[PATCH v2 0/3] Add support for Mayqueen Pixpaper e-ink panel

[PATCH v2 0/3] Add support for Mayqueen Pixpaper e-ink panel

[LiangCheng Wang]

This patch series adds support for the Mayqueen Pixpaper e-ink display panel,
controlled via SPI.

The series includes:
- A new vendor-prefix entry for "mayqueen"
- Device tree binding documentation for the Pixpaper panel
- A DRM tiny driver implementation for the Pixpaper panel
- A MAINTAINERS entry for the Pixpaper DRM driver and binding

The panel supports 122x250 resolution with XRGB8888 format and uses SPI,
along with GPIO lines for reset, busy, and data/command control.

The driver has been tested on:
- Raspberry Pi 2 Model B
with Linux kernel 6.16.

---
Changes in v2:
- Reordered patches so that DT bindings come before the driver (suggested by Rob Herring)
- Fixed sparse warning: removed duplicate `.reset` initializer in `pixpaper_plane_funcs`
- Fixed checkpatch issues reported by Media CI:
  - Removed unnecessary blank line before closing brace
  - Moved opening parentheses up to function call lines (e.g., `DRM_WARN(...)`)
  - Fixed alignment of conditionals
  - Fixed `dev_warn(` and `drm_universal_plane_init(` formatting
- Thanks to Rob Herring for ack on vendor-prefix patch
- Link to v1: https://lore.kernel.org/r/20250708-drm-v1-0-45055fdadc8a@gmail.com

Thanks for the feedback!

Best regards,
LiangCheng Wang
<zaq14760@gmail.com>

---
LiangCheng Wang (2):
      dt-bindings: display: Add Mayqueen Pixpaper e-ink panel
      drm: tiny: Add support for Mayqueen Pixpaper e-ink panel

Wig Cheng (1):
      dt-bindings: vendor-prefixes: Add Mayqueen name

 .../bindings/display/mayqueen,pixpaper.yaml        |  63 ++
 .../devicetree/bindings/vendor-prefixes.yaml       |   2 +
 MAINTAINERS                                        |   6 +
 drivers/gpu/drm/tiny/Kconfig                       |  15 +
 drivers/gpu/drm/tiny/Makefile                      |   1 +
 drivers/gpu/drm/tiny/pixpaper.c                    | 777 +++++++++++++++++++++
 6 files changed, 864 insertions(+)
---
base-commit: d7b8f8e20813f0179d8ef519541a3527e7661d3a
change-id: 20250708-drm-6021df0715d7

Best regards,
-- 
LiangCheng Wang <zaq14760@gmail.com>

[PATCH v2 1/3] dt-bindings: vendor-prefixes: Add Mayqueen name

[LiangCheng Wang]

From: Wig Cheng <onlywig@gmail.com>

Mayqueen is a Taiwan-based company primarily focused on the development
of arm64 development boards and e-paper displays.

Signed-off-by: Wig Cheng <onlywig@gmail.com>
---
 Documentation/devicetree/bindings/vendor-prefixes.yaml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Documentation/devicetree/bindings/vendor-prefixes.yaml b/Documentation/devicetree/bindings/vendor-prefixes.yaml
index 5d2a7a8d3ac6c666c8b557c2ef385918e5e97bf9..9207c25a3490a3aa5cc9d513290e7890799f92cf 100644
--- a/Documentation/devicetree/bindings/vendor-prefixes.yaml
+++ b/Documentation/devicetree/bindings/vendor-prefixes.yaml
@@ -916,6 +916,8 @@ patternProperties:
     description: Maxim Integrated Products
   "^maxlinear,.*":
     description: MaxLinear Inc.
+  "^mayqueen,.*":
+    description: Mayqueen Technologies Ltd.
   "^mbvl,.*":
     description: Mobiveil Inc.
   "^mcube,.*":

-- 
2.34.1

[PATCH v2 2/3] dt-bindings: display: Add Mayqueen Pixpaper e-ink panel

[LiangCheng Wang]

The binding is for the Mayqueen Pixpaper e-ink display panel,
controlled via an SPI interface.

Signed-off-by: LiangCheng Wang <zaq14760@gmail.com>
---
 .../bindings/display/mayqueen,pixpaper.yaml        | 63 ++++++++++++++++++++++
 1 file changed, 63 insertions(+)

diff --git a/Documentation/devicetree/bindings/display/mayqueen,pixpaper.yaml b/Documentation/devicetree/bindings/display/mayqueen,pixpaper.yaml
new file mode 100644
index 0000000000000000000000000000000000000000..cd27f8ba5ae1d94660818525b5fa71db98c8acb7
--- /dev/null
+++ b/Documentation/devicetree/bindings/display/mayqueen,pixpaper.yaml
@@ -0,0 +1,63 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/mayqueen,pixpaper.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Mayqueen Pixpaper e-ink display panel
+
+maintainers:
+  - LiangCheng Wang <zaq14760@gmail.com>
+
+description:
+  The Pixpaper is an e-ink display panel controlled via an SPI interface.
+  The panel has a resolution of 122x250 pixels and requires GPIO pins for
+  reset, busy, and data/command control.
+
+allOf:
+  - $ref: /schemas/spi/spi-peripheral-props.yaml#
+
+properties:
+  compatible:
+    const: mayqueen,pixpaper
+
+  reg:
+    maxItems: 1
+
+  spi-max-frequency:
+    maximum: 1000000
+    default: 1000000
+
+  reset-gpios:
+    maxItems: 1
+
+  busy-gpios:
+    maxItems: 1
+
+  dc-gpios:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - reset-gpios
+  - busy-gpios
+  - dc-gpios
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+        display@0 {
+            compatible = "mayqueen,pixpaper";
+            reg = <0>;
+            spi-max-frequency = <1000000>;
+            reset-gpios = <&gpio1 17 GPIO_ACTIVE_HIGH>;
+            busy-gpios = <&gpio1 18 GPIO_ACTIVE_HIGH>;
+            dc-gpios = <&gpio1 19 GPIO_ACTIVE_HIGH>;
+        };
+    };

-- 
2.34.1

[PATCH v2 3/3] drm: tiny: Add support for Mayqueen Pixpaper e-ink panel

[LiangCheng Wang]

Introduce a DRM driver for the Mayqueen Pixpaper e-ink display panel,
which is controlled via SPI. The driver supports a 122x250 resolution
display with XRGB8888 format.

Also, add a MAINTAINERS entry for the Pixpaper driver.

Signed-off-by: LiangCheng Wang <zaq14760@gmail.com>
---
 MAINTAINERS                     |   6 +
 drivers/gpu/drm/tiny/Kconfig    |  15 +
 drivers/gpu/drm/tiny/Makefile   |   1 +
 drivers/gpu/drm/tiny/pixpaper.c | 777 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 799 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index fad6cb025a1918beec113b576cf28b76151745ef..0613f32ef8a702e508c9a2e51853f8fe6a38ba42 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7756,6 +7756,12 @@ T:	git https://gitlab.freedesktop.org/drm/misc/kernel.git
 F:	Documentation/devicetree/bindings/display/repaper.txt
 F:	drivers/gpu/drm/tiny/repaper.c
 
+DRM DRIVER FOR PIXPAPER E-INK PANEL
+M:	LiangCheng Wang <zaq14760@gmail.com>
+S:	Maintained
+F:	Documentation/devicetree/bindings/display/mayqueen,pixpaper.yaml
+F:	drivers/gpu/drm/tiny/pixpaper.c
+
 DRM DRIVER FOR QEMU'S CIRRUS DEVICE
 M:	Dave Airlie <airlied@redhat.com>
 M:	Gerd Hoffmann <kraxel@redhat.com>
diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig
index 06e54694a7f2fe1649e1886f039926b24f698e0d..f9b814e87348cad1946dd5e2ff54d304100ef264 100644
--- a/drivers/gpu/drm/tiny/Kconfig
+++ b/drivers/gpu/drm/tiny/Kconfig
@@ -164,6 +164,21 @@ config TINYDRM_MI0283QT
 	  DRM driver for the Multi-Inno MI0283QT display panel
 	  If M is selected the module will be called mi0283qt.
 
+config TINYDRM_PIXPAPER
+	tristate "DRM support for PIXPAPER display panels"
+	depends on DRM && SPI
+	select DRM_CLIENT_SELECTION
+	select DRM_KMS_HELPER
+	select DRM_GEM_DMA_HELPER
+	help
+	  DRM driver for the Mayqueen Pixpaper e-ink display panel.
+
+	  This driver supports small e-paper displays connected over SPI,
+	  with a resolution of 122x250 and XRGB8888 framebuffer format.
+	  It is intended for low-power embedded applications.
+
+	  If M is selected, the module will be built as pixpaper.ko.
+
 config TINYDRM_REPAPER
 	tristate "DRM support for Pervasive Displays RePaper panels (V231)"
 	depends on DRM && SPI
diff --git a/drivers/gpu/drm/tiny/Makefile b/drivers/gpu/drm/tiny/Makefile
index 4a9ff61ec25420e2c0a648c04eaab7ca25dd5407..40d613b57f5ee990dbf170d69939a39546be21b7 100644
--- a/drivers/gpu/drm/tiny/Makefile
+++ b/drivers/gpu/drm/tiny/Makefile
@@ -12,5 +12,6 @@ obj-$(CONFIG_TINYDRM_ILI9225)		+= ili9225.o
 obj-$(CONFIG_TINYDRM_ILI9341)		+= ili9341.o
 obj-$(CONFIG_TINYDRM_ILI9486)		+= ili9486.o
 obj-$(CONFIG_TINYDRM_MI0283QT)		+= mi0283qt.o
+obj-$(CONFIG_TINYDRM_PIXPAPER)		+= pixpaper.o
 obj-$(CONFIG_TINYDRM_REPAPER)		+= repaper.o
 obj-$(CONFIG_TINYDRM_SHARP_MEMORY)	+= sharp-memory.o
diff --git a/drivers/gpu/drm/tiny/pixpaper.c b/drivers/gpu/drm/tiny/pixpaper.c
new file mode 100644
index 0000000000000000000000000000000000000000..f134cacbb3d2b2792b94fc37cddb0b264348f192
--- /dev/null
+++ b/drivers/gpu/drm/tiny/pixpaper.c
@@ -0,0 +1,777 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * DRM driver for PIXPAPER e-ink panel
+ *
+ * Author: LiangCheng Wang <zaq14760@gmail.com>,
+ */
+#include <drm/clients/drm_client_setup.h>
+
+#include <drm/drm_atomic.h>
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_fbdev_dma.h>
+#include <drm/drm_framebuffer.h>
+#include <drm/drm_gem_atomic_helper.h>
+#include <drm/drm_gem_dma_helper.h>
+#include <drm/drm_gem_framebuffer_helper.h>
+#include <drm/drm_probe_helper.h>
+
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/spi/spi.h>
+
+MODULE_IMPORT_NS("DMA_BUF");
+
+#define PIXPAPER_WIDTH 122
+#define PIXPAPER_HEIGHT 250
+
+#define PANEL_BUFFER_WIDTH 128
+#define PANEL_BUFFER_TWO_BYTES_PER_ROW (PANEL_BUFFER_WIDTH / 4)
+
+#define PIXPAPER_SPI_SPEED_DEFAULT 1000000
+
+#define PIXPAPER_CMD_PANEL_SETTING 0x00
+#define PIXPAPER_CMD_POWER_SETTING 0x01
+#define PIXPAPER_CMD_POWER_OFF 0x02
+#define PIXPAPER_CMD_POWER_OFF_SEQUENCE 0x03
+#define PIXPAPER_CMD_POWER_ON 0x04
+#define PIXPAPER_CMD_BOOSTER_SOFT_START 0x06
+#define PIXPAPER_CMD_DEEP_SLEEP 0x07
+#define PIXPAPER_CMD_DATA_START_TRANSMISSION 0x10
+#define PIXPAPER_CMD_DISPLAY_REFRESH 0x12
+#define PIXPAPER_CMD_PLL_CONTROL 0x30
+#define PIXPAPER_CMD_TEMP_SENSOR_CALIB 0x41
+#define PIXPAPER_CMD_UNKNOWN_4D 0x4D
+#define PIXPAPER_CMD_VCOM_INTERVAL 0x50
+#define PIXPAPER_CMD_TCON_SETTING 0x60
+#define PIXPAPER_CMD_RESOLUTION_SETTING 0x61
+#define PIXPAPER_CMD_GATE_SOURCE_START 0x65
+#define PIXPAPER_CMD_UNKNOWN_B4 0xB4
+#define PIXPAPER_CMD_UNKNOWN_B5 0xB5
+#define PIXPAPER_CMD_CASCADE_SETTING 0xE0
+#define PIXPAPER_CMD_POWER_SAVING 0xE3
+#define PIXPAPER_CMD_AUTO_MEASURE_VCOM 0xE7
+#define PIXPAPER_CMD_UNKNOWN_E9 0xE9
+
+static int pixpaper_crtc_helper_atomic_check(struct drm_crtc *crtc,
+					     struct drm_atomic_state *state);
+static int pixpaper_plane_helper_atomic_check(struct drm_plane *plane,
+					      struct drm_atomic_state *state);
+static void pixpaper_crtc_atomic_enable(struct drm_crtc *crtc,
+					struct drm_atomic_state *state);
+static void pixpaper_crtc_atomic_disable(struct drm_crtc *crtc,
+					 struct drm_atomic_state *state);
+static void pixpaper_plane_atomic_update(struct drm_plane *plane,
+					 struct drm_atomic_state *state);
+static int pixpaper_connector_get_modes(struct drm_connector *connector);
+
+struct pixpaper_panel {
+	struct drm_device drm;
+	struct drm_plane plane;
+	struct drm_crtc crtc;
+	struct drm_encoder encoder;
+	struct drm_connector connector;
+
+	struct spi_device *spi;
+	struct gpio_desc *reset;
+	struct gpio_desc *busy;
+	struct gpio_desc *dc;
+};
+
+static const struct drm_plane_funcs pixpaper_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,
+};
+
+static const struct drm_plane_helper_funcs pixpaper_plane_helper_funcs = {
+	DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
+	.atomic_check = pixpaper_plane_helper_atomic_check,
+	.atomic_update = pixpaper_plane_atomic_update,
+};
+
+static const struct drm_crtc_funcs pixpaper_crtc_funcs = {
+	.set_config = drm_atomic_helper_set_config,
+	.page_flip = drm_atomic_helper_page_flip,
+	.reset = drm_atomic_helper_crtc_reset,
+	.destroy = drm_crtc_cleanup,
+	.atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_crtc_destroy_state,
+};
+
+static const struct drm_crtc_helper_funcs pixpaper_crtc_helper_funcs = {
+	.atomic_check = pixpaper_crtc_helper_atomic_check,
+	.atomic_enable = pixpaper_crtc_atomic_enable,
+	.atomic_disable = pixpaper_crtc_atomic_disable,
+};
+
+static const struct drm_encoder_funcs pixpaper_encoder_funcs = {
+	.destroy = drm_encoder_cleanup,
+};
+
+static const struct drm_connector_funcs pixpaper_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_connector_helper_funcs pixpaper_connector_helper_funcs = {
+	.get_modes = pixpaper_connector_get_modes,
+};
+
+static int pixpaper_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;
+	int ret;
+
+	if (new_crtc)
+		new_crtc_state = drm_atomic_get_new_crtc_state(state, new_crtc);
+
+	ret = drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
+						  DRM_PLANE_NO_SCALING,
+						  DRM_PLANE_NO_SCALING,
+						  false, false);
+	if (ret)
+		return ret;
+	else if (!new_plane_state->visible)
+		return 0;
+
+	return 0;
+}
+
+static int pixpaper_crtc_helper_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);
+
+	if (!crtc_state->enable)
+		return 0;
+
+	return drm_atomic_helper_check_crtc_primary_plane(crtc_state);
+}
+
+static void pixpaper_wait_busy(struct pixpaper_panel *panel)
+{
+	unsigned int delay_us = 1000;
+
+	usleep_range(delay_us, delay_us + 500);
+	while (true)
+		if (gpiod_get_value_cansleep(panel->busy) == 1)
+			break;
+}
+
+static int pixpaper_spi_sync(struct spi_device *spi, struct spi_message *msg)
+{
+	int ret;
+
+	ret = spi_sync(spi, msg);
+	if (ret < 0)
+		dev_err(&spi->dev, "SPI sync failed: %d\n", ret);
+
+	return ret;
+}
+
+static int pixpaper_send_cmd(struct pixpaper_panel *panel, u8 cmd)
+{
+	struct spi_transfer xfer = {
+		.tx_buf = &cmd,
+		.len = 1,
+	};
+	struct spi_message msg;
+	int ret;
+
+	spi_message_init(&msg);
+	spi_message_add_tail(&xfer, &msg);
+
+	gpiod_set_value_cansleep(panel->dc, 0);
+	usleep_range(1, 5);
+	ret = pixpaper_spi_sync(panel->spi, &msg);
+
+	return ret;
+}
+
+static int pixpaper_send_data(struct pixpaper_panel *panel, u8 data)
+{
+	struct spi_transfer xfer = {
+		.tx_buf = &data,
+		.len = 1,
+	};
+	struct spi_message msg;
+	int ret;
+
+	spi_message_init(&msg);
+	spi_message_add_tail(&xfer, &msg);
+
+	gpiod_set_value_cansleep(panel->dc, 1);
+	usleep_range(1, 5);
+	ret = pixpaper_spi_sync(panel->spi, &msg);
+
+	return ret;
+}
+
+static int pixpaper_panel_hw_init(struct pixpaper_panel *panel)
+{
+	struct device *dev = &panel->spi->dev;
+	int ret = 0;
+
+	dev_info(dev, "%s: Starting hardware initialization\n", __func__);
+
+	gpiod_set_value_cansleep(panel->reset, 0);
+	msleep(50);
+	gpiod_set_value_cansleep(panel->reset, 1);
+	msleep(50);
+
+	pixpaper_wait_busy(panel);
+	dev_info(dev, "Hardware reset complete, panel idle.\n");
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_UNKNOWN_4D);
+	ret |= pixpaper_send_data(panel, 0x78);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_PANEL_SETTING);
+	ret |= pixpaper_send_data(panel, 0x0F);
+	ret |= pixpaper_send_data(panel, 0x09);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_POWER_SETTING);
+	ret |= pixpaper_send_data(panel, 0x07);
+	ret |= pixpaper_send_data(panel, 0x00);
+	ret |= pixpaper_send_data(panel, 0x22);
+	ret |= pixpaper_send_data(panel, 0x78);
+	ret |= pixpaper_send_data(panel, 0x0A);
+	ret |= pixpaper_send_data(panel, 0x22);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_POWER_OFF_SEQUENCE);
+	ret |= pixpaper_send_data(panel, 0x10);
+	ret |= pixpaper_send_data(panel, 0x54);
+	ret |= pixpaper_send_data(panel, 0x44);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_BOOSTER_SOFT_START);
+	ret |= pixpaper_send_data(panel, 0x0F);
+	ret |= pixpaper_send_data(panel, 0x0A);
+	ret |= pixpaper_send_data(panel, 0x2F);
+	ret |= pixpaper_send_data(panel, 0x25);
+	ret |= pixpaper_send_data(panel, 0x22);
+	ret |= pixpaper_send_data(panel, 0x2E);
+	ret |= pixpaper_send_data(panel, 0x21);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_PLL_CONTROL);
+	ret |= pixpaper_send_data(panel, 0x02);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_TEMP_SENSOR_CALIB);
+	ret |= pixpaper_send_data(panel, 0x00);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_VCOM_INTERVAL);
+	ret |= pixpaper_send_data(panel, 0x37);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_TCON_SETTING);
+	ret |= pixpaper_send_data(panel, 0x02);
+	ret |= pixpaper_send_data(panel, 0x02);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_RESOLUTION_SETTING);
+	ret |= pixpaper_send_data(panel, 0x00);
+	ret |= pixpaper_send_data(panel, 0x80);
+	ret |= pixpaper_send_data(panel, 0x00);
+	ret |= pixpaper_send_data(panel, 0xFA);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_GATE_SOURCE_START);
+	ret |= pixpaper_send_data(panel, 0x00);
+	ret |= pixpaper_send_data(panel, 0x00);
+	ret |= pixpaper_send_data(panel, 0x00);
+	ret |= pixpaper_send_data(panel, 0x00);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_AUTO_MEASURE_VCOM);
+	ret |= pixpaper_send_data(panel, 0x1C);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_POWER_SAVING);
+	ret |= pixpaper_send_data(panel, 0x22);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_CASCADE_SETTING);
+	ret |= pixpaper_send_data(panel, 0x00);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_UNKNOWN_B4);
+	ret |= pixpaper_send_data(panel, 0xD0);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_UNKNOWN_B5);
+	ret |= pixpaper_send_data(panel, 0x03);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_UNKNOWN_E9);
+	ret |= pixpaper_send_data(panel, 0x01);
+	if (ret)
+		goto init_fail;
+	pixpaper_wait_busy(panel);
+
+	dev_info(dev, "%s: Hardware initialization successful\n", __func__);
+	return 0;
+
+init_fail:
+	dev_err(dev, "%s: Hardware initialization failed (err=%d)\n", __func__,
+		ret);
+	return ret;
+}
+
+static void pixpaper_crtc_atomic_enable(struct drm_crtc *crtc,
+					struct drm_atomic_state *state)
+{
+	struct pixpaper_panel *panel =
+		container_of(crtc, struct pixpaper_panel, crtc);
+	struct drm_device *drm = &panel->drm;
+	int ret;
+
+	dev_info(drm->dev, "%s: Enabling pipe\n", __func__);
+
+	ret = pixpaper_panel_hw_init(panel);
+	if (ret) {
+		dev_err(drm->dev, "Panel HW Init failed during enable: %d\n",
+			ret);
+		return;
+	}
+
+	dev_info(drm->dev, "Sending Power ON (PON)\n");
+	ret = pixpaper_send_cmd(panel, PIXPAPER_CMD_POWER_ON);
+	if (ret) {
+		dev_err(drm->dev, "Failed to send PON command: %d\n", ret);
+		return;
+	}
+
+	usleep_range(10000, 11000);
+
+	pixpaper_wait_busy(panel);
+
+	dev_info(drm->dev, "Panel enabled and powered on\n");
+}
+
+static void pixpaper_crtc_atomic_disable(struct drm_crtc *crtc,
+					 struct drm_atomic_state *state)
+{
+	struct pixpaper_panel *panel =
+		container_of(crtc, struct pixpaper_panel, crtc);
+	struct drm_device *drm = &panel->drm;
+	int ret;
+
+	dev_dbg(drm->dev, "%s: Disabling pipe\n", __func__);
+
+	ret = pixpaper_send_cmd(panel, PIXPAPER_CMD_POWER_OFF);
+	if (!ret) {
+		usleep_range(10000, 11000);
+		pixpaper_wait_busy(panel);
+	} else {
+		dev_warn(drm->dev, "Failed to send POF command: %d\n", ret);
+	}
+	dev_info(drm->dev, "Panel disabled\n");
+}
+
+static u8 pack_pixels_to_byte(u32 *src_pixels, int i, int j,
+			      struct drm_framebuffer *fb)
+{
+	u8 packed_byte = 0;
+	int k;
+
+	for (k = 0; k < 4; k++) {
+		int current_pixel_x = j * 4 + k;
+		u8 two_bit_val;
+
+		if (current_pixel_x < PIXPAPER_WIDTH) {
+			u32 pixel_offset =
+				(i * (fb->pitches[0] / 4)) + current_pixel_x;
+			u32 pixel = src_pixels[pixel_offset];
+			u32 r = (pixel >> 16) & 0xFF;
+			u32 g = (pixel >> 8) & 0xFF;
+			u32 b = pixel & 0xFF;
+			u32 gray_val =
+				(r * 299 + g * 587 + b * 114 + 500) / 1000;
+
+			if (gray_val < 64)
+				two_bit_val = 0b00;
+			else if (gray_val < 128)
+				two_bit_val = 0b01;
+			else if (gray_val < 192)
+				two_bit_val = 0b10;
+			else
+				two_bit_val = 0b11;
+		} else {
+			two_bit_val = 0b11;
+		}
+
+		packed_byte |= two_bit_val << ((3 - k) * 2);
+	}
+
+	return packed_byte;
+}
+
+static void pixpaper_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_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(plane_state);
+	struct drm_crtc *crtc = plane_state->crtc;
+	struct pixpaper_panel *panel =
+		container_of(crtc, struct pixpaper_panel, crtc);
+
+	struct drm_device *drm = &panel->drm;
+	struct drm_framebuffer *fb = plane_state->fb;
+	struct iosys_map map = shadow_plane_state->data[0];
+	void *vaddr = map.vaddr;
+	int i, j, ret = 0;
+	u32 *src_pixels = NULL;
+
+	dev_info(drm->dev, "Starting frame update (phys=%dx%d, buf_w=%d)\n",
+		 PIXPAPER_WIDTH, PIXPAPER_HEIGHT, PANEL_BUFFER_WIDTH);
+
+	if (!fb || !plane_state->visible) {
+		dev_err(drm->dev,
+			"No framebuffer or plane not visible, skipping update\n");
+		return;
+	}
+
+	if (ret) {
+		dev_err(drm->dev, "Failed to vmap dma_buf\n");
+		return;
+	}
+
+	src_pixels = (u32 *)vaddr;
+
+	dev_info(drm->dev, "Sending DTM command\n");
+	ret = pixpaper_send_cmd(panel, PIXPAPER_CMD_DATA_START_TRANSMISSION);
+	if (ret)
+		goto update_cleanup;
+
+	usleep_range(10000, 11000);
+	pixpaper_wait_busy(panel);
+
+	dev_info(drm->dev,
+		 "Panel idle after DTM command, starting data batch send.\n");
+
+	for (i = 0; i < PIXPAPER_HEIGHT; i++) {
+		for (j = 0; j < PANEL_BUFFER_TWO_BYTES_PER_ROW; j++) {
+			u8 packed_byte =
+				pack_pixels_to_byte(src_pixels, i, j, fb);
+
+			pixpaper_wait_busy(panel);
+			pixpaper_send_data(panel, packed_byte);
+		}
+	}
+	pixpaper_wait_busy(panel);
+
+	dev_info(drm->dev, "Sending PON + 0x00 before DRF\n");
+	ret = pixpaper_send_cmd(panel, PIXPAPER_CMD_POWER_ON);
+	if (ret)
+		goto update_cleanup;
+	ret = pixpaper_send_data(panel, 0x00);
+	if (ret) {
+		dev_err(drm->dev,
+			"Failed sending data after PON-before-DRF: %d\n", ret);
+		goto update_cleanup;
+	}
+	usleep_range(10000, 11000);
+	pixpaper_wait_busy(panel);
+
+	dev_info(drm->dev, "Triggering display refresh (DRF)\n");
+	ret = pixpaper_send_cmd(panel, PIXPAPER_CMD_DISPLAY_REFRESH);
+	if (ret)
+		goto update_cleanup;
+	ret = pixpaper_send_data(panel, 0x00);
+	if (ret) {
+		dev_err(drm->dev, "Failed sending data after DRF: %d\n", ret);
+		goto update_cleanup;
+	}
+	usleep_range(10000, 11000);
+	pixpaper_wait_busy(panel);
+
+	dev_info(drm->dev, "Frame update completed and refresh triggered\n");
+
+update_cleanup:
+	if (ret && ret != -ETIMEDOUT)
+		dev_err(drm->dev,
+			"Frame update function failed with error %d\n", ret);
+}
+
+static int pixpaper_connector_get_modes(struct drm_connector *connector)
+{
+	struct drm_display_mode *mode;
+
+	dev_info(connector->dev->dev, "%s: CALLED for connector %s (id: %d)\n",
+		 __func__, connector->name, connector->base.id);
+
+	mode = drm_mode_create(connector->dev);
+	if (!mode) {
+		DRM_ERROR("Failed to create mode for connector %s\n",
+			  connector->name);
+		return 0;
+	}
+
+	mode->hdisplay = PIXPAPER_WIDTH;
+	mode->vdisplay = PIXPAPER_HEIGHT;
+
+	mode->htotal = mode->hdisplay + 80;
+	mode->hsync_start = mode->hdisplay + 8;
+	mode->hsync_end = mode->hdisplay + 8 + 32;
+	mode->vtotal = mode->vdisplay + 10;
+	mode->vsync_start = mode->vdisplay + 2;
+	mode->vsync_end = mode->vdisplay + 2 + 2;
+
+	mode->clock = 6000;
+
+	mode->type = DRM_MODE_TYPE_DRIVER | DRM_MODE_TYPE_PREFERRED;
+	drm_mode_set_name(mode);
+
+	if (drm_mode_validate_size(mode, connector->dev->mode_config.max_width,
+				   connector->dev->mode_config.max_height) !=
+	    MODE_OK) {
+		DRM_WARN("%s: Mode %s (%dx%d) failed size validation against max %dx%d\n",
+			 __func__, mode->name, mode->hdisplay, mode->vdisplay,
+			 connector->dev->mode_config.max_width,
+			 connector->dev->mode_config.max_height);
+		drm_mode_destroy(connector->dev, mode);
+		return 0;
+	}
+
+	drm_mode_probed_add(connector, mode);
+	dev_info(connector->dev->dev,
+		 "%s: Added mode '%s' (%dx%d@%d) to connector %s\n", __func__,
+		 mode->name, mode->hdisplay, mode->vdisplay,
+		 drm_mode_vrefresh(mode), connector->name);
+
+	connector->display_info.width_mm = 30;
+	connector->display_info.height_mm = 47;
+
+	return 1;
+}
+
+DEFINE_DRM_GEM_DMA_FOPS(pixpaper_fops);
+
+static struct drm_driver pixpaper_drm_driver = {
+	.driver_features = DRIVER_GEM | DRIVER_MODESET | DRIVER_ATOMIC,
+	.fops = &pixpaper_fops,
+	.name = "pixpaper",
+	.desc = "DRM driver for PIXPAPER e-ink",
+	.major = 1,
+	.minor = 0,
+	DRM_GEM_DMA_DRIVER_OPS_VMAP,
+	DRM_FBDEV_DMA_DRIVER_OPS,
+};
+
+static int pixpaper_mode_valid(struct drm_device *dev,
+			       const struct drm_display_mode *mode)
+{
+	if (mode->hdisplay == PIXPAPER_WIDTH &&
+	    mode->vdisplay == PIXPAPER_HEIGHT) {
+		return MODE_OK;
+	}
+	dev_dbg(dev->dev, "Rejecting mode %dx%d (supports only %dx%d)\n",
+		mode->hdisplay, mode->vdisplay, PIXPAPER_WIDTH,
+		PIXPAPER_HEIGHT);
+	return MODE_BAD;
+}
+
+static const struct drm_mode_config_funcs pixpaper_mode_config_funcs = {
+	.fb_create = drm_gem_fb_create_with_dirty,
+	.mode_valid = pixpaper_mode_valid,
+	.atomic_check = drm_atomic_helper_check,
+	.atomic_commit = drm_atomic_helper_commit,
+};
+
+static int pixpaper_probe(struct spi_device *spi)
+{
+	struct device *dev = &spi->dev;
+	struct pixpaper_panel *panel;
+	struct drm_device *drm;
+	int ret;
+
+	dev_info(dev, "Probing PIXPAPER panel driver\n");
+
+	panel = devm_drm_dev_alloc(dev, &pixpaper_drm_driver,
+				   struct pixpaper_panel, drm);
+	if (IS_ERR(panel)) {
+		ret = PTR_ERR(panel);
+		dev_err(dev, "Failed to allocate DRM device: %d\n", ret);
+		return ret;
+	}
+	drm = &panel->drm;
+	panel->spi = spi;
+	spi_set_drvdata(spi, panel);
+
+	spi->mode = SPI_MODE_0;
+	spi->bits_per_word = 8;
+
+	if (!spi->max_speed_hz) {
+		dev_warn(dev, "spi-max-frequency not specified in DT, using default %u Hz\n",
+			 PIXPAPER_SPI_SPEED_DEFAULT);
+		spi->max_speed_hz = PIXPAPER_SPI_SPEED_DEFAULT;
+	} else {
+		dev_info(dev, "Using spi-max-frequency from DT: %u Hz\n",
+			 spi->max_speed_hz);
+	}
+
+	ret = spi_setup(spi);
+	if (ret < 0) {
+		dev_err(dev, "SPI setup failed: %d\n", ret);
+		return ret;
+	}
+	dev_info(dev, "SPI setup OK (mode=%d, speed=%u Hz, bpw=%d)\n",
+		 spi->mode, spi->max_speed_hz, spi->bits_per_word);
+
+	if (!dev->dma_mask)
+		dev->dma_mask = &dev->coherent_dma_mask;
+	ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32));
+	if (ret) {
+		dev_err(dev, "Failed to set DMA mask: %d\n", ret);
+		return ret;
+	}
+	dev_dbg(dev, "DMA mask set\n");
+
+	panel->reset = devm_gpiod_get(dev, "reset", GPIOD_OUT_HIGH);
+	if (IS_ERR(panel->reset))
+		return dev_err_probe(dev, PTR_ERR(panel->reset),
+				     "Failed to get 'reset' GPIO\n");
+	panel->busy = devm_gpiod_get(dev, "busy", GPIOD_IN);
+	if (IS_ERR(panel->busy))
+		return dev_err_probe(dev, PTR_ERR(panel->busy),
+				     "Failed to get 'busy' GPIO\n");
+	panel->dc = devm_gpiod_get(dev, "dc", GPIOD_OUT_HIGH);
+	if (IS_ERR(panel->dc))
+		return dev_err_probe(dev, PTR_ERR(panel->dc),
+				     "Failed to get 'dc' GPIO\n");
+	dev_info(dev, "All required GPIOs obtained successfully.\n");
+
+	ret = drmm_mode_config_init(drm);
+	if (ret)
+		return ret;
+	drm->mode_config.funcs = &pixpaper_mode_config_funcs;
+	drm->mode_config.min_width = PIXPAPER_WIDTH;
+	drm->mode_config.max_width = PIXPAPER_WIDTH;
+	drm->mode_config.min_height = PIXPAPER_HEIGHT;
+	drm->mode_config.max_height = PIXPAPER_HEIGHT;
+
+	ret = drm_universal_plane_init(drm, &panel->plane, 1, &pixpaper_plane_funcs,
+		(const uint32_t[]){ DRM_FORMAT_XRGB8888 }, 1, NULL,
+		DRM_PLANE_TYPE_PRIMARY, NULL);
+	drm_plane_enable_fb_damage_clips(&panel->plane);
+	if (ret)
+		return ret;
+	drm_plane_helper_add(&panel->plane, &pixpaper_plane_helper_funcs);
+
+	ret = drm_crtc_init_with_planes(drm, &panel->crtc, &panel->plane, NULL,
+					&pixpaper_crtc_funcs, NULL);
+	if (ret)
+		return ret;
+	drm_crtc_helper_add(&panel->crtc, &pixpaper_crtc_helper_funcs);
+
+	ret = drm_encoder_init(drm, &panel->encoder, &pixpaper_encoder_funcs,
+			       DRM_MODE_ENCODER_DAC, NULL);
+	if (ret)
+		return ret;
+	panel->encoder.possible_crtcs = drm_crtc_mask(&panel->crtc);
+
+	ret = drm_connector_init(drm, &panel->connector,
+				 &pixpaper_connector_funcs,
+				 DRM_MODE_CONNECTOR_SPI);
+	if (ret)
+		return ret;
+
+	drm_connector_helper_add(&panel->connector,
+				 &pixpaper_connector_helper_funcs);
+	drm_connector_attach_encoder(&panel->connector, &panel->encoder);
+
+	drm_mode_config_reset(drm);
+
+	ret = drm_dev_register(drm, 0);
+	if (ret)
+		return ret;
+
+	drm_client_setup(drm, NULL);
+
+	dev_info(dev, "Initialized PIXPAPER panel driver successfully\n");
+	return 0;
+}
+
+static void pixpaper_remove(struct spi_device *spi)
+{
+	struct pixpaper_panel *panel = spi_get_drvdata(spi);
+
+	if (!panel)
+		return;
+
+	dev_info(&spi->dev, "Removing PIXPAPER panel driver\n");
+
+	drm_dev_unplug(&panel->drm);
+	drm_atomic_helper_shutdown(&panel->drm);
+}
+
+static const struct spi_device_id pixpaper_ids[] = { { "pixpaper", 0 }, {} };
+MODULE_DEVICE_TABLE(spi, pixpaper_ids);
+
+static const struct of_device_id pixpaper_dt_ids[] = {
+	{ .compatible = "mayqueen,pixpaper" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, pixpaper_dt_ids);
+
+static struct spi_driver pixpaper_spi_driver = {
+	.driver = {
+		.name = "pixpaper",
+		.of_match_table = pixpaper_dt_ids,
+	},
+	.id_table = pixpaper_ids,
+	.probe = pixpaper_probe,
+	.remove = pixpaper_remove,
+};
+
+module_spi_driver(pixpaper_spi_driver);
+
+MODULE_AUTHOR("LiangCheng Wang");
+MODULE_DESCRIPTION("DRM SPI driver for PIXPAPER e-ink panel");
+MODULE_LICENSE("GPL");

-- 
2.34.1

Re: [PATCH v2 0/3] Add support for Mayqueen Pixpaper e-ink panel

[Krzysztof Kozlowski]

On 14/07/2025 04:59, LiangCheng Wang wrote:
> ---
> Changes in v2:
> - Reordered patches so that DT bindings come before the driver (suggested by Rob Herring)
> - Fixed sparse warning: removed duplicate `.reset` initializer in `pixpaper_plane_funcs`
> - Fixed checkpatch issues reported by Media CI:
>   - Removed unnecessary blank line before closing brace
>   - Moved opening parentheses up to function call lines (e.g., `DRM_WARN(...)`)
>   - Fixed alignment of conditionals
>   - Fixed `dev_warn(` and `drm_universal_plane_init(` formatting
> - Thanks to Rob Herring for ack on vendor-prefix patch

And what did you do about it?

Best regards,
Krzysztof

Re: [PATCH v2 1/3] dt-bindings: vendor-prefixes: Add Mayqueen name

[Krzysztof Kozlowski]

On 14/07/2025 04:59, LiangCheng Wang wrote:
> From: Wig Cheng <onlywig@gmail.com>
> 
> Mayqueen is a Taiwan-based company primarily focused on the development
> of arm64 development boards and e-paper displays.
> 
> Signed-off-by: Wig Cheng <onlywig@gmail.com>
> ---
<form letter>
This is a friendly reminder during the review process.

It looks like you received a tag and forgot to add it.

If you do not know the process, here is a short explanation:
Please add Acked-by/Reviewed-by/Tested-by tags when posting new versions
of patchset, under or above your Signed-off-by tag, unless patch changed
significantly (e.g. new properties added to the DT bindings). Tag is
"received", when provided in a message replied to you on the mailing
list. Tools like b4 can help here. However, there's no need to repost
patches *only* to add the tags. The upstream maintainer will do that for
tags received on the version they apply.

Please read:
https://elixir.bootlin.com/linux/v6.12-rc3/source/Documentation/process/submitting-patches.rst#L577

If a tag was not added on purpose, please state why and what changed.
</form letter>


Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

Best regards,
Krzysztof

Re: [PATCH v2 2/3] dt-bindings: display: Add Mayqueen Pixpaper e-ink panel

[Krzysztof Kozlowski]

On 14/07/2025 04:59, LiangCheng Wang wrote:
> The binding is for the Mayqueen Pixpaper e-ink display panel,
> controlled via an SPI interface.
> 
> Signed-off-by: LiangCheng Wang <zaq14760@gmail.com>

<form letter>
This is a friendly reminder during the review process.

It looks like you received a tag and forgot to add it.

If you do not know the process, here is a short explanation:
Please add Acked-by/Reviewed-by/Tested-by tags when posting new versions
of patchset, under or above your Signed-off-by tag, unless patch changed
significantly (e.g. new properties added to the DT bindings). Tag is
"received", when provided in a message replied to you on the mailing
list. Tools like b4 can help here. However, there's no need to repost
patches *only* to add the tags. The upstream maintainer will do that for
tags received on the version they apply.

Please read:
https://elixir.bootlin.com/linux/v6.12-rc3/source/Documentation/process/submitting-patches.rst#L577

If a tag was not added on purpose, please state why and what changed.
</form letter>

Best regards,
Krzysztof

Re: [PATCH v2 3/3] drm: tiny: Add support for Mayqueen Pixpaper e-ink panel

[Thomas Zimmermann]

Hi

Am 14.07.25 um 04:59 schrieb LiangCheng Wang:
> Introduce a DRM driver for the Mayqueen Pixpaper e-ink display panel,
> which is controlled via SPI. The driver supports a 122x250 resolution
> display with XRGB8888 format.
>
> Also, add a MAINTAINERS entry for the Pixpaper driver.
>
> Signed-off-by: LiangCheng Wang <zaq14760@gmail.com>
> ---
>   MAINTAINERS                     |   6 +
>   drivers/gpu/drm/tiny/Kconfig    |  15 +
>   drivers/gpu/drm/tiny/Makefile   |   1 +
>   drivers/gpu/drm/tiny/pixpaper.c | 777 ++++++++++++++++++++++++++++++++++++++++
>   4 files changed, 799 insertions(+)
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index fad6cb025a1918beec113b576cf28b76151745ef..0613f32ef8a702e508c9a2e51853f8fe6a38ba42 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -7756,6 +7756,12 @@ T:	git https://gitlab.freedesktop.org/drm/misc/kernel.git
>   F:	Documentation/devicetree/bindings/display/repaper.txt
>   F:	drivers/gpu/drm/tiny/repaper.c
>   
> +DRM DRIVER FOR PIXPAPER E-INK PANEL
> +M:	LiangCheng Wang <zaq14760@gmail.com>
> +S:	Maintained
> +F:	Documentation/devicetree/bindings/display/mayqueen,pixpaper.yaml
> +F:	drivers/gpu/drm/tiny/pixpaper.c
> +
>   DRM DRIVER FOR QEMU'S CIRRUS DEVICE
>   M:	Dave Airlie <airlied@redhat.com>
>   M:	Gerd Hoffmann <kraxel@redhat.com>
> diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig
> index 06e54694a7f2fe1649e1886f039926b24f698e0d..f9b814e87348cad1946dd5e2ff54d304100ef264 100644
> --- a/drivers/gpu/drm/tiny/Kconfig
> +++ b/drivers/gpu/drm/tiny/Kconfig
> @@ -164,6 +164,21 @@ config TINYDRM_MI0283QT
>   	  DRM driver for the Multi-Inno MI0283QT display panel
>   	  If M is selected the module will be called mi0283qt.
>   
> +config TINYDRM_PIXPAPER

We don't use the TINYDRM_ prefix any longer. Just call it DRM_PIXPAPER.

> +	tristate "DRM support for PIXPAPER display panels"
> +	depends on DRM && SPI

> +	select DRM_CLIENT_SELECTION
> +	select DRM_KMS_HELPER
> +	select DRM_GEM_DMA_HELPER

Alphabetical sorting please.

> +	help
> +	  DRM driver for the Mayqueen Pixpaper e-ink display panel.
> +
> +	  This driver supports small e-paper displays connected over SPI,
> +	  with a resolution of 122x250 and XRGB8888 framebuffer format.
> +	  It is intended for low-power embedded applications.
> +
> +	  If M is selected, the module will be built as pixpaper.ko.
> +
>   config TINYDRM_REPAPER
>   	tristate "DRM support for Pervasive Displays RePaper panels (V231)"
>   	depends on DRM && SPI
> diff --git a/drivers/gpu/drm/tiny/Makefile b/drivers/gpu/drm/tiny/Makefile
> index 4a9ff61ec25420e2c0a648c04eaab7ca25dd5407..40d613b57f5ee990dbf170d69939a39546be21b7 100644
> --- a/drivers/gpu/drm/tiny/Makefile
> +++ b/drivers/gpu/drm/tiny/Makefile
> @@ -12,5 +12,6 @@ obj-$(CONFIG_TINYDRM_ILI9225)		+= ili9225.o
>   obj-$(CONFIG_TINYDRM_ILI9341)		+= ili9341.o
>   obj-$(CONFIG_TINYDRM_ILI9486)		+= ili9486.o
>   obj-$(CONFIG_TINYDRM_MI0283QT)		+= mi0283qt.o
> +obj-$(CONFIG_TINYDRM_PIXPAPER)		+= pixpaper.o
>   obj-$(CONFIG_TINYDRM_REPAPER)		+= repaper.o
>   obj-$(CONFIG_TINYDRM_SHARP_MEMORY)	+= sharp-memory.o
> diff --git a/drivers/gpu/drm/tiny/pixpaper.c b/drivers/gpu/drm/tiny/pixpaper.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..f134cacbb3d2b2792b94fc37cddb0b264348f192
> --- /dev/null
> +++ b/drivers/gpu/drm/tiny/pixpaper.c
> @@ -0,0 +1,777 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * DRM driver for PIXPAPER e-ink panel
> + *
> + * Author: LiangCheng Wang <zaq14760@gmail.com>,
> + */
> +#include <drm/clients/drm_client_setup.h>
> +

Blank line before this include, not after.

> +#include <drm/drm_atomic.h>
> +#include <drm/drm_atomic_helper.h>
> +#include <drm/drm_drv.h>
> +#include <drm/drm_fbdev_dma.h>
> +#include <drm/drm_framebuffer.h>
> +#include <drm/drm_gem_atomic_helper.h>
> +#include <drm/drm_gem_dma_helper.h>
> +#include <drm/drm_gem_framebuffer_helper.h>
> +#include <drm/drm_probe_helper.h>
> +
> +#include <linux/delay.h>
> +#include <linux/module.h>
> +#include <linux/spi/spi.h>

The <linux/> includes go before the <drm/> ones.

> +
> +MODULE_IMPORT_NS("DMA_BUF");
> +
> +#define PIXPAPER_WIDTH 122
> +#define PIXPAPER_HEIGHT 250
> +
> +#define PANEL_BUFFER_WIDTH 128
> +#define PANEL_BUFFER_TWO_BYTES_PER_ROW (PANEL_BUFFER_WIDTH / 4)
> +
> +#define PIXPAPER_SPI_SPEED_DEFAULT 1000000
> +
> +#define PIXPAPER_CMD_PANEL_SETTING 0x00
> +#define PIXPAPER_CMD_POWER_SETTING 0x01
> +#define PIXPAPER_CMD_POWER_OFF 0x02
> +#define PIXPAPER_CMD_POWER_OFF_SEQUENCE 0x03
> +#define PIXPAPER_CMD_POWER_ON 0x04
> +#define PIXPAPER_CMD_BOOSTER_SOFT_START 0x06
> +#define PIXPAPER_CMD_DEEP_SLEEP 0x07
> +#define PIXPAPER_CMD_DATA_START_TRANSMISSION 0x10
> +#define PIXPAPER_CMD_DISPLAY_REFRESH 0x12
> +#define PIXPAPER_CMD_PLL_CONTROL 0x30
> +#define PIXPAPER_CMD_TEMP_SENSOR_CALIB 0x41
> +#define PIXPAPER_CMD_UNKNOWN_4D 0x4D
> +#define PIXPAPER_CMD_VCOM_INTERVAL 0x50
> +#define PIXPAPER_CMD_TCON_SETTING 0x60
> +#define PIXPAPER_CMD_RESOLUTION_SETTING 0x61
> +#define PIXPAPER_CMD_GATE_SOURCE_START 0x65
> +#define PIXPAPER_CMD_UNKNOWN_B4 0xB4
> +#define PIXPAPER_CMD_UNKNOWN_B5 0xB5
> +#define PIXPAPER_CMD_CASCADE_SETTING 0xE0
> +#define PIXPAPER_CMD_POWER_SAVING 0xE3
> +#define PIXPAPER_CMD_AUTO_MEASURE_VCOM 0xE7
> +#define PIXPAPER_CMD_UNKNOWN_E9 0xE9
> +
> +static int pixpaper_crtc_helper_atomic_check(struct drm_crtc *crtc,
> +					     struct drm_atomic_state *state);
> +static int pixpaper_plane_helper_atomic_check(struct drm_plane *plane,
> +					      struct drm_atomic_state *state);
> +static void pixpaper_crtc_atomic_enable(struct drm_crtc *crtc,
> +					struct drm_atomic_state *state);
> +static void pixpaper_crtc_atomic_disable(struct drm_crtc *crtc,
> +					 struct drm_atomic_state *state);
> +static void pixpaper_plane_atomic_update(struct drm_plane *plane,
> +					 struct drm_atomic_state *state);
> +static int pixpaper_connector_get_modes(struct drm_connector *connector);

Please don't declare those functions. Interleave the implementation with 
the structs that use them.

> +
> +struct pixpaper_panel {
> +	struct drm_device drm;
> +	struct drm_plane plane;
> +	struct drm_crtc crtc;
> +	struct drm_encoder encoder;
> +	struct drm_connector connector;
> +
> +	struct spi_device *spi;
> +	struct gpio_desc *reset;
> +	struct gpio_desc *busy;
> +	struct gpio_desc *dc;
> +};
> +
> +static const struct drm_plane_funcs pixpaper_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,
> +};
> +
> +static const struct drm_plane_helper_funcs pixpaper_plane_helper_funcs = {
> +	DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
> +	.atomic_check = pixpaper_plane_helper_atomic_check,
> +	.atomic_update = pixpaper_plane_atomic_update,

For example, these functions should be implemented  right before 
declaring the global variable; same goes for the others.

> +};
> +
> +static const struct drm_crtc_funcs pixpaper_crtc_funcs = {
> +	.set_config = drm_atomic_helper_set_config,
> +	.page_flip = drm_atomic_helper_page_flip,
> +	.reset = drm_atomic_helper_crtc_reset,
> +	.destroy = drm_crtc_cleanup,
> +	.atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,
> +	.atomic_destroy_state = drm_atomic_helper_crtc_destroy_state,
> +};
> +
> +static const struct drm_crtc_helper_funcs pixpaper_crtc_helper_funcs = {
> +	.atomic_check = pixpaper_crtc_helper_atomic_check,
> +	.atomic_enable = pixpaper_crtc_atomic_enable,
> +	.atomic_disable = pixpaper_crtc_atomic_disable,
> +};
> +
> +static const struct drm_encoder_funcs pixpaper_encoder_funcs = {
> +	.destroy = drm_encoder_cleanup,
> +};
> +
> +static const struct drm_connector_funcs pixpaper_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_connector_helper_funcs pixpaper_connector_helper_funcs = {
> +	.get_modes = pixpaper_connector_get_modes,
> +};
> +
> +static int pixpaper_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;
> +	int ret;
> +
> +	if (new_crtc)
> +		new_crtc_state = drm_atomic_get_new_crtc_state(state, new_crtc);
> +
> +	ret = drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
> +						  DRM_PLANE_NO_SCALING,
> +						  DRM_PLANE_NO_SCALING,
> +						  false, false);
> +	if (ret)
> +		return ret;
> +	else if (!new_plane_state->visible)
> +		return 0;
> +
> +	return 0;
> +}
> +
> +static int pixpaper_crtc_helper_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);
> +
> +	if (!crtc_state->enable)
> +		return 0;
> +
> +	return drm_atomic_helper_check_crtc_primary_plane(crtc_state);
> +}
> +
> +static void pixpaper_wait_busy(struct pixpaper_panel *panel)
> +{
> +	unsigned int delay_us = 1000;
> +
> +	usleep_range(delay_us, delay_us + 500);
> +	while (true)
> +		if (gpiod_get_value_cansleep(panel->busy) == 1)
> +			break;
> +}

This function should eventually time out.

> +
> +static int pixpaper_spi_sync(struct spi_device *spi, struct spi_message *msg)
> +{
> +	int ret;
> +
> +	ret = spi_sync(spi, msg);
> +	if (ret < 0)
> +		dev_err(&spi->dev, "SPI sync failed: %d\n", ret);

Please use DRM's error reporting. dev_err() becomes drm_err(), dev_dbg() 
becomes drm_dbg().  Further below is WARN_ON(), which should become 
drm_WARN_ON().  Here and everwhere else in the driver.  The only 
exception is in places where you don't have a DRM device yet, sch as 
early device probing.

> +
> +	return ret;
> +}
> +
> +static int pixpaper_send_cmd(struct pixpaper_panel *panel, u8 cmd)
> +{
> +	struct spi_transfer xfer = {
> +		.tx_buf = &cmd,
> +		.len = 1,
> +	};
> +	struct spi_message msg;
> +	int ret;
> +
> +	spi_message_init(&msg);
> +	spi_message_add_tail(&xfer, &msg);
> +
> +	gpiod_set_value_cansleep(panel->dc, 0);
> +	usleep_range(1, 5);
> +	ret = pixpaper_spi_sync(panel->spi, &msg);
> +
> +	return ret;
> +}
> +
> +static int pixpaper_send_data(struct pixpaper_panel *panel, u8 data)
> +{
> +	struct spi_transfer xfer = {
> +		.tx_buf = &data,
> +		.len = 1,
> +	};
> +	struct spi_message msg;
> +	int ret;
> +
> +	spi_message_init(&msg);
> +	spi_message_add_tail(&xfer, &msg);
> +
> +	gpiod_set_value_cansleep(panel->dc, 1);
> +	usleep_range(1, 5);
> +	ret = pixpaper_spi_sync(panel->spi, &msg);
> +
> +	return ret;
> +}
> +
> +static int pixpaper_panel_hw_init(struct pixpaper_panel *panel)
> +{
> +	struct device *dev = &panel->spi->dev;
> +	int ret = 0;
> +
> +	dev_info(dev, "%s: Starting hardware initialization\n", __func__);
> +
> +	gpiod_set_value_cansleep(panel->reset, 0);
> +	msleep(50);
> +	gpiod_set_value_cansleep(panel->reset, 1);
> +	msleep(50);
> +
> +	pixpaper_wait_busy(panel);
> +	dev_info(dev, "Hardware reset complete, panel idle.\n");
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_UNKNOWN_4D);
> +	ret |= pixpaper_send_data(panel, 0x78);

This error handling isn't working. Your code OR's multiple errno codes 
and the result will have a different meaning.

The easiest way to avoid excessive error checking is to add an error 
context as final parameter, like this

struct pixpaper_error_ctx {
     int errno_code;
};

pixpaper_spi_sync(..., pixpaper_error_ctx *err) { if (err->errno_code) 
return; ret = spi_sync(...) if (ret) err->errno_code = ret; }

send_cmd(..., pix_error_ctx *err)
{
         pixppaper_spi_sync(..., err);
}


send_data(..., pix_error_ctx *err)
{
         pixppaper_spi_sync(..., err);
}

int my_pixpaper_driver_func()
{
     sturct pixpaper_error_ctx = {}

     send_cmd(..., &err);
     send_data(..., &err);
     send_data(..., &err);
     send_data(..., &err);

     send_cmd(..., &err);
     send_data(..., &err);
     send_data(..., &err);
     send_data(..., &err);

     if (err->errno_code)
         return errno_code

     return 0;
}

This pushes error handling down into the call tree and you only have to 
test for the final result.

> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);

And you can extend other functions, such as pixpaper_wait_busy(), with 
the error context. Integrates them with the rest of the I/O code.

> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_PANEL_SETTING);
> +	ret |= pixpaper_send_data(panel, 0x0F);
> +	ret |= pixpaper_send_data(panel, 0x09);

There are *a lot* of magic values in this function. Please document the 
meaning of these.

> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_POWER_SETTING);
> +	ret |= pixpaper_send_data(panel, 0x07);
> +	ret |= pixpaper_send_data(panel, 0x00);
> +	ret |= pixpaper_send_data(panel, 0x22);
> +	ret |= pixpaper_send_data(panel, 0x78);
> +	ret |= pixpaper_send_data(panel, 0x0A);
> +	ret |= pixpaper_send_data(panel, 0x22);
> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_POWER_OFF_SEQUENCE);
> +	ret |= pixpaper_send_data(panel, 0x10);
> +	ret |= pixpaper_send_data(panel, 0x54);
> +	ret |= pixpaper_send_data(panel, 0x44);
> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_BOOSTER_SOFT_START);
> +	ret |= pixpaper_send_data(panel, 0x0F);
> +	ret |= pixpaper_send_data(panel, 0x0A);
> +	ret |= pixpaper_send_data(panel, 0x2F);
> +	ret |= pixpaper_send_data(panel, 0x25);
> +	ret |= pixpaper_send_data(panel, 0x22);
> +	ret |= pixpaper_send_data(panel, 0x2E);
> +	ret |= pixpaper_send_data(panel, 0x21);
> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_PLL_CONTROL);
> +	ret |= pixpaper_send_data(panel, 0x02);
> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_TEMP_SENSOR_CALIB);
> +	ret |= pixpaper_send_data(panel, 0x00);
> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_VCOM_INTERVAL);
> +	ret |= pixpaper_send_data(panel, 0x37);
> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_TCON_SETTING);
> +	ret |= pixpaper_send_data(panel, 0x02);
> +	ret |= pixpaper_send_data(panel, 0x02);
> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_RESOLUTION_SETTING);
> +	ret |= pixpaper_send_data(panel, 0x00);
> +	ret |= pixpaper_send_data(panel, 0x80);
> +	ret |= pixpaper_send_data(panel, 0x00);
> +	ret |= pixpaper_send_data(panel, 0xFA);
> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_GATE_SOURCE_START);
> +	ret |= pixpaper_send_data(panel, 0x00);
> +	ret |= pixpaper_send_data(panel, 0x00);
> +	ret |= pixpaper_send_data(panel, 0x00);
> +	ret |= pixpaper_send_data(panel, 0x00);
> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_AUTO_MEASURE_VCOM);
> +	ret |= pixpaper_send_data(panel, 0x1C);
> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_POWER_SAVING);
> +	ret |= pixpaper_send_data(panel, 0x22);
> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_CASCADE_SETTING);
> +	ret |= pixpaper_send_data(panel, 0x00);
> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_UNKNOWN_B4);
> +	ret |= pixpaper_send_data(panel, 0xD0);
> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_UNKNOWN_B5);
> +	ret |= pixpaper_send_data(panel, 0x03);
> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	ret |= pixpaper_send_cmd(panel, PIXPAPER_CMD_UNKNOWN_E9);
> +	ret |= pixpaper_send_data(panel, 0x01);
> +	if (ret)
> +		goto init_fail;
> +	pixpaper_wait_busy(panel);
> +
> +	dev_info(dev, "%s: Hardware initialization successful\n", __func__);

Never print this type of status messages. If nothing exceptional 
happens, you driver should be quite. At most, use drm_dbg() here.

> +	return 0;
> +
> +init_fail:
> +	dev_err(dev, "%s: Hardware initialization failed (err=%d)\n", __func__,
> +		ret);

Error messages are OK, but don't include the function name.

> +	return ret;
> +}
> +
> +static void pixpaper_crtc_atomic_enable(struct drm_crtc *crtc,
> +					struct drm_atomic_state *state)
> +{
> +	struct pixpaper_panel *panel =
> +		container_of(crtc, struct pixpaper_panel, crtc);

Instead of semi-manual upcast, please write a helper that upcasts from 
struct drm_device

struct pixpaper_panel *to_pixpaper_panel(struct drm_device *drm)
{
     return container_of(drm, struct pixpaper_panel, drm);
}

and call it with the CRTC's device

         to_pixpaper_panel(crtc->dev);

> +	struct drm_device *drm = &panel->drm;
> +	int ret;
> +
> +	dev_info(drm->dev, "%s: Enabling pipe\n", __func__);

Same here. The driver should just be quite.

> +
> +	ret = pixpaper_panel_hw_init(panel);

Do you really need a full hardware init for an atomic_enable? You should 
rather do this during device probing.

> +	if (ret) {
> +		dev_err(drm->dev, "Panel HW Init failed during enable: %d\n",
> +			ret);
> +		return;
> +	}
> +
> +	dev_info(drm->dev, "Sending Power ON (PON)\n");
> +	ret = pixpaper_send_cmd(panel, PIXPAPER_CMD_POWER_ON);
> +	if (ret) {
> +		dev_err(drm->dev, "Failed to send PON command: %d\n", ret);
> +		return;
> +	}
> +
> +	usleep_range(10000, 11000);
> +
> +	pixpaper_wait_busy(panel);
> +
> +	dev_info(drm->dev, "Panel enabled and powered on\n");
> +}
> +
> +static void pixpaper_crtc_atomic_disable(struct drm_crtc *crtc,
> +					 struct drm_atomic_state *state)
> +{
> +	struct pixpaper_panel *panel =
> +		container_of(crtc, struct pixpaper_panel, crtc);
> +	struct drm_device *drm = &panel->drm;
> +	int ret;
> +
> +	dev_dbg(drm->dev, "%s: Disabling pipe\n", __func__);
> +
> +	ret = pixpaper_send_cmd(panel, PIXPAPER_CMD_POWER_OFF);
> +	if (!ret) {
> +		usleep_range(10000, 11000);
> +		pixpaper_wait_busy(panel);
> +	} else {
> +		dev_warn(drm->dev, "Failed to send POF command: %d\n", ret);
> +	}
> +	dev_info(drm->dev, "Panel disabled\n");
> +}
> +
> +static u8 pack_pixels_to_byte(u32 *src_pixels, int i, int j,
> +			      struct drm_framebuffer *fb)
> +{
> +	u8 packed_byte = 0;
> +	int k;
> +
> +	for (k = 0; k < 4; k++) {
> +		int current_pixel_x = j * 4 + k;
> +		u8 two_bit_val;
> +
> +		if (current_pixel_x < PIXPAPER_WIDTH) {
> +			u32 pixel_offset =
> +				(i * (fb->pitches[0] / 4)) + current_pixel_x;
> +			u32 pixel = src_pixels[pixel_offset];
> +			u32 r = (pixel >> 16) & 0xFF;
> +			u32 g = (pixel >> 8) & 0xFF;
> +			u32 b = pixel & 0xFF;
> +			u32 gray_val =
> +				(r * 299 + g * 587 + b * 114 + 500) / 1000;
> +
> +			if (gray_val < 64)
> +				two_bit_val = 0b00;
> +			else if (gray_val < 128)
> +				two_bit_val = 0b01;
> +			else if (gray_val < 192)
> +				two_bit_val = 0b10;
> +			else
> +				two_bit_val = 0b11;
> +		} else {
> +			two_bit_val = 0b11;
> +		}
> +
> +		packed_byte |= two_bit_val << ((3 - k) * 2);
> +	}
> +
> +	return packed_byte;
> +}
> +
> +static void pixpaper_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_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(plane_state);
> +	struct drm_crtc *crtc = plane_state->crtc;
> +	struct pixpaper_panel *panel =
> +		container_of(crtc, struct pixpaper_panel, crtc);
> +
> +	struct drm_device *drm = &panel->drm;
> +	struct drm_framebuffer *fb = plane_state->fb;
> +	struct iosys_map map = shadow_plane_state->data[0];
> +	void *vaddr = map.vaddr;
> +	int i, j, ret = 0;
> +	u32 *src_pixels = NULL;
> +
> +	dev_info(drm->dev, "Starting frame update (phys=%dx%d, buf_w=%d)\n",
> +		 PIXPAPER_WIDTH, PIXPAPER_HEIGHT, PANEL_BUFFER_WIDTH);

Remove all these info statements please. At most, they should be drm_dbg().

> +
> +	if (!fb || !plane_state->visible) {
> +		dev_err(drm->dev,
> +			"No framebuffer or plane not visible, skipping update\n");
> +		return;
> +	}
> +
> +	if (ret) {
> +		dev_err(drm->dev, "Failed to vmap dma_buf\n");
> +		return;
> +	}
> +
> +	src_pixels = (u32 *)vaddr;
> +
> +	dev_info(drm->dev, "Sending DTM command\n");
> +	ret = pixpaper_send_cmd(panel, PIXPAPER_CMD_DATA_START_TRANSMISSION);
> +	if (ret)
> +		goto update_cleanup;
> +
> +	usleep_range(10000, 11000);
> +	pixpaper_wait_busy(panel);

That driver does quite a bit of waiting. Is that really necessary or in 
case?

> +
> +	dev_info(drm->dev,
> +		 "Panel idle after DTM command, starting data batch send.\n");
> +
> +	for (i = 0; i < PIXPAPER_HEIGHT; i++) {
> +		for (j = 0; j < PANEL_BUFFER_TWO_BYTES_PER_ROW; j++) {
> +			u8 packed_byte =
> +				pack_pixels_to_byte(src_pixels, i, j, fb);
> +
> +			pixpaper_wait_busy(panel);
> +			pixpaper_send_data(panel, packed_byte);
> +		}
> +	}

You're updating the full display AFAICT. That's not optimal, but OK if 
the hardware can't do better.


> +	pixpaper_wait_busy(panel);
> +
> +	dev_info(drm->dev, "Sending PON + 0x00 before DRF\n");
> +	ret = pixpaper_send_cmd(panel, PIXPAPER_CMD_POWER_ON);
> +	if (ret)
> +		goto update_cleanup;
> +	ret = pixpaper_send_data(panel, 0x00);
> +	if (ret) {
> +		dev_err(drm->dev,
> +			"Failed sending data after PON-before-DRF: %d\n", ret);
> +		goto update_cleanup;
> +	}
> +	usleep_range(10000, 11000);
> +	pixpaper_wait_busy(panel);
> +
> +	dev_info(drm->dev, "Triggering display refresh (DRF)\n");
> +	ret = pixpaper_send_cmd(panel, PIXPAPER_CMD_DISPLAY_REFRESH);
> +	if (ret)
> +		goto update_cleanup;
> +	ret = pixpaper_send_data(panel, 0x00);
> +	if (ret) {
> +		dev_err(drm->dev, "Failed sending data after DRF: %d\n", ret);
> +		goto update_cleanup;
> +	}
> +	usleep_range(10000, 11000);
> +	pixpaper_wait_busy(panel);
> +
> +	dev_info(drm->dev, "Frame update completed and refresh triggered\n");
> +
> +update_cleanup:
> +	if (ret && ret != -ETIMEDOUT)
> +		dev_err(drm->dev,
> +			"Frame update function failed with error %d\n", ret);
> +}
> +
> +static int pixpaper_connector_get_modes(struct drm_connector *connector)
> +{
> +	struct drm_display_mode *mode;
> +
> +	dev_info(connector->dev->dev, "%s: CALLED for connector %s (id: %d)\n",
> +		 __func__, connector->name, connector->base.id);
> +
> +	mode = drm_mode_create(connector->dev);
> +	if (!mode) {
> +		DRM_ERROR("Failed to create mode for connector %s\n",
> +			  connector->name);
> +		return 0;
> +	}
> +
> +	mode->hdisplay = PIXPAPER_WIDTH;
> +	mode->vdisplay = PIXPAPER_HEIGHT;
> +
> +	mode->htotal = mode->hdisplay + 80;
> +	mode->hsync_start = mode->hdisplay + 8;
> +	mode->hsync_end = mode->hdisplay + 8 + 32;
> +	mode->vtotal = mode->vdisplay + 10;
> +	mode->vsync_start = mode->vdisplay + 2;
> +	mode->vsync_end = mode->vdisplay + 2 + 2;
> +
> +	mode->clock = 6000;
> +
> +	mode->type = DRM_MODE_TYPE_DRIVER | DRM_MODE_TYPE_PREFERRED;
> +	drm_mode_set_name(mode);
> +
> +	if (drm_mode_validate_size(mode, connector->dev->mode_config.max_width,
> +				   connector->dev->mode_config.max_height) !=
> +	    MODE_OK) {
> +		DRM_WARN("%s: Mode %s (%dx%d) failed size validation against max %dx%d\n",
> +			 __func__, mode->name, mode->hdisplay, mode->vdisplay,
> +			 connector->dev->mode_config.max_width,
> +			 connector->dev->mode_config.max_height);
> +		drm_mode_destroy(connector->dev, mode);
> +		return 0;
> +	}
> +
> +	drm_mode_probed_add(connector, mode);
> +	dev_info(connector->dev->dev,
> +		 "%s: Added mode '%s' (%dx%d@%d) to connector %s\n", __func__,
> +		 mode->name, mode->hdisplay, mode->vdisplay,
> +		 drm_mode_vrefresh(mode), connector->name);
> +
> +	connector->display_info.width_mm = 30;
> +	connector->display_info.height_mm = 47;
> +
> +	return 1;
> +}
> +
> +DEFINE_DRM_GEM_DMA_FOPS(pixpaper_fops);
> +
> +static struct drm_driver pixpaper_drm_driver = {
> +	.driver_features = DRIVER_GEM | DRIVER_MODESET | DRIVER_ATOMIC,
> +	.fops = &pixpaper_fops,
> +	.name = "pixpaper",
> +	.desc = "DRM driver for PIXPAPER e-ink",
> +	.major = 1,
> +	.minor = 0,
> +	DRM_GEM_DMA_DRIVER_OPS_VMAP,
> +	DRM_FBDEV_DMA_DRIVER_OPS,

Is there a specific reason why you need GEM DMA? Since you're hardware 
doesn't use DMA, GEM SHMEM might be a better choice.

> +};
> +
> +static int pixpaper_mode_valid(struct drm_device *dev,
> +			       const struct drm_display_mode *mode)
> +{
> +	if (mode->hdisplay == PIXPAPER_WIDTH &&
> +	    mode->vdisplay == PIXPAPER_HEIGHT) {
> +		return MODE_OK;
> +	}
> +	dev_dbg(dev->dev, "Rejecting mode %dx%d (supports only %dx%d)\n",
> +		mode->hdisplay, mode->vdisplay, PIXPAPER_WIDTH,
> +		PIXPAPER_HEIGHT);
> +	return MODE_BAD;
> +}
> +
> +static const struct drm_mode_config_funcs pixpaper_mode_config_funcs = {
> +	.fb_create = drm_gem_fb_create_with_dirty,
> +	.mode_valid = pixpaper_mode_valid,
> +	.atomic_check = drm_atomic_helper_check,
> +	.atomic_commit = drm_atomic_helper_commit,
> +};
> +
> +static int pixpaper_probe(struct spi_device *spi)
> +{
> +	struct device *dev = &spi->dev;
> +	struct pixpaper_panel *panel;
> +	struct drm_device *drm;
> +	int ret;
> +
> +	dev_info(dev, "Probing PIXPAPER panel driver\n");
> +
> +	panel = devm_drm_dev_alloc(dev, &pixpaper_drm_driver,
> +				   struct pixpaper_panel, drm);
> +	if (IS_ERR(panel)) {
> +		ret = PTR_ERR(panel);
> +		dev_err(dev, "Failed to allocate DRM device: %d\n", ret);
> +		return ret;
> +	}
> +	drm = &panel->drm;
> +	panel->spi = spi;
> +	spi_set_drvdata(spi, panel);
> +
> +	spi->mode = SPI_MODE_0;
> +	spi->bits_per_word = 8;
> +
> +	if (!spi->max_speed_hz) {
> +		dev_warn(dev, "spi-max-frequency not specified in DT, using default %u Hz\n",
> +			 PIXPAPER_SPI_SPEED_DEFAULT);
> +		spi->max_speed_hz = PIXPAPER_SPI_SPEED_DEFAULT;
> +	} else {
> +		dev_info(dev, "Using spi-max-frequency from DT: %u Hz\n",
> +			 spi->max_speed_hz);
> +	}
> +
> +	ret = spi_setup(spi);
> +	if (ret < 0) {
> +		dev_err(dev, "SPI setup failed: %d\n", ret);
> +		return ret;
> +	}
> +	dev_info(dev, "SPI setup OK (mode=%d, speed=%u Hz, bpw=%d)\n",
> +		 spi->mode, spi->max_speed_hz, spi->bits_per_word);
> +
> +	if (!dev->dma_mask)
> +		dev->dma_mask = &dev->coherent_dma_mask;
> +	ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32));
> +	if (ret) {
> +		dev_err(dev, "Failed to set DMA mask: %d\n", ret);
> +		return ret;
> +	}
> +	dev_dbg(dev, "DMA mask set\n");
> +
> +	panel->reset = devm_gpiod_get(dev, "reset", GPIOD_OUT_HIGH);
> +	if (IS_ERR(panel->reset))
> +		return dev_err_probe(dev, PTR_ERR(panel->reset),
> +				     "Failed to get 'reset' GPIO\n");
> +	panel->busy = devm_gpiod_get(dev, "busy", GPIOD_IN);
> +	if (IS_ERR(panel->busy))
> +		return dev_err_probe(dev, PTR_ERR(panel->busy),
> +				     "Failed to get 'busy' GPIO\n");
> +	panel->dc = devm_gpiod_get(dev, "dc", GPIOD_OUT_HIGH);
> +	if (IS_ERR(panel->dc))
> +		return dev_err_probe(dev, PTR_ERR(panel->dc),
> +				     "Failed to get 'dc' GPIO\n");
> +	dev_info(dev, "All required GPIOs obtained successfully.\n");
> +
> +	ret = drmm_mode_config_init(drm);
> +	if (ret)
> +		return ret;
> +	drm->mode_config.funcs = &pixpaper_mode_config_funcs;
> +	drm->mode_config.min_width = PIXPAPER_WIDTH;
> +	drm->mode_config.max_width = PIXPAPER_WIDTH;
> +	drm->mode_config.min_height = PIXPAPER_HEIGHT;
> +	drm->mode_config.max_height = PIXPAPER_HEIGHT;
> +
> +	ret = drm_universal_plane_init(drm, &panel->plane, 1, &pixpaper_plane_funcs,
> +		(const uint32_t[]){ DRM_FORMAT_XRGB8888 }, 1, NULL,
> +		DRM_PLANE_TYPE_PRIMARY, NULL);

> +	drm_plane_enable_fb_damage_clips(&panel->plane);

Since the driver always updates the full display anyway, you don't need 
to enable damage clipping.

> +	if (ret)
> +		return ret;
> +	drm_plane_helper_add(&panel->plane, &pixpaper_plane_helper_funcs);
> +
> +	ret = drm_crtc_init_with_planes(drm, &panel->crtc, &panel->plane, NULL,
> +					&pixpaper_crtc_funcs, NULL);
> +	if (ret)
> +		return ret;
> +	drm_crtc_helper_add(&panel->crtc, &pixpaper_crtc_helper_funcs);
> +
> +	ret = drm_encoder_init(drm, &panel->encoder, &pixpaper_encoder_funcs,
> +			       DRM_MODE_ENCODER_DAC, NULL);

ENCODER_DAC is for VGA connectors. Rather use ENCODER_NONE here.

> +	if (ret)
> +		return ret;
> +	panel->encoder.possible_crtcs = drm_crtc_mask(&panel->crtc);
> +
> +	ret = drm_connector_init(drm, &panel->connector,
> +				 &pixpaper_connector_funcs,
> +				 DRM_MODE_CONNECTOR_SPI);
> +	if (ret)
> +		return ret;
> +
> +	drm_connector_helper_add(&panel->connector,
> +				 &pixpaper_connector_helper_funcs);
> +	drm_connector_attach_encoder(&panel->connector, &panel->encoder);
> +
> +	drm_mode_config_reset(drm);
> +
> +	ret = drm_dev_register(drm, 0);
> +	if (ret)
> +		return ret;
> +
> +	drm_client_setup(drm, NULL);
> +
> +	dev_info(dev, "Initialized PIXPAPER panel driver successfully\n");
> +	return 0;
> +}
> +
> +static void pixpaper_remove(struct spi_device *spi)
> +{
> +	struct pixpaper_panel *panel = spi_get_drvdata(spi);
> +
> +	if (!panel)
> +		return;
> +
> +	dev_info(&spi->dev, "Removing PIXPAPER panel driver\n");
> +
> +	drm_dev_unplug(&panel->drm);

This signals to DRM that the hardware device has been removed. You 
should put drm_dev_enter() and drm_dev_exit() to the top and bottom of 
each of the DRM callbacks. The driver will then not try to access the 
device.

Best regards
Thomas

> +	drm_atomic_helper_shutdown(&panel->drm);
> +}
> +
> +static const struct spi_device_id pixpaper_ids[] = { { "pixpaper", 0 }, {} };
> +MODULE_DEVICE_TABLE(spi, pixpaper_ids);
> +
> +static const struct of_device_id pixpaper_dt_ids[] = {
> +	{ .compatible = "mayqueen,pixpaper" },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(of, pixpaper_dt_ids);
> +
> +static struct spi_driver pixpaper_spi_driver = {
> +	.driver = {
> +		.name = "pixpaper",
> +		.of_match_table = pixpaper_dt_ids,
> +	},
> +	.id_table = pixpaper_ids,
> +	.probe = pixpaper_probe,
> +	.remove = pixpaper_remove,
> +};
> +
> +module_spi_driver(pixpaper_spi_driver);
> +
> +MODULE_AUTHOR("LiangCheng Wang");
> +MODULE_DESCRIPTION("DRM SPI driver for PIXPAPER e-ink panel");
> +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)