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

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

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@xxxxxxxxxx>
> ---
>
>   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@xxxxxxxxxx>");
> +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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