel/panel-timing.yaml#
+    description: |
+      The panel-timing node specifies the display resolution and timing
+      parameters. The hactive and vactive properties are mandatory.
+      The vback-porch property specifies the start line of the display.
+      The other properties should be set to zero.
+
+required:
+  - compatible
+  - reg
+  - reset-gpios
+  - width-mm
+  - height-mm
+  - panel-timing
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        display@3f {
+          compatible = "sitronix,st7571";
+          reg = <0x3f>;
+          reset-gpios = <&gpio0 3 GPIO_ACTIVE_LOW>;
+          width-mm = <37>;
+          height-mm = <27>;
+
+            panel-timing {
+                hactive = <128>;
+                vactive = <96>;
+                hback-porch = <0>;
+                vback-porch = <0>;
+                clock-frequency = <0>;
+                hfront-porch = <0>;
+                hsync-len = <0>;
+                vfront-porch = <0>;
+                vsync-len = <0>;
+            };
+        };
+    };

-- 
2.49.0

[PATCH v2 2/3] drm/st7571-i2c: add support for Sitronix ST7571 LCD controller

[Marcus Folkesson]

Sitronix ST7571 is a 4bit gray scale dot matrix LCD controller.
The controller has a SPI, I2C and 8bit parallel interface, this
driver is for the I2C interface only.

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
---
 drivers/gpu/drm/tiny/Kconfig      |  11 +
 drivers/gpu/drm/tiny/Makefile     |   1 +
 drivers/gpu/drm/tiny/st7571-i2c.c | 720 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 732 insertions(+)

diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig
index 94cbdb1337c07f1628a33599a7130369b9d59d98..6c711f4b799e05a8edc8e5fd68de0542d9cb6cab 100644
--- a/drivers/gpu/drm/tiny/Kconfig
+++ b/drivers/gpu/drm/tiny/Kconfig
@@ -232,6 +232,17 @@ config TINYDRM_ST7586
 
 	  If M is selected the module will be called st7586.
 
+config TINYDRM_ST7571_I2C
+	tristate "DRM support for Sitronix ST7571 display panels (I2C)"
+	depends on DRM && I2C
+	select DRM_KMS_HELPER
+	select DRM_GEM_SHMEM_HELPER
+	select REGMAP_I2C
+	help
+	  DRM driver for Sitronix ST7571 panels controlled over I2C.
+
+	  if M is selected the module will be called st7571-i2c.
+
 config TINYDRM_ST7735R
 	tristate "DRM support for Sitronix ST7715R/ST7735R display panels"
 	depends on DRM && SPI
diff --git a/drivers/gpu/drm/tiny/Makefile b/drivers/gpu/drm/tiny/Makefile
index 60816d2eb4ff93b87228ed8eadd60a0a33a1144b..ed767dd9d22b3bb98f50fa2007cad7fb3f3d95e4 100644
--- a/drivers/gpu/drm/tiny/Makefile
+++ b/drivers/gpu/drm/tiny/Makefile
@@ -15,5 +15,6 @@ obj-$(CONFIG_TINYDRM_ILI9486)		+= ili9486.o
 obj-$(CONFIG_TINYDRM_MI0283QT)		+= mi0283qt.o
 obj-$(CONFIG_TINYDRM_REPAPER)		+= repaper.o
 obj-$(CONFIG_TINYDRM_SHARP_MEMORY)	+= sharp-memory.o
+obj-$(CONFIG_TINYDRM_ST7571_I2C)	+= st7571-i2c.o
 obj-$(CONFIG_TINYDRM_ST7586)		+= st7586.o
 obj-$(CONFIG_TINYDRM_ST7735R)		+= st7735r.o
diff --git a/drivers/gpu/drm/tiny/st7571-i2c.c b/drivers/gpu/drm/tiny/st7571-i2c.c
new file mode 100644
index 0000000000000000000000000000000000000000..196ecd662c73dfaa9940fc601a656305c81a1619
--- /dev/null
+++ b/drivers/gpu/drm/tiny/st7571-i2c.c
@@ -0,0 +1,720 @@
+// 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/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 | ((c) & 0xf))
+#define ST7571_SET_COLUMN_MSB(c)		(0x10 | ((c) >> 4))
+#define ST7571_SET_COM0_LSB(x)			((x) & 0x7f)
+#define ST7571_SET_COM0_MSB			(0x44)
+#define ST7571_SET_COM_SCAN_DIR(d)		(0xc0 | (((d) << 3) & 0x8))
+#define ST7571_SET_CONTRAST_LSB(c)		((c) & 0x3f)
+#define ST7571_SET_CONTRAST_MSB			(0x81)
+#define ST7571_SET_DISPLAY_DUTY_LSB(d)		((d) & 0xff)
+#define ST7571_SET_DISPLAY_DUTY_MSB		(0x48)
+#define ST7571_SET_ENTIRE_DISPLAY_ON(p)		(0xa4 | ((p) & 0x1))
+#define ST7571_SET_LCD_BIAS(b)			(0x50 | ((b) & 0x7))
+#define ST7571_SET_MODE_LSB(m)			((m) & 0xfc)
+#define ST7571_SET_MODE_MSB			(0x38)
+#define ST7571_SET_PAGE(p)			(0xb0 | (p))
+#define ST7571_SET_POWER(p)			(0x28 | ((p) & 0x7))
+#define ST7571_SET_REGULATOR_REG(r)		(0x20 | ((r) & 0x7))
+#define ST7571_SET_REVERSE(r)			(0xa6 | ((r) & 0x1))
+#define ST7571_SET_SEG_SCAN_DIR(d)		(0xa0 | ((d) & 0x1))
+#define ST7571_SET_START_LINE_LSB(l)		((l) & 0x3f)
+#define ST7571_SET_START_LINE_MSB		(0x40)
+
+/* Extension command set 3 */
+#define ST7571_COMMAND_SET_3			(0x7b)
+#define ST7571_SET_COLOR_MODE(c)		(0x10 | ((c) & 0x1))
+#define ST7571_COMMAND_SET_NORMAL		(0x00)
+
+
+/* hactive is fixed to 128 */
+#define ST7571_HACTIVE				(128)
+
+#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,
+};
+
+#define drm_to_st7571(_dev) container_of(_dev, struct st7571_device, dev)
+
+struct st7571_device {
+	struct drm_plane primary_plane;
+	struct drm_connector connector;
+	struct drm_display_mode mode;
+	struct drm_encoder encoder;
+	struct drm_device dev;
+	struct drm_crtc crtc;
+
+	struct i2c_client *client;
+	struct regmap *regmap;
+	bool ignore_nak;
+
+	struct gpio_desc *reset;
+
+	u32 width_mm;
+	u32 height_mm;
+	u32 nlines;
+	u32 startline;
+};
+
+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);
+	/*
+	 * This is a workaround for the ST7571, which sometimes fails to acknowledge
+	 *
+	 * 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;
+}
+
+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 / 8),
+	};
+
+	return st7571_send_command_list(st7571, cmd_list, ARRAY_SIZE(cmd_list));
+}
+
+static int st7571_fb_blit_rect(struct drm_framebuffer *fb,
+			       const struct iosys_map *vmap,
+			       struct drm_rect *rect)
+{
+	struct st7571_device *st7571 = drm_to_st7571(fb->dev);
+	int bpp = fb->format->format == DRM_FORMAT_C1 ? 1 : 2;
+	char *pixel = vmap->vaddr;
+	int x1 = rect->x1 * bpp;
+	int x2 = rect->x2 * bpp;
+	char row[256];
+
+	for (int y = rect->y1; y < rect->y2; y += 8) {
+		for (int x = x1; x < x2; x++)
+			row[x] = st7571_transform_xy(pixel, 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);
+	}
+
+	return 0;
+}
+
+static int st7571_set_color_mode(struct st7571_device *st7571, enum st7571_color_mode  mode)
+{
+	u8 cmd_list[] = {
+		ST7571_COMMAND_SET_3,
+		ST7571_SET_COLOR_MODE(mode),
+		ST7571_COMMAND_SET_NORMAL,
+	};
+
+	return st7571_send_command_list(st7571, cmd_list, ARRAY_SIZE(cmd_list));
+}
+
+static int st7571_set_pixel_format(struct st7571_device *st7571,
+				   u32 pixel_format)
+{
+	switch (pixel_format) {
+	case DRM_FORMAT_C1:
+		return st7571_set_color_mode(st7571, ST7571_COLOR_MODE_BLACKWHITE);
+	case DRM_FORMAT_C2:
+		return st7571_set_color_mode(st7571, ST7571_COLOR_MODE_GRAY);
+	default:
+		return -EINVAL;
+	}
+}
+
+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 uint32_t st7571_primary_plane_formats[] = {
+	DRM_FORMAT_C1,
+	DRM_FORMAT_C2,
+};
+
+static const uint64_t 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))
+		return;
+
+	ret = st7571_set_pixel_format(st7571, fb->format->format);
+	if (ret) {
+		dev_err(dev->dev, "Failed to set pixel format: %d\n", ret);
+		return;
+	}
+
+	drm_atomic_helper_damage_iter_init(&iter, old_plane_state, plane_state);
+	drm_atomic_for_each_plane_damage(&iter, &damage) {
+		st7571_fb_blit_rect(fb, &shadow_plane_state->data[0], &damage);
+	}
+
+	drm_dev_exit(idx);
+	drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);
+}
+
+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,
+};
+
+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 const struct drm_crtc_helper_funcs st7571_crtc_helper_funcs = {
+	.atomic_check = drm_crtc_helper_atomic_check,
+};
+
+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 const struct drm_encoder_funcs st7571_encoder_funcs = {
+	.destroy = drm_encoder_cleanup,
+};
+
+/*
+ * 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 enum drm_mode_status st7571_mode_config_mode_valid(struct drm_device *dev,
+						       const struct drm_display_mode *mode)
+{
+	struct st7571_device *st7571 = drm_to_st7571(dev);
+
+	return drm_crtc_helper_mode_valid_fixed(&st7571->crtc, mode, &st7571->mode);
+}
+
+static const struct drm_mode_config_funcs st7571_mode_config_funcs = {
+	.fb_create = drm_gem_fb_create_with_dirty,
+	.mode_valid = st7571_mode_config_mode_valid,
+	.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_HACTIVE, 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;
+	int ret;
+
+	ret = drmm_mode_config_init(dev);
+	if (ret)
+		return ret;
+
+	dev->mode_config.min_width = ST7571_HACTIVE;
+	dev->mode_config.min_height = 1;
+	dev->mode_config.max_width = ST7571_HACTIVE;
+	dev->mode_config.max_height = 128;
+	dev->mode_config.preferred_depth = 1;
+	dev->mode_config.funcs = &st7571_mode_config_funcs;
+
+	return 0;
+}
+
+static int st7571_plane_init(struct st7571_device *st7571)
+{
+	struct drm_plane *primary_plane = &st7571->primary_plane;
+	struct drm_device *dev = &st7571->dev;
+	int ret;
+
+	ret = drm_universal_plane_init(dev, primary_plane, 1,
+				       &st7571_primary_plane_funcs,
+				       st7571_primary_plane_formats,
+				       ARRAY_SIZE(st7571_primary_plane_formats),
+				       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;
+
+	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_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->startline = dt.vfront_porch.typ;
+	st7571->nlines = dt.vactive.typ;
+
+	if (dt.hactive.typ != ST7571_HACTIVE) {
+		dev_err(dev, "Invalid timing configuration (hactive != %i).\n",
+			ST7571_HACTIVE);
+		return -EINVAL;
+	}
+
+	if (st7571->width_mm == 0 || st7571->height_mm == 0) {
+		dev_err(dev, "Invalid panel dimensions.\n");
+		return -EINVAL;
+	}
+
+	if (st7571->startline + st7571->nlines > 128) {
+		dev_err(dev, "Invalid timing configuration.\n");
+		return -EINVAL;
+	}
+
+	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);
+	udelay(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(0x94),
+		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_SET_REVERSE(0),
+		ST7571_SET_ENTIRE_DISPLAY_ON(0),
+
+		ST7571_DISPLAY_ON,
+	};
+
+	/* 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);
+
+	ret = st7571_parse_dt(st7571);
+	if (ret)
+		return ret;
+
+	st7571->mode = st7571_mode(st7571);
+
+	/*
+	 * The chip nacks some messages but still works as expected.
+	 * 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)) {
+		dev_err(&client->dev, "Failed to initialize regmap\n");
+		return PTR_ERR(st7571->regmap);
+	}
+
+	ret = st7571_lcd_init(st7571);
+	if (ret)
+		return ret;
+
+	ret = st7571_mode_config_init(st7571);
+	if (ret) {
+		dev_err(&client->dev, "Failed to initialize mode config\n");
+		return ret;
+	}
+
+	ret = st7571_plane_init(st7571);
+	if (ret) {
+		dev_err(dev->dev, "Failed to initialize primary plane\n");
+		return ret;
+	}
+
+	ret = st7571_crtc_init(st7571);
+	if (ret < 0) {
+		dev_err(dev->dev, "Failed to initialize CRTC\n");
+		return ret;
+	}
+
+	ret = st7571_encoder_init(st7571);
+	if (ret < 0) {
+		dev_err(dev->dev, "Failed to initialize encoder\n");
+		return ret;
+	}
+
+	ret = st7571_connector_init(st7571);
+	if (ret < 0) {
+		dev_err(dev->dev, "Failed to initialize connector\n");
+		return ret;
+	}
+
+	drm_mode_config_reset(dev);
+
+	ret = drm_dev_register(dev, 0);
+	if (ret) {
+		dev_err(dev->dev, "Failed to register DRM device\n");
+		return ret;
+	}
+
+	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);
+	drm_atomic_helper_shutdown(&st7571->dev);
+}
+
+static const struct of_device_id st7571_of_match[] = {
+	{ .compatible = "sitronix,st7571" },
+	{},
+};
+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");

-- 
2.49.0

[PATCH v2 3/3] MAINTAINERS: add antry for Sitronix ST7571 LCD controller

[Marcus Folkesson]

Add MAINTAINERS entry for the Sitronix ST7571 dot matrix LCD
controller.

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
---
 MAINTAINERS | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 889bd4a59551c9bc125f94944a6e1c7e3ef2de83..eeae24fda846b9f63400ebb08c3fa7f02f3f4b19 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7572,6 +7572,12 @@ T:	git https://gitlab.freedesktop.org/drm/misc/kernel.git
 F:	Documentation/devicetree/bindings/display/sitronix,st7586.txt
 F:	drivers/gpu/drm/tiny/st7586.c
 
+DRM DRIVER FOR SITRONIX ST7571 PANELS
+M:	Marcus Folkesson <marcus.folkesson@gmail.com>
+S:	Maintained
+F:	Documentation/devicetree/bindings/display/sitronix,st7571.yaml
+F:	drivers/gpu/drm/tiny/st7571-i2c.c
+
 DRM DRIVER FOR SITRONIX ST7701 PANELS
 M:	Jagan Teki <jagan@amarulasolutions.com>
 S:	Maintained

-- 
2.49.0

Re: [PATCH v2 1/3] dt-bindings: display: Add Sitronix ST7571 panel

[Conor Dooley]

[-- Attachment #1: Type: text/plain, Size: 1371 bytes --]

On Fri, Apr 04, 2025 at 03:50:32PM +0200, Marcus Folkesson wrote:
> Sitronix ST7571 is a 4bit gray scale dot matrix LCD controller.
> 
> Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
> ---
>  .../bindings/display/sitronix,st7571.yaml          | 73 ++++++++++++++++++++++
>  1 file changed, 73 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/display/sitronix,st7571.yaml b/Documentation/devicetree/bindings/display/sitronix,st7571.yaml
> new file mode 100644
> index 0000000000000000000000000000000000000000..11575b820c59c5ada427fbb6b015c331215c8db6
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/sitronix,st7571.yaml
> @@ -0,0 +1,73 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/display/sitronix,st7571.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Sitronix ST7571 Display Panels
> +
> +maintainers:
> +  - Marcus Folkesson <marcus.folkesson@gmail.com>
> +
> +description:
> +  This binding is for display panels using a Sitronix ST7571 controller in I2C
> +  mode.
> +
> +allOf:
> +  - $ref: panel/panel-common.yaml#
> +
> +properties:
> +  compatible:
> +    const: sitronix,st7571
> +
> +  reg: true

You need to constrain this, so maxItems: 1.
Otherwise, seems okay.

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Re: [PATCH v2 1/3] dt-bindings: display: Add Sitronix ST7571 panel

[Krzysztof Kozlowski]

On 04/04/2025 15:50, Marcus Folkesson wrote:
> Sitronix ST7571 is a 4bit gray scale dot matrix LCD controller.
> 
> Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
> ---
>  .../bindings/display/sitronix,st7571.yaml          | 73 ++++++++++++++++++++++
>  1 file changed, 73 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/display/sitronix,st7571.yaml b/Documentation/devicetree/bindings/display/sitronix,st7571.yaml
> new file mode 100644
> index 0000000000000000000000000000000000000000..11575b820c59c5ada427fbb6b015c331215c8db6
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/sitronix,st7571.yaml
> @@ -0,0 +1,73 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/display/sitronix,st7571.yaml#

Why isn't this in panels directory?

> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Sitronix ST7571 Display Panels
> +
> +maintainers:
> +  - Marcus Folkesson <marcus.folkesson@gmail.com>
> +
> +description:
> +  This binding is for display panels using a Sitronix ST7571 controller in I2C

Do not explain for a binding that it is a binding. Redundant. Instead
describe the hardware.

> +  mode.
> +
> +allOf:
> +  - $ref: panel/panel-common.yaml#
> +
> +properties:
> +  compatible:
> +    const: sitronix,st7571
> +
> +  reg: true
> +  reset-gpios: true
> +  width-mm: true
> +  height-mm: true
> +
> +  panel-timing:
> +    $ref: panel/panel-timing.yaml#

Drop, already part of panel.

> +    description: |
> +      The panel-timing node specifies the display resolution and timing
> +      parameters. The hactive and vactive properties are mandatory.
> +      The vback-porch property specifies the start line of the display.
> +      The other properties should be set to zero.

Drop description as well.

> +
> +required:
> +  - compatible
> +  - reg
> +  - reset-gpios
> +  - width-mm
> +  - height-mm
> +  - panel-timing
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/gpio/gpio.h>
> +    
> +    i2c {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        display@3f {

Not much improved. How is this called in every other binding? panel.

> +          compatible = "sitronix,st7571";

Messed indentation.

> +          reg = <0x3f>;
> +          reset-gpios = <&gpio0 3 GPIO_ACTIVE_LOW>;
> +          width-mm = <37>;
> +          height-mm = <27>;
> +
> +            panel-timing {

And here is even more confusing.

Best regards,
Krzysztof

Re: [PATCH v2 1/3] dt-bindings: display: Add Sitronix ST7571 panel

[Krzysztof Kozlowski]

On 04/04/2025 19:30, Krzysztof Kozlowski wrote:
>> +
>> +examples:
>> +  - |
>> +    #include <dt-bindings/gpio/gpio.h>
>> +    
>> +    i2c {
>> +        #address-cells = <1>;
>> +        #size-cells = <0>;
>> +
>> +        display@3f {
> 
> Not much improved. How is this called in every other binding? panel.

Hmmm, unless this is not a panel, but it looks like a panel and
description partially suggests it. Other sitronix devices are split
between these two, but OTOH your driver is more complex than just simple
panel.

Your commit msg is one sentence and binding description is basically
non-existing, so not sure how to help. You need to describe the hardware
so people understand what this device is.

Best regards,
Krzysztof

Re: [PATCH v2 1/3] dt-bindings: display: Add Sitronix ST7571 panel

[Marcus Folkesson]

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Hi Krzysztof,

On Fri, Apr 04, 2025 at 07:36:12PM +0200, Krzysztof Kozlowski wrote:
> On 04/04/2025 19:30, Krzysztof Kozlowski wrote:
> >> +
> >> +examples:
> >> +  - |
> >> +    #include <dt-bindings/gpio/gpio.h>
> >> +    
> >> +    i2c {
> >> +        #address-cells = <1>;
> >> +        #size-cells = <0>;
> >> +
> >> +        display@3f {
> > 
> > Not much improved. How is this called in every other binding? panel.
> 
> Hmmm, unless this is not a panel, but it looks like a panel and
> description partially suggests it. Other sitronix devices are split
> between these two, but OTOH your driver is more complex than just simple
> panel.

I've counted this as a display, but the border is not crystal
clear, and, as you say, other Sitronix devices are split between the two.
It is a controller/driver for a LCD panel.

> 
> Your commit msg is one sentence and binding description is basically
> non-existing, so not sure how to help. You need to describe the hardware
> so people understand what this device is.

I've prepared this description for the next version of the patch:

description:
  Sitronix ST7571 is a driver and controller for up to 4-level gray
  scale dot-matrix LCD panels.
  It drives 128 segment outputs and 128+1 common outputs.
  It provides several system interfaces like SPI, I2C and 8-bit parallel bus.

But still, it is not obvious if I should move it to panel or not.

> 
> Best regards,
> Krzysztof

Best regards,
Marcus Folkesson

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Re: [PATCH v2 2/3] drm/st7571-i2c: add support for Sitronix ST7571 LCD controller

[Thomas Zimmermann]

Hi

Am 04.04.25 um 15:50 schrieb Marcus Folkesson:
> Sitronix ST7571 is a 4bit gray scale dot matrix LCD controller.
> The controller has a SPI, I2C and 8bit parallel interface, this
> driver is for the I2C interface only.
>
> Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>

Reviewed-by: Thomas Zimmermann <tzimmrmann@suse.de>

I have a few points below, but it's all minor details. The driver looks 
good overall.

> ---
>   drivers/gpu/drm/tiny/Kconfig      |  11 +
>   drivers/gpu/drm/tiny/Makefile     |   1 +
>   drivers/gpu/drm/tiny/st7571-i2c.c | 720 ++++++++++++++++++++++++++++++++++++++
>   3 files changed, 732 insertions(+)
>
> diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig
> index 94cbdb1337c07f1628a33599a7130369b9d59d98..6c711f4b799e05a8edc8e5fd68de0542d9cb6cab 100644
> --- a/drivers/gpu/drm/tiny/Kconfig
> +++ b/drivers/gpu/drm/tiny/Kconfig
> @@ -232,6 +232,17 @@ config TINYDRM_ST7586
>   
>   	  If M is selected the module will be called st7586.
>   
> +config TINYDRM_ST7571_I2C

Nit: we don't call anything TINYDRM_ any longer; just DRM_.

> +	tristate "DRM support for Sitronix ST7571 display panels (I2C)"
> +	depends on DRM && I2C

> +	select DRM_KMS_HELPER
> +	select DRM_GEM_SHMEM_HELPER

Alphabetical sorting please

> +	select REGMAP_I2C
> +	help
> +	  DRM driver for Sitronix ST7571 panels controlled over I2C.
> +
> +	  if M is selected the module will be called st7571-i2c.

Is there a reason why it is called _i2c? There's another interface, I 
assume?

> +
>   config TINYDRM_ST7735R
>   	tristate "DRM support for Sitronix ST7715R/ST7735R display panels"
>   	depends on DRM && SPI
> diff --git a/drivers/gpu/drm/tiny/Makefile b/drivers/gpu/drm/tiny/Makefile
> index 60816d2eb4ff93b87228ed8eadd60a0a33a1144b..ed767dd9d22b3bb98f50fa2007cad7fb3f3d95e4 100644
> --- a/drivers/gpu/drm/tiny/Makefile
> +++ b/drivers/gpu/drm/tiny/Makefile
> @@ -15,5 +15,6 @@ obj-$(CONFIG_TINYDRM_ILI9486)		+= ili9486.o
>   obj-$(CONFIG_TINYDRM_MI0283QT)		+= mi0283qt.o
>   obj-$(CONFIG_TINYDRM_REPAPER)		+= repaper.o
>   obj-$(CONFIG_TINYDRM_SHARP_MEMORY)	+= sharp-memory.o
> +obj-$(CONFIG_TINYDRM_ST7571_I2C)	+= st7571-i2c.o
>   obj-$(CONFIG_TINYDRM_ST7586)		+= st7586.o
>   obj-$(CONFIG_TINYDRM_ST7735R)		+= st7735r.o
> diff --git a/drivers/gpu/drm/tiny/st7571-i2c.c b/drivers/gpu/drm/tiny/st7571-i2c.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..196ecd662c73dfaa9940fc601a656305c81a1619
> --- /dev/null
> +++ b/drivers/gpu/drm/tiny/st7571-i2c.c
> @@ -0,0 +1,720 @@
> +// 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/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 | ((c) & 0xf))
> +#define ST7571_SET_COLUMN_MSB(c)		(0x10 | ((c) >> 4))
> +#define ST7571_SET_COM0_LSB(x)			((x) & 0x7f)
> +#define ST7571_SET_COM0_MSB			(0x44)
> +#define ST7571_SET_COM_SCAN_DIR(d)		(0xc0 | (((d) << 3) & 0x8))
> +#define ST7571_SET_CONTRAST_LSB(c)		((c) & 0x3f)
> +#define ST7571_SET_CONTRAST_MSB			(0x81)
> +#define ST7571_SET_DISPLAY_DUTY_LSB(d)		((d) & 0xff)
> +#define ST7571_SET_DISPLAY_DUTY_MSB		(0x48)
> +#define ST7571_SET_ENTIRE_DISPLAY_ON(p)		(0xa4 | ((p) & 0x1))
> +#define ST7571_SET_LCD_BIAS(b)			(0x50 | ((b) & 0x7))
> +#define ST7571_SET_MODE_LSB(m)			((m) & 0xfc)
> +#define ST7571_SET_MODE_MSB			(0x38)
> +#define ST7571_SET_PAGE(p)			(0xb0 | (p))
> +#define ST7571_SET_POWER(p)			(0x28 | ((p) & 0x7))
> +#define ST7571_SET_REGULATOR_REG(r)		(0x20 | ((r) & 0x7))
> +#define ST7571_SET_REVERSE(r)			(0xa6 | ((r) & 0x1))
> +#define ST7571_SET_SEG_SCAN_DIR(d)		(0xa0 | ((d) & 0x1))
> +#define ST7571_SET_START_LINE_LSB(l)		((l) & 0x3f)
> +#define ST7571_SET_START_LINE_MSB		(0x40)
> +
> +/* Extension command set 3 */
> +#define ST7571_COMMAND_SET_3			(0x7b)
> +#define ST7571_SET_COLOR_MODE(c)		(0x10 | ((c) & 0x1))
> +#define ST7571_COMMAND_SET_NORMAL		(0x00)
> +
> +
> +/* hactive is fixed to 128 */
> +#define ST7571_HACTIVE				(128)
> +
> +#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,
> +};
> +
> +#define drm_to_st7571(_dev) container_of(_dev, struct st7571_device, dev)
> +
> +struct st7571_device {
> +	struct drm_plane primary_plane;
> +	struct drm_connector connector;
> +	struct drm_display_mode mode;
> +	struct drm_encoder encoder;
> +	struct drm_device dev;
> +	struct drm_crtc crtc;

I suggest to visually group this to make it a bit easier to understand. 
Something like this:

{
  drm_device

  plane
  crtc
  encoder
  connector

   display_mode
   ...
}

The DRM device is just a device, the block in the middle it the 
modesetting pipeline. The display mode is something between pipeline and 
hardware state.

> +
> +	struct i2c_client *client;
> +	struct regmap *regmap;
> +	bool ignore_nak;
> +
> +	struct gpio_desc *reset;
> +
> +	u32 width_mm;
> +	u32 height_mm;
> +	u32 nlines;
> +	u32 startline;
> +};
> +
> +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);
> +	/*
> +	 * This is a workaround for the ST7571, which sometimes fails to acknowledge
> +	 *
> +	 * 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;
> +}
> +
> +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 / 8),
> +	};
> +
> +	return st7571_send_command_list(st7571, cmd_list, ARRAY_SIZE(cmd_list));
> +}
> +
> +static int st7571_fb_blit_rect(struct drm_framebuffer *fb,
> +			       const struct iosys_map *vmap,
> +			       struct drm_rect *rect)
> +{
> +	struct st7571_device *st7571 = drm_to_st7571(fb->dev);
> +	int bpp = fb->format->format == DRM_FORMAT_C1 ? 1 : 2;
> +	char *pixel = vmap->vaddr;
> +	int x1 = rect->x1 * bpp;
> +	int x2 = rect->x2 * bpp;
> +	char row[256];
> +
> +	for (int y = rect->y1; y < rect->y2; y += 8) {
> +		for (int x = x1; x < x2; x++)
> +			row[x] = st7571_transform_xy(pixel, 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);
> +	}
> +
> +	return 0;
> +}
> +
> +static int st7571_set_color_mode(struct st7571_device *st7571, enum st7571_color_mode  mode)
> +{
> +	u8 cmd_list[] = {
> +		ST7571_COMMAND_SET_3,
> +		ST7571_SET_COLOR_MODE(mode),
> +		ST7571_COMMAND_SET_NORMAL,
> +	};
> +
> +	return st7571_send_command_list(st7571, cmd_list, ARRAY_SIZE(cmd_list));
> +}
> +
> +static int st7571_set_pixel_format(struct st7571_device *st7571,
> +				   u32 pixel_format)
> +{
> +	switch (pixel_format) {
> +	case DRM_FORMAT_C1:
> +		return st7571_set_color_mode(st7571, ST7571_COLOR_MODE_BLACKWHITE);
> +	case DRM_FORMAT_C2:
> +		return st7571_set_color_mode(st7571, ST7571_COLOR_MODE_GRAY);
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +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 uint32_t st7571_primary_plane_formats[] = {
> +	DRM_FORMAT_C1,
> +	DRM_FORMAT_C2,
> +};

I assume that you only get fbcon output for now. Some ancient X11window 
managers might also work. Today's GUIs usually need something like XRGB 
to work. We do have DRM helpers to convert from XRGB to Cn, but they 
currently don't support formats with multiple pixels per byte. It's on 
my TODO list and you driver could add XRGB support at some point.

> +
> +static const uint64_t 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))
> +		return;
> +
> +	ret = st7571_set_pixel_format(st7571, fb->format->format);
> +	if (ret) {
> +		dev_err(dev->dev, "Failed to set pixel format: %d\n", ret);
> +		return;
> +	}
> +
> +	drm_atomic_helper_damage_iter_init(&iter, old_plane_state, plane_state);
> +	drm_atomic_for_each_plane_damage(&iter, &damage) {
> +		st7571_fb_blit_rect(fb, &shadow_plane_state->data[0], &damage);
> +	}
> +
> +	drm_dev_exit(idx);
> +	drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);
> +}
> +
> +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,
> +};
> +
> +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 const struct drm_crtc_helper_funcs st7571_crtc_helper_funcs = {
> +	.atomic_check = drm_crtc_helper_atomic_check,
> +};
> +
> +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 const struct drm_encoder_funcs st7571_encoder_funcs = {
> +	.destroy = drm_encoder_cleanup,
> +};
> +
> +/*
> + * 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 enum drm_mode_status st7571_mode_config_mode_valid(struct drm_device *dev,
> +						       const struct drm_display_mode *mode)
> +{
> +	struct st7571_device *st7571 = drm_to_st7571(dev);
> +
> +	return drm_crtc_helper_mode_valid_fixed(&st7571->crtc, mode, &st7571->mode);
> +}
> +
> +static const struct drm_mode_config_funcs st7571_mode_config_funcs = {
> +	.fb_create = drm_gem_fb_create_with_dirty,
> +	.mode_valid = st7571_mode_config_mode_valid,
> +	.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_HACTIVE, 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;
> +	int ret;
> +
> +	ret = drmm_mode_config_init(dev);
> +	if (ret)
> +		return ret;
> +
> +	dev->mode_config.min_width = ST7571_HACTIVE;
> +	dev->mode_config.min_height = 1;
> +	dev->mode_config.max_width = ST7571_HACTIVE;
> +	dev->mode_config.max_height = 128;
> +	dev->mode_config.preferred_depth = 1;
> +	dev->mode_config.funcs = &st7571_mode_config_funcs;
> +
> +	return 0;
> +}
> +
> +static int st7571_plane_init(struct st7571_device *st7571)
> +{
> +	struct drm_plane *primary_plane = &st7571->primary_plane;
> +	struct drm_device *dev = &st7571->dev;
> +	int ret;
> +
> +	ret = drm_universal_plane_init(dev, primary_plane, 1,
> +				       &st7571_primary_plane_funcs,
> +				       st7571_primary_plane_formats,
> +				       ARRAY_SIZE(st7571_primary_plane_formats),
> +				       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;
> +
> +	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_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->startline = dt.vfront_porch.typ;
> +	st7571->nlines = dt.vactive.typ;
> +
> +	if (dt.hactive.typ != ST7571_HACTIVE) {
> +		dev_err(dev, "Invalid timing configuration (hactive != %i).\n",
> +			ST7571_HACTIVE);
> +		return -EINVAL;
> +	}
> +
> +	if (st7571->width_mm == 0 || st7571->height_mm == 0) {
> +		dev_err(dev, "Invalid panel dimensions.\n");
> +		return -EINVAL;
> +	}
> +
> +	if (st7571->startline + st7571->nlines > 128) {
> +		dev_err(dev, "Invalid timing configuration.\n");
> +		return -EINVAL;
> +	}
> +
> +	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);
> +	udelay(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(0x94),
> +		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_SET_REVERSE(0),
> +		ST7571_SET_ENTIRE_DISPLAY_ON(0),
> +
> +		ST7571_DISPLAY_ON,
> +	};
> +
> +	/* 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);
> +
> +	ret = st7571_parse_dt(st7571);
> +	if (ret)
> +		return ret;
> +
> +	st7571->mode = st7571_mode(st7571);
> +
> +	/*
> +	 * The chip nacks some messages but still works as expected.
> +	 * 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)) {
> +		dev_err(&client->dev, "Failed to initialize regmap\n");
> +		return PTR_ERR(st7571->regmap);
> +	}
> +
> +	ret = st7571_lcd_init(st7571);
> +	if (ret)
> +		return ret;
> +


> +	ret = st7571_mode_config_init(st7571);
> +	if (ret) {
> +		dev_err(&client->dev, "Failed to initialize mode config\n");
> +		return ret;
> +	}
> +
> +	ret = st7571_plane_init(st7571);
> +	if (ret) {
> +		dev_err(dev->dev, "Failed to initialize primary plane\n");
> +		return ret;
> +	}
> +
> +	ret = st7571_crtc_init(st7571);
> +	if (ret < 0) {
> +		dev_err(dev->dev, "Failed to initialize CRTC\n");
> +		return ret;
> +	}
> +
> +	ret = st7571_encoder_init(st7571);
> +	if (ret < 0) {
> +		dev_err(dev->dev, "Failed to initialize encoder\n");
> +		return ret;
> +	}
> +
> +	ret = st7571_connector_init(st7571);
> +	if (ret < 0) {
> +		dev_err(dev->dev, "Failed to initialize connector\n");
> +		return ret;
> +	}
> +
> +	drm_mode_config_reset(dev);

No need for all these individual _init functions. For such simple 
drivers, it might be easier to put all pipeline setup here. Or put 
everything including (drm_mode_config_reset()) into 
st7571_mode_config_init(). Just an advise; your choice.

> +
> +	ret = drm_dev_register(dev, 0);
> +	if (ret) {
> +		dev_err(dev->dev, "Failed to register DRM device\n");
> +		return ret;
> +	}
> +
> +	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);

> +	drm_atomic_helper_shutdown(&st7571->dev);

This would disable the mode-setting pipeline. But as the device has been 
unplugged already, it won't really do anything. You can leave it out.

Best regards
Thomas


> +}
> +
> +static const struct of_device_id st7571_of_match[] = {
> +	{ .compatible = "sitronix,st7571" },
> +	{},
> +};
> +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");
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

Re: [PATCH v2 3/3] MAINTAINERS: add antry for Sitronix ST7571 LCD controller

[Thomas Zimmermann]

Am 04.04.25 um 15:50 schrieb Marcus Folkesson:
> Add MAINTAINERS entry for the Sitronix ST7571 dot matrix LCD
> controller.
>
> Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>

> ---
>   MAINTAINERS | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 889bd4a59551c9bc125f94944a6e1c7e3ef2de83..eeae24fda846b9f63400ebb08c3fa7f02f3f4b19 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -7572,6 +7572,12 @@ T:	git https://gitlab.freedesktop.org/drm/misc/kernel.git
>   F:	Documentation/devicetree/bindings/display/sitronix,st7586.txt
>   F:	drivers/gpu/drm/tiny/st7586.c
>   
> +DRM DRIVER FOR SITRONIX ST7571 PANELS
> +M:	Marcus Folkesson <marcus.folkesson@gmail.com>
> +S:	Maintained
> +F:	Documentation/devicetree/bindings/display/sitronix,st7571.yaml
> +F:	drivers/gpu/drm/tiny/st7571-i2c.c
> +
>   DRM DRIVER FOR SITRONIX ST7701 PANELS
>   M:	Jagan Teki <jagan@amarulasolutions.com>
>   S:	Maintained
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

Re: [PATCH v2 2/3] drm/st7571-i2c: add support for Sitronix ST7571 LCD controller

[Marcus Folkesson]

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Hi Thomas,

Thank you for your review and feedback!

On Mon, Apr 07, 2025 at 10:30:28AM +0200, Thomas Zimmermann wrote:
> Hi
> 
> Am 04.04.25 um 15:50 schrieb Marcus Folkesson:
> > Sitronix ST7571 is a 4bit gray scale dot matrix LCD controller.
> > The controller has a SPI, I2C and 8bit parallel interface, this
> > driver is for the I2C interface only.
> > 
> > Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
> 
> Reviewed-by: Thomas Zimmermann <tzimmrmann@suse.de>
> 
> I have a few points below, but it's all minor details. The driver looks good
> overall.
> 
> > ---
> >   drivers/gpu/drm/tiny/Kconfig      |  11 +
> >   drivers/gpu/drm/tiny/Makefile     |   1 +
> >   drivers/gpu/drm/tiny/st7571-i2c.c | 720 ++++++++++++++++++++++++++++++++++++++
> >   3 files changed, 732 insertions(+)
> > 


[...]
> 
> > +	select REGMAP_I2C
> > +	help
> > +	  DRM driver for Sitronix ST7571 panels controlled over I2C.
> > +
> > +	  if M is selected the module will be called st7571-i2c.
> 
> Is there a reason why it is called _i2c? There's another interface, I
> assume?

Yes exactly, the ST7571 has a SPI and 8bit parallel interface as well. All
common parts has been written so that it could easily be put into a
common file later on.
It should pretty much just be to create a new driver with another regmap
interface to support other interfaces then.

I only have the I2C interface to test with for now, so I leave it to the
future.

[...]

> > +static const struct drm_connector_helper_funcs st7571_connector_helper_funcs = {
> > +	.get_modes = st7571_connector_get_modes,
> > +};
> > +
> > +static const uint32_t st7571_primary_plane_formats[] = {
> > +	DRM_FORMAT_C1,
> > +	DRM_FORMAT_C2,
> > +};
> 
> I assume that you only get fbcon output for now. Some ancient X11window
> managers might also work. Today's GUIs usually need something like XRGB to
> work. We do have DRM helpers to convert from XRGB to Cn, but they currently
> don't support formats with multiple pixels per byte. It's on my TODO list
> and you driver could add XRGB support at some point.

Yes I do.
Oh, sounds good. I will keep myself updated.


[...]

> > +	ret = st7571_lcd_init(st7571);
> > +	if (ret)
> > +		return ret;
> > +
> 
> 
> > +	ret = st7571_mode_config_init(st7571);
> > +	if (ret) {
> > +		dev_err(&client->dev, "Failed to initialize mode config\n");
> > +		return ret;
> > +	}
> > +
> > +	ret = st7571_plane_init(st7571);
> > +	if (ret) {
> > +		dev_err(dev->dev, "Failed to initialize primary plane\n");
> > +		return ret;
> > +	}
> > +
> > +	ret = st7571_crtc_init(st7571);
> > +	if (ret < 0) {
> > +		dev_err(dev->dev, "Failed to initialize CRTC\n");
> > +		return ret;
> > +	}
> > +
> > +	ret = st7571_encoder_init(st7571);
> > +	if (ret < 0) {
> > +		dev_err(dev->dev, "Failed to initialize encoder\n");
> > +		return ret;
> > +	}
> > +
> > +	ret = st7571_connector_init(st7571);
> > +	if (ret < 0) {
> > +		dev_err(dev->dev, "Failed to initialize connector\n");
> > +		return ret;
> > +	}
> > +
> > +	drm_mode_config_reset(dev);
> 
> No need for all these individual _init functions. For such simple drivers,
> it might be easier to put all pipeline setup here. Or put everything
> including (drm_mode_config_reset()) into st7571_mode_config_init(). Just an
> advise; your choice.

Yeah I know. It's partly to make it easier for me separate things
in my head since I'm new to this subsystem, and partly as I plan to move
these functions to a common file later when I add support for the
other interfaces.

When I started to dig into the code of other drivers, clear lines as
this would have helped me, so I think I would like to keep it as it is if it
doesn't hurt too many eyes.

[...]

> 
> > +
> > +	ret = drm_dev_register(dev, 0);
> > +	if (ret) {
> > +		dev_err(dev->dev, "Failed to register DRM device\n");
> > +		return ret;
> > +	}
> > +
> > +	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);
> 
> > +	drm_atomic_helper_shutdown(&st7571->dev);
> 
> This would disable the mode-setting pipeline. But as the device has been
> unplugged already, it won't really do anything. You can leave it out.
> 
> Best regards
> Thomas


Best regards,
Marcus Folkesson

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