[PATCH 0/3] drm/sitronix/st7920: Add support for the ST7920 controller

[PATCH 0/3] drm/sitronix/st7920: Add support for the ST7920 controller

[Iker Pedrosa]

This patch-series adds support for the Sitronix ST7920 controller, which
is a monochrome dot-matrix graphical LCD controller that has SPI and
parallel interfaces.

The st7920 driver only has support for SPI so displays using other
transport protocols are currently not supported.

* Patch #1 adds the driver.
* Patch #2 adds the DT binding schema.
* Patch #3 adds the MAINTAINERS information.

Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>
---
Iker Pedrosa (3):
      drm: Add driver for Sitronix ST7920 LCD displays
      dt-bindings: display: sitronix,st7920: Add DT schema
      MAINTAINERS: Add entry for Sitronix ST7920 driver

 .../bindings/display/sitronix,st7920.yaml          |  55 ++
 MAINTAINERS                                        |   7 +
 drivers/gpu/drm/sitronix/Kconfig                   |  10 +
 drivers/gpu/drm/sitronix/Makefile                  |   1 +
 drivers/gpu/drm/sitronix/st7920.c                  | 869 +++++++++++++++++++++
 drivers/gpu/drm/sitronix/st7920.h                  |  55 ++
 6 files changed, 997 insertions(+)
---
base-commit: c571cb70e1ed43ee543c70151e61a001ab2eefa2
change-id: 20250806-st7920-e7aba32b3ab6

Best regards,
-- 
Iker Pedrosa <ikerpedrosam@gmail.com>

[PATCH 1/3] drm: Add driver for Sitronix ST7920 LCD displays

[Iker Pedrosa]

This adds a functional DRM driver for ST7920 that communicates with the
display via the SPI bus.

Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>
---
 drivers/gpu/drm/sitronix/Kconfig  |  10 +
 drivers/gpu/drm/sitronix/Makefile |   1 +
 drivers/gpu/drm/sitronix/st7920.c | 869 ++++++++++++++++++++++++++++++++++++++
 drivers/gpu/drm/sitronix/st7920.h |  55 +++
 4 files changed, 935 insertions(+)

diff --git a/drivers/gpu/drm/sitronix/Kconfig b/drivers/gpu/drm/sitronix/Kconfig
index 6de7d92d9b74c72746915b945869dba91f161d2b..68f792dda14e83f457579ae7c240f4cc6a469d33 100644
--- a/drivers/gpu/drm/sitronix/Kconfig
+++ b/drivers/gpu/drm/sitronix/Kconfig
@@ -40,3 +40,13 @@ config DRM_ST7735R
 
 	  If M is selected the module will be called st7735r.
 
+config DRM_ST7920
+	tristate "DRM support for Sitronix ST7920 LCD displays"
+	depends on DRM && SPI
+	select DRM_GEM_SHMEM_HELPER
+	select DRM_KMS_HELPER
+	select REGMAP_SPI
+	help
+	  DRM driver for the ST7920 Sitronix LCD controllers.
+
+	  If M is selected the module will be called st7920.
diff --git a/drivers/gpu/drm/sitronix/Makefile b/drivers/gpu/drm/sitronix/Makefile
index bd139e5a6995fa026cc635b3c29782473d1efad7..2f064a518121bfee3cca73acd42589e8c54cd4d7 100644
--- a/drivers/gpu/drm/sitronix/Makefile
+++ b/drivers/gpu/drm/sitronix/Makefile
@@ -1,3 +1,4 @@
 obj-$(CONFIG_DRM_ST7571_I2C)		+= st7571-i2c.o
 obj-$(CONFIG_DRM_ST7586)		+= st7586.o
 obj-$(CONFIG_DRM_ST7735R)		+= st7735r.o
+obj-$(CONFIG_DRM_ST7920))		+= st7920.o
diff --git a/drivers/gpu/drm/sitronix/st7920.c b/drivers/gpu/drm/sitronix/st7920.c
new file mode 100644
index 0000000000000000000000000000000000000000..c3226f352e39c626e3654250631521d07edf6784
--- /dev/null
+++ b/drivers/gpu/drm/sitronix/st7920.c
@@ -0,0 +1,869 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * DRM driver for Sitronix ST7920 LCD displays
+ *
+ * Copyright 2025 Iker Pedrosa <ikerpedrosam@gmail.com>
+ *
+ */
+
+#include <linux/bitrev.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/spi/spi.h>
+
+#include <drm/drm_atomic.h>
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_client_setup.h>
+#include <drm/drm_crtc_helper.h>
+#include <drm/drm_damage_helper.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_fbdev_shmem.h>
+#include <drm/drm_framebuffer.h>
+#include <drm/drm_gem_atomic_helper.h>
+#include <drm/drm_gem_framebuffer_helper.h>
+#include <drm/drm_gem_shmem_helper.h>
+#include <drm/drm_plane.h>
+#include <drm/drm_probe_helper.h>
+
+#include "st7920.h"
+
+#define DRIVER_NAME	"sitronix_st7920"
+#define DRIVER_DESC	"DRM driver for Sitronix ST7920 LCD displays"
+#define DRIVER_DATE	"20250723"
+#define DRIVER_MAJOR	1
+#define DRIVER_MINOR	0
+
+/* Display organization */
+#define WIDTH_BYTES		16
+#define HEIGHT_IN_PIXELS	64
+#define BYTES_IN_DISPLAY	(WIDTH_BYTES * HEIGHT_IN_PIXELS)
+#define BYTES_IN_SEGMENT	2
+#define PIXELS_IN_SEGMENT	(BYTES_IN_SEGMENT * 8)
+
+/* Sync sequence */
+#define SYNC_BITS			0xF8
+#define RW_HIGH				0x04
+#define RS_HIGH				0x02
+
+/* Commands */
+#define SET_DISPLAY_ON			0x0C
+#define SET_DISPLAY_OFF			0x08
+#define SET_DISPLAY_CLEAR		0x01
+#define SET_BASIC_INSTRUCTION_SET	0x30
+#define SET_EXT_INSTRUCTION_SET		0x34
+#define SET_GRAPHICS_DISPLAY		0x36
+#define SET_GDRAM_ADDRESS		0x80
+#define SET_GDRAM_DATA			0xFF /* Driver internal command */
+
+/* Masks */
+#define HIGH_DATA_MASK			0xF0
+#define LOW_DATA_MASK			0x0F
+#define TOP_VERTICAL_ADDRESS		0x80
+#define BOTTOM_VERTICAL_ADDRESS		0x60
+#define TOP_HORIZONTAL_ADDRESS		0x00
+#define BOTTOM_HORIZONTAL_ADDRESS	0x80
+
+#define CMD_SIZE			35
+
+const struct st7920_deviceinfo st7920_variants[] = {
+	[ST7920_ID] = {
+		.default_width = 128,
+		.default_height = 64,
+		.family_id = ST7920_FAMILY,
+	}
+};
+EXPORT_SYMBOL_NS_GPL(st7920_variants, DRM_ST7920);
+
+struct st7920_plane_state {
+	struct drm_shadow_plane_state base;
+	/* Intermediate buffer to convert pixels from XRGB8888 to HW format */
+	u8 *buffer;
+};
+
+struct st7920_crtc_state {
+	struct drm_crtc_state base;
+	/* Buffer to store pixels in HW format and written to the panel */
+	u8 *data_array;
+};
+
+static inline struct st7920_plane_state *to_st7920_plane_state(struct drm_plane_state *state)
+{
+	return container_of(state, struct st7920_plane_state, base.base);
+}
+
+static inline struct st7920_crtc_state *to_st7920_crtc_state(struct drm_crtc_state *state)
+{
+	return container_of(state, struct st7920_crtc_state, base);
+}
+
+static inline struct st7920_device *drm_to_st7920(struct drm_device *drm)
+{
+	return container_of(drm, struct st7920_device, drm);
+}
+
+static int st7920_spi_write(struct spi_device *spi, int cmd, const void *data, size_t size)
+{
+	u8 reg[CMD_SIZE] = {0};
+	int i = 0, j = 0;
+	int ret;
+
+	/*
+	 * First the sync bits are sent: 11111WS0.
+	 * Where W is the read/write (RW) bit and S is the register/data (RS) bit.
+	 * Then, every 8 bits instruction/data will be separated into 2 groups.
+	 * Higher 4 bits (DB7~DB4) will be placed in the first section followed by
+	 * 4 '0's. And lower 4 bits (DB3~DB0) will be placed in the second section
+	 * followed by 4 '0's.
+	 */
+	if (cmd == SET_GDRAM_ADDRESS) {
+		const u8 y_addr = *(const u8 *)data;
+		bool bottom_screen = (y_addr >= 32);
+
+		reg[i++] = SYNC_BITS;
+		/* Set vertical address */
+		if (!bottom_screen)
+			reg[i++] = TOP_VERTICAL_ADDRESS + (*(uint8_t *)data & HIGH_DATA_MASK);
+		else
+			reg[i++] = BOTTOM_VERTICAL_ADDRESS + (*(uint8_t *)data & HIGH_DATA_MASK);
+
+		reg[i++] = *(uint8_t *)data << 4;
+		/* Set horizontal address */
+		reg[i++] = SET_GDRAM_ADDRESS;
+		if (!bottom_screen)
+			reg[i++] = TOP_HORIZONTAL_ADDRESS;
+		else
+			reg[i++] = BOTTOM_HORIZONTAL_ADDRESS;
+	} else if (cmd == SET_GDRAM_DATA) {
+		const u8 *line_data = data;
+
+		reg[i++] = SYNC_BITS | RS_HIGH;
+
+		for (j = 0; j < 16; j++) {
+			reg[i++] = line_data[j] & 0xF0;
+			reg[i++] = (line_data[j] << 4) & 0xF0;
+		}
+	} else {
+		reg[i++] = SYNC_BITS;
+		reg[i++] = cmd & HIGH_DATA_MASK;
+		reg[i++] = (cmd & LOW_DATA_MASK) << 4;
+	}
+
+	ret = spi_write(spi, reg, i);
+
+	return ret;
+}
+
+static const struct regmap_config st7920_spi_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+};
+
+static const struct of_device_id st7920_of_match[] = {
+	/* st7920 family */
+	{
+		.compatible = "sitronix,st7920",
+		.data = &st7920_variants[ST7920_ID],
+	},
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, st7920_of_match);
+
+/*
+ * The SPI core always reports a MODALIAS uevent of the form "spi:<dev>", even
+ * if the device was registered via OF. This means that the module will not be
+ * auto loaded, unless it contains an alias that matches the MODALIAS reported.
+ *
+ * To workaround this issue, add a SPI device ID table. Even when this should
+ * not be needed for this driver to match the registered SPI devices.
+ */
+static const struct spi_device_id st7920_spi_id[] = {
+	/* st7920 family */
+	{ "st7920",  ST7920_ID },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(spi, st7920_spi_id);
+
+static int st7920_power_on(struct st7920_device *st7920)
+{
+	int ret;
+
+	ret = st7920_spi_write(st7920->spi, SET_DISPLAY_ON, NULL, 0);
+	if (ret < 0)
+		return ret;
+	udelay(72);
+
+	return ret;
+}
+
+static int st7920_power_off(struct st7920_device *st7920)
+{
+	int ret;
+
+	ret = st7920_spi_write(st7920->spi, SET_DISPLAY_CLEAR, NULL, 0);
+	udelay(1600);
+	ret = st7920_spi_write(st7920->spi, SET_DISPLAY_OFF, NULL, 0);
+	udelay(72);
+
+	return ret;
+}
+
+static int st7920_init(struct st7920_device *st7920)
+{
+	int ret;
+
+	ret = st7920_spi_write(st7920->spi, SET_BASIC_INSTRUCTION_SET, NULL, 0);
+	if (ret < 0)
+		return ret;
+	udelay(72);
+
+	ret = st7920_power_on(st7920);
+	if (ret < 0)
+		return ret;
+
+	ret = st7920_spi_write(st7920->spi, SET_GRAPHICS_DISPLAY, NULL, 0);
+	if (ret < 0)
+		return ret;
+	udelay(72);
+
+	ret = st7920_spi_write(st7920->spi, SET_DISPLAY_CLEAR, NULL, 0);
+	if (ret < 0)
+		return ret;
+	udelay(1600);
+
+	return 0;
+}
+
+static int st7920_update_rect(struct st7920_device *st7920,
+			       struct drm_rect *rect, u8 *buf,
+			       u8 *data_array)
+{
+	u32 array_idx = 0;
+	int i, j;
+	int ret;
+
+	/*
+	 * The screen is divided in 64(Y)x8(X) segments and each segment is
+	 * further divided in 2 bytes (D15~D0).
+	 *
+	 * Segment 0x0 is in the top-right corner, while segment 63x15 is in the
+	 * bottom-left. They would be displayed in the screen in the following way:
+	 * 0x0  0x1  0x2  ... 0x15
+	 * 1x0  1x1  1x2  ... 1x15
+	 * ...
+	 * 63x0 63x1 63x2 ... 63x15
+	 *
+	 * The data in each byte is big endian.
+	 */
+
+	for (i = 0; i < HEIGHT_IN_PIXELS; i++) {
+		u8 *line_start = buf + (i * WIDTH_BYTES);
+		u8 line_buffer[WIDTH_BYTES];
+
+		for (j = 0; j < WIDTH_BYTES; j++) {
+			line_buffer[j] = bitrev8(line_start[j]);
+			data_array[array_idx++] = line_buffer[j];
+		}
+
+		ret = st7920_spi_write(st7920->spi, SET_GDRAM_ADDRESS, &i, 1);
+		if (ret < 0)
+			return ret;
+		udelay(72);
+
+		ret = st7920_spi_write(st7920->spi, SET_GDRAM_DATA, line_buffer, WIDTH_BYTES);
+		if (ret < 0)
+			return ret;
+		udelay(72);
+	}
+
+	return ret;
+}
+
+static void st7920_clear_screen(struct st7920_device *st7920, u8 *data_array)
+{
+	memset(data_array, 0, BYTES_IN_DISPLAY);
+
+	st7920_spi_write(st7920->spi, SET_DISPLAY_CLEAR, NULL, 0);
+	udelay(1600);
+}
+
+static int st7920_fb_blit_rect(struct drm_framebuffer *fb,
+				const struct iosys_map *vmap,
+				struct drm_rect *rect,
+				u8 *buf, u8 *data_array,
+				struct drm_format_conv_state *fmtcnv_state)
+{
+	struct st7920_device *st7920 = drm_to_st7920(fb->dev);
+	struct iosys_map dst;
+	unsigned int dst_pitch;
+	int ret = 0;
+
+	/* Align y to display page boundaries */
+	rect->y1 = round_down(rect->y1, PIXELS_IN_SEGMENT);
+	rect->y2 = min_t(unsigned int, round_up(rect->y2, PIXELS_IN_SEGMENT), st7920->height);
+
+	dst_pitch = DIV_ROUND_UP(drm_rect_width(rect), 8);
+
+	ret = drm_gem_fb_begin_cpu_access(fb, DMA_FROM_DEVICE);
+	if (ret)
+		return ret;
+
+	iosys_map_set_vaddr(&dst, buf);
+	drm_fb_xrgb8888_to_mono(&dst, &dst_pitch, vmap, fb, rect, fmtcnv_state);
+
+	drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);
+
+	st7920_update_rect(st7920, rect, buf, data_array);
+
+	return ret;
+}
+
+static int st7920_primary_plane_atomic_check(struct drm_plane *plane,
+					      struct drm_atomic_state *state)
+{
+	struct drm_device *drm = plane->dev;
+	struct st7920_device *st7920 = drm_to_st7920(drm);
+	struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
+	struct st7920_plane_state *st7920_state = to_st7920_plane_state(plane_state);
+	struct drm_shadow_plane_state *shadow_plane_state = &st7920_state->base;
+	struct drm_crtc *crtc = plane_state->crtc;
+	struct drm_crtc_state *crtc_state = NULL;
+	const struct drm_format_info *fi;
+	unsigned int pitch;
+	int ret;
+
+	if (crtc)
+		crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
+
+	ret = drm_atomic_helper_check_plane_state(plane_state, crtc_state,
+						  DRM_PLANE_NO_SCALING,
+						  DRM_PLANE_NO_SCALING,
+						  false, false);
+	if (ret)
+		return ret;
+	else if (!plane_state->visible)
+		return 0;
+
+	fi = drm_format_info(DRM_FORMAT_R1);
+	if (!fi)
+		return -EINVAL;
+
+	pitch = drm_format_info_min_pitch(fi, 0, st7920->width);
+
+	if (plane_state->fb->format != fi) {
+		void *buf;
+
+		/* format conversion necessary; reserve buffer */
+		buf = drm_format_conv_state_reserve(&shadow_plane_state->fmtcnv_state,
+						    pitch, GFP_KERNEL);
+		if (!buf)
+			return -ENOMEM;
+	}
+
+	st7920_state->buffer = kcalloc(pitch, st7920->height, GFP_KERNEL);
+	if (!st7920_state->buffer)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static void st7920_primary_plane_atomic_update(struct drm_plane *plane,
+						struct drm_atomic_state *state)
+{
+	struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
+	struct drm_plane_state *old_plane_state = drm_atomic_get_old_plane_state(state, plane);
+	struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(plane_state);
+	struct drm_crtc_state *crtc_state = drm_atomic_get_new_crtc_state(state, plane_state->crtc);
+	struct st7920_crtc_state *st7920_crtc_state =  to_st7920_crtc_state(crtc_state);
+	struct st7920_plane_state *st7920_plane_state = to_st7920_plane_state(plane_state);
+	struct drm_framebuffer *fb = plane_state->fb;
+	struct drm_atomic_helper_damage_iter iter;
+	struct drm_device *drm = plane->dev;
+	struct drm_rect dst_clip;
+	struct drm_rect damage;
+	int idx;
+
+	if (!drm_dev_enter(drm, &idx))
+		return;
+
+	drm_atomic_helper_damage_iter_init(&iter, old_plane_state, plane_state);
+	drm_atomic_for_each_plane_damage(&iter, &damage) {
+		dst_clip = plane_state->dst;
+
+		if (!drm_rect_intersect(&dst_clip, &damage))
+			continue;
+
+		st7920_fb_blit_rect(fb, &shadow_plane_state->data[0], &dst_clip,
+				     st7920_plane_state->buffer,
+				     st7920_crtc_state->data_array,
+				     &shadow_plane_state->fmtcnv_state);
+	}
+
+	drm_dev_exit(idx);
+}
+
+static void st7920_primary_plane_atomic_disable(struct drm_plane *plane,
+						 struct drm_atomic_state *state)
+{
+	struct drm_device *drm = plane->dev;
+	struct st7920_device *st7920 = drm_to_st7920(drm);
+	struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
+	struct drm_crtc_state *crtc_state;
+	struct st7920_crtc_state *st7920_crtc_state;
+	int idx;
+
+	if (!plane_state->crtc)
+		return;
+
+	crtc_state = drm_atomic_get_new_crtc_state(state, plane_state->crtc);
+	st7920_crtc_state = to_st7920_crtc_state(crtc_state);
+
+	if (!drm_dev_enter(drm, &idx))
+		return;
+
+	st7920_clear_screen(st7920, st7920_crtc_state->data_array);
+
+	drm_dev_exit(idx);
+}
+
+/* Called during init to allocate the plane's atomic state. */
+static void st7920_primary_plane_reset(struct drm_plane *plane)
+{
+	struct st7920_plane_state *st7920_state;
+
+	WARN_ON(plane->state);
+
+	st7920_state = kzalloc(sizeof(*st7920_state), GFP_KERNEL);
+	if (!st7920_state)
+		return;
+
+	__drm_gem_reset_shadow_plane(plane, &st7920_state->base);
+}
+
+static struct drm_plane_state *st7920_primary_plane_duplicate_state(struct drm_plane *plane)
+{
+	struct drm_shadow_plane_state *new_shadow_plane_state;
+	struct st7920_plane_state *old_st7920_state;
+	struct st7920_plane_state *st7920_state;
+
+	if (WARN_ON(!plane->state))
+		return NULL;
+
+	old_st7920_state = to_st7920_plane_state(plane->state);
+	st7920_state = kmemdup(old_st7920_state, sizeof(*st7920_state), GFP_KERNEL);
+	if (!st7920_state)
+		return NULL;
+
+	/* The buffer is not duplicated and is allocated in .atomic_check */
+	st7920_state->buffer = NULL;
+
+	new_shadow_plane_state = &st7920_state->base;
+
+	__drm_gem_duplicate_shadow_plane_state(plane, new_shadow_plane_state);
+
+	return &new_shadow_plane_state->base;
+}
+
+static void st7920_primary_plane_destroy_state(struct drm_plane *plane,
+						struct drm_plane_state *state)
+{
+	struct st7920_plane_state *st7920_state = to_st7920_plane_state(state);
+
+	kfree(st7920_state->buffer);
+
+	__drm_gem_destroy_shadow_plane_state(&st7920_state->base);
+
+	kfree(st7920_state);
+}
+
+static const struct drm_plane_helper_funcs st7920_primary_plane_helper_funcs[] = {
+	[ST7920_FAMILY] = {
+		DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
+		.atomic_check = st7920_primary_plane_atomic_check,
+		.atomic_update = st7920_primary_plane_atomic_update,
+		.atomic_disable = st7920_primary_plane_atomic_disable,
+	}
+};
+
+static const struct drm_plane_funcs st7920_primary_plane_funcs = {
+	.update_plane = drm_atomic_helper_update_plane,
+	.disable_plane = drm_atomic_helper_disable_plane,
+	.reset = st7920_primary_plane_reset,
+	.atomic_duplicate_state = st7920_primary_plane_duplicate_state,
+	.atomic_destroy_state = st7920_primary_plane_destroy_state,
+	.destroy = drm_plane_cleanup,
+};
+
+static enum drm_mode_status st7920_crtc_mode_valid(struct drm_crtc *crtc,
+						    const struct drm_display_mode *mode)
+{
+	struct st7920_device *st7920 = drm_to_st7920(crtc->dev);
+
+	if (mode->hdisplay != st7920->mode.hdisplay &&
+	    mode->vdisplay != st7920->mode.vdisplay)
+		return MODE_ONE_SIZE;
+	else if (mode->hdisplay != st7920->mode.hdisplay)
+		return MODE_ONE_WIDTH;
+	else if (mode->vdisplay != st7920->mode.vdisplay)
+		return MODE_ONE_HEIGHT;
+
+	return MODE_OK;
+}
+
+static int st7920_crtc_atomic_check(struct drm_crtc *crtc,
+				     struct drm_atomic_state *state)
+{
+	struct drm_crtc_state *crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
+	struct st7920_crtc_state *st7920_state = to_st7920_crtc_state(crtc_state);
+	int ret;
+
+	ret = drm_crtc_helper_atomic_check(crtc, state);
+	if (ret)
+		return ret;
+
+	st7920_state->data_array = kmalloc(BYTES_IN_DISPLAY, GFP_KERNEL);
+	if (!st7920_state->data_array)
+		return -ENOMEM;
+
+	return 0;
+}
+
+/* Called during init to allocate the CRTC's atomic state. */
+static void st7920_crtc_reset(struct drm_crtc *crtc)
+{
+	struct st7920_crtc_state *st7920_state;
+
+	WARN_ON(crtc->state);
+
+	st7920_state = kzalloc(sizeof(*st7920_state), GFP_KERNEL);
+	if (!st7920_state)
+		return;
+
+	__drm_atomic_helper_crtc_reset(crtc, &st7920_state->base);
+}
+
+static struct drm_crtc_state *st7920_crtc_duplicate_state(struct drm_crtc *crtc)
+{
+	struct st7920_crtc_state *old_st7920_state;
+	struct st7920_crtc_state *st7920_state;
+
+	if (WARN_ON(!crtc->state))
+		return NULL;
+
+	old_st7920_state = to_st7920_crtc_state(crtc->state);
+	st7920_state = kmemdup(old_st7920_state, sizeof(*st7920_state), GFP_KERNEL);
+	if (!st7920_state)
+		return NULL;
+
+	/* The buffer is not duplicated and is allocated in .atomic_check */
+	st7920_state->data_array = NULL;
+
+	__drm_atomic_helper_crtc_duplicate_state(crtc, &st7920_state->base);
+
+	return &st7920_state->base;
+}
+
+static void st7920_crtc_destroy_state(struct drm_crtc *crtc,
+						struct drm_crtc_state *state)
+{
+	struct st7920_crtc_state *st7920_state = to_st7920_crtc_state(state);
+
+	kfree(st7920_state->data_array);
+
+	__drm_atomic_helper_crtc_destroy_state(state);
+
+	kfree(st7920_state);
+}
+
+/*
+ * The CRTC is always enabled. Screen updates are performed by
+ * the primary plane's atomic_update function. Disabling clears
+ * the screen in the primary plane's atomic_disable function.
+ */
+static const struct drm_crtc_helper_funcs st7920_crtc_helper_funcs[] = {
+	[ST7920_FAMILY] = {
+		.mode_valid = st7920_crtc_mode_valid,
+		.atomic_check = st7920_crtc_atomic_check,
+	}
+};
+
+static const struct drm_crtc_funcs st7920_crtc_funcs = {
+	.reset = st7920_crtc_reset,
+	.destroy = drm_crtc_cleanup,
+	.set_config = drm_atomic_helper_set_config,
+	.page_flip = drm_atomic_helper_page_flip,
+	.atomic_duplicate_state = st7920_crtc_duplicate_state,
+	.atomic_destroy_state = st7920_crtc_destroy_state,
+};
+
+static void st7920_encoder_atomic_enable(struct drm_encoder *encoder,
+						struct drm_atomic_state *state)
+{
+	struct drm_device *drm = encoder->dev;
+	struct st7920_device *st7920 = drm_to_st7920(drm);
+	int ret;
+
+	ret = st7920_init(st7920);
+	if (ret)
+		goto power_off;
+
+	return;
+
+power_off:
+	st7920_power_off(st7920);
+}
+
+static void st7920_encoder_atomic_disable(struct drm_encoder *encoder,
+					struct drm_atomic_state *state)
+{
+	struct drm_device *drm = encoder->dev;
+	struct st7920_device *st7920 = drm_to_st7920(drm);
+
+	st7920_power_off(st7920);
+}
+
+static const struct drm_encoder_helper_funcs st7920_encoder_helper_funcs[] = {
+	[ST7920_FAMILY] = {
+		.atomic_enable = st7920_encoder_atomic_enable,
+		.atomic_disable = st7920_encoder_atomic_disable,
+	}
+};
+
+static const struct drm_encoder_funcs st7920_encoder_funcs = {
+	.destroy = drm_encoder_cleanup,
+};
+
+static int st7920_connector_get_modes(struct drm_connector *connector)
+{
+	struct st7920_device *st7920 = drm_to_st7920(connector->dev);
+	struct drm_display_mode *mode;
+	struct device *dev = st7920->dev;
+
+	mode = drm_mode_duplicate(connector->dev, &st7920->mode);
+	if (!mode) {
+		dev_err(dev, "Failed to duplicated mode\n");
+		return 0;
+	}
+
+	drm_mode_probed_add(connector, mode);
+	drm_set_preferred_mode(connector, mode->hdisplay, mode->vdisplay);
+
+	/* There is only a single mode */
+	return 1;
+}
+
+static const struct drm_connector_helper_funcs st7920_connector_helper_funcs = {
+	.get_modes = st7920_connector_get_modes,
+};
+
+static const struct drm_connector_funcs st7920_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 st7920_mode_config_funcs = {
+	.fb_create = drm_gem_fb_create_with_dirty,
+	.atomic_check = drm_atomic_helper_check,
+	.atomic_commit = drm_atomic_helper_commit,
+};
+
+static const uint32_t st7920_formats[] = {
+	DRM_FORMAT_XRGB8888,
+};
+
+DEFINE_DRM_GEM_FOPS(st7920_fops);
+
+static const struct drm_driver st7920_drm_driver = {
+	DRM_GEM_SHMEM_DRIVER_OPS,
+	DRM_FBDEV_SHMEM_DRIVER_OPS,
+	.name			= DRIVER_NAME,
+	.desc			= DRIVER_DESC,
+	.date			= DRIVER_DATE,
+	.major			= DRIVER_MAJOR,
+	.minor			= DRIVER_MINOR,
+	.driver_features = DRIVER_ATOMIC | DRIVER_GEM | DRIVER_MODESET,
+	.fops			= &st7920_fops,
+};
+
+static int st7920_init_modeset(struct st7920_device *st7920)
+{
+	enum st7920_family_ids family_id = st7920->device_info->family_id;
+	struct drm_display_mode *mode = &st7920->mode;
+	struct device *dev = st7920->dev;
+	struct drm_device *drm = &st7920->drm;
+	unsigned long max_width, max_height;
+	struct drm_plane *primary_plane;
+	struct drm_crtc *crtc;
+	struct drm_encoder *encoder;
+	struct drm_connector *connector;
+	int ret;
+
+	/*
+	 * Modesetting
+	 */
+
+	ret = drmm_mode_config_init(drm);
+	if (ret) {
+		dev_err(dev, "DRM mode config init failed: %d\n", ret);
+		return ret;
+	}
+
+	mode->type = DRM_MODE_TYPE_DRIVER;
+	mode->clock = 1;
+	mode->hdisplay = mode->htotal = st7920->device_info->default_width;
+	mode->hsync_start = mode->hsync_end = st7920->device_info->default_width;
+	mode->vdisplay = mode->vtotal = st7920->device_info->default_height;
+	mode->vsync_start = mode->vsync_end = st7920->device_info->default_height;
+	mode->width_mm = 27;
+	mode->height_mm = 27;
+
+	max_width = max_t(unsigned long, mode->hdisplay, DRM_SHADOW_PLANE_MAX_WIDTH);
+	max_height = max_t(unsigned long, mode->vdisplay, DRM_SHADOW_PLANE_MAX_HEIGHT);
+
+	drm->mode_config.min_width = mode->hdisplay;
+	drm->mode_config.max_width = max_width;
+	drm->mode_config.min_height = mode->vdisplay;
+	drm->mode_config.max_height = max_height;
+	drm->mode_config.preferred_depth = 24;
+	drm->mode_config.funcs = &st7920_mode_config_funcs;
+
+	/* Primary plane */
+
+	primary_plane = &st7920->primary_plane;
+	ret = drm_universal_plane_init(drm, primary_plane, 0, &st7920_primary_plane_funcs,
+				    st7920_formats, ARRAY_SIZE(st7920_formats),
+				    NULL, DRM_PLANE_TYPE_PRIMARY, NULL);
+	if (ret) {
+		dev_err(dev, "DRM primary plane init failed: %d\n", ret);
+		return ret;
+	}
+
+	drm_plane_helper_add(primary_plane, &st7920_primary_plane_helper_funcs[family_id]);
+
+	drm_plane_enable_fb_damage_clips(primary_plane);
+
+	/* CRTC */
+
+	crtc = &st7920->crtc;
+	ret = drm_crtc_init_with_planes(drm, crtc, primary_plane, NULL,
+					&st7920_crtc_funcs, NULL);
+	if (ret) {
+		dev_err(dev, "DRM crtc init failed: %d\n", ret);
+		return ret;
+	}
+
+	drm_crtc_helper_add(crtc, &st7920_crtc_helper_funcs[family_id]);
+
+	/* Encoder */
+
+	encoder = &st7920->encoder;
+	ret = drm_encoder_init(drm, encoder, &st7920_encoder_funcs,
+			       DRM_MODE_ENCODER_NONE, NULL);
+	if (ret) {
+		dev_err(dev, "DRM encoder init failed: %d\n", ret);
+		return ret;
+	}
+
+	drm_encoder_helper_add(encoder, &st7920_encoder_helper_funcs[family_id]);
+
+	encoder->possible_crtcs = drm_crtc_mask(crtc);
+
+	/* Connector */
+
+	connector = &st7920->connector;
+	ret = drm_connector_init(drm, connector, &st7920_connector_funcs,
+				 DRM_MODE_CONNECTOR_Unknown);
+	if (ret) {
+		dev_err(dev, "DRM connector init failed: %d\n", ret);
+		return ret;
+	}
+
+	drm_connector_helper_add(connector, &st7920_connector_helper_funcs);
+
+	ret = drm_connector_attach_encoder(connector, encoder);
+	if (ret) {
+		dev_err(dev, "DRM attach connector to encoder failed: %d\n", ret);
+		return ret;
+	}
+
+	drm_mode_config_reset(drm);
+
+	return 0;
+}
+
+static int st7920_probe(struct spi_device *spi)
+{
+	struct st7920_device *st7920;
+	struct regmap *regmap;
+	struct device *dev = &spi->dev;
+	struct drm_device *drm;
+	int ret;
+
+	regmap = devm_regmap_init_spi(spi, &st7920_spi_regmap_config);
+	if (IS_ERR(regmap))
+		return PTR_ERR(regmap);
+
+	st7920 = devm_drm_dev_alloc(dev, &st7920_drm_driver,
+				    struct st7920_device, drm);
+	if (IS_ERR(st7920))
+		return dev_err_probe(dev, PTR_ERR(st7920),
+							 "Failed to allocate DRM device\n");
+
+	drm = &st7920->drm;
+
+	st7920->dev = dev;
+	st7920->regmap = regmap;
+	st7920->spi = spi;
+	st7920->device_info = device_get_match_data(dev);
+	st7920->width = st7920->device_info->default_width;
+	st7920->height = st7920->device_info->default_height;
+
+	ret = st7920_init_modeset(st7920);
+	if (ret)
+		return ret;
+
+	ret = drm_dev_register(drm, 0);
+	if (ret)
+		return dev_err_probe(dev, ret, "DRM device register failed\n");
+
+	drm_client_setup(drm, NULL);
+
+	spi_set_drvdata(spi, st7920);
+
+	st7920_init(st7920);
+
+	return 0;
+}
+
+static void st7920_remove(struct spi_device *spi)
+{
+	struct st7920_device *st7920 = spi_get_drvdata(spi);
+
+	drm_dev_unplug(&st7920->drm);
+	drm_atomic_helper_shutdown(&st7920->drm);
+}
+
+static void st7920_shutdown(struct spi_device *spi)
+{
+	struct st7920_device *st7920 = spi_get_drvdata(spi);
+
+	drm_atomic_helper_shutdown(&st7920->drm);
+}
+
+static struct spi_driver st7920_spi_driver = {
+	.driver = {
+		.name = DRIVER_NAME,
+		.of_match_table = st7920_of_match,
+	},
+	.id_table = st7920_spi_id,
+	.probe = st7920_probe,
+	.remove = st7920_remove,
+	.shutdown = st7920_shutdown,
+};
+module_spi_driver(st7920_spi_driver);
+
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_AUTHOR("Iker Pedrosa <ipedrosam@gmail.com>");
+MODULE_LICENSE("GPL v2");
diff --git a/drivers/gpu/drm/sitronix/st7920.h b/drivers/gpu/drm/sitronix/st7920.h
new file mode 100644
index 0000000000000000000000000000000000000000..83032baa7e82c2718deeb943fc564cc132c416a3
--- /dev/null
+++ b/drivers/gpu/drm/sitronix/st7920.h
@@ -0,0 +1,55 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Header file for:
+ * DRM driver for Sitronix ST7920 LCD displays
+ *
+ * Copyright 2025 Iker Pedrosa <ikerpedrosam@gmail.com>
+ *
+ * Based on drivers/video/fbdev/ssd130x.c
+ * Copyright 2022 Red Hat Inc.
+ */
+
+#ifndef __ST7920_H__
+#define __ST7920_H__
+
+#include <drm/drm_connector.h>
+#include <drm/drm_crtc.h>
+#include <drm/drm_encoder.h>
+
+enum st7920_family_ids {
+	ST7920_FAMILY
+};
+
+enum st7920_variants {
+	/* st7920 family */
+	ST7920_ID
+};
+
+struct st7920_deviceinfo {
+	u32 default_dclk_div;
+	u32 default_dclk_frq;
+	u32 default_width;
+	u32 default_height;
+
+	enum st7920_family_ids family_id;
+};
+
+struct st7920_device {
+	struct drm_device drm;
+	struct device *dev;
+	struct drm_display_mode mode;
+	struct drm_plane primary_plane;
+	struct drm_crtc crtc;
+	struct drm_encoder encoder;
+	struct drm_connector connector;
+	struct spi_device *spi;
+
+	struct regmap *regmap;
+
+	const struct st7920_deviceinfo *device_info;
+
+	u32 height;
+	u32 width;
+};
+
+#endif /* __ST7920_H__ */

-- 
2.50.1

Re: [PATCH 1/3] drm: Add driver for Sitronix ST7920 LCD displays

[kernel test robot]

Hi Iker,

kernel test robot noticed the following build warnings:

[auto build test WARNING on c571cb70e1ed43ee543c70151e61a001ab2eefa2]

url:    https://github.com/intel-lab-lkp/linux/commits/Iker-Pedrosa/drm-Add-driver-for-Sitronix-ST7920-LCD-displays/20250806-205210
base:   c571cb70e1ed43ee543c70151e61a001ab2eefa2
patch link:    https://lore.kernel.org/r/20250806-st7920-v1-1-64ab5a34f9a0%40gmail.com
patch subject: [PATCH 1/3] drm: Add driver for Sitronix ST7920 LCD displays
config: riscv-kismet-CONFIG_DRM_GEM_SHMEM_HELPER-CONFIG_DRM_ST7920-0-0 (https://download.01.org/0day-ci/archive/20250807/202508071554.hJ1Avou0-lkp@intel.com/config)
reproduce: (https://download.01.org/0day-ci/archive/20250807/202508071554.hJ1Avou0-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202508071554.hJ1Avou0-lkp@intel.com/

kismet warnings: (new ones prefixed by >>)
>> kismet: WARNING: unmet direct dependencies detected for DRM_GEM_SHMEM_HELPER when selected by DRM_ST7920
   WARNING: unmet direct dependencies detected for DRM_GEM_SHMEM_HELPER
     Depends on [n]: HAS_IOMEM [=y] && DRM [=y] && MMU [=n]
     Selected by [y]:
     - DRM_ST7920 [=y] && HAS_IOMEM [=y] && DRM [=y] && SPI [=y]

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH 1/3] drm: Add driver for Sitronix ST7920 LCD displays

[Krzysztof Kozlowski]

On 06/08/2025 14:48, Iker Pedrosa wrote:
> This adds a functional DRM driver for ST7920 that communicates with the
> display via the SPI bus.

Please do not use "This commit/patch/change", but imperative mood. See
longer explanation here:
https://elixir.bootlin.com/linux/v5.17.1/source/Documentation/process/submitting-patches.rst#L95

> 
> Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>
> ---


...


> +#define BOTTOM_HORIZONTAL_ADDRESS	0x80
> +
> +#define CMD_SIZE			35
> +
> +const struct st7920_deviceinfo st7920_variants[] = {
> +	[ST7920_ID] = {
> +		.default_width = 128,
> +		.default_height = 64,
> +		.family_id = ST7920_FAMILY,

Don't add dead code. This cannot be anything else than ST7920_FAMILY.

Several places here can be simplified (and "possible" future code is not
an argument here - this patch must be correct, simple and stand on its
own because we do not write code just in case).


...

> +static int st7920_probe(struct spi_device *spi)
> +{
> +	struct st7920_device *st7920;
> +	struct regmap *regmap;
> +	struct device *dev = &spi->dev;
> +	struct drm_device *drm;
> +	int ret;
> +
> +	regmap = devm_regmap_init_spi(spi, &st7920_spi_regmap_config);
> +	if (IS_ERR(regmap))
> +		return PTR_ERR(regmap);
> +
> +	st7920 = devm_drm_dev_alloc(dev, &st7920_drm_driver,
> +				    struct st7920_device, drm);
> +	if (IS_ERR(st7920))
> +		return dev_err_probe(dev, PTR_ERR(st7920),
> +							 "Failed to allocate DRM device\n");

Misaligned but also this looks like ENOMEM error and such should never
have dev_err.



Best regards,
Krzysztof

Re: [PATCH 1/3] drm: Add driver for Sitronix ST7920 LCD displays

[Thomas Zimmermann]

Hi,

thanks for the driver. Review is below.

Am 06.08.25 um 14:48 schrieb Iker Pedrosa:
> This adds a functional DRM driver for ST7920 that communicates with the
> display via the SPI bus.
>
> Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>
> ---
>   drivers/gpu/drm/sitronix/Kconfig  |  10 +
>   drivers/gpu/drm/sitronix/Makefile |   1 +
>   drivers/gpu/drm/sitronix/st7920.c | 869 ++++++++++++++++++++++++++++++++++++++
>   drivers/gpu/drm/sitronix/st7920.h |  55 +++
>   4 files changed, 935 insertions(+)
>
> diff --git a/drivers/gpu/drm/sitronix/Kconfig b/drivers/gpu/drm/sitronix/Kconfig
> index 6de7d92d9b74c72746915b945869dba91f161d2b..68f792dda14e83f457579ae7c240f4cc6a469d33 100644
> --- a/drivers/gpu/drm/sitronix/Kconfig
> +++ b/drivers/gpu/drm/sitronix/Kconfig
> @@ -40,3 +40,13 @@ config DRM_ST7735R
>   
>   	  If M is selected the module will be called st7735r.
>   
> +config DRM_ST7920
> +	tristate "DRM support for Sitronix ST7920 LCD displays"
> +	depends on DRM && SPI
> +	select DRM_GEM_SHMEM_HELPER
> +	select DRM_KMS_HELPER
> +	select REGMAP_SPI
> +	help
> +	  DRM driver for the ST7920 Sitronix LCD controllers.
> +
> +	  If M is selected the module will be called st7920.
> diff --git a/drivers/gpu/drm/sitronix/Makefile b/drivers/gpu/drm/sitronix/Makefile
> index bd139e5a6995fa026cc635b3c29782473d1efad7..2f064a518121bfee3cca73acd42589e8c54cd4d7 100644
> --- a/drivers/gpu/drm/sitronix/Makefile
> +++ b/drivers/gpu/drm/sitronix/Makefile
> @@ -1,3 +1,4 @@
>   obj-$(CONFIG_DRM_ST7571_I2C)		+= st7571-i2c.o
>   obj-$(CONFIG_DRM_ST7586)		+= st7586.o
>   obj-$(CONFIG_DRM_ST7735R)		+= st7735r.o
> +obj-$(CONFIG_DRM_ST7920))		+= st7920.o
> diff --git a/drivers/gpu/drm/sitronix/st7920.c b/drivers/gpu/drm/sitronix/st7920.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..c3226f352e39c626e3654250631521d07edf6784
> --- /dev/null
> +++ b/drivers/gpu/drm/sitronix/st7920.c
> @@ -0,0 +1,869 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * DRM driver for Sitronix ST7920 LCD displays
> + *
> + * Copyright 2025 Iker Pedrosa <ikerpedrosam@gmail.com>
> + *
> + */
> +
> +#include <linux/bitrev.h>
> +#include <linux/module.h>
> +#include <linux/regmap.h>
> +#include <linux/spi/spi.h>
> +
> +#include <drm/drm_atomic.h>
> +#include <drm/drm_atomic_helper.h>
> +#include <drm/drm_client_setup.h>
> +#include <drm/drm_crtc_helper.h>
> +#include <drm/drm_damage_helper.h>
> +#include <drm/drm_drv.h>
> +#include <drm/drm_fbdev_shmem.h>
> +#include <drm/drm_framebuffer.h>
> +#include <drm/drm_gem_atomic_helper.h>
> +#include <drm/drm_gem_framebuffer_helper.h>
> +#include <drm/drm_gem_shmem_helper.h>
> +#include <drm/drm_plane.h>
> +#include <drm/drm_probe_helper.h>
> +
> +#include "st7920.h"
> +
> +#define DRIVER_NAME	"sitronix_st7920"
> +#define DRIVER_DESC	"DRM driver for Sitronix ST7920 LCD displays"
> +#define DRIVER_DATE	"20250723"
> +#define DRIVER_MAJOR	1
> +#define DRIVER_MINOR	0
> +
> +/* Display organization */
> +#define WIDTH_BYTES		16
> +#define HEIGHT_IN_PIXELS	64
> +#define BYTES_IN_DISPLAY	(WIDTH_BYTES * HEIGHT_IN_PIXELS)
> +#define BYTES_IN_SEGMENT	2
> +#define PIXELS_IN_SEGMENT	(BYTES_IN_SEGMENT * 8)
> +
> +/* Sync sequence */
> +#define SYNC_BITS			0xF8
> +#define RW_HIGH				0x04
> +#define RS_HIGH				0x02
> +
> +/* Commands */
> +#define SET_DISPLAY_ON			0x0C
> +#define SET_DISPLAY_OFF			0x08
> +#define SET_DISPLAY_CLEAR		0x01
> +#define SET_BASIC_INSTRUCTION_SET	0x30
> +#define SET_EXT_INSTRUCTION_SET		0x34
> +#define SET_GRAPHICS_DISPLAY		0x36
> +#define SET_GDRAM_ADDRESS		0x80
> +#define SET_GDRAM_DATA			0xFF /* Driver internal command */
> +
> +/* Masks */
> +#define HIGH_DATA_MASK			0xF0
> +#define LOW_DATA_MASK			0x0F
> +#define TOP_VERTICAL_ADDRESS		0x80
> +#define BOTTOM_VERTICAL_ADDRESS		0x60
> +#define TOP_HORIZONTAL_ADDRESS		0x00
> +#define BOTTOM_HORIZONTAL_ADDRESS	0x80
> +
> +#define CMD_SIZE			35
> +
> +const struct st7920_deviceinfo st7920_variants[] = {
> +	[ST7920_ID] = {
> +		.default_width = 128,
> +		.default_height = 64,
> +		.family_id = ST7920_FAMILY,
> +	}
> +};
> +EXPORT_SYMBOL_NS_GPL(st7920_variants, DRM_ST7920);
> +
> +struct st7920_plane_state {
> +	struct drm_shadow_plane_state base;
> +	/* Intermediate buffer to convert pixels from XRGB8888 to HW format */
> +	u8 *buffer;
> +};
> +
> +struct st7920_crtc_state {
> +	struct drm_crtc_state base;
> +	/* Buffer to store pixels in HW format and written to the panel */
> +	u8 *data_array;
> +};
> +
> +static inline struct st7920_plane_state *to_st7920_plane_state(struct drm_plane_state *state)
> +{
> +	return container_of(state, struct st7920_plane_state, base.base);
> +}
> +
> +static inline struct st7920_crtc_state *to_st7920_crtc_state(struct drm_crtc_state *state)
> +{
> +	return container_of(state, struct st7920_crtc_state, base);
> +}
> +
> +static inline struct st7920_device *drm_to_st7920(struct drm_device *drm)
> +{
> +	return container_of(drm, struct st7920_device, drm);
> +}
> +
> +static int st7920_spi_write(struct spi_device *spi, int cmd, const void *data, size_t size)

Many calls to this helper looks like

ret = st7920_spi_write()
if (ret)
    return ret
udelay()


I suggest to internalize this pattern in the helper, like this

struct spi7920_error{
   int errno;
}

spi7920_spi_write(  delay_us, struct spi7920_error *err)
{
     if (err->errno)
       return errno;

     /* no do current spi_write() */

   ret  = spi_write()
   if (ret) {
     err->errno = ret
     return ret;
   }

   if (delay_us)
     udelay(delay_us)

   return ret;
}

This way, you can make multiple calls in a row and only test after the 
final final call for an error. That makes the caller side much nicer to 
read.


> +{
> +	u8 reg[CMD_SIZE] = {0};
> +	int i = 0, j = 0;
> +	int ret;
> +
> +	/*
> +	 * First the sync bits are sent: 11111WS0.
> +	 * Where W is the read/write (RW) bit and S is the register/data (RS) bit.
> +	 * Then, every 8 bits instruction/data will be separated into 2 groups.
> +	 * Higher 4 bits (DB7~DB4) will be placed in the first section followed by
> +	 * 4 '0's. And lower 4 bits (DB3~DB0) will be placed in the second section
> +	 * followed by 4 '0's.
> +	 */
> +	if (cmd == SET_GDRAM_ADDRESS) {

It's much nicer to write a single function for each branch than to put 
everything into a single helper with the in-transparent, non-typesafe 
data arguments.

> +		const u8 y_addr = *(const u8 *)data;
> +		bool bottom_screen = (y_addr >= 32);
> +
> +		reg[i++] = SYNC_BITS;
> +		/* Set vertical address */
> +		if (!bottom_screen)
> +			reg[i++] = TOP_VERTICAL_ADDRESS + (*(uint8_t *)data & HIGH_DATA_MASK);
> +		else
> +			reg[i++] = BOTTOM_VERTICAL_ADDRESS + (*(uint8_t *)data & HIGH_DATA_MASK);
> +
> +		reg[i++] = *(uint8_t *)data << 4;
> +		/* Set horizontal address */
> +		reg[i++] = SET_GDRAM_ADDRESS;
> +		if (!bottom_screen)
> +			reg[i++] = TOP_HORIZONTAL_ADDRESS;
> +		else
> +			reg[i++] = BOTTOM_HORIZONTAL_ADDRESS;
> +	} else if (cmd == SET_GDRAM_DATA) {
> +		const u8 *line_data = data;
> +
> +		reg[i++] = SYNC_BITS | RS_HIGH;
> +
> +		for (j = 0; j < 16; j++) {
> +			reg[i++] = line_data[j] & 0xF0;
> +			reg[i++] = (line_data[j] << 4) & 0xF0;
> +		}
> +	} else {
> +		reg[i++] = SYNC_BITS;
> +		reg[i++] = cmd & HIGH_DATA_MASK;
> +		reg[i++] = (cmd & LOW_DATA_MASK) << 4;
> +	}
> +
> +	ret = spi_write(spi, reg, i);
> +
> +	return ret;
> +}
> +
> +static const struct regmap_config st7920_spi_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +};
> +
> +static const struct of_device_id st7920_of_match[] = {
> +	/* st7920 family */
> +	{
> +		.compatible = "sitronix,st7920",
> +		.data = &st7920_variants[ST7920_ID],
> +	},
> +	{ /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, st7920_of_match);
> +
> +/*
> + * The SPI core always reports a MODALIAS uevent of the form "spi:<dev>", even
> + * if the device was registered via OF. This means that the module will not be
> + * auto loaded, unless it contains an alias that matches the MODALIAS reported.
> + *
> + * To workaround this issue, add a SPI device ID table. Even when this should
> + * not be needed for this driver to match the registered SPI devices.
> + */
> +static const struct spi_device_id st7920_spi_id[] = {
> +	/* st7920 family */
> +	{ "st7920",  ST7920_ID },
> +	{ /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(spi, st7920_spi_id);
> +
> +static int st7920_power_on(struct st7920_device *st7920)
> +{
> +	int ret;
> +
> +	ret = st7920_spi_write(st7920->spi, SET_DISPLAY_ON, NULL, 0);
> +	if (ret < 0)
> +		return ret;
> +	udelay(72);
> +
> +	return ret;
> +}
> +
> +static int st7920_power_off(struct st7920_device *st7920)
> +{
> +	int ret;
> +
> +	ret = st7920_spi_write(st7920->spi, SET_DISPLAY_CLEAR, NULL, 0);
> +	udelay(1600);
> +	ret = st7920_spi_write(st7920->spi, SET_DISPLAY_OFF, NULL, 0);
> +	udelay(72);
> +
> +	return ret;
> +}
> +
> +static int st7920_init(struct st7920_device *st7920)
> +{
> +	int ret;
> +
> +	ret = st7920_spi_write(st7920->spi, SET_BASIC_INSTRUCTION_SET, NULL, 0);
> +	if (ret < 0)
> +		return ret;
> +	udelay(72);
> +
> +	ret = st7920_power_on(st7920);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = st7920_spi_write(st7920->spi, SET_GRAPHICS_DISPLAY, NULL, 0);
> +	if (ret < 0)
> +		return ret;
> +	udelay(72);
> +
> +	ret = st7920_spi_write(st7920->spi, SET_DISPLAY_CLEAR, NULL, 0);
> +	if (ret < 0)
> +		return ret;
> +	udelay(1600);
> +
> +	return 0;
> +}
> +
> +static int st7920_update_rect(struct st7920_device *st7920,
> +			       struct drm_rect *rect, u8 *buf,
> +			       u8 *data_array)
> +{
> +	u32 array_idx = 0;
> +	int i, j;
> +	int ret;
> +
> +	/*
> +	 * The screen is divided in 64(Y)x8(X) segments and each segment is
> +	 * further divided in 2 bytes (D15~D0).
> +	 *
> +	 * Segment 0x0 is in the top-right corner, while segment 63x15 is in the
> +	 * bottom-left. They would be displayed in the screen in the following way:
> +	 * 0x0  0x1  0x2  ... 0x15
> +	 * 1x0  1x1  1x2  ... 1x15
> +	 * ...
> +	 * 63x0 63x1 63x2 ... 63x15
> +	 *
> +	 * The data in each byte is big endian.
> +	 */
> +
> +	for (i = 0; i < HEIGHT_IN_PIXELS; i++) {
> +		u8 *line_start = buf + (i * WIDTH_BYTES);
> +		u8 line_buffer[WIDTH_BYTES];
> +
> +		for (j = 0; j < WIDTH_BYTES; j++) {
> +			line_buffer[j] = bitrev8(line_start[j]);
> +			data_array[array_idx++] = line_buffer[j];
> +		}
> +
> +		ret = st7920_spi_write(st7920->spi, SET_GDRAM_ADDRESS, &i, 1);
> +		if (ret < 0)
> +			return ret;
> +		udelay(72);
> +
> +		ret = st7920_spi_write(st7920->spi, SET_GDRAM_DATA, line_buffer, WIDTH_BYTES);
> +		if (ret < 0)
> +			return ret;
> +		udelay(72);
> +	}
> +
> +	return ret;
> +}
> +
> +static void st7920_clear_screen(struct st7920_device *st7920, u8 *data_array)
> +{
> +	memset(data_array, 0, BYTES_IN_DISPLAY);
> +
> +	st7920_spi_write(st7920->spi, SET_DISPLAY_CLEAR, NULL, 0);
> +	udelay(1600);
> +}
> +
> +static int st7920_fb_blit_rect(struct drm_framebuffer *fb,
> +				const struct iosys_map *vmap,
> +				struct drm_rect *rect,
> +				u8 *buf, u8 *data_array,
> +				struct drm_format_conv_state *fmtcnv_state)
> +{
> +	struct st7920_device *st7920 = drm_to_st7920(fb->dev);
> +	struct iosys_map dst;
> +	unsigned int dst_pitch;
> +	int ret = 0;
> +
> +	/* Align y to display page boundaries */
> +	rect->y1 = round_down(rect->y1, PIXELS_IN_SEGMENT);
> +	rect->y2 = min_t(unsigned int, round_up(rect->y2, PIXELS_IN_SEGMENT), st7920->height);
> +
> +	dst_pitch = DIV_ROUND_UP(drm_rect_width(rect), 8);
> +
> +	ret = drm_gem_fb_begin_cpu_access(fb, DMA_FROM_DEVICE);
> +	if (ret)
> +		return ret;

Please call this in st7920_primary_plane_atomic_update() after 
drm_dev_enter().


> +
> +	iosys_map_set_vaddr(&dst, buf);
> +	drm_fb_xrgb8888_to_mono(&dst, &dst_pitch, vmap, fb, rect, fmtcnv_state);
> +


> +	drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);

And this call belongs before drm_dev_exit().

> +
> +	st7920_update_rect(st7920, rect, buf, data_array);
> +
> +	return ret;
> +}
> +
> +static int st7920_primary_plane_atomic_check(struct drm_plane *plane,
> +					      struct drm_atomic_state *state)
> +{
> +	struct drm_device *drm = plane->dev;
> +	struct st7920_device *st7920 = drm_to_st7920(drm);
> +	struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
> +	struct st7920_plane_state *st7920_state = to_st7920_plane_state(plane_state);
> +	struct drm_shadow_plane_state *shadow_plane_state = &st7920_state->base;
> +	struct drm_crtc *crtc = plane_state->crtc;
> +	struct drm_crtc_state *crtc_state = NULL;
> +	const struct drm_format_info *fi;
> +	unsigned int pitch;
> +	int ret;
> +
> +	if (crtc)
> +		crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
> +
> +	ret = drm_atomic_helper_check_plane_state(plane_state, crtc_state,
> +						  DRM_PLANE_NO_SCALING,
> +						  DRM_PLANE_NO_SCALING,
> +						  false, false);
> +	if (ret)
> +		return ret;
> +	else if (!plane_state->visible)
> +		return 0;
> +
> +	fi = drm_format_info(DRM_FORMAT_R1);
> +	if (!fi)
> +		return -EINVAL;
> +
> +	pitch = drm_format_info_min_pitch(fi, 0, st7920->width);
> +
> +	if (plane_state->fb->format != fi) {
> +		void *buf;
> +
> +		/* format conversion necessary; reserve buffer */
> +		buf = drm_format_conv_state_reserve(&shadow_plane_state->fmtcnv_state,
> +						    pitch, GFP_KERNEL);
> +		if (!buf)
> +			return -ENOMEM;
> +	}
> +
> +	st7920_state->buffer = kcalloc(pitch, st7920->height, GFP_KERNEL);
> +	if (!st7920_state->buffer)
> +		return -ENOMEM;
> +
> +	return 0;
> +}
> +
> +static void st7920_primary_plane_atomic_update(struct drm_plane *plane,
> +						struct drm_atomic_state *state)
> +{
> +	struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
> +	struct drm_plane_state *old_plane_state = drm_atomic_get_old_plane_state(state, plane);
> +	struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(plane_state);
> +	struct drm_crtc_state *crtc_state = drm_atomic_get_new_crtc_state(state, plane_state->crtc);
> +	struct st7920_crtc_state *st7920_crtc_state =  to_st7920_crtc_state(crtc_state);
> +	struct st7920_plane_state *st7920_plane_state = to_st7920_plane_state(plane_state);
> +	struct drm_framebuffer *fb = plane_state->fb;
> +	struct drm_atomic_helper_damage_iter iter;
> +	struct drm_device *drm = plane->dev;
> +	struct drm_rect dst_clip;
> +	struct drm_rect damage;
> +	int idx;
> +
> +	if (!drm_dev_enter(drm, &idx))
> +		return;
> +
> +	drm_atomic_helper_damage_iter_init(&iter, old_plane_state, plane_state);
> +	drm_atomic_for_each_plane_damage(&iter, &damage) {
> +		dst_clip = plane_state->dst;
> +
> +		if (!drm_rect_intersect(&dst_clip, &damage))
> +			continue;
> +
> +		st7920_fb_blit_rect(fb, &shadow_plane_state->data[0], &dst_clip,
> +				     st7920_plane_state->buffer,
> +				     st7920_crtc_state->data_array,
> +				     &shadow_plane_state->fmtcnv_state);
> +	}
> +
> +	drm_dev_exit(idx);
> +}
> +
> +static void st7920_primary_plane_atomic_disable(struct drm_plane *plane,
> +						 struct drm_atomic_state *state)
> +{
> +	struct drm_device *drm = plane->dev;
> +	struct st7920_device *st7920 = drm_to_st7920(drm);
> +	struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
> +	struct drm_crtc_state *crtc_state;
> +	struct st7920_crtc_state *st7920_crtc_state;
> +	int idx;
> +
> +	if (!plane_state->crtc)
> +		return;
> +
> +	crtc_state = drm_atomic_get_new_crtc_state(state, plane_state->crtc);
> +	st7920_crtc_state = to_st7920_crtc_state(crtc_state);
> +
> +	if (!drm_dev_enter(drm, &idx))
> +		return;
> +
> +	st7920_clear_screen(st7920, st7920_crtc_state->data_array);
> +
> +	drm_dev_exit(idx);
> +}
> +
> +/* Called during init to allocate the plane's atomic state. */
> +static void st7920_primary_plane_reset(struct drm_plane *plane)
> +{
> +	struct st7920_plane_state *st7920_state;
> +
> +	WARN_ON(plane->state);

Please use drm_WARN_ON_ONCE()

> +
> +	st7920_state = kzalloc(sizeof(*st7920_state), GFP_KERNEL);
> +	if (!st7920_state)
> +		return;
> +
> +	__drm_gem_reset_shadow_plane(plane, &st7920_state->base);
> +}
> +
> +static struct drm_plane_state *st7920_primary_plane_duplicate_state(struct drm_plane *plane)
> +{
> +	struct drm_shadow_plane_state *new_shadow_plane_state;
> +	struct st7920_plane_state *old_st7920_state;
> +	struct st7920_plane_state *st7920_state;
> +
> +	if (WARN_ON(!plane->state))
> +		return NULL;

dmr_WARN_ON_ONCE()

> +
> +	old_st7920_state = to_st7920_plane_state(plane->state);
> +	st7920_state = kmemdup(old_st7920_state, sizeof(*st7920_state), GFP_KERNEL);
> +	if (!st7920_state)
> +		return NULL;
> +
> +	/* The buffer is not duplicated and is allocated in .atomic_check */
> +	st7920_state->buffer = NULL;
> +
> +	new_shadow_plane_state = &st7920_state->base;
> +
> +	__drm_gem_duplicate_shadow_plane_state(plane, new_shadow_plane_state);
> +
> +	return &new_shadow_plane_state->base;
> +}
> +
> +static void st7920_primary_plane_destroy_state(struct drm_plane *plane,
> +						struct drm_plane_state *state)
> +{
> +	struct st7920_plane_state *st7920_state = to_st7920_plane_state(state);
> +
> +	kfree(st7920_state->buffer);
> +
> +	__drm_gem_destroy_shadow_plane_state(&st7920_state->base);
> +
> +	kfree(st7920_state);
> +}
> +
> +static const struct drm_plane_helper_funcs st7920_primary_plane_helper_funcs[] = {
> +	[ST7920_FAMILY] = {
> +		DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
> +		.atomic_check = st7920_primary_plane_atomic_check,
> +		.atomic_update = st7920_primary_plane_atomic_update,
> +		.atomic_disable = st7920_primary_plane_atomic_disable,
> +	}
> +};
> +
> +static const struct drm_plane_funcs st7920_primary_plane_funcs = {
> +	.update_plane = drm_atomic_helper_update_plane,
> +	.disable_plane = drm_atomic_helper_disable_plane,
> +	.reset = st7920_primary_plane_reset,
> +	.atomic_duplicate_state = st7920_primary_plane_duplicate_state,
> +	.atomic_destroy_state = st7920_primary_plane_destroy_state,
> +	.destroy = drm_plane_cleanup,
> +};
> +
> +static enum drm_mode_status st7920_crtc_mode_valid(struct drm_crtc *crtc,
> +						    const struct drm_display_mode *mode)
> +{
> +	struct st7920_device *st7920 = drm_to_st7920(crtc->dev);
> +
> +	if (mode->hdisplay != st7920->mode.hdisplay &&
> +	    mode->vdisplay != st7920->mode.vdisplay)
> +		return MODE_ONE_SIZE;
> +	else if (mode->hdisplay != st7920->mode.hdisplay)
> +		return MODE_ONE_WIDTH;
> +	else if (mode->vdisplay != st7920->mode.vdisplay)
> +		return MODE_ONE_HEIGHT;

Please call drm_crtc_helper_mode_valid_fixed() to do this test for you.

> +
> +	return MODE_OK;
> +}
> +
> +static int st7920_crtc_atomic_check(struct drm_crtc *crtc,
> +				     struct drm_atomic_state *state)
> +{
> +	struct drm_crtc_state *crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
> +	struct st7920_crtc_state *st7920_state = to_st7920_crtc_state(crtc_state);
> +	int ret;
> +
> +	ret = drm_crtc_helper_atomic_check(crtc, state);
> +	if (ret)
> +		return ret;
> +
> +	st7920_state->data_array = kmalloc(BYTES_IN_DISPLAY, GFP_KERNEL);
> +	if (!st7920_state->data_array)
> +		return -ENOMEM;
> +
> +	return 0;
> +}
> +
> +/* Called during init to allocate the CRTC's atomic state. */
> +static void st7920_crtc_reset(struct drm_crtc *crtc)
> +{
> +	struct st7920_crtc_state *st7920_state;
> +
> +	WARN_ON(crtc->state);
> +
> +	st7920_state = kzalloc(sizeof(*st7920_state), GFP_KERNEL);
> +	if (!st7920_state)
> +		return;
> +
> +	__drm_atomic_helper_crtc_reset(crtc, &st7920_state->base);
> +}
> +
> +static struct drm_crtc_state *st7920_crtc_duplicate_state(struct drm_crtc *crtc)
> +{
> +	struct st7920_crtc_state *old_st7920_state;
> +	struct st7920_crtc_state *st7920_state;
> +
> +	if (WARN_ON(!crtc->state))
> +		return NULL;
> +
> +	old_st7920_state = to_st7920_crtc_state(crtc->state);
> +	st7920_state = kmemdup(old_st7920_state, sizeof(*st7920_state), GFP_KERNEL);
> +	if (!st7920_state)
> +		return NULL;
> +
> +	/* The buffer is not duplicated and is allocated in .atomic_check */
> +	st7920_state->data_array = NULL;
> +
> +	__drm_atomic_helper_crtc_duplicate_state(crtc, &st7920_state->base);
> +
> +	return &st7920_state->base;
> +}
> +
> +static void st7920_crtc_destroy_state(struct drm_crtc *crtc,
> +						struct drm_crtc_state *state)
> +{
> +	struct st7920_crtc_state *st7920_state = to_st7920_crtc_state(state);
> +
> +	kfree(st7920_state->data_array);
> +
> +	__drm_atomic_helper_crtc_destroy_state(state);
> +
> +	kfree(st7920_state);
> +}
> +
> +/*
> + * The CRTC is always enabled. Screen updates are performed by
> + * the primary plane's atomic_update function. Disabling clears
> + * the screen in the primary plane's atomic_disable function.
> + */
> +static const struct drm_crtc_helper_funcs st7920_crtc_helper_funcs[] = {
> +	[ST7920_FAMILY] = {

Are there other chips to support here? Because there's otherwise no 
point in using this additional array element.

> +		.mode_valid = st7920_crtc_mode_valid,
> +		.atomic_check = st7920_crtc_atomic_check,
> +	}
> +};
> +
> +static const struct drm_crtc_funcs st7920_crtc_funcs = {
> +	.reset = st7920_crtc_reset,
> +	.destroy = drm_crtc_cleanup,
> +	.set_config = drm_atomic_helper_set_config,
> +	.page_flip = drm_atomic_helper_page_flip,
> +	.atomic_duplicate_state = st7920_crtc_duplicate_state,
> +	.atomic_destroy_state = st7920_crtc_destroy_state,
> +};
> +
> +static void st7920_encoder_atomic_enable(struct drm_encoder *encoder,
> +						struct drm_atomic_state *state)
> +{
> +	struct drm_device *drm = encoder->dev;
> +	struct st7920_device *st7920 = drm_to_st7920(drm);
> +	int ret;
> +
> +	ret = st7920_init(st7920);
> +	if (ret)
> +		goto power_off;
> +
> +	return;
> +
> +power_off:
> +	st7920_power_off(st7920);
> +}
> +
> +static void st7920_encoder_atomic_disable(struct drm_encoder *encoder,
> +					struct drm_atomic_state *state)
> +{
> +	struct drm_device *drm = encoder->dev;
> +	struct st7920_device *st7920 = drm_to_st7920(drm);
> +
> +	st7920_power_off(st7920);
> +}
> +
> +static const struct drm_encoder_helper_funcs st7920_encoder_helper_funcs[] = {
> +	[ST7920_FAMILY] = {
> +		.atomic_enable = st7920_encoder_atomic_enable,
> +		.atomic_disable = st7920_encoder_atomic_disable,
> +	}
> +};
> +
> +static const struct drm_encoder_funcs st7920_encoder_funcs = {
> +	.destroy = drm_encoder_cleanup,
> +};
> +
> +static int st7920_connector_get_modes(struct drm_connector *connector)
> +{
> +	struct st7920_device *st7920 = drm_to_st7920(connector->dev);
> +	struct drm_display_mode *mode;
> +	struct device *dev = st7920->dev;
> +
> +	mode = drm_mode_duplicate(connector->dev, &st7920->mode);
> +	if (!mode) {
> +		dev_err(dev, "Failed to duplicated mode\n");
> +		return 0;
> +	}
> +
> +	drm_mode_probed_add(connector, mode);
> +	drm_set_preferred_mode(connector, mode->hdisplay, mode->vdisplay);

Please use drm_connector_helper_get_modes_fixed() to do this work for you.


> +
> +	/* There is only a single mode */
> +	return 1;
> +}
> +
> +static const struct drm_connector_helper_funcs st7920_connector_helper_funcs = {
> +	.get_modes = st7920_connector_get_modes,
> +};
> +
> +static const struct drm_connector_funcs st7920_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 st7920_mode_config_funcs = {
> +	.fb_create = drm_gem_fb_create_with_dirty,
> +	.atomic_check = drm_atomic_helper_check,
> +	.atomic_commit = drm_atomic_helper_commit,
> +};
> +
> +static const uint32_t st7920_formats[] = {
> +	DRM_FORMAT_XRGB8888,
> +};
> +
> +DEFINE_DRM_GEM_FOPS(st7920_fops);
> +
> +static const struct drm_driver st7920_drm_driver = {
> +	DRM_GEM_SHMEM_DRIVER_OPS,
> +	DRM_FBDEV_SHMEM_DRIVER_OPS,
> +	.name			= DRIVER_NAME,
> +	.desc			= DRIVER_DESC,
> +	.date			= DRIVER_DATE,
> +	.major			= DRIVER_MAJOR,
> +	.minor			= DRIVER_MINOR,
> +	.driver_features = DRIVER_ATOMIC | DRIVER_GEM | DRIVER_MODESET,
> +	.fops			= &st7920_fops,
> +};
> +
> +static int st7920_init_modeset(struct st7920_device *st7920)
> +{
> +	enum st7920_family_ids family_id = st7920->device_info->family_id;
> +	struct drm_display_mode *mode = &st7920->mode;
> +	struct device *dev = st7920->dev;
> +	struct drm_device *drm = &st7920->drm;
> +	unsigned long max_width, max_height;
> +	struct drm_plane *primary_plane;
> +	struct drm_crtc *crtc;
> +	struct drm_encoder *encoder;
> +	struct drm_connector *connector;
> +	int ret;
> +
> +	/*
> +	 * Modesetting
> +	 */
> +
> +	ret = drmm_mode_config_init(drm);
> +	if (ret) {
> +		dev_err(dev, "DRM mode config init failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	mode->type = DRM_MODE_TYPE_DRIVER;
> +	mode->clock = 1;
> +	mode->hdisplay = mode->htotal = st7920->device_info->default_width;

Only single assignments per line.  I know it's all made up, but htotal 
does very likely include every horizontal line; not just hdisplay.  Same 
for vtotal.

> +	mode->hsync_start = mode->hsync_end = st7920->device_info->default_width;
> +	mode->vdisplay = mode->vtotal = st7920->device_info->default_height;
> +	mode->vsync_start = mode->vsync_end = st7920->device_info->default_height;
> +	mode->width_mm = 27;
> +	mode->height_mm = 27;

> +
> +	max_width = max_t(unsigned long, mode->hdisplay, DRM_SHADOW_PLANE_MAX_WIDTH);
> +	max_height = max_t(unsigned long, mode->vdisplay, DRM_SHADOW_PLANE_MAX_HEIGHT);
> +
> +	drm->mode_config.min_width = mode->hdisplay;
> +	drm->mode_config.max_width = max_width;
> +	drm->mode_config.min_height = mode->vdisplay;
> +	drm->mode_config.max_height = max_height;
> +	drm->mode_config.preferred_depth = 24;
> +	drm->mode_config.funcs = &st7920_mode_config_funcs;
> +
> +	/* Primary plane */
> +
> +	primary_plane = &st7920->primary_plane;
> +	ret = drm_universal_plane_init(drm, primary_plane, 0, &st7920_primary_plane_funcs,
> +				    st7920_formats, ARRAY_SIZE(st7920_formats),
> +				    NULL, DRM_PLANE_TYPE_PRIMARY, NULL);
> +	if (ret) {
> +		dev_err(dev, "DRM primary plane init failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	drm_plane_helper_add(primary_plane, &st7920_primary_plane_helper_funcs[family_id]);
> +
> +	drm_plane_enable_fb_damage_clips(primary_plane);
> +
> +	/* CRTC */
> +
> +	crtc = &st7920->crtc;
> +	ret = drm_crtc_init_with_planes(drm, crtc, primary_plane, NULL,
> +					&st7920_crtc_funcs, NULL);
> +	if (ret) {
> +		dev_err(dev, "DRM crtc init failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	drm_crtc_helper_add(crtc, &st7920_crtc_helper_funcs[family_id]);
> +
> +	/* Encoder */
> +
> +	encoder = &st7920->encoder;
> +	ret = drm_encoder_init(drm, encoder, &st7920_encoder_funcs,
> +			       DRM_MODE_ENCODER_NONE, NULL);
> +	if (ret) {
> +		dev_err(dev, "DRM encoder init failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	drm_encoder_helper_add(encoder, &st7920_encoder_helper_funcs[family_id]);
> +
> +	encoder->possible_crtcs = drm_crtc_mask(crtc);
> +
> +	/* Connector */
> +
> +	connector = &st7920->connector;
> +	ret = drm_connector_init(drm, connector, &st7920_connector_funcs,
> +				 DRM_MODE_CONNECTOR_Unknown);
> +	if (ret) {
> +		dev_err(dev, "DRM connector init failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	drm_connector_helper_add(connector, &st7920_connector_helper_funcs);
> +
> +	ret = drm_connector_attach_encoder(connector, encoder);
> +	if (ret) {
> +		dev_err(dev, "DRM attach connector to encoder failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	drm_mode_config_reset(drm);
> +
> +	return 0;
> +}
> +
> +static int st7920_probe(struct spi_device *spi)
> +{
> +	struct st7920_device *st7920;
> +	struct regmap *regmap;
> +	struct device *dev = &spi->dev;
> +	struct drm_device *drm;
> +	int ret;
> +
> +	regmap = devm_regmap_init_spi(spi, &st7920_spi_regmap_config);
> +	if (IS_ERR(regmap))
> +		return PTR_ERR(regmap);
> +
> +	st7920 = devm_drm_dev_alloc(dev, &st7920_drm_driver,
> +				    struct st7920_device, drm);
> +	if (IS_ERR(st7920))
> +		return dev_err_probe(dev, PTR_ERR(st7920),
> +							 "Failed to allocate DRM device\n");
> +
> +	drm = &st7920->drm;
> +
> +	st7920->dev = dev;
> +	st7920->regmap = regmap;
> +	st7920->spi = spi;
> +	st7920->device_info = device_get_match_data(dev);
> +	st7920->width = st7920->device_info->default_width;
> +	st7920->height = st7920->device_info->default_height;
> +
> +	ret = st7920_init_modeset(st7920);
> +	if (ret)
> +		return ret;
> +
> +	ret = drm_dev_register(drm, 0);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "DRM device register failed\n");
> +
> +	drm_client_setup(drm, NULL);
> +

> +	spi_set_drvdata(spi, st7920);
> +
> +	st7920_init(st7920);

Those two calls need to go much earlier. After drm_dev_register(), your 
driver is available to the world. drm_client_setup() is in fact the 
first user.

> +
> +	return 0;
> +}
> +
> +static void st7920_remove(struct spi_device *spi)
> +{
> +	struct st7920_device *st7920 = spi_get_drvdata(spi);
> +
> +	drm_dev_unplug(&st7920->drm);
> +	drm_atomic_helper_shutdown(&st7920->drm);
> +}
> +
> +static void st7920_shutdown(struct spi_device *spi)
> +{
> +	struct st7920_device *st7920 = spi_get_drvdata(spi);
> +
> +	drm_atomic_helper_shutdown(&st7920->drm);
> +}
> +
> +static struct spi_driver st7920_spi_driver = {
> +	.driver = {
> +		.name = DRIVER_NAME,
> +		.of_match_table = st7920_of_match,
> +	},
> +	.id_table = st7920_spi_id,
> +	.probe = st7920_probe,
> +	.remove = st7920_remove,
> +	.shutdown = st7920_shutdown,
> +};
> +module_spi_driver(st7920_spi_driver);
> +
> +MODULE_DESCRIPTION(DRIVER_DESC);
> +MODULE_AUTHOR("Iker Pedrosa <ipedrosam@gmail.com>");
> +MODULE_LICENSE("GPL v2");
> diff --git a/drivers/gpu/drm/sitronix/st7920.h b/drivers/gpu/drm/sitronix/st7920.h

Is there another user of this header? No extra header otherwise, please.

Best regards
Thomas

> new file mode 100644
> index 0000000000000000000000000000000000000000..83032baa7e82c2718deeb943fc564cc132c416a3
> --- /dev/null
> +++ b/drivers/gpu/drm/sitronix/st7920.h
> @@ -0,0 +1,55 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Header file for:
> + * DRM driver for Sitronix ST7920 LCD displays
> + *
> + * Copyright 2025 Iker Pedrosa <ikerpedrosam@gmail.com>
> + *
> + * Based on drivers/video/fbdev/ssd130x.c
> + * Copyright 2022 Red Hat Inc.
> + */
> +
> +#ifndef __ST7920_H__
> +#define __ST7920_H__
> +
> +#include <drm/drm_connector.h>
> +#include <drm/drm_crtc.h>
> +#include <drm/drm_encoder.h>
> +
> +enum st7920_family_ids {
> +	ST7920_FAMILY
> +};
> +
> +enum st7920_variants {
> +	/* st7920 family */
> +	ST7920_ID
> +};
> +
> +struct st7920_deviceinfo {
> +	u32 default_dclk_div;
> +	u32 default_dclk_frq;
> +	u32 default_width;
> +	u32 default_height;
> +
> +	enum st7920_family_ids family_id;
> +};
> +
> +struct st7920_device {
> +	struct drm_device drm;
> +	struct device *dev;
> +	struct drm_display_mode mode;
> +	struct drm_plane primary_plane;
> +	struct drm_crtc crtc;
> +	struct drm_encoder encoder;
> +	struct drm_connector connector;
> +	struct spi_device *spi;
> +
> +	struct regmap *regmap;
> +
> +	const struct st7920_deviceinfo *device_info;
> +
> +	u32 height;
> +	u32 width;
> +};
> +
> +#endif /* __ST7920_H__ */
>

-- 
--
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)

[PATCH 2/3] dt-bindings: display: sitronix,st7920: Add DT schema

[Iker Pedrosa]

Add binding for Sitronix ST7920 display.

Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>
---
 .../bindings/display/sitronix,st7920.yaml          | 55 ++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/Documentation/devicetree/bindings/display/sitronix,st7920.yaml b/Documentation/devicetree/bindings/display/sitronix,st7920.yaml
new file mode 100644
index 0000000000000000000000000000000000000000..caee85f98c6d242dfab73729210f8c34b23a3a99
--- /dev/null
+++ b/Documentation/devicetree/bindings/display/sitronix,st7920.yaml
@@ -0,0 +1,55 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/sitronix,st7920.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Sitronix ST7920 LCD Display Controllers
+
+maintainers:
+  - Iker Pedrosa <ikerpedrosam@gmail.com>
+
+description: |
+  The Sitronix ST7920 is a controller for monochrome dot-matrix graphical LCDs,
+  most commonly used for 128x64 pixel displays.
+  This binding supports connecting the display via a standard SPI bus.
+
+properties:
+  compatible:
+    const: sitronix,st7920
+
+  reg:
+    description: The chip-select number for the device on the SPI bus.
+    maxItems: 1
+
+  spi-max-frequency:
+    description: Maximum SPI clock frequency in Hz.
+    maximum: 600000
+
+  spi-cs-high:
+    type: boolean
+    description: Indicates the chip select is active high.
+
+required:
+  - compatible
+  - reg
+  - spi-max-frequency
+
+additionalProperties: false
+
+examples:
+  - |
+    // Example: ST7920 connected to an SPI bus
+    #include <dt-bindings/gpio/gpio.h>
+
+    spi0 {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        display@0 {
+            compatible = "sitronix,st7920";
+            reg = <0>; // Chip select 0
+            spi-max-frequency = <600000>;
+            spi-cs-high;
+        };
+    };

-- 
2.50.1

Re: [PATCH 2/3] dt-bindings: display: sitronix,st7920: Add DT schema

[Conor Dooley]

[-- Attachment #1: Type: text/plain, Size: 2491 bytes --]

On Wed, Aug 06, 2025 at 02:48:10PM +0200, Iker Pedrosa wrote:
> Add binding for Sitronix ST7920 display.
> 
> Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>
> ---
>  .../bindings/display/sitronix,st7920.yaml          | 55 ++++++++++++++++++++++
>  1 file changed, 55 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/display/sitronix,st7920.yaml b/Documentation/devicetree/bindings/display/sitronix,st7920.yaml
> new file mode 100644
> index 0000000000000000000000000000000000000000..caee85f98c6d242dfab73729210f8c34b23a3a99
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/sitronix,st7920.yaml
> @@ -0,0 +1,55 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/display/sitronix,st7920.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Sitronix ST7920 LCD Display Controllers
> +
> +maintainers:
> +  - Iker Pedrosa <ikerpedrosam@gmail.com>
> +
> +description: |
> +  The Sitronix ST7920 is a controller for monochrome dot-matrix graphical LCDs,
> +  most commonly used for 128x64 pixel displays.
> +  This binding supports connecting the display via a standard SPI bus.
> +
> +properties:
> +  compatible:
> +    const: sitronix,st7920
> +
> +  reg:
> +    description: The chip-select number for the device on the SPI bus.
> +    maxItems: 1
> +
> +  spi-max-frequency:
> +    description: Maximum SPI clock frequency in Hz.
> +    maximum: 600000
> +
> +  spi-cs-high:
> +    type: boolean
> +    description: Indicates the chip select is active high.

Don't redefine this, it's defined in spi-peripheral-props.yaml:
  spi-cs-high:
    $ref: /schemas/types.yaml#/definitions/flag
    description:
      The device requires the chip select active high.

spi-max-frequency's type comes from there, so you need it for that too.


> +
> +required:
> +  - compatible
> +  - reg
> +  - spi-max-frequency
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    // Example: ST7920 connected to an SPI bus
> +    #include <dt-bindings/gpio/gpio.h>
> +
> +    spi0 {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        display@0 {
> +            compatible = "sitronix,st7920";
> +            reg = <0>; // Chip select 0
> +            spi-max-frequency = <600000>;
> +            spi-cs-high;
> +        };
> +    };
> 
> -- 
> 2.50.1
> 

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Re: [PATCH 2/3] dt-bindings: display: sitronix,st7920: Add DT schema

[Krzysztof Kozlowski]

On 06/08/2025 14:48, Iker Pedrosa wrote:
> +title: Sitronix ST7920 LCD Display Controllers
> +
> +maintainers:
> +  - Iker Pedrosa <ikerpedrosam@gmail.com>
> +
> +description: |

Do not need '|' unless you need to preserve formatting.

> +  The Sitronix ST7920 is a controller for monochrome dot-matrix graphical LCDs,
> +  most commonly used for 128x64 pixel displays.
> +  This binding supports connecting the display via a standard SPI bus.

Drop last sentence. You should write complete bindings for complete
hardware. Binding cannot support something and should not cover only one
bus.

> +
> +properties:
> +  compatible:
> +    const: sitronix,st7920
> +
> +  reg:
> +    description: The chip-select number for the device on the SPI bus.
> +    maxItems: 1
> +
> +  spi-max-frequency:
> +    description: Maximum SPI clock frequency in Hz.
> +    maximum: 600000
> +
> +  spi-cs-high:
> +    type: boolean
> +    description: Indicates the chip select is active high.

No supplies?

> +
> +required:
> +  - compatible
> +  - reg
> +  - spi-max-frequency

Missing allOf: with ref to spi properties

> +
> +additionalProperties: false

And this is unevaluatedProperties. Please look at other examples of
devices like that.

> +
> +examples:
> +  - |
> +    // Example: ST7920 connected to an SPI bus
> +    #include <dt-bindings/gpio/gpio.h>
> +
> +    spi0 {

spi {

> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        display@0 {
> +            compatible = "sitronix,st7920";
> +            reg = <0>; // Chip select 0

Drop comment, obvious.

> +            spi-max-frequency = <600000>;
> +            spi-cs-high;
> +        };
> +    };
> 


Best regards,
Krzysztof

[PATCH 3/3] MAINTAINERS: Add entry for Sitronix ST7920 driver

[Iker Pedrosa]

Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>
---
 MAINTAINERS | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 5ddf37f0acc960039422ef988cadfa7176972fc5..79b8a277e38b55ebcff05450d6c565c0d87c6b51 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7861,6 +7861,13 @@ T:	git https://gitlab.freedesktop.org/drm/misc/kernel.git
 F:	Documentation/devicetree/bindings/display/sitronix,st7735r.yaml
 F:	drivers/gpu/drm/sitronix/st7735r.c
 
+DRM DRIVER FOR SITRONIX ST7920 LCD DISPLAYS
+M:	Iker Pedrosa <ikerpedrosam@gmail.com>
+S:	Maintained
+T:	git https://gitlab.freedesktop.org/drm/misc/kernel.git
+F:	Documentation/devicetree/bindings/display/sitronix,st7920.yaml
+F:	drivers/gpu/drm/sitronix/st7920.c
+
 DRM DRIVER FOR SOLOMON SSD130X OLED DISPLAYS
 M:	Javier Martinez Canillas <javierm@redhat.com>
 S:	Maintained

-- 
2.50.1

Re: [PATCH 3/3] MAINTAINERS: Add entry for Sitronix ST7920 driver

[Krzysztof Kozlowski]

On 06/08/2025 14:48, Iker Pedrosa wrote:
> Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>

Missing commit msg or just squash it with patch #2.

> ---
>  MAINTAINERS | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 5ddf37f0acc960039422ef988cadfa7176972fc5..79b8a277e38b55ebcff05450d6c565c0d87c6b51 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -7861,6 +7861,13 @@ T:	git https://gitlab.freedesktop.org/drm/misc/kernel.git
>  F:	Documentation/devicetree/bindings/display/sitronix,st7735r.yaml
>  F:	drivers/gpu/drm/sitronix/st7735r.c
>  
> +DRM DRIVER FOR SITRONIX ST7920 LCD DISPLAYS
> +M:	Iker Pedrosa <ikerpedrosam@gmail.com>
> +S:	Maintained
> +T:	git https://gitlab.freedesktop.org/drm/misc/kernel.git


Drop, unless you have commit rights there. Parent entry already covers
this, doesn't it?

Best regards,
Krzysztof

Re: [PATCH 3/3] MAINTAINERS: Add entry for Sitronix ST7920 driver

[Iker Pedrosa]

[-- Attachment #1: Type: text/plain, Size: 1245 bytes --]

El jue, 7 ago 2025 a las 10:13, Krzysztof Kozlowski (<krzk@kernel.org>)
escribió:

> On 06/08/2025 14:48, Iker Pedrosa wrote:
> > Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>
>
> Missing commit msg or just squash it with patch #2.
>
> > ---
> >  MAINTAINERS | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index
> 5ddf37f0acc960039422ef988cadfa7176972fc5..79b8a277e38b55ebcff05450d6c565c0d87c6b51
> 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -7861,6 +7861,13 @@ T:     git
> https://gitlab.freedesktop.org/drm/misc/kernel.git
> >  F:   Documentation/devicetree/bindings/display/sitronix,st7735r.yaml
> >  F:   drivers/gpu/drm/sitronix/st7735r.c
> >
> > +DRM DRIVER FOR SITRONIX ST7920 LCD DISPLAYS
> > +M:   Iker Pedrosa <ikerpedrosam@gmail.com>
> > +S:   Maintained
> > +T:   git https://gitlab.freedesktop.org/drm/misc/kernel.git
>
>
> Drop, unless you have commit rights there. Parent entry already covers
> this, doesn't it?
>

I don't have them, but I'm working with Javier and I think he does have
permissions. Let me ask him when he gets back.

Thank you for the feedback, by the way.


>
> Best regards,
> Krzysztof
>

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Re: [PATCH 3/3] MAINTAINERS: Add entry for Sitronix ST7920 driver

[Krzysztof Kozlowski]

On 20/08/2025 14:23, Iker Pedrosa wrote:
>>>
>>> +DRM DRIVER FOR SITRONIX ST7920 LCD DISPLAYS
>>> +M:   Iker Pedrosa <ikerpedrosam@gmail.com>
>>> +S:   Maintained
>>> +T:   git https://gitlab.freedesktop.org/drm/misc/kernel.git
>>
>>
>> Drop, unless you have commit rights there. Parent entry already covers
>> this, doesn't it?
>>
> 
> I don't have them, but I'm working with Javier and I think he does have
> permissions. Let me ask him when he gets back.

Javier is not mentioned here. You are adding redundant and useless
information. T: is for subsystem maintainers, not for individual drivers.



Best regards,
Krzysztof

Re: [PATCH 3/3] MAINTAINERS: Add entry for Sitronix ST7920 driver

[Maxime Ripard]

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On Wed, Aug 20, 2025 at 03:10:16PM +0200, Krzysztof Kozlowski wrote:
> On 20/08/2025 14:23, Iker Pedrosa wrote:
> >>>
> >>> +DRM DRIVER FOR SITRONIX ST7920 LCD DISPLAYS
> >>> +M:   Iker Pedrosa <ikerpedrosam@gmail.com>
> >>> +S:   Maintained
> >>> +T:   git https://gitlab.freedesktop.org/drm/misc/kernel.git
> >>
> >>
> >> Drop, unless you have commit rights there. Parent entry already covers
> >> this, doesn't it?
> >>
> > 
> > I don't have them, but I'm working with Javier and I think he does have
> > permissions. Let me ask him when he gets back.
> 
> Javier is not mentioned here. You are adding redundant and useless
> information. T: is for subsystem maintainers, not for individual drivers.

Kinda. I mean, you're absolutely right for pretty that it's implicit in
most places in the kernel.

However, it's not here. The drm-misc tree is meant to collect the
patches for all those small drivers, and we don't have a folder to put
these drivers under.

It was pretty confusing to differentiate a driver maintained through its
own tree, and one maintained through drm-misc, so at least explicitly
having the git tree set to drm-misc is how we show that's where the
patches are going to land.

Maxime

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Re: [PATCH 3/3] MAINTAINERS: Add entry for Sitronix ST7920 driver

[Javier Martinez Canillas]

Maxime Ripard <mripard@kernel.org> writes:

Hello Maxime,

> On Wed, Aug 20, 2025 at 03:10:16PM +0200, Krzysztof Kozlowski wrote:
>> On 20/08/2025 14:23, Iker Pedrosa wrote:
>> >>>
>> >>> +DRM DRIVER FOR SITRONIX ST7920 LCD DISPLAYS
>> >>> +M:   Iker Pedrosa <ikerpedrosam@gmail.com>
>> >>> +S:   Maintained
>> >>> +T:   git https://gitlab.freedesktop.org/drm/misc/kernel.git
>> >>
>> >>
>> >> Drop, unless you have commit rights there. Parent entry already covers
>> >> this, doesn't it?
>> >>
>> > 
>> > I don't have them, but I'm working with Javier and I think he does have
>> > permissions. Let me ask him when he gets back.
>> 
>> Javier is not mentioned here. You are adding redundant and useless
>> information. T: is for subsystem maintainers, not for individual drivers.
>
> Kinda. I mean, you're absolutely right for pretty that it's implicit in
> most places in the kernel.
>
> However, it's not here. The drm-misc tree is meant to collect the
> patches for all those small drivers, and we don't have a folder to put
> these drivers under.
>
> It was pretty confusing to differentiate a driver maintained through its
> own tree, and one maintained through drm-misc, so at least explicitly
> having the git tree set to drm-misc is how we show that's where the
> patches are going to land.
>

Thanks a lot for the clarification.

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat