@@ -0,0 +1,394 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Backlight driver for Maxim MAX25014
+ *
+ * Copyright (C) 2025 GOcontroll B.V.
+ * Author: Maud Spierings <maudspierings@gocontroll.com>
+ */
+
+#include <linux/backlight.h>
+#include <linux/gpio/consumer.h>
+#include <linux/i2c.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+
+#define MAX25014_ISET_DEFAULT_100 11
+#define MAX_BRIGHTNESS 100
+#define MIN_BRIGHTNESS 0
+#define TON_MAX 130720 /* @153Hz */
+#define TON_STEP 1307 /* @153Hz */
+#define TON_MIN 0
+
+#define MAX25014_DEV_ID 0x00
+#define MAX25014_REV_ID 0x01
+#define MAX25014_ISET 0x02
+#define MAX25014_IMODE 0x03
+#define MAX25014_TON1H 0x04
+#define MAX25014_TON1L 0x05
+#define MAX25014_TON2H 0x06
+#define MAX25014_TON2L 0x07
+#define MAX25014_TON3H 0x08
+#define MAX25014_TON3L 0x09
+#define MAX25014_TON4H 0x0A
+#define MAX25014_TON4L 0x0B
+#define MAX25014_TON_1_4_LSB 0x0C
+#define MAX25014_SETTING 0x12
+#define MAX25014_DISABLE 0x13
+#define MAX25014_BSTMON 0x14
+#define MAX25014_IOUT1 0x15
+#define MAX25014_IOUT2 0x16
+#define MAX25014_IOUT3 0x17
+#define MAX25014_IOUT4 0x18
+#define MAX25014_OPEN 0x1B
+#define MAX25014_SHORT_GND 0x1C
+#define MAX25014_SHORT_LED 0x1D
+#define MAX25014_MASK 0x1E
+#define MAX25014_DIAG 0x1F
+
+#define MAX25014_IMODE_HDIM BIT(2)
+#define MAX25014_ISET_ENABLE BIT(5)
+#define MAX25014_ISET_PSEN BIT(4)
+#define MAX25014_DIAG_HW_RST BIT(2)
+#define MAX25014_SETTING_FPWM GENMASK(6, 4)
+
+struct max25014 {
+ struct i2c_client *client;
+ struct backlight_device *bl;
+ struct regmap *regmap;
+ struct gpio_desc *enable;
+ struct regulator *vin; /* regulator for boost converter Vin rail */
+ uint32_t iset;
+ uint8_t strings_mask;
+};
+
+static const struct regmap_config max25014_regmap_config = {
+ .reg_bits = 8,
+ .val_bits = 8,
+ .max_register = MAX25014_DIAG,
+};
+
+/**
+ * @brief control the brightness with i2c registers
+ *
+ * @param regmap trivial
+ * @param brt brightness
+ * @return int
+ */
+static int max25014_register_control(struct regmap *regmap, uint32_t brt)
+{
+ uint32_t reg = TON_STEP * brt;
+ int ret;
+ /*
+ * 18 bit number lowest, 2 bits in first register,
+ * next lowest 8 in the L register, next 8 in the H register
+ * Seemingly setting the strength of only one string controls all of
+ * them, individual settings don't affect the outcome.
+ */
+
+ ret = regmap_write(regmap, MAX25014_TON_1_4_LSB, reg & 0b00000011);
+ if (ret != 0)
+ return ret;
+ ret = regmap_write(regmap, MAX25014_TON1L, (reg >> 2) & 0b11111111);
+ if (ret != 0)
+ return ret;
+ return regmap_write(regmap, MAX25014_TON1H, (reg >> 10) & 0b11111111);
+}
+
+static int max25014_check_errors(struct max25014 *maxim)
+{
+ uint8_t i;
+ int ret;
+ uint32_t val;
+
+ ret = regmap_read(maxim->regmap, MAX25014_OPEN, &val);
+ if (ret != 0)
+ return ret;
+ if (val > 0) {
+ dev_err(&maxim->client->dev, "Open led strings detected on:\n");
+ for (i = 0; i < 4; i++) {
+ if (val & 1 << i)
+ dev_err(&maxim->client->dev, "string %d\n", i + 1);
+ }
+ return -EIO;
+ }
+
+ ret = regmap_read(maxim->regmap, MAX25014_SHORT_GND, &val);
+ if (ret != 0)
+ return ret;
+ if (val > 0) {
+ dev_err(&maxim->client->dev, "Short to ground detected on:\n");
+ for (i = 0; i < 4; i++) {
+ if (val & 1 << i)
+ dev_err(&maxim->client->dev, "string %d\n", i + 1);
+ }
+ return -EIO;
+ }
+
+ ret = regmap_read(maxim->regmap, MAX25014_SHORT_GND, &val);
+ if (ret != 0)
+ return ret;
+ if (val > 0) {
+ dev_err(&maxim->client->dev, "Shorted led detected on:\n");
+ for (i = 0; i < 4; i++) {
+ if (val & 1 << i)
+ dev_err(&maxim->client->dev, "string %d\n", i + 1);
+ }
+ return -EIO;
+ }
+
+ ret = regmap_read(maxim->regmap, MAX25014_DIAG, &val);
+ if (ret != 0)
+ return ret;
+ /*
+ * The HW_RST bit always starts at 1 after power up.
+ * It is reset on first read, does not indicate an error.
+ */
+ if (val > 0 && val != MAX25014_DIAG_HW_RST) {
+ if (val & 0b1)
+ dev_err(&maxim->client->dev, "Overtemperature shutdown\n");
+ if (val & 0b10)
+ dev_warn(&maxim->client->dev,
+ "Chip is getting too hot (>125C)\n");
+ if (val & 0b1000)
+ dev_err(&maxim->client->dev, "Boost converter overvoltage\n");
+ if (val & 0b10000)
+ dev_err(&maxim->client->dev, "Boost converter undervoltage\n");
+ if (val & 0b100000)
+ dev_err(&maxim->client->dev, "IREF out of range\n");
+ return -EIO;
+ }
+ return 0;
+}
+
+/*
+ * 1. disable unused strings
+ * 2. set dim mode
+ * 3. set initial brightness
+ * 4. set setting register
+ * 5. enable the backlight
+ */
+static int max25014_configure(struct max25014 *maxim, uint32_t initial_brightness)
+{
+ int ret;
+ uint32_t val;
+
+ ret = regmap_write(maxim->regmap, MAX25014_DISABLE,
+ maxim->strings_mask);
+ if (ret != 0)
+ return ret;
+
+ ret = regmap_write(maxim->regmap, MAX25014_IMODE, MAX25014_IMODE_HDIM);
+ if (ret != 0)
+ return ret;
+
+ max25014_register_control(maxim->regmap,
+ initial_brightness);
+
+ ret = regmap_read(maxim->regmap, MAX25014_SETTING, &val);
+ if (ret != 0)
+ return ret;
+
+ ret = regmap_write(
+ maxim->regmap, MAX25014_SETTING,
+ val & ~MAX25014_SETTING_FPWM);
+ if (ret != 0)
+ return ret;
+
+ ret = regmap_write(maxim->regmap, MAX25014_ISET,
+ maxim->iset | MAX25014_ISET_ENABLE | MAX25014_ISET_PSEN);
+ return ret;
+}
+
+static int max25014_update_status(struct backlight_device *bl_dev)
+{
+ struct max25014 *maxim = bl_get_data(bl_dev);
+
+ if (bl_dev->props.state & BL_CORE_SUSPENDED)
+ bl_dev->props.brightness = 0;
+
+ return max25014_register_control(maxim->regmap, bl_dev->props.brightness);
+}
+
+static const struct backlight_ops max25014_bl_ops = {
+ .options = BL_CORE_SUSPENDRESUME,
+ .update_status = max25014_update_status,
+};
+
+static int max25014_parse_dt(struct max25014 *maxim, uint32_t *initial_brightness)
+{
+ struct device *dev = &maxim->client->dev;
+ struct device_node *node = dev->of_node;
+ uint32_t strings[4];
+ int res, i;
+
+ if (!node) {
+ dev_err(dev, "no platform data\n");
+ return -EINVAL;
+ }
+
+ res = of_property_count_u32_elems(node, "maxim,strings");
+ if (res == 4) {
+ of_property_read_u32_array(node, "maxim,strings", strings, 4);
+ } else {
+ dev_err(dev, "strings property not correctly defined\n");
+ return -EINVAL;
+ }
+
+ for (i = 0; i < 4; i++) {
+ if (strings[i] == 0)
+ maxim->strings_mask |= 1 << i;
+ }
+
+ *initial_brightness = 50U;
+ of_property_read_u32(node, "default-brightness", initial_brightness);
+ maxim->iset = MAX25014_ISET_DEFAULT_100;
+ of_property_read_u32(node, "maxim,iset", &maxim->iset);
+
+ if (maxim->iset < 0 || maxim->iset > 15) {
+ dev_err(dev,
+ "Invalid iset, should be a value from 0-15, entered was %d\n",
+ maxim->iset);
+ return -EINVAL;
+ }
+
+ if (*initial_brightness < 0 || *initial_brightness > 100) {
+ dev_err(dev,
+ "Invalid initial brightness, should be a value from 0-100, entered was %d\n",
+ *initial_brightness);
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+static int max25014_probe(struct i2c_client *cl)
+{
+ struct backlight_device *bl;
+ const struct i2c_device_id *id = i2c_client_get_device_id(cl);
+ struct max25014 *maxim;
+ struct backlight_properties props;
+ int ret;
+ uint32_t initial_brightness;
+
+ maxim = devm_kzalloc(&cl->dev, sizeof(struct max25014), GFP_KERNEL);
+ if (!maxim)
+ return -ENOMEM;
+
+ maxim->client = cl;
+
+ ret = max25014_parse_dt(maxim, &initial_brightness);
+ if (ret < 0)
+ return ret;
+
+ maxim->vin = devm_regulator_get(&maxim->client->dev, "power");
+ if (IS_ERR(maxim->vin)) {
+ if (PTR_ERR(maxim->vin) == -EPROBE_DEFER)
+ return -EPROBE_DEFER;
+ maxim->vin = NULL;
+ }
+
+ if (maxim->vin) {
+ ret = regulator_enable(maxim->vin);
+ if (ret < 0) {
+ dev_err(&maxim->client->dev, "failed to enable Vin: %d\n", ret);
+ return ret;
+ }
+ }
+
+ maxim->enable =
+ devm_gpiod_get_optional(&maxim->client->dev, "enable", GPIOD_ASIS);
+ if (IS_ERR(maxim->enable)) {
+ ret = PTR_ERR(maxim->enable);
+ dev_err(&maxim->client->dev, "failed to get enable gpio: %d\n", ret);
+ goto disable_vin;
+ }
+
+ if (maxim->enable) {
+ gpiod_set_value_cansleep(maxim->enable, 1);
+
+ /* Datasheet Electrical Characteristics tSTARTUP 2ms */
+ usleep_range(2000, 2500);
+ }
+
+ maxim->regmap = devm_regmap_init_i2c(cl, &max25014_regmap_config);
+ if (IS_ERR(maxim->regmap)) {
+ ret = PTR_ERR(maxim->regmap);
+ dev_err(&maxim->client->dev, "failed to initialize the i2c regmap: %d\n", ret);
+ goto disable_full;
+ }
+
+ i2c_set_clientdata(cl, maxim);
+
+ ret = max25014_check_errors(maxim);
+ if (ret) { /* error is already reported in the above function */
+ goto disable_full;
+ }
+
+ ret = max25014_configure(maxim, initial_brightness);
+ if (ret) {
+ dev_err(&maxim->client->dev, "device config err: %d", ret);
+ goto disable_full;
+ }
+
+ memset(&props, 0, sizeof(props));
+ props.type = BACKLIGHT_PLATFORM;
+ props.max_brightness = MAX_BRIGHTNESS;
+
+ props.brightness = initial_brightness;
+
+ bl = devm_backlight_device_register(&maxim->client->dev, id->name, &maxim->client->dev,
+ maxim, &max25014_bl_ops, &props);
+ if (IS_ERR(bl))
+ return PTR_ERR(bl);
+
+ maxim->bl = bl;
+
+ return 0;
+
+disable_full:
+ if (maxim->enable)
+ gpiod_set_value_cansleep(maxim->enable, 0);
+disable_vin:
+ if (maxim->vin)
+ regulator_disable(maxim->vin);
+ return ret;
+}
+
+static void max25014_remove(struct i2c_client *cl)
+{
+ struct max25014 *maxim = i2c_get_clientdata(cl);
+
+ maxim->bl->props.brightness = 0;
+ max25014_update_status(maxim->bl);
+ if (maxim->enable)
+ gpiod_set_value_cansleep(maxim->enable, 0);
+ if (maxim->vin)
+ regulator_disable(maxim->vin);
+}
+
+static const struct of_device_id max25014_dt_ids[] = {
+ { .compatible = "maxim,max25014", },
+ { }
+};
+MODULE_DEVICE_TABLE(of, max25014_dt_ids);
+
+static const struct i2c_device_id max25014_ids[] = {
+ { "max25014" },
+ { }
+};
+MODULE_DEVICE_TABLE(i2c, max25014_ids);
+
+static struct i2c_driver max25014_driver = {
+ .driver = {
+ .name = KBUILD_MODNAME,
+ .of_match_table = of_match_ptr(max25014_dt_ids),
+ },
+ .probe = max25014_probe,
+ .remove = max25014_remove,
+ .id_table = max25014_ids,
+};
+module_i2c_driver(max25014_driver);
+
+MODULE_DESCRIPTION("Maxim MAX25014 backlight driver");
+MODULE_AUTHOR("Maud Spierings <maudspierings@gocontroll.com>");
+MODULE_LICENSE("GPL");