[PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Javier Martinez Canillas]

Add a DRM driver for SSD1305, SSD1306, SSD1307 and SSD1309 Solomon OLED
controllers that can be programmed via an I2C interface. This is a port
of the ssd1307fb driver that already supports these devices.

A Device Tree binding is not added because the DRM driver is compatible
with the existing binding for the ssd1307fb driver.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
---

 drivers/gpu/drm/tiny/Kconfig   |  12 +
 drivers/gpu/drm/tiny/Makefile  |   1 +
 drivers/gpu/drm/tiny/ssd1307.c | 976 +++++++++++++++++++++++++++++++++
 3 files changed, 989 insertions(+)
 create mode 100644 drivers/gpu/drm/tiny/ssd1307.c

diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig
index 712e0004e96e..25c9c013bcda 100644
--- a/drivers/gpu/drm/tiny/Kconfig
+++ b/drivers/gpu/drm/tiny/Kconfig
@@ -157,6 +157,18 @@ config TINYDRM_REPAPER
 
 	  If M is selected the module will be called repaper.
 
+config TINYDRM_SSD1307
+	tristate "DRM support for Solomon SSD1307 OLED displays"
+	depends on DRM && I2C
+	select DRM_KMS_HELPER
+	select DRM_GEM_SHMEM_HELPER
+	select BACKLIGHT_CLASS_DEVICE
+	help
+	  DRM driver for the SSD1305, SSD1306, SSD1307 and SSD1309 Solomon
+	  OLED controllers that can be programmed via an I2C interface.
+
+	  If M is selected the module will be called ssd1307.
+
 config TINYDRM_ST7586
 	tristate "DRM support for Sitronix ST7586 display panels"
 	depends on DRM && SPI
diff --git a/drivers/gpu/drm/tiny/Makefile b/drivers/gpu/drm/tiny/Makefile
index 5d5505d40e7b..38c4c1111e96 100644
--- a/drivers/gpu/drm/tiny/Makefile
+++ b/drivers/gpu/drm/tiny/Makefile
@@ -12,5 +12,6 @@ obj-$(CONFIG_TINYDRM_ILI9341)		+= ili9341.o
 obj-$(CONFIG_TINYDRM_ILI9486)		+= ili9486.o
 obj-$(CONFIG_TINYDRM_MI0283QT)		+= mi0283qt.o
 obj-$(CONFIG_TINYDRM_REPAPER)		+= repaper.o
+obj-$(CONFIG_TINYDRM_SSD1307)		+= ssd1307.o
 obj-$(CONFIG_TINYDRM_ST7586)		+= st7586.o
 obj-$(CONFIG_TINYDRM_ST7735R)		+= st7735r.o
diff --git a/drivers/gpu/drm/tiny/ssd1307.c b/drivers/gpu/drm/tiny/ssd1307.c
new file mode 100644
index 000000000000..4ea223674587
--- /dev/null
+++ b/drivers/gpu/drm/tiny/ssd1307.c
@@ -0,0 +1,976 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * DRM driver for Solomon SSD1307 OLED displays
+ *
+ * Copyright 2022 Red Hat Inc.
+ *
+ * Based on drivers/video/fbdev/ssd1307fb.c
+ * Copyright 2012 Free Electrons
+ *
+ */
+
+#include <linux/backlight.h>
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/property.h>
+#include <linux/pwm.h>
+#include <linux/regulator/consumer.h>
+
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_damage_helper.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_fb_cma_helper.h>
+#include <drm/drm_fb_helper.h>
+#include <drm/drm_format_helper.h>
+#include <drm/drm_gem_atomic_helper.h>
+#include <drm/drm_gem_framebuffer_helper.h>
+#include <drm/drm_gem_shmem_helper.h>
+#include <drm/drm_managed.h>
+#include <drm/drm_modes.h>
+#include <drm/drm_rect.h>
+#include <drm/drm_probe_helper.h>
+#include <drm/drm_simple_kms_helper.h>
+
+#define DRIVER_NAME	"ssd1307"
+#define DRIVER_DESC	"DRM driver for Solomon SSD1307 OLED displays"
+#define DRIVER_DATE	"20220131"
+#define DRIVER_MAJOR	1
+#define DRIVER_MINOR	0
+
+#define SSD1307_DATA				0x40
+#define SSD1307_COMMAND			0x80
+
+#define SSD1307_SET_ADDRESS_MODE		0x20
+#define SSD1307_SET_ADDRESS_MODE_HORIZONTAL	(0x00)
+#define SSD1307_SET_ADDRESS_MODE_VERTICAL	(0x01)
+#define SSD1307_SET_ADDRESS_MODE_PAGE		(0x02)
+#define SSD1307_SET_COL_RANGE			0x21
+#define SSD1307_SET_PAGE_RANGE			0x22
+#define SSD1307_CONTRAST			0x81
+#define SSD1307_SET_LOOKUP_TABLE		0x91
+#define SSD1307_CHARGE_PUMP			0x8d
+#define SSD1307_SEG_REMAP_ON			0xa1
+#define SSD1307_DISPLAY_OFF			0xae
+#define SSD1307_SET_MULTIPLEX_RATIO		0xa8
+#define SSD1307_DISPLAY_ON			0xaf
+#define SSD1307_START_PAGE_ADDRESS		0xb0
+#define SSD1307_SET_DISPLAY_OFFSET		0xd3
+#define SSD1307_SET_CLOCK_FREQ			0xd5
+#define SSD1307_SET_AREA_COLOR_MODE		0xd8
+#define SSD1307_SET_PRECHARGE_PERIOD		0xd9
+#define SSD1307_SET_COM_PINS_CONFIG		0xda
+#define SSD1307_SET_VCOMH			0xdb
+
+#define MAX_CONTRAST 255
+
+struct ssd1307_deviceinfo {
+	u32 default_vcomh;
+	u32 default_dclk_div;
+	u32 default_dclk_frq;
+	int need_pwm;
+	int need_chargepump;
+};
+
+struct ssd1307_device {
+	struct drm_device drm;
+	struct drm_simple_display_pipe pipe;
+	struct drm_display_mode mode;
+	struct drm_connector connector;
+	struct i2c_client *client;
+
+	const struct ssd1307_deviceinfo *device_info;
+
+	unsigned area_color_enable : 1;
+	unsigned com_invdir : 1;
+	unsigned com_lrremap : 1;
+	unsigned com_seq : 1;
+	unsigned lookup_table_set : 1;
+	unsigned low_power : 1;
+	unsigned seg_remap : 1;
+	u32 com_offset;
+	u32 contrast;
+	u32 dclk_div;
+	u32 dclk_frq;
+	u32 height;
+	u8 lookup_table[4];
+	u32 page_offset;
+	u32 col_offset;
+	u32 prechargep1;
+	u32 prechargep2;
+
+	struct backlight_device *bl_dev;
+	struct pwm_device *pwm;
+	struct gpio_desc *reset;
+	struct regulator *vbat_reg;
+	u32 vcomh;
+	u32 width;
+	/* Cached address ranges */
+	u8 col_start;
+	u8 col_end;
+	u8 page_start;
+	u8 page_end;
+};
+
+struct ssd1307_array {
+	u8	type;
+	u8	data[];
+};
+
+static inline struct ssd1307_device *drm_to_ssd1307(struct drm_device *drm)
+{
+	return container_of(drm, struct ssd1307_device, drm);
+}
+
+static struct ssd1307_array *ssd1307_alloc_array(u32 len, u8 type)
+{
+	struct ssd1307_array *array;
+
+	array = kzalloc(sizeof(struct ssd1307_array) + len, GFP_KERNEL);
+	if (!array)
+		return NULL;
+
+	array->type = type;
+
+	return array;
+}
+
+static int ssd1307_write_array(struct i2c_client *client,
+			       struct ssd1307_array *array, u32 len)
+{
+	int ret;
+
+	len += sizeof(struct ssd1307_array);
+
+	ret = i2c_master_send(client, (u8 *)array, len);
+	if (ret != len) {
+		dev_err(&client->dev, "Couldn't send I2C command.\n");
+		return ret;
+	}
+
+	return 0;
+}
+
+static inline int ssd1307_write_cmd(struct i2c_client *client, u8 cmd)
+{
+	struct ssd1307_array *array;
+	int ret;
+
+	array = ssd1307_alloc_array(1, SSD1307_COMMAND);
+	if (!array)
+		return -ENOMEM;
+
+	array->data[0] = cmd;
+
+	ret = ssd1307_write_array(client, array, 1);
+	kfree(array);
+
+	return ret;
+}
+
+static int ssd1307_set_col_range(struct ssd1307_device *ssd1307,
+				 u8 col_start, u8 cols)
+{
+	u8 col_end = col_start + cols - 1;
+	int ret;
+
+	if (col_start == ssd1307->col_start && col_end == ssd1307->col_end)
+		return 0;
+
+	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_COL_RANGE);
+	if (ret < 0)
+		return ret;
+
+	ret = ssd1307_write_cmd(ssd1307->client, col_start);
+	if (ret < 0)
+		return ret;
+
+	ret = ssd1307_write_cmd(ssd1307->client, col_end);
+	if (ret < 0)
+		return ret;
+
+	ssd1307->col_start = col_start;
+	ssd1307->col_end = col_end;
+	return 0;
+}
+
+static int ssd1307_set_page_range(struct ssd1307_device *ssd1307,
+				  u8 page_start, u8 pages)
+{
+	u8 page_end = page_start + pages - 1;
+	int ret;
+
+	if (page_start == ssd1307->page_start && page_end == ssd1307->page_end)
+		return 0;
+
+	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_PAGE_RANGE);
+	if (ret < 0)
+		return ret;
+
+	ret = ssd1307_write_cmd(ssd1307->client, page_start);
+	if (ret < 0)
+		return ret;
+
+	ret = ssd1307_write_cmd(ssd1307->client, page_end);
+	if (ret < 0)
+		return ret;
+
+	ssd1307->page_start = page_start;
+	ssd1307->page_end = page_end;
+	return 0;
+}
+
+static int ssd1307_update_display(struct ssd1307_device *ssd1307, u8 *buf,
+				  u32 width, u32 height)
+{
+	struct ssd1307_array *array;
+	unsigned int line_length = DIV_ROUND_UP(width, 8);
+	unsigned int pages = DIV_ROUND_UP(height, 8);
+	u32 array_idx = 0;
+	int ret, i, j, k;
+
+	array = ssd1307_alloc_array(width * pages, SSD1307_DATA);
+	if (!array)
+		return -ENOMEM;
+
+	/*
+	 * The screen is divided in pages, each having a height of 8
+	 * pixels, and the width of the screen. When sending a byte of
+	 * data to the controller, it gives the 8 bits for the current
+	 * column. I.e, the first byte are the 8 bits of the first
+	 * column, then the 8 bits for the second column, etc.
+	 *
+	 *
+	 * Representation of the screen, assuming it is 5 bits
+	 * wide. Each letter-number combination is a bit that controls
+	 * one pixel.
+	 *
+	 * A0 A1 A2 A3 A4
+	 * B0 B1 B2 B3 B4
+	 * C0 C1 C2 C3 C4
+	 * D0 D1 D2 D3 D4
+	 * E0 E1 E2 E3 E4
+	 * F0 F1 F2 F3 F4
+	 * G0 G1 G2 G3 G4
+	 * H0 H1 H2 H3 H4
+	 *
+	 * If you want to update this screen, you need to send 5 bytes:
+	 *  (1) A0 B0 C0 D0 E0 F0 G0 H0
+	 *  (2) A1 B1 C1 D1 E1 F1 G1 H1
+	 *  (3) A2 B2 C2 D2 E2 F2 G2 H2
+	 *  (4) A3 B3 C3 D3 E3 F3 G3 H3
+	 *  (5) A4 B4 C4 D4 E4 F4 G4 H4
+	 */
+
+	ret = ssd1307_set_col_range(ssd1307, ssd1307->col_offset, width);
+	if (ret < 0)
+		goto out_free;
+
+	ret = ssd1307_set_page_range(ssd1307, ssd1307->page_offset / 8, pages);
+	if (ret < 0)
+		goto out_free;
+
+	for (i = 0; i < pages; i++) {
+		int m = 8;
+
+		/* Last page may be partial */
+		if (8 * (i + 1) > ssd1307->height)
+			m = ssd1307->height % 8;
+		for (j = 0; j < width; j++) {
+			u8 data = 0;
+
+			for (k = 0; k < m; k++) {
+				u8 byte = buf[(8 * i + k) * line_length +
+					       j / 8];
+				u8 bit = (byte >> (j % 8)) & 1;
+
+				data |= bit << k;
+			}
+			array->data[array_idx++] = data;
+		}
+	}
+
+	ret = ssd1307_write_array(ssd1307->client, array, width * pages);
+
+out_free:
+	kfree(array);
+	return ret;
+}
+
+static void ssd1307_clear_screen(struct ssd1307_device *ssd1307, u32 width, u32 height)
+{
+	u8 *buf = NULL;
+
+	buf = kmalloc_array(width, height, GFP_KERNEL);
+	if (!buf)
+		return;
+
+	/* Clear screen to black if disabled */
+	memset(buf, 0, width * height);
+
+	ssd1307_update_display(ssd1307, buf, width, height);
+}
+
+static int ssd1307_fb_blit_rect(struct drm_framebuffer *fb, const struct dma_buf_map *map,
+				struct drm_rect *rect)
+{
+	struct ssd1307_device *ssd1307 = drm_to_ssd1307(fb->dev);
+	void *vmap = map->vaddr; /* TODO: Use mapping abstraction properly */
+	int ret = 0;
+	u8 *buf = NULL;
+
+	buf = kmalloc_array(fb->width, fb->height, GFP_KERNEL);
+	if (!buf) {
+		ret = -ENOMEM;
+		goto out_exit;
+	}
+
+	drm_fb_xrgb8888_to_gray8(buf, 0, vmap, fb, rect);
+
+	drm_fb_gray8_to_mono_reversed(buf, buf, rect);
+
+	ssd1307_update_display(ssd1307, buf, fb->width, fb->height);
+
+	kfree(buf);
+out_exit:
+	return ret;
+}
+
+static int ssd1307_display_pipe_mode_valid(struct drm_simple_display_pipe *pipe,
+						   const struct drm_display_mode *mode)
+{
+	struct ssd1307_device *ssd1307 = drm_to_ssd1307(pipe->crtc.dev);
+
+	if (mode->hdisplay != ssd1307->mode.hdisplay &&
+	    mode->vdisplay != ssd1307->mode.vdisplay)
+		return MODE_ONE_SIZE;
+	else if (mode->hdisplay != ssd1307->mode.hdisplay)
+		return MODE_ONE_WIDTH;
+	else if (mode->vdisplay != ssd1307->mode.vdisplay)
+		return MODE_ONE_HEIGHT;
+
+	return MODE_OK;
+}
+
+static void ssd1307_display_pipe_enable(struct drm_simple_display_pipe *pipe,
+				       struct drm_crtc_state *crtc_state,
+				       struct drm_plane_state *plane_state)
+{
+	struct ssd1307_device *ssd1307 = drm_to_ssd1307(pipe->crtc.dev);
+	struct drm_device *drm = &ssd1307->drm;
+	int idx;
+
+	if (!drm_dev_enter(drm, &idx))
+		return;
+
+	backlight_enable(ssd1307->bl_dev);
+
+	ssd1307_write_cmd(ssd1307->client, SSD1307_DISPLAY_ON);
+
+	drm_dev_exit(idx);
+}
+
+static void ssd1307_display_pipe_disable(struct drm_simple_display_pipe *pipe)
+{
+	struct ssd1307_device *ssd1307 = drm_to_ssd1307(pipe->crtc.dev);
+	struct drm_device *drm = &ssd1307->drm;
+	int idx;
+
+	if (!drm_dev_enter(drm, &idx))
+		return;
+
+	ssd1307_clear_screen(ssd1307, ssd1307->width, ssd1307->height);
+
+	ssd1307_write_cmd(ssd1307->client, SSD1307_DISPLAY_OFF);
+
+	backlight_disable(ssd1307->bl_dev);
+
+	drm_dev_exit(idx);
+}
+
+static void ssd1307_display_pipe_update(struct drm_simple_display_pipe *pipe,
+					struct drm_plane_state *old_plane_state)
+{
+	struct ssd1307_device *ssd1307 = drm_to_ssd1307(pipe->crtc.dev);
+	struct drm_plane_state *plane_state = pipe->plane.state;
+	struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(plane_state);
+	struct drm_framebuffer *fb = plane_state->fb;
+	struct drm_device *drm = &ssd1307->drm;
+	struct drm_rect rect;
+	int idx;
+
+	if (!fb)
+		return;
+
+	if (!pipe->crtc.state->active)
+		return;
+
+	if (!drm_dev_enter(drm, &idx))
+		return;
+
+	if (drm_atomic_helper_damage_merged(old_plane_state, plane_state, &rect))
+		ssd1307_fb_blit_rect(plane_state->fb, &shadow_plane_state->data[0], &rect);
+
+	drm_dev_exit(idx);
+}
+
+static const struct drm_simple_display_pipe_funcs ssd1307_pipe_funcs = {
+	.mode_valid = ssd1307_display_pipe_mode_valid,
+	.enable = ssd1307_display_pipe_enable,
+	.disable = ssd1307_display_pipe_disable,
+	.update = ssd1307_display_pipe_update,
+	DRM_GEM_SIMPLE_DISPLAY_PIPE_SHADOW_PLANE_FUNCS,
+};
+
+static int ssd1307_connector_get_modes(struct drm_connector *connector)
+{
+	struct ssd1307_device *ssd1307 = drm_to_ssd1307(connector->dev);
+	struct drm_display_mode *mode;
+
+	mode = drm_mode_duplicate(connector->dev, &ssd1307->mode);
+	if (!mode) {
+		DRM_ERROR("Failed to duplicate mode\n");
+		return 0;
+	}
+
+	connector->display_info.width_mm = mode->width_mm;
+	connector->display_info.height_mm = mode->height_mm;
+	connector->display_info.bpc = 32;
+
+	drm_mode_set_name(mode);
+	mode->type |= DRM_MODE_TYPE_PREFERRED;
+	drm_mode_probed_add(connector, mode);
+
+	return 1;
+}
+
+static const struct drm_connector_helper_funcs ssd1307_connector_helper_funcs = {
+	.get_modes = ssd1307_connector_get_modes,
+};
+
+static const struct drm_connector_funcs ssd1307_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 ssd1307_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 ssd1307_formats[] = {
+	DRM_FORMAT_XRGB8888,
+};
+
+DEFINE_DRM_GEM_FOPS(ssd1307_fops);
+
+static const struct drm_driver ssd1307_drm_driver = {
+	DRM_GEM_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			= &ssd1307_fops,
+};
+
+static int ssd1307_pwm_enable(struct ssd1307_device *ssd1307)
+{
+	struct pwm_state pwmstate;
+
+	ssd1307->pwm = pwm_get(&ssd1307->client->dev, NULL);
+	if (IS_ERR(ssd1307->pwm)) {
+		dev_err(&ssd1307->client->dev, "Could not get PWM from device tree!\n");
+		return PTR_ERR(ssd1307->pwm);
+	}
+
+	pwm_init_state(ssd1307->pwm, &pwmstate);
+	pwm_set_relative_duty_cycle(&pwmstate, 50, 100);
+	pwm_apply_state(ssd1307->pwm, &pwmstate);
+
+	/* Enable the PWM */
+	pwm_enable(ssd1307->pwm);
+
+	dev_dbg(&ssd1307->client->dev, "Using PWM%d with a %lluns period.\n",
+		ssd1307->pwm->pwm, pwm_get_period(ssd1307->pwm));
+
+	return 0;
+}
+
+static int ssd1307_init(struct ssd1307_device *ssd1307)
+{
+	u32 precharge, dclk, com_invdir, compins;
+	int ret;
+
+	/* Set initial contrast */
+	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_CONTRAST);
+	if (ret < 0)
+		return ret;
+
+	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->contrast);
+	if (ret < 0)
+		return ret;
+
+	/* Set segment re-map */
+	if (ssd1307->seg_remap) {
+		ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SEG_REMAP_ON);
+		if (ret < 0)
+			return ret;
+	}
+
+	/* Set COM direction */
+	com_invdir = 0xc0 | ssd1307->com_invdir << 3;
+	ret = ssd1307_write_cmd(ssd1307->client,  com_invdir);
+	if (ret < 0)
+		return ret;
+
+	/* Set multiplex ratio value */
+	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_MULTIPLEX_RATIO);
+	if (ret < 0)
+		return ret;
+
+	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->height - 1);
+	if (ret < 0)
+		return ret;
+
+	/* set display offset value */
+	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_DISPLAY_OFFSET);
+	if (ret < 0)
+		return ret;
+
+	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->com_offset);
+	if (ret < 0)
+		return ret;
+
+	/* Set clock frequency */
+	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_CLOCK_FREQ);
+	if (ret < 0)
+		return ret;
+
+	dclk = ((ssd1307->dclk_div - 1) & 0xf) | (ssd1307->dclk_frq & 0xf) << 4;
+	ret = ssd1307_write_cmd(ssd1307->client, dclk);
+	if (ret < 0)
+		return ret;
+
+	/* Set Area Color Mode ON/OFF & Low Power Display Mode */
+	if (ssd1307->area_color_enable || ssd1307->low_power) {
+		u32 mode;
+
+		ret = ssd1307_write_cmd(ssd1307->client,
+					SSD1307_SET_AREA_COLOR_MODE);
+		if (ret < 0)
+			return ret;
+
+		mode = (ssd1307->area_color_enable ? 0x30 : 0) |
+			(ssd1307->low_power ? 5 : 0);
+		ret = ssd1307_write_cmd(ssd1307->client, mode);
+		if (ret < 0)
+			return ret;
+	}
+
+	/* Set precharge period in number of ticks from the internal clock */
+	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_PRECHARGE_PERIOD);
+	if (ret < 0)
+		return ret;
+
+	precharge = (ssd1307->prechargep1 & 0xf) | (ssd1307->prechargep2 & 0xf) << 4;
+	ret = ssd1307_write_cmd(ssd1307->client, precharge);
+	if (ret < 0)
+		return ret;
+
+	/* Set COM pins configuration */
+	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_COM_PINS_CONFIG);
+	if (ret < 0)
+		return ret;
+
+	compins = 0x02 | !ssd1307->com_seq << 4 | ssd1307->com_lrremap << 5;
+	ret = ssd1307_write_cmd(ssd1307->client, compins);
+	if (ret < 0)
+		return ret;
+
+	/* Set VCOMH */
+	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_VCOMH);
+	if (ret < 0)
+		return ret;
+
+	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->vcomh);
+	if (ret < 0)
+		return ret;
+
+	/* Turn on the DC-DC Charge Pump */
+	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_CHARGE_PUMP);
+	if (ret < 0)
+		return ret;
+
+	ret = ssd1307_write_cmd(ssd1307->client,
+		BIT(4) | (ssd1307->device_info->need_chargepump ? BIT(2) : 0));
+	if (ret < 0)
+		return ret;
+
+	/* Set lookup table */
+	if (ssd1307->lookup_table_set) {
+		int i;
+
+		ret = ssd1307_write_cmd(ssd1307->client,
+					SSD1307_SET_LOOKUP_TABLE);
+		if (ret < 0)
+			return ret;
+
+		for (i = 0; i < ARRAY_SIZE(ssd1307->lookup_table); ++i) {
+			u8 val = ssd1307->lookup_table[i];
+
+			if (val < 31 || val > 63)
+				dev_warn(&ssd1307->client->dev,
+					 "lookup table index %d value out of range 31 <= %d <= 63\n",
+					 i, val);
+			ret = ssd1307_write_cmd(ssd1307->client, val);
+			if (ret < 0)
+				return ret;
+		}
+	}
+
+	/* Switch to horizontal addressing mode */
+	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_ADDRESS_MODE);
+	if (ret < 0)
+		return ret;
+
+	ret = ssd1307_write_cmd(ssd1307->client,
+				SSD1307_SET_ADDRESS_MODE_HORIZONTAL);
+	if (ret < 0)
+		return ret;
+
+	ssd1307_clear_screen(ssd1307, ssd1307->width, ssd1307->height);
+
+	/* Turn on the display */
+	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_DISPLAY_ON);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+static int ssd1307_update_bl(struct backlight_device *bdev)
+{
+	struct ssd1307_device *ssd1307 = bl_get_data(bdev);
+	int brightness = bdev->props.brightness;
+	int ret;
+
+	ssd1307->contrast = brightness;
+
+	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_CONTRAST);
+	if (ret < 0)
+		return ret;
+
+	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->contrast);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+static int ssd1307_get_brightness(struct backlight_device *bdev)
+{
+	struct ssd1307_device *ssd1307 = bl_get_data(bdev);
+
+	return ssd1307->contrast;
+}
+
+static const struct backlight_ops ssd1307fb_bl_ops = {
+	.update_status	= ssd1307_update_bl,
+	.get_brightness	= ssd1307_get_brightness,
+};
+
+static void ssd1307_reset(struct ssd1307_device *ssd1307)
+{
+	/* Reset the screen */
+	gpiod_set_value_cansleep(ssd1307->reset, 1);
+	udelay(4);
+	gpiod_set_value_cansleep(ssd1307->reset, 0);
+	udelay(4);
+}
+
+static void ssd1307_parse_properties(struct ssd1307_device *ssd1307)
+{
+	struct device *dev = &ssd1307->client->dev;
+
+	if (device_property_read_u32(dev, "solomon,width", &ssd1307->width))
+		ssd1307->width = 96;
+
+	if (device_property_read_u32(dev, "solomon,height", &ssd1307->height))
+		ssd1307->height = 16;
+
+	if (device_property_read_u32(dev, "solomon,page-offset", &ssd1307->page_offset))
+		ssd1307->page_offset = 1;
+
+	if (device_property_read_u32(dev, "solomon,col-offset", &ssd1307->col_offset))
+		ssd1307->col_offset = 0;
+
+	if (device_property_read_u32(dev, "solomon,com-offset", &ssd1307->com_offset))
+		ssd1307->com_offset = 0;
+
+	if (device_property_read_u32(dev, "solomon,prechargep1", &ssd1307->prechargep1))
+		ssd1307->prechargep1 = 2;
+
+	if (device_property_read_u32(dev, "solomon,prechargep2", &ssd1307->prechargep2))
+		ssd1307->prechargep2 = 2;
+
+	if (!device_property_read_u8_array(dev, "solomon,lookup-table",
+					   ssd1307->lookup_table,
+					   ARRAY_SIZE(ssd1307->lookup_table)))
+		ssd1307->lookup_table_set = 1;
+
+	ssd1307->seg_remap = !device_property_read_bool(dev, "solomon,segment-no-remap");
+	ssd1307->com_seq = device_property_read_bool(dev, "solomon,com-seq");
+	ssd1307->com_lrremap = device_property_read_bool(dev, "solomon,com-lrremap");
+	ssd1307->com_invdir = device_property_read_bool(dev, "solomon,com-invdir");
+	ssd1307->area_color_enable =
+		device_property_read_bool(dev, "solomon,area-color-enable");
+	ssd1307->low_power = device_property_read_bool(dev, "solomon,low-power");
+
+	ssd1307->contrast = 127;
+	ssd1307->vcomh = ssd1307->device_info->default_vcomh;
+
+	/* Setup display timing */
+	if (device_property_read_u32(dev, "solomon,dclk-div", &ssd1307->dclk_div))
+		ssd1307->dclk_div = ssd1307->device_info->default_dclk_div;
+	if (device_property_read_u32(dev, "solomon,dclk-frq", &ssd1307->dclk_frq))
+		ssd1307->dclk_frq = ssd1307->device_info->default_dclk_frq;
+}
+
+static void ssd1307_set_mode(struct ssd1307_device *ssd1307)
+{
+	struct drm_display_mode *mode = &ssd1307->mode;
+	struct drm_device *drm = &ssd1307->drm;
+
+	mode->type = DRM_MODE_TYPE_DRIVER;
+	mode->clock = 1;
+	mode->hdisplay = mode->htotal = ssd1307->width;
+	mode->hsync_start = mode->hsync_end = ssd1307->width;
+	mode->vdisplay = mode->vtotal = ssd1307->height;
+	mode->vsync_start = mode->vsync_end = ssd1307->height;
+	mode->width_mm = 27;
+	mode->height_mm = 27;
+
+	drm->mode_config.min_width = ssd1307->width;
+	drm->mode_config.max_width = ssd1307->width;
+	drm->mode_config.min_height = ssd1307->height;
+	drm->mode_config.max_height = ssd1307->height;
+	drm->mode_config.preferred_depth = 32;
+	drm->mode_config.funcs = &ssd1307_mode_config_funcs;
+}
+
+static int ssd1307_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct ssd1307_device *ssd1307;
+	struct backlight_device *bl;
+	struct drm_device *drm;
+	char bl_name[12];
+	int ret;
+
+	ssd1307 = devm_drm_dev_alloc(dev, &ssd1307_drm_driver,
+				 struct ssd1307_device, drm);
+	if (IS_ERR(ssd1307))
+		return PTR_ERR(ssd1307);
+
+	drm = &ssd1307->drm;
+
+	ret = drmm_mode_config_init(drm);
+	if (ret)
+		return ret;
+
+	ssd1307->client = client;
+
+	ssd1307->device_info = device_get_match_data(dev);
+
+	ssd1307_parse_properties(ssd1307);
+
+	ssd1307_set_mode(ssd1307);
+
+	ssd1307->reset = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW);
+	if (IS_ERR(ssd1307->reset)) {
+		dev_err(dev, "failed to get reset gpio: %ld\n",
+			PTR_ERR(ssd1307->reset));
+		return PTR_ERR(ssd1307->reset);
+	}
+
+	ssd1307->vbat_reg = devm_regulator_get_optional(dev, "vbat");
+	if (IS_ERR(ssd1307->vbat_reg)) {
+		ret = PTR_ERR(ssd1307->vbat_reg);
+		if (ret == -ENODEV) {
+			ssd1307->vbat_reg = NULL;
+		} else {
+			dev_err(dev, "failed to get VBAT regulator: %d\n", ret);
+			return ret;
+		}
+	}
+
+	drm_connector_helper_add(&ssd1307->connector, &ssd1307_connector_helper_funcs);
+	ret = drm_connector_init(drm, &ssd1307->connector, &ssd1307_connector_funcs,
+				 DRM_MODE_CONNECTOR_Unknown);
+	if (ret)
+		return ret;
+
+	i2c_set_clientdata(client, ssd1307);
+
+	if (ssd1307->reset)
+		ssd1307_reset(ssd1307);
+
+	if (ssd1307->vbat_reg) {
+		ret = regulator_enable(ssd1307->vbat_reg);
+		if (ret) {
+			dev_err(dev, "failed to enable VBAT: %d\n", ret);
+			return ret;
+		}
+	}
+
+	ret = ssd1307_init(ssd1307);
+	if (ret)
+		goto regulator_disable;
+
+	if (ssd1307->device_info->need_pwm) {
+		ret = ssd1307_pwm_enable(ssd1307);
+		if (ret)
+			goto regulator_disable;
+	}
+
+	snprintf(bl_name, sizeof(bl_name), "ssd1307%d", drm->primary->index);
+	bl = backlight_device_register(bl_name, dev, ssd1307, &ssd1307fb_bl_ops,
+				       NULL);
+	if (IS_ERR(bl)) {
+		ret = PTR_ERR(bl);
+		dev_err(dev, "unable to register backlight device: %d\n", ret);
+		goto pwm_disable;
+	}
+
+	bl->props.brightness = ssd1307->contrast;
+	bl->props.max_brightness = MAX_CONTRAST;
+	ssd1307->bl_dev = bl;
+
+	ret = drm_simple_display_pipe_init(drm, &ssd1307->pipe, &ssd1307_pipe_funcs,
+					   ssd1307_formats, ARRAY_SIZE(ssd1307_formats),
+					   NULL, &ssd1307->connector);
+	if (ret)
+		goto pwm_disable;
+
+	drm_plane_enable_fb_damage_clips(&ssd1307->pipe.plane);
+
+	drm_mode_config_reset(drm);
+
+	ret = drm_dev_register(drm, 0);
+	if (ret)
+		goto backlight_unregister;
+
+	drm_fbdev_generic_setup(drm, 0);
+
+	return 0;
+
+backlight_unregister:
+	backlight_device_unregister(ssd1307->bl_dev);
+pwm_disable:
+	if (ssd1307->device_info->need_pwm) {
+		pwm_disable(ssd1307->pwm);
+		pwm_put(ssd1307->pwm);
+	}
+regulator_disable:
+	if (ssd1307->vbat_reg)
+		regulator_disable(ssd1307->vbat_reg);
+	return ret;
+}
+
+static int ssd1307_remove(struct i2c_client *client)
+{
+	struct ssd1307_device *ssd1307 = i2c_get_clientdata(client);
+
+	drm_dev_unplug(&ssd1307->drm);
+
+	ssd1307_write_cmd(ssd1307->client, SSD1307_DISPLAY_OFF);
+
+	backlight_device_unregister(ssd1307->bl_dev);
+
+	if (ssd1307->device_info->need_pwm) {
+		pwm_disable(ssd1307->pwm);
+		pwm_put(ssd1307->pwm);
+	}
+	if (ssd1307->vbat_reg)
+		regulator_disable(ssd1307->vbat_reg);
+
+	return 0;
+}
+
+static void ssd1307_shutdown(struct i2c_client *client)
+{
+	struct ssd1307_device *ssd1307 = i2c_get_clientdata(client);
+
+	drm_atomic_helper_shutdown(&ssd1307->drm);
+}
+
+static struct ssd1307_deviceinfo ssd1307_ssd1305_deviceinfo = {
+	.default_vcomh = 0x34,
+	.default_dclk_div = 1,
+	.default_dclk_frq = 7,
+};
+
+static struct ssd1307_deviceinfo ssd1307_ssd1306_deviceinfo = {
+	.default_vcomh = 0x20,
+	.default_dclk_div = 1,
+	.default_dclk_frq = 8,
+	.need_chargepump = 1,
+};
+
+static struct ssd1307_deviceinfo ssd1307_ssd1307_deviceinfo = {
+	.default_vcomh = 0x20,
+	.default_dclk_div = 2,
+	.default_dclk_frq = 12,
+	.need_pwm = 1,
+};
+
+static struct ssd1307_deviceinfo ssd1307_ssd1309_deviceinfo = {
+	.default_vcomh = 0x34,
+	.default_dclk_div = 1,
+	.default_dclk_frq = 10,
+};
+
+static const struct of_device_id ssd1307_of_match[] = {
+	{
+		.compatible = "solomon,ssd1305fb-i2c",
+		.data = (void *)&ssd1307_ssd1305_deviceinfo,
+	},
+	{
+		.compatible = "solomon,ssd1306fb-i2c",
+		.data = (void *)&ssd1307_ssd1306_deviceinfo,
+	},
+	{
+		.compatible = "solomon,ssd1307fb-i2c",
+		.data = (void *)&ssd1307_ssd1307_deviceinfo,
+	},
+	{
+		.compatible = "solomon,ssd1309fb-i2c",
+		.data = (void *)&ssd1307_ssd1309_deviceinfo,
+	},
+	{},
+};
+MODULE_DEVICE_TABLE(of, ssd1307_of_match);
+
+
+static struct i2c_driver ssd1307_i2c_driver = {
+	.driver = {
+		.name = DRIVER_NAME,
+		.of_match_table = ssd1307_of_match,
+	},
+	.probe_new = ssd1307_probe,
+	.remove = ssd1307_remove,
+	.shutdown = ssd1307_shutdown,
+};
+
+module_i2c_driver(ssd1307_i2c_driver);
+
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_AUTHOR("Javier Martinez Canillas <javierm@redhat.com>");
+MODULE_LICENSE("GPL v2");
-- 
2.34.1

Re: [PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Sam Ravnborg]

Hi Javier,

On Mon, Jan 31, 2022 at 09:29:16PM +0100, Javier Martinez Canillas wrote:
> Add a DRM driver for SSD1305, SSD1306, SSD1307 and SSD1309 Solomon OLED
> controllers that can be programmed via an I2C interface. This is a port
> of the ssd1307fb driver that already supports these devices.
> 
> A Device Tree binding is not added because the DRM driver is compatible
> with the existing binding for the ssd1307fb driver.

The driver uses the pwms property for the backlight.
It would have been much better to bite the bullet and require the
backlight to be specified using a backlight node in the DT.
This is the standard way to do it and then the driver could use the
existing backlight driver rather than embedding a backlight driver here.

It would cost some backward compatibility - but looking forward this is
the right thing to do.

> 
> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>

Some random comments in the following.

	Sam

> ---
> 
>  drivers/gpu/drm/tiny/Kconfig   |  12 +
>  drivers/gpu/drm/tiny/Makefile  |   1 +
>  drivers/gpu/drm/tiny/ssd1307.c | 976 +++++++++++++++++++++++++++++++++
>  3 files changed, 989 insertions(+)
>  create mode 100644 drivers/gpu/drm/tiny/ssd1307.c
> 
> diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig
> index 712e0004e96e..25c9c013bcda 100644
> --- a/drivers/gpu/drm/tiny/Kconfig
> +++ b/drivers/gpu/drm/tiny/Kconfig
> @@ -157,6 +157,18 @@ config TINYDRM_REPAPER
>  
>  	  If M is selected the module will be called repaper.
>  
> +config TINYDRM_SSD1307
> +	tristate "DRM support for Solomon SSD1307 OLED displays"
Use SSD130X here - so SSD1306 users can find it.

> +	depends on DRM && I2C
> +	select DRM_KMS_HELPER
> +	select DRM_GEM_SHMEM_HELPER
> +	select BACKLIGHT_CLASS_DEVICE
> +	help
> +	  DRM driver for the SSD1305, SSD1306, SSD1307 and SSD1309 Solomon
> +	  OLED controllers that can be programmed via an I2C interface.
> +
> +	  If M is selected the module will be called ssd1307.
> +
>  config TINYDRM_ST7586
>  	tristate "DRM support for Sitronix ST7586 display panels"
>  	depends on DRM && SPI
> diff --git a/drivers/gpu/drm/tiny/Makefile b/drivers/gpu/drm/tiny/Makefile
> index 5d5505d40e7b..38c4c1111e96 100644
> --- a/drivers/gpu/drm/tiny/Makefile
> +++ b/drivers/gpu/drm/tiny/Makefile
> @@ -12,5 +12,6 @@ obj-$(CONFIG_TINYDRM_ILI9341)		+= ili9341.o
>  obj-$(CONFIG_TINYDRM_ILI9486)		+= ili9486.o
>  obj-$(CONFIG_TINYDRM_MI0283QT)		+= mi0283qt.o
>  obj-$(CONFIG_TINYDRM_REPAPER)		+= repaper.o
> +obj-$(CONFIG_TINYDRM_SSD1307)		+= ssd1307.o
>  obj-$(CONFIG_TINYDRM_ST7586)		+= st7586.o
>  obj-$(CONFIG_TINYDRM_ST7735R)		+= st7735r.o
> diff --git a/drivers/gpu/drm/tiny/ssd1307.c b/drivers/gpu/drm/tiny/ssd1307.c
> new file mode 100644
> index 000000000000..4ea223674587
> --- /dev/null
> +++ b/drivers/gpu/drm/tiny/ssd1307.c
> @@ -0,0 +1,976 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * DRM driver for Solomon SSD1307 OLED displays
> + *
> + * Copyright 2022 Red Hat Inc.
> + *
> + * Based on drivers/video/fbdev/ssd1307fb.c
> + * Copyright 2012 Free Electrons
> + *
> + */
> +
> +#include <linux/backlight.h>
> +#include <linux/delay.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/i2c.h>
> +#include <linux/module.h>
> +#include <linux/property.h>
> +#include <linux/pwm.h>
> +#include <linux/regulator/consumer.h>
> +
> +#include <drm/drm_atomic_helper.h>
> +#include <drm/drm_damage_helper.h>
> +#include <drm/drm_drv.h>
> +#include <drm/drm_fb_cma_helper.h>
> +#include <drm/drm_fb_helper.h>
> +#include <drm/drm_format_helper.h>
> +#include <drm/drm_gem_atomic_helper.h>
> +#include <drm/drm_gem_framebuffer_helper.h>
> +#include <drm/drm_gem_shmem_helper.h>
> +#include <drm/drm_managed.h>
> +#include <drm/drm_modes.h>
> +#include <drm/drm_rect.h>
> +#include <drm/drm_probe_helper.h>
> +#include <drm/drm_simple_kms_helper.h>
> +
> +#define DRIVER_NAME	"ssd1307"
> +#define DRIVER_DESC	"DRM driver for Solomon SSD1307 OLED displays"
> +#define DRIVER_DATE	"20220131"
> +#define DRIVER_MAJOR	1
> +#define DRIVER_MINOR	0
> +
> +#define SSD1307_DATA				0x40
> +#define SSD1307_COMMAND			0x80
> +
> +#define SSD1307_SET_ADDRESS_MODE		0x20
> +#define SSD1307_SET_ADDRESS_MODE_HORIZONTAL	(0x00)
> +#define SSD1307_SET_ADDRESS_MODE_VERTICAL	(0x01)
> +#define SSD1307_SET_ADDRESS_MODE_PAGE		(0x02)
> +#define SSD1307_SET_COL_RANGE			0x21
> +#define SSD1307_SET_PAGE_RANGE			0x22
> +#define SSD1307_CONTRAST			0x81
> +#define SSD1307_SET_LOOKUP_TABLE		0x91
> +#define SSD1307_CHARGE_PUMP			0x8d
> +#define SSD1307_SEG_REMAP_ON			0xa1
> +#define SSD1307_DISPLAY_OFF			0xae
> +#define SSD1307_SET_MULTIPLEX_RATIO		0xa8
> +#define SSD1307_DISPLAY_ON			0xaf
> +#define SSD1307_START_PAGE_ADDRESS		0xb0
> +#define SSD1307_SET_DISPLAY_OFFSET		0xd3
> +#define SSD1307_SET_CLOCK_FREQ			0xd5
> +#define SSD1307_SET_AREA_COLOR_MODE		0xd8
> +#define SSD1307_SET_PRECHARGE_PERIOD		0xd9
> +#define SSD1307_SET_COM_PINS_CONFIG		0xda
> +#define SSD1307_SET_VCOMH			0xdb
> +
> +#define MAX_CONTRAST 255
> +
> +struct ssd1307_deviceinfo {
> +	u32 default_vcomh;
> +	u32 default_dclk_div;
> +	u32 default_dclk_frq;
> +	int need_pwm;
> +	int need_chargepump;
> +};
> +
> +struct ssd1307_device {
> +	struct drm_device drm;
> +	struct drm_simple_display_pipe pipe;
> +	struct drm_display_mode mode;
> +	struct drm_connector connector;
> +	struct i2c_client *client;
> +
> +	const struct ssd1307_deviceinfo *device_info;
> +
> +	unsigned area_color_enable : 1;
> +	unsigned com_invdir : 1;
> +	unsigned com_lrremap : 1;
> +	unsigned com_seq : 1;
> +	unsigned lookup_table_set : 1;
> +	unsigned low_power : 1;
> +	unsigned seg_remap : 1;
> +	u32 com_offset;
> +	u32 contrast;
> +	u32 dclk_div;
> +	u32 dclk_frq;
> +	u32 height;
> +	u8 lookup_table[4];
> +	u32 page_offset;
> +	u32 col_offset;
> +	u32 prechargep1;
> +	u32 prechargep2;
> +
> +	struct backlight_device *bl_dev;
> +	struct pwm_device *pwm;
> +	struct gpio_desc *reset;
> +	struct regulator *vbat_reg;
> +	u32 vcomh;
> +	u32 width;
> +	/* Cached address ranges */
> +	u8 col_start;
> +	u8 col_end;
> +	u8 page_start;
> +	u8 page_end;
> +};
> +
> +struct ssd1307_array {
> +	u8	type;
> +	u8	data[];
> +};
> +
> +static inline struct ssd1307_device *drm_to_ssd1307(struct drm_device *drm)
> +{
> +	return container_of(drm, struct ssd1307_device, drm);
> +}
> +
> +static struct ssd1307_array *ssd1307_alloc_array(u32 len, u8 type)
> +{
> +	struct ssd1307_array *array;
> +
> +	array = kzalloc(sizeof(struct ssd1307_array) + len, GFP_KERNEL);
> +	if (!array)
> +		return NULL;
> +
> +	array->type = type;
> +
> +	return array;
> +}
> +
> +static int ssd1307_write_array(struct i2c_client *client,
> +			       struct ssd1307_array *array, u32 len)
> +{
> +	int ret;
> +
> +	len += sizeof(struct ssd1307_array);
> +
> +	ret = i2c_master_send(client, (u8 *)array, len);
> +	if (ret != len) {
> +		dev_err(&client->dev, "Couldn't send I2C command.\n");
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static inline int ssd1307_write_cmd(struct i2c_client *client, u8 cmd)
> +{
> +	struct ssd1307_array *array;
> +	int ret;
> +
> +	array = ssd1307_alloc_array(1, SSD1307_COMMAND);
> +	if (!array)
> +		return -ENOMEM;
> +
> +	array->data[0] = cmd;
> +
> +	ret = ssd1307_write_array(client, array, 1);
> +	kfree(array);
> +
> +	return ret;
> +}
> +
> +static int ssd1307_set_col_range(struct ssd1307_device *ssd1307,
> +				 u8 col_start, u8 cols)
> +{
> +	u8 col_end = col_start + cols - 1;
> +	int ret;
> +
> +	if (col_start == ssd1307->col_start && col_end == ssd1307->col_end)
> +		return 0;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_COL_RANGE);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, col_start);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, col_end);
> +	if (ret < 0)
> +		return ret;
> +
> +	ssd1307->col_start = col_start;
> +	ssd1307->col_end = col_end;
> +	return 0;
> +}
> +
> +static int ssd1307_set_page_range(struct ssd1307_device *ssd1307,
> +				  u8 page_start, u8 pages)
> +{
> +	u8 page_end = page_start + pages - 1;
> +	int ret;
> +
> +	if (page_start == ssd1307->page_start && page_end == ssd1307->page_end)
> +		return 0;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_PAGE_RANGE);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, page_start);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, page_end);
> +	if (ret < 0)
> +		return ret;
> +
> +	ssd1307->page_start = page_start;
> +	ssd1307->page_end = page_end;
> +	return 0;
> +}
> +
> +static int ssd1307_update_display(struct ssd1307_device *ssd1307, u8 *buf,
> +				  u32 width, u32 height)
> +{
> +	struct ssd1307_array *array;
> +	unsigned int line_length = DIV_ROUND_UP(width, 8);
> +	unsigned int pages = DIV_ROUND_UP(height, 8);
> +	u32 array_idx = 0;
> +	int ret, i, j, k;
> +
> +	array = ssd1307_alloc_array(width * pages, SSD1307_DATA);
> +	if (!array)
> +		return -ENOMEM;
> +
> +	/*
> +	 * The screen is divided in pages, each having a height of 8
> +	 * pixels, and the width of the screen. When sending a byte of
> +	 * data to the controller, it gives the 8 bits for the current
> +	 * column. I.e, the first byte are the 8 bits of the first
> +	 * column, then the 8 bits for the second column, etc.
> +	 *
> +	 *
> +	 * Representation of the screen, assuming it is 5 bits
> +	 * wide. Each letter-number combination is a bit that controls
> +	 * one pixel.
> +	 *
> +	 * A0 A1 A2 A3 A4
> +	 * B0 B1 B2 B3 B4
> +	 * C0 C1 C2 C3 C4
> +	 * D0 D1 D2 D3 D4
> +	 * E0 E1 E2 E3 E4
> +	 * F0 F1 F2 F3 F4
> +	 * G0 G1 G2 G3 G4
> +	 * H0 H1 H2 H3 H4
> +	 *
> +	 * If you want to update this screen, you need to send 5 bytes:
> +	 *  (1) A0 B0 C0 D0 E0 F0 G0 H0
> +	 *  (2) A1 B1 C1 D1 E1 F1 G1 H1
> +	 *  (3) A2 B2 C2 D2 E2 F2 G2 H2
> +	 *  (4) A3 B3 C3 D3 E3 F3 G3 H3
> +	 *  (5) A4 B4 C4 D4 E4 F4 G4 H4
> +	 */
> +
> +	ret = ssd1307_set_col_range(ssd1307, ssd1307->col_offset, width);
> +	if (ret < 0)
> +		goto out_free;
> +
> +	ret = ssd1307_set_page_range(ssd1307, ssd1307->page_offset / 8, pages);
> +	if (ret < 0)
> +		goto out_free;
> +
> +	for (i = 0; i < pages; i++) {
> +		int m = 8;
> +
> +		/* Last page may be partial */
> +		if (8 * (i + 1) > ssd1307->height)
> +			m = ssd1307->height % 8;
> +		for (j = 0; j < width; j++) {
> +			u8 data = 0;
> +
> +			for (k = 0; k < m; k++) {
> +				u8 byte = buf[(8 * i + k) * line_length +
> +					       j / 8];
> +				u8 bit = (byte >> (j % 8)) & 1;
> +
> +				data |= bit << k;
> +			}
> +			array->data[array_idx++] = data;
> +		}
> +	}
> +
> +	ret = ssd1307_write_array(ssd1307->client, array, width * pages);
> +
> +out_free:
> +	kfree(array);
> +	return ret;
> +}
> +
> +static void ssd1307_clear_screen(struct ssd1307_device *ssd1307, u32 width, u32 height)
> +{
> +	u8 *buf = NULL;
> +
> +	buf = kmalloc_array(width, height, GFP_KERNEL);
> +	if (!buf)
> +		return;
> +
> +	/* Clear screen to black if disabled */
> +	memset(buf, 0, width * height);
> +
> +	ssd1307_update_display(ssd1307, buf, width, height);
> +}
> +
> +static int ssd1307_fb_blit_rect(struct drm_framebuffer *fb, const struct dma_buf_map *map,
> +				struct drm_rect *rect)
> +{
> +	struct ssd1307_device *ssd1307 = drm_to_ssd1307(fb->dev);
> +	void *vmap = map->vaddr; /* TODO: Use mapping abstraction properly */
Hmm, can we fix this TODO now?

> +	int ret = 0;
> +	u8 *buf = NULL;
> +
> +	buf = kmalloc_array(fb->width, fb->height, GFP_KERNEL);
> +	if (!buf) {
> +		ret = -ENOMEM;
> +		goto out_exit;
> +	}
> +
> +	drm_fb_xrgb8888_to_gray8(buf, 0, vmap, fb, rect);
> +
> +	drm_fb_gray8_to_mono_reversed(buf, buf, rect);
> +
> +	ssd1307_update_display(ssd1307, buf, fb->width, fb->height);
> +
> +	kfree(buf);
> +out_exit:
> +	return ret;
> +}
> +
> +static int ssd1307_display_pipe_mode_valid(struct drm_simple_display_pipe *pipe,
> +						   const struct drm_display_mode *mode)
> +{
> +	struct ssd1307_device *ssd1307 = drm_to_ssd1307(pipe->crtc.dev);
> +
> +	if (mode->hdisplay != ssd1307->mode.hdisplay &&
> +	    mode->vdisplay != ssd1307->mode.vdisplay)
> +		return MODE_ONE_SIZE;
> +	else if (mode->hdisplay != ssd1307->mode.hdisplay)
> +		return MODE_ONE_WIDTH;
> +	else if (mode->vdisplay != ssd1307->mode.vdisplay)
> +		return MODE_ONE_HEIGHT;
> +
> +	return MODE_OK;
> +}
> +
> +static void ssd1307_display_pipe_enable(struct drm_simple_display_pipe *pipe,
> +				       struct drm_crtc_state *crtc_state,
> +				       struct drm_plane_state *plane_state)
> +{
> +	struct ssd1307_device *ssd1307 = drm_to_ssd1307(pipe->crtc.dev);
> +	struct drm_device *drm = &ssd1307->drm;
> +	int idx;
> +
> +	if (!drm_dev_enter(drm, &idx))
> +		return;
> +
> +	backlight_enable(ssd1307->bl_dev);
This seems backward - I would have assumed backlight was enabled
after the display was enabled - so you potentially hide some flickering.
This is the order done in drm_panel.

> +
> +	ssd1307_write_cmd(ssd1307->client, SSD1307_DISPLAY_ON);
> +
> +	drm_dev_exit(idx);
> +}
> +
> +static void ssd1307_display_pipe_disable(struct drm_simple_display_pipe *pipe)
> +{
> +	struct ssd1307_device *ssd1307 = drm_to_ssd1307(pipe->crtc.dev);
> +	struct drm_device *drm = &ssd1307->drm;
> +	int idx;
> +
> +	if (!drm_dev_enter(drm, &idx))
> +		return;
> +
> +	ssd1307_clear_screen(ssd1307, ssd1307->width, ssd1307->height);
> +
> +	ssd1307_write_cmd(ssd1307->client, SSD1307_DISPLAY_OFF);
> +
> +	backlight_disable(ssd1307->bl_dev);
And here backlight could be disabled before disabling the display.

> +
> +	drm_dev_exit(idx);
> +}
> +
> +static void ssd1307_display_pipe_update(struct drm_simple_display_pipe *pipe,
> +					struct drm_plane_state *old_plane_state)
> +{
> +	struct ssd1307_device *ssd1307 = drm_to_ssd1307(pipe->crtc.dev);
> +	struct drm_plane_state *plane_state = pipe->plane.state;
> +	struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(plane_state);
> +	struct drm_framebuffer *fb = plane_state->fb;
> +	struct drm_device *drm = &ssd1307->drm;
> +	struct drm_rect rect;
> +	int idx;
> +
> +	if (!fb)
> +		return;
> +
> +	if (!pipe->crtc.state->active)
> +		return;
> +
> +	if (!drm_dev_enter(drm, &idx))
> +		return;
> +
> +	if (drm_atomic_helper_damage_merged(old_plane_state, plane_state, &rect))
> +		ssd1307_fb_blit_rect(plane_state->fb, &shadow_plane_state->data[0], &rect);
> +
> +	drm_dev_exit(idx);
> +}
> +
> +static const struct drm_simple_display_pipe_funcs ssd1307_pipe_funcs = {
> +	.mode_valid = ssd1307_display_pipe_mode_valid,
> +	.enable = ssd1307_display_pipe_enable,
> +	.disable = ssd1307_display_pipe_disable,
> +	.update = ssd1307_display_pipe_update,
> +	DRM_GEM_SIMPLE_DISPLAY_PIPE_SHADOW_PLANE_FUNCS,
> +};
> +
> +static int ssd1307_connector_get_modes(struct drm_connector *connector)
> +{
> +	struct ssd1307_device *ssd1307 = drm_to_ssd1307(connector->dev);
> +	struct drm_display_mode *mode;
> +
> +	mode = drm_mode_duplicate(connector->dev, &ssd1307->mode);
> +	if (!mode) {
> +		DRM_ERROR("Failed to duplicate mode\n");
> +		return 0;
> +	}
> +
> +	connector->display_info.width_mm = mode->width_mm;
> +	connector->display_info.height_mm = mode->height_mm;
> +	connector->display_info.bpc = 32;
> +
> +	drm_mode_set_name(mode);
> +	mode->type |= DRM_MODE_TYPE_PREFERRED;
> +	drm_mode_probed_add(connector, mode);
> +
> +	return 1;
> +}
> +
> +static const struct drm_connector_helper_funcs ssd1307_connector_helper_funcs = {
> +	.get_modes = ssd1307_connector_get_modes,
> +};
> +
> +static const struct drm_connector_funcs ssd1307_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 ssd1307_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 ssd1307_formats[] = {
> +	DRM_FORMAT_XRGB8888,
> +};
> +
> +DEFINE_DRM_GEM_FOPS(ssd1307_fops);
> +
> +static const struct drm_driver ssd1307_drm_driver = {
> +	DRM_GEM_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			= &ssd1307_fops,
> +};
> +
> +static int ssd1307_pwm_enable(struct ssd1307_device *ssd1307)
> +{
> +	struct pwm_state pwmstate;
> +
> +	ssd1307->pwm = pwm_get(&ssd1307->client->dev, NULL);
> +	if (IS_ERR(ssd1307->pwm)) {
> +		dev_err(&ssd1307->client->dev, "Could not get PWM from device tree!\n");
> +		return PTR_ERR(ssd1307->pwm);
> +	}
> +
> +	pwm_init_state(ssd1307->pwm, &pwmstate);
> +	pwm_set_relative_duty_cycle(&pwmstate, 50, 100);
> +	pwm_apply_state(ssd1307->pwm, &pwmstate);
> +
> +	/* Enable the PWM */
> +	pwm_enable(ssd1307->pwm);
> +
> +	dev_dbg(&ssd1307->client->dev, "Using PWM%d with a %lluns period.\n",
> +		ssd1307->pwm->pwm, pwm_get_period(ssd1307->pwm));
> +
> +	return 0;
> +}
> +
> +static int ssd1307_init(struct ssd1307_device *ssd1307)
> +{
> +	u32 precharge, dclk, com_invdir, compins;
> +	int ret;
> +
> +	/* Set initial contrast */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_CONTRAST);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->contrast);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Set segment re-map */
> +	if (ssd1307->seg_remap) {
> +		ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SEG_REMAP_ON);
> +		if (ret < 0)
> +			return ret;
> +	}
> +
> +	/* Set COM direction */
> +	com_invdir = 0xc0 | ssd1307->com_invdir << 3;
> +	ret = ssd1307_write_cmd(ssd1307->client,  com_invdir);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Set multiplex ratio value */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_MULTIPLEX_RATIO);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->height - 1);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* set display offset value */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_DISPLAY_OFFSET);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->com_offset);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Set clock frequency */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_CLOCK_FREQ);
> +	if (ret < 0)
> +		return ret;
> +
> +	dclk = ((ssd1307->dclk_div - 1) & 0xf) | (ssd1307->dclk_frq & 0xf) << 4;
> +	ret = ssd1307_write_cmd(ssd1307->client, dclk);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Set Area Color Mode ON/OFF & Low Power Display Mode */
> +	if (ssd1307->area_color_enable || ssd1307->low_power) {
> +		u32 mode;
> +
> +		ret = ssd1307_write_cmd(ssd1307->client,
> +					SSD1307_SET_AREA_COLOR_MODE);
> +		if (ret < 0)
> +			return ret;
> +
> +		mode = (ssd1307->area_color_enable ? 0x30 : 0) |
> +			(ssd1307->low_power ? 5 : 0);
> +		ret = ssd1307_write_cmd(ssd1307->client, mode);
> +		if (ret < 0)
> +			return ret;
> +	}
> +
> +	/* Set precharge period in number of ticks from the internal clock */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_PRECHARGE_PERIOD);
> +	if (ret < 0)
> +		return ret;
> +
> +	precharge = (ssd1307->prechargep1 & 0xf) | (ssd1307->prechargep2 & 0xf) << 4;
> +	ret = ssd1307_write_cmd(ssd1307->client, precharge);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Set COM pins configuration */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_COM_PINS_CONFIG);
> +	if (ret < 0)
> +		return ret;
> +
> +	compins = 0x02 | !ssd1307->com_seq << 4 | ssd1307->com_lrremap << 5;
> +	ret = ssd1307_write_cmd(ssd1307->client, compins);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Set VCOMH */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_VCOMH);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->vcomh);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Turn on the DC-DC Charge Pump */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_CHARGE_PUMP);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client,
> +		BIT(4) | (ssd1307->device_info->need_chargepump ? BIT(2) : 0));
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Set lookup table */
> +	if (ssd1307->lookup_table_set) {
> +		int i;
> +
> +		ret = ssd1307_write_cmd(ssd1307->client,
> +					SSD1307_SET_LOOKUP_TABLE);
> +		if (ret < 0)
> +			return ret;
> +
> +		for (i = 0; i < ARRAY_SIZE(ssd1307->lookup_table); ++i) {
> +			u8 val = ssd1307->lookup_table[i];
> +
> +			if (val < 31 || val > 63)
> +				dev_warn(&ssd1307->client->dev,
> +					 "lookup table index %d value out of range 31 <= %d <= 63\n",
> +					 i, val);
> +			ret = ssd1307_write_cmd(ssd1307->client, val);
> +			if (ret < 0)
> +				return ret;
> +		}
> +	}
> +
> +	/* Switch to horizontal addressing mode */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_ADDRESS_MODE);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client,
> +				SSD1307_SET_ADDRESS_MODE_HORIZONTAL);
> +	if (ret < 0)
> +		return ret;
> +
> +	ssd1307_clear_screen(ssd1307, ssd1307->width, ssd1307->height);
> +
> +	/* Turn on the display */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_DISPLAY_ON);
> +	if (ret < 0)
> +		return ret;
I would assume the display is turned on later - and should be left off
here. The pipe function will do this when needed.

> +
> +	return 0;
> +}
> +
> +static int ssd1307_update_bl(struct backlight_device *bdev)
> +{
> +	struct ssd1307_device *ssd1307 = bl_get_data(bdev);
> +	int brightness = bdev->props.brightness;
Use backlight_get_brightness(bdev) here.

> +	int ret;
> +
> +	ssd1307->contrast = brightness;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_CONTRAST);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->contrast);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
> +
> +static int ssd1307_get_brightness(struct backlight_device *bdev)
> +{
> +	struct ssd1307_device *ssd1307 = bl_get_data(bdev);
> +
> +	return ssd1307->contrast;
I am pretty sure this function can be omitted - as the brightness value
is not changed unless we write it.

> +}
> +
> +static const struct backlight_ops ssd1307fb_bl_ops = {
> +	.update_status	= ssd1307_update_bl,
> +	.get_brightness	= ssd1307_get_brightness,
> +};
> +
> +static void ssd1307_reset(struct ssd1307_device *ssd1307)
> +{
> +	/* Reset the screen */
> +	gpiod_set_value_cansleep(ssd1307->reset, 1);
> +	udelay(4);
> +	gpiod_set_value_cansleep(ssd1307->reset, 0);
> +	udelay(4);
> +}
> +
> +static void ssd1307_parse_properties(struct ssd1307_device *ssd1307)
> +{
> +	struct device *dev = &ssd1307->client->dev;
> +
> +	if (device_property_read_u32(dev, "solomon,width", &ssd1307->width))
> +		ssd1307->width = 96;
> +
> +	if (device_property_read_u32(dev, "solomon,height", &ssd1307->height))
> +		ssd1307->height = 16;
> +
> +	if (device_property_read_u32(dev, "solomon,page-offset", &ssd1307->page_offset))
> +		ssd1307->page_offset = 1;
> +
> +	if (device_property_read_u32(dev, "solomon,col-offset", &ssd1307->col_offset))
> +		ssd1307->col_offset = 0;
> +
> +	if (device_property_read_u32(dev, "solomon,com-offset", &ssd1307->com_offset))
> +		ssd1307->com_offset = 0;
> +
> +	if (device_property_read_u32(dev, "solomon,prechargep1", &ssd1307->prechargep1))
> +		ssd1307->prechargep1 = 2;
> +
> +	if (device_property_read_u32(dev, "solomon,prechargep2", &ssd1307->prechargep2))
> +		ssd1307->prechargep2 = 2;
> +
> +	if (!device_property_read_u8_array(dev, "solomon,lookup-table",
> +					   ssd1307->lookup_table,
> +					   ARRAY_SIZE(ssd1307->lookup_table)))
> +		ssd1307->lookup_table_set = 1;
> +
> +	ssd1307->seg_remap = !device_property_read_bool(dev, "solomon,segment-no-remap");
> +	ssd1307->com_seq = device_property_read_bool(dev, "solomon,com-seq");
> +	ssd1307->com_lrremap = device_property_read_bool(dev, "solomon,com-lrremap");
> +	ssd1307->com_invdir = device_property_read_bool(dev, "solomon,com-invdir");
> +	ssd1307->area_color_enable =
> +		device_property_read_bool(dev, "solomon,area-color-enable");
> +	ssd1307->low_power = device_property_read_bool(dev, "solomon,low-power");
> +
> +	ssd1307->contrast = 127;
> +	ssd1307->vcomh = ssd1307->device_info->default_vcomh;
> +
> +	/* Setup display timing */
> +	if (device_property_read_u32(dev, "solomon,dclk-div", &ssd1307->dclk_div))
> +		ssd1307->dclk_div = ssd1307->device_info->default_dclk_div;
> +	if (device_property_read_u32(dev, "solomon,dclk-frq", &ssd1307->dclk_frq))
> +		ssd1307->dclk_frq = ssd1307->device_info->default_dclk_frq;
> +}
> +
> +static void ssd1307_set_mode(struct ssd1307_device *ssd1307)
> +{
> +	struct drm_display_mode *mode = &ssd1307->mode;
> +	struct drm_device *drm = &ssd1307->drm;
> +
> +	mode->type = DRM_MODE_TYPE_DRIVER;
> +	mode->clock = 1;
> +	mode->hdisplay = mode->htotal = ssd1307->width;
> +	mode->hsync_start = mode->hsync_end = ssd1307->width;
> +	mode->vdisplay = mode->vtotal = ssd1307->height;
> +	mode->vsync_start = mode->vsync_end = ssd1307->height;
> +	mode->width_mm = 27;
> +	mode->height_mm = 27;
> +
> +	drm->mode_config.min_width = ssd1307->width;
> +	drm->mode_config.max_width = ssd1307->width;
> +	drm->mode_config.min_height = ssd1307->height;
> +	drm->mode_config.max_height = ssd1307->height;
> +	drm->mode_config.preferred_depth = 32;
> +	drm->mode_config.funcs = &ssd1307_mode_config_funcs;
> +}
> +
> +static int ssd1307_probe(struct i2c_client *client)
> +{
> +	struct device *dev = &client->dev;
> +	struct ssd1307_device *ssd1307;
> +	struct backlight_device *bl;
> +	struct drm_device *drm;
> +	char bl_name[12];
> +	int ret;
> +
> +	ssd1307 = devm_drm_dev_alloc(dev, &ssd1307_drm_driver,
> +				 struct ssd1307_device, drm);
> +	if (IS_ERR(ssd1307))
> +		return PTR_ERR(ssd1307);
> +
> +	drm = &ssd1307->drm;
> +
> +	ret = drmm_mode_config_init(drm);
> +	if (ret)
> +		return ret;
> +
> +	ssd1307->client = client;
> +
> +	ssd1307->device_info = device_get_match_data(dev);
> +
> +	ssd1307_parse_properties(ssd1307);
> +
> +	ssd1307_set_mode(ssd1307);
> +
> +	ssd1307->reset = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW);
> +	if (IS_ERR(ssd1307->reset)) {
> +		dev_err(dev, "failed to get reset gpio: %ld\n",
> +			PTR_ERR(ssd1307->reset));
> +		return PTR_ERR(ssd1307->reset);
> +	}
> +
> +	ssd1307->vbat_reg = devm_regulator_get_optional(dev, "vbat");
> +	if (IS_ERR(ssd1307->vbat_reg)) {
> +		ret = PTR_ERR(ssd1307->vbat_reg);
> +		if (ret == -ENODEV) {
> +			ssd1307->vbat_reg = NULL;
> +		} else {
> +			dev_err(dev, "failed to get VBAT regulator: %d\n", ret);
> +			return ret;
> +		}
> +	}
> +
> +	drm_connector_helper_add(&ssd1307->connector, &ssd1307_connector_helper_funcs);
> +	ret = drm_connector_init(drm, &ssd1307->connector, &ssd1307_connector_funcs,
> +				 DRM_MODE_CONNECTOR_Unknown);
Why not the I2C connector?

> +	if (ret)
> +		return ret;
> +
> +	i2c_set_clientdata(client, ssd1307);
> +
> +	if (ssd1307->reset)
> +		ssd1307_reset(ssd1307);
> +
> +	if (ssd1307->vbat_reg) {
> +		ret = regulator_enable(ssd1307->vbat_reg);
> +		if (ret) {
> +			dev_err(dev, "failed to enable VBAT: %d\n", ret);
> +			return ret;
> +		}
> +	}
> +
> +	ret = ssd1307_init(ssd1307);
> +	if (ret)
> +		goto regulator_disable;
> +
> +	if (ssd1307->device_info->need_pwm) {
> +		ret = ssd1307_pwm_enable(ssd1307);
> +		if (ret)
> +			goto regulator_disable;
> +	}
> +
> +	snprintf(bl_name, sizeof(bl_name), "ssd1307%d", drm->primary->index);
> +	bl = backlight_device_register(bl_name, dev, ssd1307, &ssd1307fb_bl_ops,
> +				       NULL);
devm_backlight_device_register?
And use (dev, dev_name(dev), - so you can drop bl_name[]


> +	if (IS_ERR(bl)) {
> +		ret = PTR_ERR(bl);
> +		dev_err(dev, "unable to register backlight device: %d\n", ret);
> +		goto pwm_disable;
> +	}
> +
> +	bl->props.brightness = ssd1307->contrast;
> +	bl->props.max_brightness = MAX_CONTRAST;
> +	ssd1307->bl_dev = bl;
> +
> +	ret = drm_simple_display_pipe_init(drm, &ssd1307->pipe, &ssd1307_pipe_funcs,
> +					   ssd1307_formats, ARRAY_SIZE(ssd1307_formats),
> +					   NULL, &ssd1307->connector);
> +	if (ret)
> +		goto pwm_disable;
> +
> +	drm_plane_enable_fb_damage_clips(&ssd1307->pipe.plane);
> +
> +	drm_mode_config_reset(drm);
> +
> +	ret = drm_dev_register(drm, 0);
> +	if (ret)
> +		goto backlight_unregister;
> +
> +	drm_fbdev_generic_setup(drm, 0);
> +
> +	return 0;
> +
> +backlight_unregister:
> +	backlight_device_unregister(ssd1307->bl_dev);
> +pwm_disable:
> +	if (ssd1307->device_info->need_pwm) {
> +		pwm_disable(ssd1307->pwm);
> +		pwm_put(ssd1307->pwm);
> +	}
> +regulator_disable:
> +	if (ssd1307->vbat_reg)
> +		regulator_disable(ssd1307->vbat_reg);
No need for the if (sd1307->vbat_reg) here.

> +	return ret;
> +}
> +
> +static int ssd1307_remove(struct i2c_client *client)
> +{
> +	struct ssd1307_device *ssd1307 = i2c_get_clientdata(client);
> +
> +	drm_dev_unplug(&ssd1307->drm);
> +
> +	ssd1307_write_cmd(ssd1307->client, SSD1307_DISPLAY_OFF);
> +
> +	backlight_device_unregister(ssd1307->bl_dev);
> +
> +	if (ssd1307->device_info->need_pwm) {
> +		pwm_disable(ssd1307->pwm);
> +		pwm_put(ssd1307->pwm);
> +	}
> +	if (ssd1307->vbat_reg)
> +		regulator_disable(ssd1307->vbat_reg);
Drop if.

> +
> +	return 0;
> +}
> +
> +static void ssd1307_shutdown(struct i2c_client *client)
> +{
> +	struct ssd1307_device *ssd1307 = i2c_get_clientdata(client);
> +
> +	drm_atomic_helper_shutdown(&ssd1307->drm);
> +}
> +
> +static struct ssd1307_deviceinfo ssd1307_ssd1305_deviceinfo = {
> +	.default_vcomh = 0x34,
> +	.default_dclk_div = 1,
> +	.default_dclk_frq = 7,
> +};
> +
> +static struct ssd1307_deviceinfo ssd1307_ssd1306_deviceinfo = {
> +	.default_vcomh = 0x20,
> +	.default_dclk_div = 1,
> +	.default_dclk_frq = 8,
> +	.need_chargepump = 1,
> +};
> +
> +static struct ssd1307_deviceinfo ssd1307_ssd1307_deviceinfo = {
> +	.default_vcomh = 0x20,
> +	.default_dclk_div = 2,
> +	.default_dclk_frq = 12,
> +	.need_pwm = 1,
> +};
> +
> +static struct ssd1307_deviceinfo ssd1307_ssd1309_deviceinfo = {
> +	.default_vcomh = 0x34,
> +	.default_dclk_div = 1,
> +	.default_dclk_frq = 10,
> +};
> +
> +static const struct of_device_id ssd1307_of_match[] = {
> +	{
> +		.compatible = "solomon,ssd1305fb-i2c",
> +		.data = (void *)&ssd1307_ssd1305_deviceinfo,
> +	},
> +	{
> +		.compatible = "solomon,ssd1306fb-i2c",
> +		.data = (void *)&ssd1307_ssd1306_deviceinfo,
> +	},
> +	{
> +		.compatible = "solomon,ssd1307fb-i2c",
> +		.data = (void *)&ssd1307_ssd1307_deviceinfo,
> +	},
> +	{
> +		.compatible = "solomon,ssd1309fb-i2c",
> +		.data = (void *)&ssd1307_ssd1309_deviceinfo,
> +	},
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, ssd1307_of_match);
> +
> +
> +static struct i2c_driver ssd1307_i2c_driver = {
> +	.driver = {
> +		.name = DRIVER_NAME,
> +		.of_match_table = ssd1307_of_match,
> +	},
> +	.probe_new = ssd1307_probe,
> +	.remove = ssd1307_remove,
> +	.shutdown = ssd1307_shutdown,
> +};
> +
> +module_i2c_driver(ssd1307_i2c_driver);
> +
> +MODULE_DESCRIPTION(DRIVER_DESC);
> +MODULE_AUTHOR("Javier Martinez Canillas <javierm@redhat.com>");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.34.1

Re: [PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Javier Martinez Canillas]

Hello Sam,

Thanks for your suggestions.

On 1/31/22 22:30, Sam Ravnborg wrote:
> Hi Javier,
> 
> On Mon, Jan 31, 2022 at 09:29:16PM +0100, Javier Martinez Canillas wrote:
>> Add a DRM driver for SSD1305, SSD1306, SSD1307 and SSD1309 Solomon OLED
>> controllers that can be programmed via an I2C interface. This is a port
>> of the ssd1307fb driver that already supports these devices.
>>
>> A Device Tree binding is not added because the DRM driver is compatible
>> with the existing binding for the ssd1307fb driver.
> 
> The driver uses the pwms property for the backlight.
> It would have been much better to bite the bullet and require the
> backlight to be specified using a backlight node in the DT.
> This is the standard way to do it and then the driver could use the
> existing backlight driver rather than embedding a backlight driver here.
>

I did consider that. Because that would allow me to use a struct drm_panel
and as you said make the core to manage the backlight. But then decied to
just keep the backward compatibility with the existing binding to make it
easier for users to migrate to the DRM driver.

I wonder if we could make the driver to support both ? That is, to query
if there's a backlight with drm_panel_of_backlight() and if not found then
registering it's own backlight like the driver is currently doing.
 
> It would cost some backward compatibility - but looking forward this is
> the right thing to do.
>

I don't have a strong opinion. As mentioned I thought that was more worthy
to keep the backward compat over doing it correctly. After all, this driver
is for a very niche hardware (small OLED monochromatic panels), so I wasn't
that concerned about supporting the proper DT conventions.

I would also like to know Andy's opinion. Since he mentioned that embedded
x86/ACPI hardware is using the PRP0001 _DSD extension to match against the
OF driver. I wonder how feasible is for those platforms to change the DSDT.

Another option is to have different compatible strings for this ? I wanted
to drop the "fb" suffix and just have OF entries with compatible "ssd1307"
instead of "ssd1307fb", but again left the latter for backward compat.

But maybe we can have the "fb" ones creating the backlight and the new ones
expecting it to have a backlight DT node.

>>
>> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
> 
> Some random comments in the following.
> 
> 	Sam

[snip]

>> +config TINYDRM_SSD1307
>> +	tristate "DRM support for Solomon SSD1307 OLED displays"
> Use SSD130X here - so SSD1306 users can find it.
>

Agreed. That's what I had before (and also in the driver, MAINTAINERS entry,
etc) but then changed to SSD1307 everywhere. Unsure what could be more clear
to users grepping to figure out if there's a DRM driver for their device.

I'll follow your suggestion and change in the Kconfig description for v2.

[snip]

>> +
>> +static int ssd1307_fb_blit_rect(struct drm_framebuffer *fb, const struct dma_buf_map *map,
>> +				struct drm_rect *rect)
>> +{
>> +	struct ssd1307_device *ssd1307 = drm_to_ssd1307(fb->dev);
>> +	void *vmap = map->vaddr; /* TODO: Use mapping abstraction properly */
> Hmm, can we fix this TODO now?
>

I did try to fix it while writing the driver but couldn't figure out what was
the proper abstraction to use. Looked at other drivers but *many* do the same
and have the exact same comment :)

$ git grep "TODO: Use mapping abstraction properly" -- drivers/gpu/  | wc -l
15

I'll be happy to fix it if someone could elaborate what this comment expects.

[snip]

>> +
>> +	if (!drm_dev_enter(drm, &idx))
>> +		return;
>> +
>> +	backlight_enable(ssd1307->bl_dev);
> This seems backward - I would have assumed backlight was enabled
> after the display was enabled - so you potentially hide some flickering.
> This is the order done in drm_panel.
>

I see. Sure, I'll change this in v2 as well.

[snip]
 
>> +
>> +	backlight_disable(ssd1307->bl_dev);
> And here backlight could be disabled before disabling the display.
> 

Ok.

[snip]

>> +
>> +	/* Turn on the display */
>> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_DISPLAY_ON);
>> +	if (ret < 0)
>> +		return ret;
> I would assume the display is turned on later - and should be left off
> here. The pipe function will do this when needed.
>

Indeed. I based this on the the ssd1307fb probe logi but forgot to remove
this that's not needed since will be managed by display pipe {en,dis}able.
 
>> +
>> +	return 0;
>> +}
>> +
>> +static int ssd1307_update_bl(struct backlight_device *bdev)
>> +{
>> +	struct ssd1307_device *ssd1307 = bl_get_data(bdev);
>> +	int brightness = bdev->props.brightness;
> Use backlight_get_brightness(bdev) here.
>

Ok.
 
>> +	int ret;
>> +
>> +	ssd1307->contrast = brightness;
>> +
>> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_CONTRAST);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->contrast);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	return 0;
>> +}
>> +
>> +static int ssd1307_get_brightness(struct backlight_device *bdev)
>> +{
>> +	struct ssd1307_device *ssd1307 = bl_get_data(bdev);
>> +
>> +	return ssd1307->contrast;
> I am pretty sure this function can be omitted - as the brightness value
> is not changed unless we write it.
>

Gotcha. I will remove this too then.

[snip] 

>> +
>> +	drm_connector_helper_add(&ssd1307->connector, &ssd1307_connector_helper_funcs);
>> +	ret = drm_connector_init(drm, &ssd1307->connector, &ssd1307_connector_funcs,
>> +				 DRM_MODE_CONNECTOR_Unknown);
> Why not the I2C connector?
>

Doh, I forgot to update the driver after introducing patch 1/4...
 
[snip]

>> +
>> +	snprintf(bl_name, sizeof(bl_name), "ssd1307%d", drm->primary->index);
>> +	bl = backlight_device_register(bl_name, dev, ssd1307, &ssd1307fb_bl_ops,
>> +				       NULL);
> devm_backlight_device_register?
> And use (dev, dev_name(dev), - so you can drop bl_name[]
>

Right. Good suggestion.

[snip]
 
>> +	}
>> +regulator_disable:
>> +	if (ssd1307->vbat_reg)
>> +		regulator_disable(ssd1307->vbat_reg);
> No need for the if (sd1307->vbat_reg) here.
>

Ok.

[snip]
 
>> +	if (ssd1307->vbat_reg)
>> +		regulator_disable(ssd1307->vbat_reg);
> Drop if.
>

Ok.

If you don't mind I'll wait a few days before re-spining v2, in case
others could have more feedback. Thanks a lot again for your review.
 
Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat

Re: [PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Thomas Zimmermann]

[-- Attachment #1.1: Type: text/plain, Size: 33752 bytes --]

Hi Javier,

please see comments and questions below.

Am 31.01.22 um 21:29 schrieb Javier Martinez Canillas:
> Add a DRM driver for SSD1305, SSD1306, SSD1307 and SSD1309 Solomon OLED
> controllers that can be programmed via an I2C interface. This is a port
> of the ssd1307fb driver that already supports these devices.
> 
> A Device Tree binding is not added because the DRM driver is compatible
> with the existing binding for the ssd1307fb driver.
> 
> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
> ---
> 
>   drivers/gpu/drm/tiny/Kconfig   |  12 +
>   drivers/gpu/drm/tiny/Makefile  |   1 +
>   drivers/gpu/drm/tiny/ssd1307.c | 976 +++++++++++++++++++++++++++++++++
>   3 files changed, 989 insertions(+)
>   create mode 100644 drivers/gpu/drm/tiny/ssd1307.c
> 
> diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig
> index 712e0004e96e..25c9c013bcda 100644
> --- a/drivers/gpu/drm/tiny/Kconfig
> +++ b/drivers/gpu/drm/tiny/Kconfig
> @@ -157,6 +157,18 @@ config TINYDRM_REPAPER
>   
>   	  If M is selected the module will be called repaper.
>   
> +config TINYDRM_SSD1307

TINYDRM is so 2010's. Just call it DRM.

Some of the drivers use TINY for historical reasons. Simple pipe and 
mipi helpers originated from here IIRC. And now it's just regular DRM 
drivers.

> +	tristate "DRM support for Solomon SSD1307 OLED displays"
> +	depends on DRM && I2C
> +	select DRM_KMS_HELPER
> +	select DRM_GEM_SHMEM_HELPER
> +	select BACKLIGHT_CLASS_DEVICE

Alphabetical order please.

> +	help
> +	  DRM driver for the SSD1305, SSD1306, SSD1307 and SSD1309 Solomon
> +	  OLED controllers that can be programmed via an I2C interface.
> +
> +	  If M is selected the module will be called ssd1307.
> +
>   config TINYDRM_ST7586
>   	tristate "DRM support for Sitronix ST7586 display panels"
>   	depends on DRM && SPI
> diff --git a/drivers/gpu/drm/tiny/Makefile b/drivers/gpu/drm/tiny/Makefile
> index 5d5505d40e7b..38c4c1111e96 100644
> --- a/drivers/gpu/drm/tiny/Makefile
> +++ b/drivers/gpu/drm/tiny/Makefile
> @@ -12,5 +12,6 @@ obj-$(CONFIG_TINYDRM_ILI9341)		+= ili9341.o
>   obj-$(CONFIG_TINYDRM_ILI9486)		+= ili9486.o
>   obj-$(CONFIG_TINYDRM_MI0283QT)		+= mi0283qt.o
>   obj-$(CONFIG_TINYDRM_REPAPER)		+= repaper.o
> +obj-$(CONFIG_TINYDRM_SSD1307)		+= ssd1307.o

Maybe call it ssd130x

>   obj-$(CONFIG_TINYDRM_ST7586)		+= st7586.o
>   obj-$(CONFIG_TINYDRM_ST7735R)		+= st7735r.o
> diff --git a/drivers/gpu/drm/tiny/ssd1307.c b/drivers/gpu/drm/tiny/ssd1307.c
> new file mode 100644
> index 000000000000..4ea223674587
> --- /dev/null
> +++ b/drivers/gpu/drm/tiny/ssd1307.c
> @@ -0,0 +1,976 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * DRM driver for Solomon SSD1307 OLED displays
> + *
> + * Copyright 2022 Red Hat Inc.
> + *
> + * Based on drivers/video/fbdev/ssd1307fb.c
> + * Copyright 2012 Free Electrons
> + *
> + */
> +
> +#include <linux/backlight.h>
> +#include <linux/delay.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/i2c.h>
> +#include <linux/module.h>
> +#include <linux/property.h>
> +#include <linux/pwm.h>
> +#include <linux/regulator/consumer.h>
> +
> +#include <drm/drm_atomic_helper.h>
> +#include <drm/drm_damage_helper.h>
> +#include <drm/drm_drv.h>
> +#include <drm/drm_fb_cma_helper.h>
> +#include <drm/drm_fb_helper.h>
> +#include <drm/drm_format_helper.h>
> +#include <drm/drm_gem_atomic_helper.h>
> +#include <drm/drm_gem_framebuffer_helper.h>
> +#include <drm/drm_gem_shmem_helper.h>
> +#include <drm/drm_managed.h>
> +#include <drm/drm_modes.h>
> +#include <drm/drm_rect.h>
> +#include <drm/drm_probe_helper.h>
> +#include <drm/drm_simple_kms_helper.h>
> +
> +#define DRIVER_NAME	"ssd1307"
> +#define DRIVER_DESC	"DRM driver for Solomon SSD1307 OLED displays"
> +#define DRIVER_DATE	"20220131"
> +#define DRIVER_MAJOR	1
> +#define DRIVER_MINOR	0
> +
> +#define SSD1307_DATA				0x40
> +#define SSD1307_COMMAND			0x80
> +
> +#define SSD1307_SET_ADDRESS_MODE		0x20
> +#define SSD1307_SET_ADDRESS_MODE_HORIZONTAL	(0x00)
> +#define SSD1307_SET_ADDRESS_MODE_VERTICAL	(0x01)
> +#define SSD1307_SET_ADDRESS_MODE_PAGE		(0x02)
> +#define SSD1307_SET_COL_RANGE			0x21
> +#define SSD1307_SET_PAGE_RANGE			0x22
> +#define SSD1307_CONTRAST			0x81
> +#define SSD1307_SET_LOOKUP_TABLE		0x91
> +#define SSD1307_CHARGE_PUMP			0x8d
> +#define SSD1307_SEG_REMAP_ON			0xa1
> +#define SSD1307_DISPLAY_OFF			0xae
> +#define SSD1307_SET_MULTIPLEX_RATIO		0xa8
> +#define SSD1307_DISPLAY_ON			0xaf
> +#define SSD1307_START_PAGE_ADDRESS		0xb0
> +#define SSD1307_SET_DISPLAY_OFFSET		0xd3
> +#define SSD1307_SET_CLOCK_FREQ			0xd5
> +#define SSD1307_SET_AREA_COLOR_MODE		0xd8
> +#define SSD1307_SET_PRECHARGE_PERIOD		0xd9
> +#define SSD1307_SET_COM_PINS_CONFIG		0xda
> +#define SSD1307_SET_VCOMH			0xdb
> +
> +#define MAX_CONTRAST 255
> +
> +struct ssd1307_deviceinfo {
> +	u32 default_vcomh;
> +	u32 default_dclk_div;
> +	u32 default_dclk_frq;
> +	int need_pwm;
> +	int need_chargepump;
> +};
> +
> +struct ssd1307_device {
> +	struct drm_device drm;
> +	struct drm_simple_display_pipe pipe;
> +	struct drm_display_mode mode;
> +	struct drm_connector connector;
> +	struct i2c_client *client;
> +
> +	const struct ssd1307_deviceinfo *device_info;
> +
> +	unsigned area_color_enable : 1;
> +	unsigned com_invdir : 1;
> +	unsigned com_lrremap : 1;
> +	unsigned com_seq : 1;
> +	unsigned lookup_table_set : 1;
> +	unsigned low_power : 1;
> +	unsigned seg_remap : 1;
> +	u32 com_offset;
> +	u32 contrast;
> +	u32 dclk_div;
> +	u32 dclk_frq;
> +	u32 height;
> +	u8 lookup_table[4];
> +	u32 page_offset;
> +	u32 col_offset;
> +	u32 prechargep1;
> +	u32 prechargep2;
> +
> +	struct backlight_device *bl_dev;
> +	struct pwm_device *pwm;
> +	struct gpio_desc *reset;
> +	struct regulator *vbat_reg;
> +	u32 vcomh;
> +	u32 width;
> +	/* Cached address ranges */
> +	u8 col_start;
> +	u8 col_end;
> +	u8 page_start;
> +	u8 page_end;
> +};
> +
> +struct ssd1307_array {
> +	u8	type;

'cmd'?

> +	u8	data[];
> +};

The name 'array' is misleading. At first I thought that it's a C array 
type. But it's actually an element of the adapter's i2c protocol. Is 
there a better name that makes this more obvious? ssd130x_i2c_cmd?

If this common enough that it could be part of some kind of i2c helper 
library?

> +
> +static inline struct ssd1307_device *drm_to_ssd1307(struct drm_device *drm)
> +{
> +	return container_of(drm, struct ssd1307_device, drm);
> +}
> +
> +static struct ssd1307_array *ssd1307_alloc_array(u32 len, u8 type)
> +{
> +	struct ssd1307_array *array;
> +
> +	array = kzalloc(sizeof(struct ssd1307_array) + len, GFP_KERNEL);

sizeof(*array) is slighly more reliable. But wasn't there even a macro 
for such allocations (struct + length)?

> +	if (!array)
> +		return NULL;

Personally I prefer pointer-encoded errors instead of NULL. But I don't 
thing there's a strict rule about it.

> +
> +	array->type = type;
> +
> +	return array;
> +}
> +
> +static int ssd1307_write_array(struct i2c_client *client,
> +			       struct ssd1307_array *array, u32 len)
> +{
> +	int ret;
> +
> +	len += sizeof(struct ssd1307_array);

Same thing about sizeof: sizeof(var) is better than sizeof(type);

Since you're using a separate array structure anyway, wouldn't it make 
sense to store

> +
> +	ret = i2c_master_send(client, (u8 *)array, len);
> +	if (ret != len) {
> +		dev_err(&client->dev, "Couldn't send I2C command.\n");
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static inline int ssd1307_write_cmd(struct i2c_client *client, u8 cmd)
> +{
> +	struct ssd1307_array *array;
> +	int ret;
> +
> +	array = ssd1307_alloc_array(1, SSD1307_COMMAND);
> +	if (!array)
> +		return -ENOMEM;
> +
> +	array->data[0] = cmd;
> +
> +	ret = ssd1307_write_array(client, array, 1);
> +	kfree(array);
> +
> +	return ret;
> +}
> +
> +static int ssd1307_set_col_range(struct ssd1307_device *ssd1307,
> +				 u8 col_start, u8 cols)
> +{
> +	u8 col_end = col_start + cols - 1;
> +	int ret;
> +
> +	if (col_start == ssd1307->col_start && col_end == ssd1307->col_end)
> +		return 0;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_COL_RANGE);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, col_start);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, col_end);
> +	if (ret < 0)
> +		return ret;

Can you write these cmds in one step, such as setting up an array and 
sending it with ssd1307_write_array?

> +
> +	ssd1307->col_start = col_start;
> +	ssd1307->col_end = col_end;
> +	return 0;
> +}
> +
> +static int ssd1307_set_page_range(struct ssd1307_device *ssd1307,
> +				  u8 page_start, u8 pages)
> +{
> +	u8 page_end = page_start + pages - 1;
> +	int ret;
> +
> +	if (page_start == ssd1307->page_start && page_end == ssd1307->page_end)
> +		return 0;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_PAGE_RANGE);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, page_start);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, page_end);
> +	if (ret < 0)
> +		return ret;
> +
> +	ssd1307->page_start = page_start;
> +	ssd1307->page_end = page_end;
> +	return 0;
> +}
> +
> +static int ssd1307_update_display(struct ssd1307_device *ssd1307, u8 *buf,
> +				  u32 width, u32 height)
> +{
> +	struct ssd1307_array *array;
> +	unsigned int line_length = DIV_ROUND_UP(width, 8);
> +	unsigned int pages = DIV_ROUND_UP(height, 8);
> +	u32 array_idx = 0;
> +	int ret, i, j, k;
> +
> +	array = ssd1307_alloc_array(width * pages, SSD1307_DATA);
> +	if (!array)
> +		return -ENOMEM;
> +
> +	/*
> +	 * The screen is divided in pages, each having a height of 8
> +	 * pixels, and the width of the screen. When sending a byte of
> +	 * data to the controller, it gives the 8 bits for the current
> +	 * column. I.e, the first byte are the 8 bits of the first
> +	 * column, then the 8 bits for the second column, etc.
> +	 *
> +	 *
> +	 * Representation of the screen, assuming it is 5 bits
> +	 * wide. Each letter-number combination is a bit that controls
> +	 * one pixel.
> +	 *
> +	 * A0 A1 A2 A3 A4
> +	 * B0 B1 B2 B3 B4
> +	 * C0 C1 C2 C3 C4
> +	 * D0 D1 D2 D3 D4
> +	 * E0 E1 E2 E3 E4
> +	 * F0 F1 F2 F3 F4
> +	 * G0 G1 G2 G3 G4
> +	 * H0 H1 H2 H3 H4
> +	 *
> +	 * If you want to update this screen, you need to send 5 bytes:
> +	 *  (1) A0 B0 C0 D0 E0 F0 G0 H0
> +	 *  (2) A1 B1 C1 D1 E1 F1 G1 H1
> +	 *  (3) A2 B2 C2 D2 E2 F2 G2 H2
> +	 *  (4) A3 B3 C3 D3 E3 F3 G3 H3
> +	 *  (5) A4 B4 C4 D4 E4 F4 G4 H4
> +	 */
> +
> +	ret = ssd1307_set_col_range(ssd1307, ssd1307->col_offset, width);
> +	if (ret < 0)
> +		goto out_free;
> +
> +	ret = ssd1307_set_page_range(ssd1307, ssd1307->page_offset / 8, pages);
> +	if (ret < 0)
> +		goto out_free;
> +
> +	for (i = 0; i < pages; i++) {
> +		int m = 8;
> +
> +		/* Last page may be partial */
> +		if (8 * (i + 1) > ssd1307->height)
> +			m = ssd1307->height % 8;
> +		for (j = 0; j < width; j++) {
> +			u8 data = 0;
> +
> +			for (k = 0; k < m; k++) {
> +				u8 byte = buf[(8 * i + k) * line_length +
> +					       j / 8];
> +				u8 bit = (byte >> (j % 8)) & 1;
> +
> +				data |= bit << k;
> +			}
> +			array->data[array_idx++] = data;
> +		}
> +	}
> +
> +	ret = ssd1307_write_array(ssd1307->client, array, width * pages);
> +
> +out_free:
> +	kfree(array);
> +	return ret;
> +}
> +
> +static void ssd1307_clear_screen(struct ssd1307_device *ssd1307, u32 width, u32 height)
> +{
> +	u8 *buf = NULL;
> +
> +	buf = kmalloc_array(width, height, GFP_KERNEL);

There's kcalloc().

> +	if (!buf)
> +		return;
> +
> +	/* Clear screen to black if disabled */
> +	memset(buf, 0, width * height);
> +
> +	ssd1307_update_display(ssd1307, buf, width, height);
> +}
> +
> +static int ssd1307_fb_blit_rect(struct drm_framebuffer *fb, const struct dma_buf_map *map,
> +				struct drm_rect *rect)
> +{
> +	struct ssd1307_device *ssd1307 = drm_to_ssd1307(fb->dev);
> +	void *vmap = map->vaddr; /* TODO: Use mapping abstraction properly */
> +	int ret = 0;
> +	u8 *buf = NULL;
> +
> +	buf = kmalloc_array(fb->width, fb->height, GFP_KERNEL);

Maybe leave a short comment that these arrays will be consumed by 
i2c_master_send().

> +	if (!buf) {
> +		ret = -ENOMEM;
> +		goto out_exit;

It's the first error. Just return directly.

> +	}
> +
> +	drm_fb_xrgb8888_to_gray8(buf, 0, vmap, fb, rect);
> +
> +	drm_fb_gray8_to_mono_reversed(buf, buf, rect);
> +
> +	ssd1307_update_display(ssd1307, buf, fb->width, fb->height);
> +
> +	kfree(buf);
> +out_exit:
> +	return ret;
> +}
> +
> +static int ssd1307_display_pipe_mode_valid(struct drm_simple_display_pipe *pipe,
> +						   const struct drm_display_mode *mode)
> +{
> +	struct ssd1307_device *ssd1307 = drm_to_ssd1307(pipe->crtc.dev);
> +
> +	if (mode->hdisplay != ssd1307->mode.hdisplay &&
> +	    mode->vdisplay != ssd1307->mode.vdisplay)
> +		return MODE_ONE_SIZE;
> +	else if (mode->hdisplay != ssd1307->mode.hdisplay)
> +		return MODE_ONE_WIDTH;
> +	else if (mode->vdisplay != ssd1307->mode.vdisplay)
> +		return MODE_ONE_HEIGHT;
> +
> +	return MODE_OK;
> +}
> +
> +static void ssd1307_display_pipe_enable(struct drm_simple_display_pipe *pipe,
> +				       struct drm_crtc_state *crtc_state,
> +				       struct drm_plane_state *plane_state)
> +{
> +	struct ssd1307_device *ssd1307 = drm_to_ssd1307(pipe->crtc.dev);
> +	struct drm_device *drm = &ssd1307->drm;
> +	int idx;
> +
> +	if (!drm_dev_enter(drm, &idx))
> +		return;
> +
> +	backlight_enable(ssd1307->bl_dev);
> +
> +	ssd1307_write_cmd(ssd1307->client, SSD1307_DISPLAY_ON);
> +
> +	drm_dev_exit(idx);
> +}
> +
> +static void ssd1307_display_pipe_disable(struct drm_simple_display_pipe *pipe)
> +{
> +	struct ssd1307_device *ssd1307 = drm_to_ssd1307(pipe->crtc.dev);
> +	struct drm_device *drm = &ssd1307->drm;
> +	int idx;
> +
> +	if (!drm_dev_enter(drm, &idx))
> +		return;
> +
> +	ssd1307_clear_screen(ssd1307, ssd1307->width, ssd1307->height);
> +
> +	ssd1307_write_cmd(ssd1307->client, SSD1307_DISPLAY_OFF);
> +
> +	backlight_disable(ssd1307->bl_dev);
> +
> +	drm_dev_exit(idx);
> +}
> +
> +static void ssd1307_display_pipe_update(struct drm_simple_display_pipe *pipe,
> +					struct drm_plane_state *old_plane_state)
> +{
> +	struct ssd1307_device *ssd1307 = drm_to_ssd1307(pipe->crtc.dev);
> +	struct drm_plane_state *plane_state = pipe->plane.state;
> +	struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(plane_state);
> +	struct drm_framebuffer *fb = plane_state->fb;
> +	struct drm_device *drm = &ssd1307->drm;
> +	struct drm_rect rect;
> +	int idx;
> +
> +	if (!fb)
> +		return;
> +
> +	if (!pipe->crtc.state->active)
> +		return;
> +
> +	if (!drm_dev_enter(drm, &idx))
> +		return;
> +
> +	if (drm_atomic_helper_damage_merged(old_plane_state, plane_state, &rect))
> +		ssd1307_fb_blit_rect(plane_state->fb, &shadow_plane_state->data[0], &rect);

Shadow-plane helpers have recently gotten the ability to use virtual 
screens with sizes much larger than the display.

If you want to get fancy, you could add this here. It'll give you large 
display sizes for easy scrolling and fbcon panning.

Example code is at

https://elixir.bootlin.com/linux/v5.17-rc2/source/drivers/gpu/drm/tiny/simpledrm.c#L652
https://elixir.bootlin.com/linux/v5.17-rc2/source/drivers/gpu/drm/tiny/simpledrm.c#L703
https://elixir.bootlin.com/linux/v5.17-rc2/source/drivers/gpu/drm/tiny/simpledrm.c#L785

> +
> +	drm_dev_exit(idx);
> +}
> +
> +static const struct drm_simple_display_pipe_funcs ssd1307_pipe_funcs = {
> +	.mode_valid = ssd1307_display_pipe_mode_valid,
> +	.enable = ssd1307_display_pipe_enable,
> +	.disable = ssd1307_display_pipe_disable,
> +	.update = ssd1307_display_pipe_update,
> +	DRM_GEM_SIMPLE_DISPLAY_PIPE_SHADOW_PLANE_FUNCS,
> +};
> +
> +static int ssd1307_connector_get_modes(struct drm_connector *connector)
> +{
> +	struct ssd1307_device *ssd1307 = drm_to_ssd1307(connector->dev);
> +	struct drm_display_mode *mode;
> +
> +	mode = drm_mode_duplicate(connector->dev, &ssd1307->mode);
> +	if (!mode) {
> +		DRM_ERROR("Failed to duplicate mode\n");
> +		return 0;
> +	}
> +
> +	connector->display_info.width_mm = mode->width_mm;
> +	connector->display_info.height_mm = mode->height_mm;
> +	connector->display_info.bpc = 32;

Not just 1 bit?

> +
> +	drm_mode_set_name(mode);
> +	mode->type |= DRM_MODE_TYPE_PREFERRED;

There's drm_set_preferred_mode().

> +	drm_mode_probed_add(connector, mode);
> +
> +	return 1;
> +}
> +
> +static const struct drm_connector_helper_funcs ssd1307_connector_helper_funcs = {
> +	.get_modes = ssd1307_connector_get_modes,
> +};
> +
> +static const struct drm_connector_funcs ssd1307_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 ssd1307_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 ssd1307_formats[] = {
> +	DRM_FORMAT_XRGB8888,
> +};
> +
> +DEFINE_DRM_GEM_FOPS(ssd1307_fops);
> +
> +static const struct drm_driver ssd1307_drm_driver = {
> +	DRM_GEM_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			= &ssd1307_fops,
> +};
> +
> +static int ssd1307_pwm_enable(struct ssd1307_device *ssd1307)
> +{
> +	struct pwm_state pwmstate;
> +
> +	ssd1307->pwm = pwm_get(&ssd1307->client->dev, NULL);
> +	if (IS_ERR(ssd1307->pwm)) {
> +		dev_err(&ssd1307->client->dev, "Could not get PWM from device tree!\n");
> +		return PTR_ERR(ssd1307->pwm);
> +	}
> +
> +	pwm_init_state(ssd1307->pwm, &pwmstate);
> +	pwm_set_relative_duty_cycle(&pwmstate, 50, 100);
> +	pwm_apply_state(ssd1307->pwm, &pwmstate);
> +
> +	/* Enable the PWM */
> +	pwm_enable(ssd1307->pwm);
> +
> +	dev_dbg(&ssd1307->client->dev, "Using PWM%d with a %lluns period.\n",
> +		ssd1307->pwm->pwm, pwm_get_period(ssd1307->pwm));
> +
> +	return 0;
> +}
> +
> +static int ssd1307_init(struct ssd1307_device *ssd1307)
> +{
> +	u32 precharge, dclk, com_invdir, compins;
> +	int ret;
> +
> +	/* Set initial contrast */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_CONTRAST);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->contrast);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Set segment re-map */
> +	if (ssd1307->seg_remap) {
> +		ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SEG_REMAP_ON);
> +		if (ret < 0)
> +			return ret;
> +	}
> +
> +	/* Set COM direction */
> +	com_invdir = 0xc0 | ssd1307->com_invdir << 3;
> +	ret = ssd1307_write_cmd(ssd1307->client,  com_invdir);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Set multiplex ratio value */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_MULTIPLEX_RATIO);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->height - 1);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* set display offset value */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_DISPLAY_OFFSET);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->com_offset);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Set clock frequency */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_CLOCK_FREQ);
> +	if (ret < 0)
> +		return ret;
> +
> +	dclk = ((ssd1307->dclk_div - 1) & 0xf) | (ssd1307->dclk_frq & 0xf) << 4;
> +	ret = ssd1307_write_cmd(ssd1307->client, dclk);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Set Area Color Mode ON/OFF & Low Power Display Mode */
> +	if (ssd1307->area_color_enable || ssd1307->low_power) {
> +		u32 mode;
> +
> +		ret = ssd1307_write_cmd(ssd1307->client,
> +					SSD1307_SET_AREA_COLOR_MODE);
> +		if (ret < 0)
> +			return ret;
> +
> +		mode = (ssd1307->area_color_enable ? 0x30 : 0) |
> +			(ssd1307->low_power ? 5 : 0);
> +		ret = ssd1307_write_cmd(ssd1307->client, mode);
> +		if (ret < 0)
> +			return ret;
> +	}
> +
> +	/* Set precharge period in number of ticks from the internal clock */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_PRECHARGE_PERIOD);
> +	if (ret < 0)
> +		return ret;
> +
> +	precharge = (ssd1307->prechargep1 & 0xf) | (ssd1307->prechargep2 & 0xf) << 4;
> +	ret = ssd1307_write_cmd(ssd1307->client, precharge);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Set COM pins configuration */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_COM_PINS_CONFIG);
> +	if (ret < 0)
> +		return ret;
> +
> +	compins = 0x02 | !ssd1307->com_seq << 4 | ssd1307->com_lrremap << 5;
> +	ret = ssd1307_write_cmd(ssd1307->client, compins);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Set VCOMH */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_VCOMH);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->vcomh);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Turn on the DC-DC Charge Pump */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_CHARGE_PUMP);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client,
> +		BIT(4) | (ssd1307->device_info->need_chargepump ? BIT(2) : 0));
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Set lookup table */
> +	if (ssd1307->lookup_table_set) {
> +		int i;
> +
> +		ret = ssd1307_write_cmd(ssd1307->client,
> +					SSD1307_SET_LOOKUP_TABLE);
> +		if (ret < 0)
> +			return ret;
> +
> +		for (i = 0; i < ARRAY_SIZE(ssd1307->lookup_table); ++i) {
> +			u8 val = ssd1307->lookup_table[i];
> +
> +			if (val < 31 || val > 63)
> +				dev_warn(&ssd1307->client->dev,
> +					 "lookup table index %d value out of range 31 <= %d <= 63\n",
> +					 i, val);
> +			ret = ssd1307_write_cmd(ssd1307->client, val);
> +			if (ret < 0)
> +				return ret;
> +		}
> +	}
> +
> +	/* Switch to horizontal addressing mode */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_ADDRESS_MODE);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client,
> +				SSD1307_SET_ADDRESS_MODE_HORIZONTAL);
> +	if (ret < 0)
> +		return ret;
> +
> +	ssd1307_clear_screen(ssd1307, ssd1307->width, ssd1307->height);
> +
> +	/* Turn on the display */
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_DISPLAY_ON);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
> +
> +static int ssd1307_update_bl(struct backlight_device *bdev)
> +{
> +	struct ssd1307_device *ssd1307 = bl_get_data(bdev);
> +	int brightness = bdev->props.brightness;
> +	int ret;
> +
> +	ssd1307->contrast = brightness;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_CONTRAST);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = ssd1307_write_cmd(ssd1307->client, ssd1307->contrast);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
> +
> +static int ssd1307_get_brightness(struct backlight_device *bdev)
> +{
> +	struct ssd1307_device *ssd1307 = bl_get_data(bdev);
> +
> +	return ssd1307->contrast;
> +}
> +
> +static const struct backlight_ops ssd1307fb_bl_ops = {
> +	.update_status	= ssd1307_update_bl,
> +	.get_brightness	= ssd1307_get_brightness,
> +};
> +
> +static void ssd1307_reset(struct ssd1307_device *ssd1307)
> +{
> +	/* Reset the screen */
> +	gpiod_set_value_cansleep(ssd1307->reset, 1);
> +	udelay(4);
> +	gpiod_set_value_cansleep(ssd1307->reset, 0);
> +	udelay(4);
> +}
> +
> +static void ssd1307_parse_properties(struct ssd1307_device *ssd1307)
> +{
> +	struct device *dev = &ssd1307->client->dev;
> +
> +	if (device_property_read_u32(dev, "solomon,width", &ssd1307->width))
> +		ssd1307->width = 96;
> +
> +	if (device_property_read_u32(dev, "solomon,height", &ssd1307->height))
> +		ssd1307->height = 16;
> +
> +	if (device_property_read_u32(dev, "solomon,page-offset", &ssd1307->page_offset))
> +		ssd1307->page_offset = 1;
> +
> +	if (device_property_read_u32(dev, "solomon,col-offset", &ssd1307->col_offset))
> +		ssd1307->col_offset = 0;
> +
> +	if (device_property_read_u32(dev, "solomon,com-offset", &ssd1307->com_offset))
> +		ssd1307->com_offset = 0;
> +
> +	if (device_property_read_u32(dev, "solomon,prechargep1", &ssd1307->prechargep1))
> +		ssd1307->prechargep1 = 2;
> +
> +	if (device_property_read_u32(dev, "solomon,prechargep2", &ssd1307->prechargep2))
> +		ssd1307->prechargep2 = 2;
> +
> +	if (!device_property_read_u8_array(dev, "solomon,lookup-table",
> +					   ssd1307->lookup_table,
> +					   ARRAY_SIZE(ssd1307->lookup_table)))
> +		ssd1307->lookup_table_set = 1;
> +
> +	ssd1307->seg_remap = !device_property_read_bool(dev, "solomon,segment-no-remap");
> +	ssd1307->com_seq = device_property_read_bool(dev, "solomon,com-seq");
> +	ssd1307->com_lrremap = device_property_read_bool(dev, "solomon,com-lrremap");
> +	ssd1307->com_invdir = device_property_read_bool(dev, "solomon,com-invdir");
> +	ssd1307->area_color_enable =
> +		device_property_read_bool(dev, "solomon,area-color-enable");
> +	ssd1307->low_power = device_property_read_bool(dev, "solomon,low-power");
> +
> +	ssd1307->contrast = 127;
> +	ssd1307->vcomh = ssd1307->device_info->default_vcomh;
> +
> +	/* Setup display timing */
> +	if (device_property_read_u32(dev, "solomon,dclk-div", &ssd1307->dclk_div))
> +		ssd1307->dclk_div = ssd1307->device_info->default_dclk_div;
> +	if (device_property_read_u32(dev, "solomon,dclk-frq", &ssd1307->dclk_frq))
> +		ssd1307->dclk_frq = ssd1307->device_info->default_dclk_frq;
> +}
> +
> +static void ssd1307_set_mode(struct ssd1307_device *ssd1307)
> +{
> +	struct drm_display_mode *mode = &ssd1307->mode;
> +	struct drm_device *drm = &ssd1307->drm;
> +
> +	mode->type = DRM_MODE_TYPE_DRIVER;
> +	mode->clock = 1;
> +	mode->hdisplay = mode->htotal = ssd1307->width;
> +	mode->hsync_start = mode->hsync_end = ssd1307->width;
> +	mode->vdisplay = mode->vtotal = ssd1307->height;
> +	mode->vsync_start = mode->vsync_end = ssd1307->height;
> +	mode->width_mm = 27;
> +	mode->height_mm = 27;
> +
> +	drm->mode_config.min_width = ssd1307->width;
> +	drm->mode_config.max_width = ssd1307->width;
> +	drm->mode_config.min_height = ssd1307->height;
> +	drm->mode_config.max_height = ssd1307->height;
> +	drm->mode_config.preferred_depth = 32;
> +	drm->mode_config.funcs = &ssd1307_mode_config_funcs;
> +}
> +
> +static int ssd1307_probe(struct i2c_client *client)

This function is fairly confusing. device init, modeconfig init, OF 
functions are all mixed up. Please bring some structure to this.

> +{
> +	struct device *dev = &client->dev;
> +	struct ssd1307_device *ssd1307;
> +	struct backlight_device *bl;
> +	struct drm_device *drm;
> +	char bl_name[12];
> +	int ret;
> +
> +	ssd1307 = devm_drm_dev_alloc(dev, &ssd1307_drm_driver,
> +				 struct ssd1307_device, drm);
> +	if (IS_ERR(ssd1307))
> +		return PTR_ERR(ssd1307);
> +
> +	drm = &ssd1307->drm;
> +
> +	ret = drmm_mode_config_init(drm);
> +	if (ret)
> +		return ret;
> +
> +	ssd1307->client = client;
> +
> +	ssd1307->device_info = device_get_match_data(dev);
> +
> +	ssd1307_parse_properties(ssd1307);
> +
> +	ssd1307_set_mode(ssd1307);
> +
> +	ssd1307->reset = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW);
> +	if (IS_ERR(ssd1307->reset)) {
> +		dev_err(dev, "failed to get reset gpio: %ld\n",
> +			PTR_ERR(ssd1307->reset));
> +		return PTR_ERR(ssd1307->reset);
> +	}
> +
> +	ssd1307->vbat_reg = devm_regulator_get_optional(dev, "vbat");
> +	if (IS_ERR(ssd1307->vbat_reg)) {
> +		ret = PTR_ERR(ssd1307->vbat_reg);
> +		if (ret == -ENODEV) {
> +			ssd1307->vbat_reg = NULL;
> +		} else {
> +			dev_err(dev, "failed to get VBAT regulator: %d\n", ret);
> +			return ret;
> +		}
> +	}
> +
> +	drm_connector_helper_add(&ssd1307->connector, &ssd1307_connector_helper_funcs);
> +	ret = drm_connector_init(drm, &ssd1307->connector, &ssd1307_connector_funcs,
> +				 DRM_MODE_CONNECTOR_Unknown);
> +	if (ret)
> +		return ret;
> +
> +	i2c_set_clientdata(client, ssd1307);
> +
> +	if (ssd1307->reset)
> +		ssd1307_reset(ssd1307);
> +
> +	if (ssd1307->vbat_reg) {
> +		ret = regulator_enable(ssd1307->vbat_reg);
> +		if (ret) {
> +			dev_err(dev, "failed to enable VBAT: %d\n", ret);
> +			return ret;
> +		}
> +	}
> +
> +	ret = ssd1307_init(ssd1307);
> +	if (ret)
> +		goto regulator_disable;
> +
> +	if (ssd1307->device_info->need_pwm) {
> +		ret = ssd1307_pwm_enable(ssd1307);
> +		if (ret)
> +			goto regulator_disable;
> +	}
> +
> +	snprintf(bl_name, sizeof(bl_name), "ssd1307%d", drm->primary->index);
> +	bl = backlight_device_register(bl_name, dev, ssd1307, &ssd1307fb_bl_ops,
> +				       NULL);
> +	if (IS_ERR(bl)) {
> +		ret = PTR_ERR(bl);
> +		dev_err(dev, "unable to register backlight device: %d\n", ret);
> +		goto pwm_disable;
> +	}
> +
> +	bl->props.brightness = ssd1307->contrast;
> +	bl->props.max_brightness = MAX_CONTRAST;
> +	ssd1307->bl_dev = bl;
> +

drmm_mode_config_init here, then connector init

> +	ret = drm_simple_display_pipe_init(drm, &ssd1307->pipe, &ssd1307_pipe_funcs,
> +					   ssd1307_formats, ARRAY_SIZE(ssd1307_formats),
> +					   NULL, &ssd1307->connector);
> +	if (ret)
> +		goto pwm_disable;
> +
> +	drm_plane_enable_fb_damage_clips(&ssd1307->pipe.plane);
> +
> +	drm_mode_config_reset(drm);

Moving anything related to mode-config into a function would improve 
readability.

> +
> +	ret = drm_dev_register(drm, 0);
> +	if (ret)
> +		goto backlight_unregister;
> +
> +	drm_fbdev_generic_setup(drm, 0);
> +
> +	return 0;
> +
> +backlight_unregister:
> +	backlight_device_unregister(ssd1307->bl_dev);
> +pwm_disable:
> +	if (ssd1307->device_info->need_pwm) {
> +		pwm_disable(ssd1307->pwm);
> +		pwm_put(ssd1307->pwm);
> +	}
> +regulator_disable:
> +	if (ssd1307->vbat_reg)
> +		regulator_disable(ssd1307->vbat_reg);
> +	return ret;

Can this be handled by managed clean-up helpers?

> +}
> +
> +static int ssd1307_remove(struct i2c_client *client)
> +{
> +	struct ssd1307_device *ssd1307 = i2c_get_clientdata(client);
> +
> +	drm_dev_unplug(&ssd1307->drm);
> +
> +	ssd1307_write_cmd(ssd1307->client, SSD1307_DISPLAY_OFF);

There's drm_atomic_helper_shutdown for switching of the device.

https://elixir.bootlin.com/linux/v5.17-rc2/source/drivers/gpu/drm/drm_atomic_helper.c#L3136

Best regards
Thomas


> +
> +	backlight_device_unregister(ssd1307->bl_dev);
> +
> +	if (ssd1307->device_info->need_pwm) {
> +		pwm_disable(ssd1307->pwm);
> +		pwm_put(ssd1307->pwm);
> +	}
> +	if (ssd1307->vbat_reg)
> +		regulator_disable(ssd1307->vbat_reg);
> +
> +	return 0;
> +}
> +
> +static void ssd1307_shutdown(struct i2c_client *client)
> +{
> +	struct ssd1307_device *ssd1307 = i2c_get_clientdata(client);
> +
> +	drm_atomic_helper_shutdown(&ssd1307->drm);
> +}
> +
> +static struct ssd1307_deviceinfo ssd1307_ssd1305_deviceinfo = {
> +	.default_vcomh = 0x34,
> +	.default_dclk_div = 1,
> +	.default_dclk_frq = 7,
> +};
> +
> +static struct ssd1307_deviceinfo ssd1307_ssd1306_deviceinfo = {
> +	.default_vcomh = 0x20,
> +	.default_dclk_div = 1,
> +	.default_dclk_frq = 8,
> +	.need_chargepump = 1,
> +};
> +
> +static struct ssd1307_deviceinfo ssd1307_ssd1307_deviceinfo = {
> +	.default_vcomh = 0x20,
> +	.default_dclk_div = 2,
> +	.default_dclk_frq = 12,
> +	.need_pwm = 1,
> +};
> +
> +static struct ssd1307_deviceinfo ssd1307_ssd1309_deviceinfo = {
> +	.default_vcomh = 0x34,
> +	.default_dclk_div = 1,
> +	.default_dclk_frq = 10,
> +};
> +
> +static const struct of_device_id ssd1307_of_match[] = {
> +	{
> +		.compatible = "solomon,ssd1305fb-i2c",
> +		.data = (void *)&ssd1307_ssd1305_deviceinfo,
> +	},
> +	{
> +		.compatible = "solomon,ssd1306fb-i2c",
> +		.data = (void *)&ssd1307_ssd1306_deviceinfo,
> +	},
> +	{
> +		.compatible = "solomon,ssd1307fb-i2c",
> +		.data = (void *)&ssd1307_ssd1307_deviceinfo,
> +	},
> +	{
> +		.compatible = "solomon,ssd1309fb-i2c",
> +		.data = (void *)&ssd1307_ssd1309_deviceinfo,
> +	},
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, ssd1307_of_match);
> +
> +
> +static struct i2c_driver ssd1307_i2c_driver = {
> +	.driver = {
> +		.name = DRIVER_NAME,
> +		.of_match_table = ssd1307_of_match,
> +	},
> +	.probe_new = ssd1307_probe,
> +	.remove = ssd1307_remove,
> +	.shutdown = ssd1307_shutdown,
> +};
> +
> +module_i2c_driver(ssd1307_i2c_driver);
> +
> +MODULE_DESCRIPTION(DRIVER_DESC);
> +MODULE_AUTHOR("Javier Martinez Canillas <javierm@redhat.com>");
> +MODULE_LICENSE("GPL v2");

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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Re: [PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Andy Shevchenko]

On Mon, Jan 31, 2022 at 10:30:46PM +0100, Sam Ravnborg wrote:
> On Mon, Jan 31, 2022 at 09:29:16PM +0100, Javier Martinez Canillas wrote:

...

> > +config TINYDRM_SSD1307
> > +	tristate "DRM support for Solomon SSD1307 OLED displays"
> Use SSD130X here - so SSD1306 users can find it.

It's better to list them all in the "help". How user would grep this?

`git grep -n -i ssd1306` ==> no match.

> > +	depends on DRM && I2C
> > +	select DRM_KMS_HELPER
> > +	select DRM_GEM_SHMEM_HELPER
> > +	select BACKLIGHT_CLASS_DEVICE
> > +	help
> > +	  DRM driver for the SSD1305, SSD1306, SSD1307 and SSD1309 Solomon
> > +	  OLED controllers that can be programmed via an I2C interface.
> > +
> > +	  If M is selected the module will be called ssd1307.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Andy Shevchenko]

On Tue, Feb 01, 2022 at 01:14:22AM +0100, Javier Martinez Canillas wrote:
> On 1/31/22 22:30, Sam Ravnborg wrote:
> > On Mon, Jan 31, 2022 at 09:29:16PM +0100, Javier Martinez Canillas wrote:

...

> > The driver uses the pwms property for the backlight.
> > It would have been much better to bite the bullet and require the
> > backlight to be specified using a backlight node in the DT.
> > This is the standard way to do it and then the driver could use the
> > existing backlight driver rather than embedding a backlight driver here.
> >
> 
> I did consider that. Because that would allow me to use a struct drm_panel
> and as you said make the core to manage the backlight. But then decied to
> just keep the backward compatibility with the existing binding to make it
> easier for users to migrate to the DRM driver.
> 
> I wonder if we could make the driver to support both ? That is, to query
> if there's a backlight with drm_panel_of_backlight() and if not found then
> registering it's own backlight like the driver is currently doing.

If we keep 100% backward compatibility, just drop the old driver.
After all module name is not so important as compatibility strings.

The problem with no backward compatibility means that removal of old driver
makes users unhappy since DT is kinda ABI and we do not break it.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Andy Shevchenko]

On Tue, Feb 01, 2022 at 10:33:31AM +0100, Thomas Zimmermann wrote:
> Am 31.01.22 um 21:29 schrieb Javier Martinez Canillas:

> > +obj-$(CONFIG_TINYDRM_SSD1307)		+= ssd1307.o
> 
> Maybe call it ssd130x

Either way it's good to list all supported models in "help" of Kconfig.

Also here is the question, should we keep backward compatibility or not?
If not, we never can remove the old driver (until last user gone).

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Javier Martinez Canillas]

On 2/1/22 10:41, Andy Shevchenko wrote:
> On Mon, Jan 31, 2022 at 10:30:46PM +0100, Sam Ravnborg wrote:
>> On Mon, Jan 31, 2022 at 09:29:16PM +0100, Javier Martinez Canillas wrote:
> 
> ...
> 
>>> +config TINYDRM_SSD1307
>>> +	tristate "DRM support for Solomon SSD1307 OLED displays"
>> Use SSD130X here - so SSD1306 users can find it.
> 
> It's better to list them all in the "help". How user would grep this?
> 
> `git grep -n -i ssd1306` ==> no match.
>

That's already the case :)

$ git grep -n -i ssd1306 drivers/gpu/drm/
drivers/gpu/drm/tiny/Kconfig:167:         DRM driver for the SSD1305, SSD1306, SSD1307 and SSD1309 Solomon
drivers/gpu/drm/tiny/ssd1307.c:922:static struct ssd1307_deviceinfo ssd1307_ssd1306_deviceinfo = {
drivers/gpu/drm/tiny/ssd1307.c:948:             .compatible = "solomon,ssd1306fb-i2c",
drivers/gpu/drm/tiny/ssd1307.c:949:             .data = (void *)&ssd1307_ssd1306_deviceinfo,
 
Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat

Re: [PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Javier Martinez Canillas]

On 2/1/22 10:44, Andy Shevchenko wrote:
> On Tue, Feb 01, 2022 at 01:14:22AM +0100, Javier Martinez Canillas wrote:
>> On 1/31/22 22:30, Sam Ravnborg wrote:
>>> On Mon, Jan 31, 2022 at 09:29:16PM +0100, Javier Martinez Canillas wrote:
> 
> ...
> 
>>> The driver uses the pwms property for the backlight.
>>> It would have been much better to bite the bullet and require the
>>> backlight to be specified using a backlight node in the DT.
>>> This is the standard way to do it and then the driver could use the
>>> existing backlight driver rather than embedding a backlight driver here.
>>>
>>
>> I did consider that. Because that would allow me to use a struct drm_panel
>> and as you said make the core to manage the backlight. But then decied to
>> just keep the backward compatibility with the existing binding to make it
>> easier for users to migrate to the DRM driver.
>>
>> I wonder if we could make the driver to support both ? That is, to query
>> if there's a backlight with drm_panel_of_backlight() and if not found then
>> registering it's own backlight like the driver is currently doing.
> 
> If we keep 100% backward compatibility, just drop the old driver.
> After all module name is not so important as compatibility strings.
>

As mentioned I don't believe those two things are related. You could make it
backward compatible but still keep the old driver around until no one else
would care about it.

This DRM driver is brand new and there may be bugs, performance issues and
whatnot. At least I won't propose to remove the old fbdev driver but would
want people using DRM to have a choice.
 
> The problem with no backward compatibility means that removal of old driver
> makes users unhappy since DT is kinda ABI and we do not break it.
> 

I think that's the crux of the issue. Do we want people to update their
kernel but using their existing Device Tree and be able to switch to the
DRM driver ?

My take is that we should and that's why I kept the backward compatibility.

Maybe we could do that in the meantime and at some point introduce new DT
bindings (with a different compatible string) that would use the latest
and greatest conventions in DT ? That seems to be a good compromise.

Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat

Re: [PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Javier Martinez Canillas]

On 2/1/22 10:33, Thomas Zimmermann wrote:
> Hi Javier,
> 
> please see comments and questions below.
>

Thanks again for your comments.

[snip] 

>>   
>> +config TINYDRM_SSD1307
> 
> TINYDRM is so 2010's. Just call it DRM.
>

Haha, Ok. I just followed what other drivers did and thought was a convention.
 
> Some of the drivers use TINY for historical reasons. Simple pipe and 
> mipi helpers originated from here IIRC. And now it's just regular DRM 
> drivers.
> 
>> +	tristate "DRM support for Solomon SSD1307 OLED displays"
>> +	depends on DRM && I2C
>> +	select DRM_KMS_HELPER
>> +	select DRM_GEM_SHMEM_HELPER
>> +	select BACKLIGHT_CLASS_DEVICE
> 
> Alphabetical order please.
>

Ok.

[snip]

>>   obj-$(CONFIG_TINYDRM_REPAPER)		+= repaper.o
>> +obj-$(CONFIG_TINYDRM_SSD1307)		+= ssd1307.o
> 
> Maybe call it ssd130x
>

Yes, that's what I had in my RFC posted yesterday but then Andy asked if it
could use the old driver name. But now it seems he also agrees with us that
ssd130x would be better. I'll change it again.
 
[snip]

>> +};
>> +
>> +struct ssd1307_array {
>> +	u8	type;
> 
> 'cmd'?
>

Sure.
 
>> +	u8	data[];
>> +};
> 
> The name 'array' is misleading. At first I thought that it's a C array 
> type. But it's actually an element of the adapter's i2c protocol. Is 
> there a better name that makes this more obvious? ssd130x_i2c_cmd?
>

Indeed. I took the name from the old driver but I agree with you that's
confusing. It's called array because ssd1307_update_display() writes an
array of SSD1307_DATA commands to update all the needed screen pages.

> If this common enough that it could be part of some kind of i2c helper 
> library?
>

That's a good question. There are some other DRM drivers doing I2C read/writes
so there may be some room for consolidation in helper functions. But I would
do it as a follow-up since it seems out of scope for this series.

>> +
>> +static inline struct ssd1307_device *drm_to_ssd1307(struct drm_device *drm)
>> +{
>> +	return container_of(drm, struct ssd1307_device, drm);
>> +}
>> +
>> +static struct ssd1307_array *ssd1307_alloc_array(u32 len, u8 type)
>> +{
>> +	struct ssd1307_array *array;
>> +
>> +	array = kzalloc(sizeof(struct ssd1307_array) + len, GFP_KERNEL);
> 
> sizeof(*array) is slighly more reliable. But wasn't there even a macro 
> for such allocations (struct + length)?
>

Agree on the sizeof(*foo) and will change to use that instead.

Thanks, I leared now about the struct_size() and flex_array_size() macros.

>> +	if (!array)
>> +		return NULL;
> 
> Personally I prefer pointer-encoded errors instead of NULL. But I don't 
> thing there's a strict rule about it.
>

Usually my rule of thumb is whether is necessary to encode different errno
codes. But in this particular case the only possible error is in kzalloc()
so I thought that is safe to assume in the caller that NULL is -ENOMEM.

>> +
>> +	array->type = type;
>> +
>> +	return array;
>> +}
>> +
>> +static int ssd1307_write_array(struct i2c_client *client,
>> +			       struct ssd1307_array *array, u32 len)
>> +{
>> +	int ret;
>> +
>> +	len += sizeof(struct ssd1307_array);
> 
> Same thing about sizeof: sizeof(var) is better than sizeof(type);
>

Agreed.
 
> Since you're using a separate array structure anyway, wouldn't it make 
> sense to store
>

Indeed.

[snip]

>> +{
>> +	u8 col_end = col_start + cols - 1;
>> +	int ret;
>> +
>> +	if (col_start == ssd1307->col_start && col_end == ssd1307->col_end)
>> +		return 0;
>> +
>> +	ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_COL_RANGE);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	ret = ssd1307_write_cmd(ssd1307->client, col_start);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	ret = ssd1307_write_cmd(ssd1307->client, col_end);
>> +	if (ret < 0)
>> +		return ret;
> 
> Can you write these cmds in one step, such as setting up an array and 
> sending it with ssd1307_write_array?
>

I don't think so because the commands are different. But I'll check the
ssd1306 datasheet again to confirma that's the case.

[snip]
 
>> +
>> +	buf = kmalloc_array(width, height, GFP_KERNEL);
> 
> There's kcalloc().
>

Indeed, forgot about it. Will use it instead...
 
>> +	if (!buf)
>> +		return;
>> +
>> +	/* Clear screen to black if disabled */
>> +	memset(buf, 0, width * height);
>> +

and then could drop this memset() call.

[snip]

>> +
>> +static int ssd1307_fb_blit_rect(struct drm_framebuffer *fb, const struct dma_buf_map *map,
>> +				struct drm_rect *rect)
>> +{
>> +	struct ssd1307_device *ssd1307 = drm_to_ssd1307(fb->dev);
>> +	void *vmap = map->vaddr; /* TODO: Use mapping abstraction properly */
>> +	int ret = 0;
>> +	u8 *buf = NULL;
>> +
>> +	buf = kmalloc_array(fb->width, fb->height, GFP_KERNEL);
> 
> Maybe leave a short comment that these arrays will be consumed by 
> i2c_master_send().
>

Ok.
 
>> +	if (!buf) {
>> +		ret = -ENOMEM;
>> +		goto out_exit;
> 
> It's the first error. Just return directly.
>

Right, reworked a little bit the function and forgot to adapt this error path.

[snip]

>> +
>> +	if (drm_atomic_helper_damage_merged(old_plane_state, plane_state, &rect))
>> +		ssd1307_fb_blit_rect(plane_state->fb, &shadow_plane_state->data[0], &rect);
> 
> Shadow-plane helpers have recently gotten the ability to use virtual 
> screens with sizes much larger than the display.
> 
> If you want to get fancy, you could add this here. It'll give you large 
> display sizes for easy scrolling and fbcon panning.
> 
> Example code is at
> 
> https://elixir.bootlin.com/linux/v5.17-rc2/source/drivers/gpu/drm/tiny/simpledrm.c#L652
> https://elixir.bootlin.com/linux/v5.17-rc2/source/drivers/gpu/drm/tiny/simpledrm.c#L703
> https://elixir.bootlin.com/linux/v5.17-rc2/source/drivers/gpu/drm/tiny/simpledrm.c#L785
>

Thanks for these pointers, very helpful!

[snip] 

>> +
>> +	connector->display_info.width_mm = mode->width_mm;
>> +	connector->display_info.height_mm = mode->height_mm;
>> +	connector->display_info.bpc = 32;
> 
> Not just 1 bit?
>

No because we always expose a fake DRM_FORMAT_XRGB8888 to user-space.

It will have to be adapted once we advertise greyscale and monochrome
formats to user-space.

>> +
>> +	drm_mode_set_name(mode);
>> +	mode->type |= DRM_MODE_TYPE_PREFERRED;
> 
> There's drm_set_preferred_mode().
>

Ok.
 
[snip]

>> +}
>> +
>> +static int ssd1307_probe(struct i2c_client *client)
> 
> This function is fairly confusing. device init, modeconfig init, OF 
> functions are all mixed up. Please bring some structure to this.
>

Yeah, I already tried to give it more structure. The original fbdev driver
just has a huge probe function and I tried to at least split it in many
functions that take care of only one thing. But I'll add more levels of
indirection to keep the probe function simpler.

[snip]

>> +
>> +	bl->props.brightness = ssd1307->contrast;
>> +	bl->props.max_brightness = MAX_CONTRAST;
>> +	ssd1307->bl_dev = bl;
>> +
> 
> drmm_mode_config_init here, then connector init
>

Ok.
 
>> +	ret = drm_simple_display_pipe_init(drm, &ssd1307->pipe, &ssd1307_pipe_funcs,
>> +					   ssd1307_formats, ARRAY_SIZE(ssd1307_formats),
>> +					   NULL, &ssd1307->connector);
>> +	if (ret)
>> +		goto pwm_disable;
>> +
>> +	drm_plane_enable_fb_damage_clips(&ssd1307->pipe.plane);
>> +
>> +	drm_mode_config_reset(drm);
> 
> Moving anything related to mode-config into a function would improve 
> readability.
>

Ok.
 
[snip]

>> +regulator_disable:
>> +	if (ssd1307->vbat_reg)
>> +		regulator_disable(ssd1307->vbat_reg);
>> +	return ret;
> 
> Can this be handled by managed clean-up helpers?
>

I believe so, I'll use the devm_* when possible.

>> +}
>> +
>> +static int ssd1307_remove(struct i2c_client *client)
>> +{
>> +	struct ssd1307_device *ssd1307 = i2c_get_clientdata(client);
>> +
>> +	drm_dev_unplug(&ssd1307->drm);
>> +
>> +	ssd1307_write_cmd(ssd1307->client, SSD1307_DISPLAY_OFF);
> 
> There's drm_atomic_helper_shutdown for switching of the device.
> 
> https://elixir.bootlin.com/linux/v5.17-rc2/source/drivers/gpu/drm/drm_atomic_helper.c#L3136
>

I'll use that then, thanks.

Best regards, -- 
Javier Martinez Canillas
Linux Engineering
Red Hat

Re: [PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Andy Shevchenko]

On Tue, Feb 01, 2022 at 12:45:53PM +0100, Javier Martinez Canillas wrote:
> On 2/1/22 10:44, Andy Shevchenko wrote:
> > On Tue, Feb 01, 2022 at 01:14:22AM +0100, Javier Martinez Canillas wrote:

...

> > The problem with no backward compatibility means that removal of old driver
> > makes users unhappy since DT is kinda ABI and we do not break it.
> > 
> 
> I think that's the crux of the issue. Do we want people to update their
> kernel but using their existing Device Tree and be able to switch to the
> DRM driver ?
> 
> My take is that we should and that's why I kept the backward compatibility.
> 
> Maybe we could do that in the meantime and at some point introduce new DT
> bindings (with a different compatible string) that would use the latest
> and greatest conventions in DT ? That seems to be a good compromise.

I have over-read in this discussion that current binding is not fully
correct from hw perspective. If it's indeed the case (and I believe it's),
then probably we should come with brand new driver with ssd130x name and
incompatible bindingas (*).

Otherwise in this driver we continue to be incorrect in them.

*) But even though I think it would be good if you take the old one under your
   maintainership.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Geert Uytterhoeven]

Hi Javier,

On Tue, Feb 1, 2022 at 2:02 PM Javier Martinez Canillas
<javierm@redhat.com> wrote:
> On 2/1/22 10:33, Thomas Zimmermann wrote:
> >> +{
> >> +    u8 col_end = col_start + cols - 1;
> >> +    int ret;
> >> +
> >> +    if (col_start == ssd1307->col_start && col_end == ssd1307->col_end)
> >> +            return 0;
> >> +
> >> +    ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_COL_RANGE);
> >> +    if (ret < 0)
> >> +            return ret;
> >> +
> >> +    ret = ssd1307_write_cmd(ssd1307->client, col_start);
> >> +    if (ret < 0)
> >> +            return ret;
> >> +
> >> +    ret = ssd1307_write_cmd(ssd1307->client, col_end);
> >> +    if (ret < 0)
> >> +            return ret;
> >
> > Can you write these cmds in one step, such as setting up an array and
> > sending it with ssd1307_write_array?
>
> I don't think so because the commands are different. But I'll check the
> ssd1306 datasheet again to confirma that's the case.

IIRC, I tried that while working on the optimizations for ssd1307fb,
and it didn't work.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Javier Martinez Canillas]

On 2/1/22 15:05, Geert Uytterhoeven wrote:
> Hi Javier,
> 
> On Tue, Feb 1, 2022 at 2:02 PM Javier Martinez Canillas
> <javierm@redhat.com> wrote:
>> On 2/1/22 10:33, Thomas Zimmermann wrote:
>>>> +{
>>>> +    u8 col_end = col_start + cols - 1;
>>>> +    int ret;
>>>> +
>>>> +    if (col_start == ssd1307->col_start && col_end == ssd1307->col_end)
>>>> +            return 0;
>>>> +
>>>> +    ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_COL_RANGE);
>>>> +    if (ret < 0)
>>>> +            return ret;
>>>> +
>>>> +    ret = ssd1307_write_cmd(ssd1307->client, col_start);
>>>> +    if (ret < 0)
>>>> +            return ret;
>>>> +
>>>> +    ret = ssd1307_write_cmd(ssd1307->client, col_end);
>>>> +    if (ret < 0)
>>>> +            return ret;
>>>
>>> Can you write these cmds in one step, such as setting up an array and
>>> sending it with ssd1307_write_array?
>>
>> I don't think so because the commands are different. But I'll check the
>> ssd1306 datasheet again to confirma that's the case.
> 
> IIRC, I tried that while working on the optimizations for ssd1307fb,
> and it didn't work.
>

That's what I would had expected by reading the datasheet. Thanks a
lot for confirming my assumption.
 

Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat

Re: [PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Javier Martinez Canillas]

On 2/1/22 15:02, Andy Shevchenko wrote:
> On Tue, Feb 01, 2022 at 12:45:53PM +0100, Javier Martinez Canillas wrote:
>> On 2/1/22 10:44, Andy Shevchenko wrote:
>>> On Tue, Feb 01, 2022 at 01:14:22AM +0100, Javier Martinez Canillas wrote:
> 
> ...
> 
>>> The problem with no backward compatibility means that removal of old driver
>>> makes users unhappy since DT is kinda ABI and we do not break it.
>>>
>>
>> I think that's the crux of the issue. Do we want people to update their
>> kernel but using their existing Device Tree and be able to switch to the
>> DRM driver ?
>>
>> My take is that we should and that's why I kept the backward compatibility.
>>
>> Maybe we could do that in the meantime and at some point introduce new DT
>> bindings (with a different compatible string) that would use the latest
>> and greatest conventions in DT ? That seems to be a good compromise.
> 
> I have over-read in this discussion that current binding is not fully
> correct from hw perspective. If it's indeed the case (and I believe it's),
> then probably we should come with brand new driver with ssd130x name and
> incompatible bindingas (*).
>
> Otherwise in this driver we continue to be incorrect in them.
>

See the comment from Geert. I believe we should use the existing binding.
 
> *) But even though I think it would be good if you take the old one under your
>    maintainership.
>

Sure, now that I got familiar with the ssd130x devices, I'll be happy to
help with the ssd1307fb driver maintainership.

Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat

Re: [PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Thomas Zimmermann]

[-- Attachment #1.1: Type: text/plain, Size: 2279 bytes --]

Hi

Am 01.02.22 um 15:36 schrieb Javier Martinez Canillas:
> On 2/1/22 15:05, Geert Uytterhoeven wrote:
>> Hi Javier,
>>
>> On Tue, Feb 1, 2022 at 2:02 PM Javier Martinez Canillas
>> <javierm@redhat.com> wrote:
>>> On 2/1/22 10:33, Thomas Zimmermann wrote:
>>>>> +{
>>>>> +    u8 col_end = col_start + cols - 1;
>>>>> +    int ret;
>>>>> +
>>>>> +    if (col_start == ssd1307->col_start && col_end == ssd1307->col_end)
>>>>> +            return 0;
>>>>> +
>>>>> +    ret = ssd1307_write_cmd(ssd1307->client, SSD1307_SET_COL_RANGE);
>>>>> +    if (ret < 0)
>>>>> +            return ret;
>>>>> +
>>>>> +    ret = ssd1307_write_cmd(ssd1307->client, col_start);
>>>>> +    if (ret < 0)
>>>>> +            return ret;
>>>>> +
>>>>> +    ret = ssd1307_write_cmd(ssd1307->client, col_end);
>>>>> +    if (ret < 0)
>>>>> +            return ret;
>>>>
>>>> Can you write these cmds in one step, such as setting up an array and
>>>> sending it with ssd1307_write_array?
>>>
>>> I don't think so because the commands are different. But I'll check the
>>> ssd1306 datasheet again to confirma that's the case.
>>
>> IIRC, I tried that while working on the optimizations for ssd1307fb,
>> and it didn't work.
>>
> 
> That's what I would had expected by reading the datasheet. Thanks a
> lot for confirming my assumption.

Thanks to both of you. I was asking because I found the code to be 
repetitive and it's not clear that these 3 statements belong together.

I'd like to suggest to add a function

   ssd1307_write_cmds(client, len, const u8 *cmds)

that loops through cmds and sends the values one by one. A call would 
look like this:

   const u8 set_col_range[] = {
     SSD1307_SET_COL_RANGE,
     col_start,
     col_end
   };

   ssd1307_write_cmds(client, ARRAY_SIZE(set_col_range), set_col_range);

AND/OR

You could have functions that take a command with arguments; either as 
va_args or with one function per number of arguments. Or you could 
combine all these somehow.

Best regards
Thomas

>   
> 
> Best regards,

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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Re: [PATCH 3/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

[Javier Martinez Canillas]

Hello Thomas,

On 2/2/22 09:23, Thomas Zimmermann wrote:

[snip]

> 
> Thanks to both of you. I was asking because I found the code to be 
> repetitive and it's not clear that these 3 statements belong together.
> 
> I'd like to suggest to add a function
> 
>    ssd1307_write_cmds(client, len, const u8 *cmds)
> 
> that loops through cmds and sends the values one by one. A call would 
> look like this:
> 
>    const u8 set_col_range[] = {
>      SSD1307_SET_COL_RANGE,
>      col_start,
>      col_end
>    };
> 
>    ssd1307_write_cmds(client, ARRAY_SIZE(set_col_range), set_col_range);
> 
> AND/OR
> 
> You could have functions that take a command with arguments; either as 
> va_args or with one function per number of arguments. Or you could 
> combine all these somehow.
>

Thanks for the suggestion, that a makes sense to me. I'll look into
it when working on v2. Probably during the weekend.

Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat