From: Maud Spierings <maudspierings@gocontroll.com>

The Maxim MAX25014 is a 4-channel automotive grade backlight driver IC
with integrated boost controller.

Signed-off-by: Maud Spierings <maudspierings@gocontroll.com>
---
 MAINTAINERS                        |   1 +
 drivers/video/backlight/Kconfig    |   7 +
 drivers/video/backlight/Makefile   |   1 +
 drivers/video/backlight/max25014.c | 409 +++++++++++++++++++++++++++++++++++++
 4 files changed, 418 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 606ce086f758..d082d3f8cfae 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15265,6 +15265,7 @@ MAX25014 BACKLIGHT DRIVER
 M:	Maud Spierings <maudspierings@gocontroll.com>
 S:	Maintained
 F:	Documentation/devicetree/bindings/leds/backlight/maxim,max25014.yaml
+F:	drivers/video/backlight/max25014.c
 
 MAX31335 RTC DRIVER
 M:	Antoniu Miclaus <antoniu.miclaus@analog.com>
diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
index d9374d208cee..d3bb6ccd4185 100644
--- a/drivers/video/backlight/Kconfig
+++ b/drivers/video/backlight/Kconfig
@@ -262,6 +262,13 @@ config BACKLIGHT_DA9052
 	help
 	  Enable the Backlight Driver for DA9052-BC and DA9053-AA/Bx PMICs.
 
+config BACKLIGHT_MAX25014
+	tristate "Backlight driver for the Maxim MAX25014 chip"
+	depends on I2C
+	select REGMAP_I2C
+	help
+	  If you are using a MAX25014 chip as a backlight driver say Y to enable it.
+
 config BACKLIGHT_MAX8925
 	tristate "Backlight driver for MAX8925"
 	depends on MFD_MAX8925
diff --git a/drivers/video/backlight/Makefile b/drivers/video/backlight/Makefile
index dfbb169bf6ea..1170d9ec40b8 100644
--- a/drivers/video/backlight/Makefile
+++ b/drivers/video/backlight/Makefile
@@ -45,6 +45,7 @@ obj-$(CONFIG_BACKLIGHT_LOCOMO)		+= locomolcd.o
 obj-$(CONFIG_BACKLIGHT_LP855X)		+= lp855x_bl.o
 obj-$(CONFIG_BACKLIGHT_LP8788)		+= lp8788_bl.o
 obj-$(CONFIG_BACKLIGHT_LV5207LP)	+= lv5207lp.o
+obj-$(CONFIG_BACKLIGHT_MAX25014)	+= max25014.o
 obj-$(CONFIG_BACKLIGHT_MAX8925)		+= max8925_bl.o
 obj-$(CONFIG_BACKLIGHT_MP3309C)		+= mp3309c.o
 obj-$(CONFIG_BACKLIGHT_MT6370)		+= mt6370-backlight.o
diff --git a/drivers/video/backlight/max25014.c b/drivers/video/backlight/max25014.c
new file mode 100644
index 000000000000..36bae508697e
--- /dev/null
+++ b/drivers/video/backlight/max25014.c
@@ -0,0 +1,409 @@
+// 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_err(&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)
+{
+	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;
+
+	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 (backlight_is_blank(maxim->bl))
+		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;
+	struct fwnode_handle *child;
+	uint32_t strings[4];
+	int res, i;
+
+	if (!node) {
+		dev_err(dev, "no platform data\n");
+		return -EINVAL;
+	}
+
+	child = device_get_next_child_node(dev, NULL);
+	if (child) {
+		res = fwnode_property_count_u32(child, "led-sources");
+		if (res > 0) {
+			fwnode_property_read_u32_array(child, "led-sources",
+						       strings, res);
+
+			/* set all strings as disabled, then enable those in led-sources*/
+			maxim->strings_mask = 0xf;
+			for (i = 0; i < res; i++) {
+				if (strings[i] <= 4)
+					maxim->strings_mask &= ~BIT(strings[i]);
+			}
+		}
+
+		fwnode_property_read_u32(child, "default-brightness",
+					 initial_brightness);
+
+		fwnode_handle_put(child);
+	}
+
+	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 = 50;
+
+	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_optional(&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);
+
+	/* Enable can be tied to vin rail wait if either is available */
+	if (maxim->enable || maxim->vin) {
+		/* 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);
+	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;
+	props.scale = BACKLIGHT_SCALE_LINEAR;
+
+	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");

-- 
2.51.2

On Fri, Nov 07, 2025 at 01:49:59PM +0100, Maud Spierings via B4 Relay wrote:
> From: Maud Spierings <maudspierings@gocontroll.com>
>
> The Maxim MAX25014 is a 4-channel automotive grade backlight driver IC
> with integrated boost controller.
>
> Signed-off-by: Maud Spierings <maudspierings@gocontroll.com>
> diff --git a/drivers/video/backlight/max25014.c b/drivers/video/backlight/max25014.c
> new file mode 100644
> index 000000000000..36bae508697e
> --- /dev/null
> +++ b/drivers/video/backlight/max25014.c
> @@ -0,0 +1,409 @@
> +// 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)

This isn't a good name for a function. It doesn't really say what it
does. Please find a more descriptive name.


> +{
> +	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_err(&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

How does this code set the initial brightness? It doens't set the
MAX25014_TON* registers.


> + * 4. set setting register
> + * 5. enable the backlight
> + */
> +static int max25014_configure(struct max25014 *maxim)
> +{
> +	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;
> +
> +	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 (backlight_is_blank(maxim->bl))
> +		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;
> +	struct fwnode_handle *child;
> +	uint32_t strings[4];
> +	int res, i;
> +
> +	if (!node) {
> +		dev_err(dev, "no platform data\n");
> +		return -EINVAL;
> +	}
> +
> +	child = device_get_next_child_node(dev, NULL);
> +	if (child) {
> +		res = fwnode_property_count_u32(child, "led-sources");
> +		if (res > 0) {
> +			fwnode_property_read_u32_array(child, "led-sources",
> +						       strings, res);
> +
> +			/* set all strings as disabled, then enable those in led-sources*/
> +			maxim->strings_mask = 0xf;
> +			for (i = 0; i < res; i++) {
> +				if (strings[i] <= 4)
> +					maxim->strings_mask &= ~BIT(strings[i]);
> +			}
> +		}
> +
> +		fwnode_property_read_u32(child, "default-brightness",
> +					 initial_brightness);
> +
> +		fwnode_handle_put(child);
> +	}
> +
> +	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 = 50;
> +
> +	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_optional(&maxim->client->dev, "power");

I would have expected to see devm_regulator_get() here. Why do you care
whether you get a real regulator or a dummy if you just NULL check
maxim->vin everywhere?


> +	if (IS_ERR(maxim->vin)) {
> +		if (PTR_ERR(maxim->vin) == -EPROBE_DEFER)
> +			return -EPROBE_DEFER;
> +		maxim->vin = NULL;
> +	}
> +
> +	if (maxim->vin) {

If you had called devm_regulator_get() there would be no need for a NULL
check here.


> +		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);

No need for NULL pointer check here (see
https://elixir.bootlin.com/linux/v6.18-rc4/source/drivers/gpio/gpiolib.c#L358-L363 ).


> +
> +	/* Enable can be tied to vin rail wait if either is available */
> +	if (maxim->enable || maxim->vin) {
> +		/* Datasheet Electrical Characteristics tSTARTUP 2ms */
> +		usleep_range(2000, 2500);
> +	}

If you really want to keep the devm_regulator_get_optional() I guess
maybe you could persuade me it's need to avoid this sleep... although
I'd be fairly happy to remove the NULL checks here too!


> +
> +	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);
> +	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;
> +	props.scale = BACKLIGHT_SCALE_LINEAR;
> +
> +	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);

Again, NULL check isn't needed.

> +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);

Lose the NULL check.

> +	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");


Daniel.

On 11/7/25 17:14, Daniel Thompson wrote:
> On Fri, Nov 07, 2025 at 01:49:59PM +0100, Maud Spierings via B4 Relay wrote:
>> From: Maud Spierings <maudspierings@gocontroll.com>
>>
>> The Maxim MAX25014 is a 4-channel automotive grade backlight driver IC
>> with integrated boost controller.
>>
>> Signed-off-by: Maud Spierings <maudspierings@gocontroll.com>
>> diff --git a/drivers/video/backlight/max25014.c b/drivers/video/backlight/max25014.c
>> new file mode 100644
>> index 000000000000..36bae508697e
>> --- /dev/null
>> +++ b/drivers/video/backlight/max25014.c
>> @@ -0,0 +1,409 @@
>> +// 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)
> 
> This isn't a good name for a function. It doesn't really say what it
> does. Please find a more descriptive name.

Having a lot of difficulties find a succinct name that fits better, 
max25014_register_brightness_control()?
max25014_i2c_brightness_control()?

> 
>> +{
>> +	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_err(&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
> 
> How does this code set the initial brightness? It doens't set the
> MAX25014_TON* registers.

Yep forgot to remove that, I discovered the backlight core takes care of 
the default brightness, so I removed it from here.

> 
>> + * 4. set setting register
>> + * 5. enable the backlight
>> + */
>> +static int max25014_configure(struct max25014 *maxim)
>> +{
>> +	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;
>> +
>> +	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 (backlight_is_blank(maxim->bl))
>> +		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;
>> +	struct fwnode_handle *child;
>> +	uint32_t strings[4];
>> +	int res, i;
>> +
>> +	if (!node) {
>> +		dev_err(dev, "no platform data\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	child = device_get_next_child_node(dev, NULL);
>> +	if (child) {
>> +		res = fwnode_property_count_u32(child, "led-sources");
>> +		if (res > 0) {
>> +			fwnode_property_read_u32_array(child, "led-sources",
>> +						       strings, res);
>> +
>> +			/* set all strings as disabled, then enable those in led-sources*/
>> +			maxim->strings_mask = 0xf;
>> +			for (i = 0; i < res; i++) {
>> +				if (strings[i] <= 4)
>> +					maxim->strings_mask &= ~BIT(strings[i]);
>> +			}
>> +		}
>> +
>> +		fwnode_property_read_u32(child, "default-brightness",
>> +					 initial_brightness);
>> +
>> +		fwnode_handle_put(child);
>> +	}
>> +
>> +	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 = 50;
>> +
>> +	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_optional(&maxim->client->dev, "power");
> 
> I would have expected to see devm_regulator_get() here. Why do you care
> whether you get a real regulator or a dummy if you just NULL check
> maxim->vin everywhere?
> 
> 
>> +	if (IS_ERR(maxim->vin)) {
>> +		if (PTR_ERR(maxim->vin) == -EPROBE_DEFER)
>> +			return -EPROBE_DEFER;
>> +		maxim->vin = NULL;
>> +	}
>> +
>> +	if (maxim->vin) {
> 
> If you had called devm_regulator_get() there would be no need for a NULL
> check here.
> 
> 
>> +		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);
> 
> No need for NULL pointer check here (see
> https://elixir.bootlin.com/linux/v6.18-rc4/source/drivers/gpio/gpiolib.c#L358-L363 ).
> 
> 
>> +
>> +	/* Enable can be tied to vin rail wait if either is available */
>> +	if (maxim->enable || maxim->vin) {
>> +		/* Datasheet Electrical Characteristics tSTARTUP 2ms */
>> +		usleep_range(2000, 2500);
>> +	}
> 
> If you really want to keep the devm_regulator_get_optional() I guess
> maybe you could persuade me it's need to avoid this sleep... although
> I'd be fairly happy to remove the NULL checks here too!

Just wait unconditionally?

kind regards,
Maud

> 
>> +
>> +	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);
>> +	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;
>> +	props.scale = BACKLIGHT_SCALE_LINEAR;
>> +
>> +	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);
> 
> Again, NULL check isn't needed.
> 
>> +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);
> 
> Lose the NULL check.
> 
>> +	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");
> 
> 
> Daniel.

On Mon, Nov 10, 2025 at 09:40:07AM +0100, Maud Spierings wrote:
> On 11/7/25 17:14, Daniel Thompson wrote:
> > On Fri, Nov 07, 2025 at 01:49:59PM +0100, Maud Spierings via B4 Relay wrote:
> > > +/**
> > > + * @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)
> >
> > This isn't a good name for a function. It doesn't really say what it
> > does. Please find a more descriptive name.
>
> Having a lot of difficulties find a succinct name that fits better,
> max25014_register_brightness_control()?
> max25014_i2c_brightness_control()?

I'd focus on what it does rather than how it does it meaning something
like max25014_update_brightness() would work.

However, at present, this code is only called from
max25014_update_status() so the simplest thing to do is to move the
code into max25014_update_status() and remove this function entirely
(then it doesn't matter what it is called ;-) ).


> > > +/*
> > > + * 1. disable unused strings
> > > + * 2. set dim mode
> > > + * 3. set initial brightness
> >
> > How does this code set the initial brightness? It doens't set the
> > MAX25014_TON* registers.
>
> Yep forgot to remove that, I discovered the backlight core takes care of the
> default brightness, so I removed it from here.

What do you mean by this? Are you sure you aren't relying on another
driver to enable the backlight rather than the backlight core?

> > > + * 4. set setting register
> > > + * 5. enable the backlight
> > > + */
> > > +static int max25014_configure(struct max25014 *maxim)


> > > +static int max25014_probe(struct i2c_client *cl)
> > > <snip>
> > > +
> > > +	/* Enable can be tied to vin rail wait if either is available */
> > > +	if (maxim->enable || maxim->vin) {
> > > +		/* Datasheet Electrical Characteristics tSTARTUP 2ms */
> > > +		usleep_range(2000, 2500);
> > > +	}
> >
> > If you really want to keep the devm_regulator_get_optional() I guess
> > maybe you could persuade me it's need to avoid this sleep... although
> > I'd be fairly happy to remove the NULL checks here too!
>
> Just wait unconditionally?

If you think it will be unusual for the driver to be used without enable
or regulator then it's ok to wait unconditionally (all examples you
have added so far have an enable pin).


Daniel.

On 11/10/25 11:01, Daniel Thompson wrote:
> On Mon, Nov 10, 2025 at 09:40:07AM +0100, Maud Spierings wrote:
>> On 11/7/25 17:14, Daniel Thompson wrote:
>>> On Fri, Nov 07, 2025 at 01:49:59PM +0100, Maud Spierings via B4 Relay wrote:
>>>> +/**
>>>> + * @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)
>>>
>>> This isn't a good name for a function. It doesn't really say what it
>>> does. Please find a more descriptive name.
>>
>> Having a lot of difficulties find a succinct name that fits better,
>> max25014_register_brightness_control()?
>> max25014_i2c_brightness_control()?
> 
> I'd focus on what it does rather than how it does it meaning something
> like max25014_update_brightness() would work.
> 
> However, at present, this code is only called from
> max25014_update_status() so the simplest thing to do is to move the
> code into max25014_update_status() and remove this function entirely
> (then it doesn't matter what it is called ;-) ).
> 

Perhaps this could be seperated out if/when pwm functionality is 
implemented. I believe the brightness may also be controlled that way in 
hybrid mode, but I am not entirely sure.

> 
>>>> +/*
>>>> + * 1. disable unused strings
>>>> + * 2. set dim mode
>>>> + * 3. set initial brightness
>>>
>>> How does this code set the initial brightness? It doens't set the
>>> MAX25014_TON* registers.
>>
>> Yep forgot to remove that, I discovered the backlight core takes care of the
>> default brightness, so I removed it from here.
> 
> What do you mean by this? Are you sure you aren't relying on another
> driver to enable the backlight rather than the backlight core?

Not that I know of, there is the systemd backlight service, but I am 
pretty sure I can see it first turn on, then get switched to the old 
value by the systemd service. Unless the simple-panel driver controls 
it? The backlight is linked to that.

>>>> + * 4. set setting register
>>>> + * 5. enable the backlight
>>>> + */
>>>> +static int max25014_configure(struct max25014 *maxim)
> 
> 
>>>> +static int max25014_probe(struct i2c_client *cl)
>>>> <snip>
>>>> +
>>>> +	/* Enable can be tied to vin rail wait if either is available */
>>>> +	if (maxim->enable || maxim->vin) {
>>>> +		/* Datasheet Electrical Characteristics tSTARTUP 2ms */
>>>> +		usleep_range(2000, 2500);
>>>> +	}
>>>
>>> If you really want to keep the devm_regulator_get_optional() I guess
>>> maybe you could persuade me it's need to avoid this sleep... although
>>> I'd be fairly happy to remove the NULL checks here too!
>>
>> Just wait unconditionally?
> 
> If you think it will be unusual for the driver to be used without enable
> or regulator then it's ok to wait unconditionally (all examples you
> have added so far have an enable pin).

I think it may actually be a very common implementation to have the 
enable pin attached to Vin, we don't have it set up that way. But it is 
displayed that way in an example schematic in the datasheet.

Kind regards,
Maud

On Mon, Nov 10, 2025 at 11:03:27AM +0100, Maud Spierings wrote:
> On 11/10/25 11:01, Daniel Thompson wrote:
> > On Mon, Nov 10, 2025 at 09:40:07AM +0100, Maud Spierings wrote:
> > > On 11/7/25 17:14, Daniel Thompson wrote:
> > > > On Fri, Nov 07, 2025 at 01:49:59PM +0100, Maud Spierings via B4 Relay wrote:
> > > > > +/*
> > > > > + * 1. disable unused strings
> > > > > + * 2. set dim mode
> > > > > + * 3. set initial brightness
> > > >
> > > > How does this code set the initial brightness? It doens't set the
> > > > MAX25014_TON* registers.
> > >
> > > Yep forgot to remove that, I discovered the backlight core takes care of the
> > > default brightness, so I removed it from here.
> >
> > What do you mean by this? Are you sure you aren't relying on another
> > driver to enable the backlight rather than the backlight core?
>
> Not that I know of, there is the systemd backlight service, but I am pretty
> sure I can see it first turn on, then get switched to the old value by the
> systemd service. Unless the simple-panel driver controls it? The backlight
> is linked to that.

I think you should look at the code. I think it's likely the backlight
is only coming on due to the link to simple-panel.

Normal way to handle that case (if you want to avoid the backlight
turning on "too early") is to set the power mode to BACKLIGHT_POWER_OFF
if (and only off) the backlight is linked to a panel. See
pwm_backlight_initial_power_state() for an example.

If you are relying on "the backlight core [to take] care of the default
brightness" then you have to request it in the driver (by calling
backlight_update_status() after registering the backlight).


> > > > > + * 4. set setting register
> > > > > + * 5. enable the backlight
> > > > > + */
> > > > > +static int max25014_configure(struct max25014 *maxim)
> >
> >
> > > > > +static int max25014_probe(struct i2c_client *cl)
> > > > > <snip>
> > > > > +
> > > > > +	/* Enable can be tied to vin rail wait if either is available */
> > > > > +	if (maxim->enable || maxim->vin) {
> > > > > +		/* Datasheet Electrical Characteristics tSTARTUP 2ms */
> > > > > +		usleep_range(2000, 2500);
> > > > > +	}
> > > >
> > > > If you really want to keep the devm_regulator_get_optional() I guess
> > > > maybe you could persuade me it's need to avoid this sleep... although
> > > > I'd be fairly happy to remove the NULL checks here too!
> > >
> > > Just wait unconditionally?
> >
> > If you think it will be unusual for the driver to be used without enable
> > or regulator then it's ok to wait unconditionally (all examples you
> > have added so far have an enable pin).
>
> I think it may actually be a very common implementation to have the enable
> pin attached to Vin, we don't have it set up that way. But it is displayed
> that way in an example schematic in the datasheet.

Your call.


Daniel.

On Fri, Nov 07, 2025 at 01:49:59PM +0100, Maud Spierings via B4 Relay wrote:
> From: Maud Spierings <maudspierings@gocontroll.com>
>
> The Maxim MAX25014 is a 4-channel automotive grade backlight driver IC
> with integrated boost controller.
>
> Signed-off-by: Maud Spierings <maudspierings@gocontroll.com>
> ---
>  MAINTAINERS                        |   1 +
>  drivers/video/backlight/Kconfig    |   7 +
>  drivers/video/backlight/Makefile   |   1 +
>  drivers/video/backlight/max25014.c | 409 +++++++++++++++++++++++++++++++++++++
>  4 files changed, 418 insertions(+)
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 606ce086f758..d082d3f8cfae 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -15265,6 +15265,7 @@ MAX25014 BACKLIGHT DRIVER
>  M:	Maud Spierings <maudspierings@gocontroll.com>
>  S:	Maintained
>  F:	Documentation/devicetree/bindings/leds/backlight/maxim,max25014.yaml
> +F:	drivers/video/backlight/max25014.c
>
>  MAX31335 RTC DRIVER
>  M:	Antoniu Miclaus <antoniu.miclaus@analog.com>
> diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
> index d9374d208cee..d3bb6ccd4185 100644
> --- a/drivers/video/backlight/Kconfig
> +++ b/drivers/video/backlight/Kconfig
> @@ -262,6 +262,13 @@ config BACKLIGHT_DA9052
>  	help
>  	  Enable the Backlight Driver for DA9052-BC and DA9053-AA/Bx PMICs.
>
> +config BACKLIGHT_MAX25014
> +	tristate "Backlight driver for the Maxim MAX25014 chip"
> +	depends on I2C
> +	select REGMAP_I2C
> +	help
> +	  If you are using a MAX25014 chip as a backlight driver say Y to enable it.
> +
>  config BACKLIGHT_MAX8925
>  	tristate "Backlight driver for MAX8925"
>  	depends on MFD_MAX8925
> diff --git a/drivers/video/backlight/Makefile b/drivers/video/backlight/Makefile
> index dfbb169bf6ea..1170d9ec40b8 100644
> --- a/drivers/video/backlight/Makefile
> +++ b/drivers/video/backlight/Makefile
> @@ -45,6 +45,7 @@ obj-$(CONFIG_BACKLIGHT_LOCOMO)		+= locomolcd.o
>  obj-$(CONFIG_BACKLIGHT_LP855X)		+= lp855x_bl.o
>  obj-$(CONFIG_BACKLIGHT_LP8788)		+= lp8788_bl.o
>  obj-$(CONFIG_BACKLIGHT_LV5207LP)	+= lv5207lp.o
> +obj-$(CONFIG_BACKLIGHT_MAX25014)	+= max25014.o
>  obj-$(CONFIG_BACKLIGHT_MAX8925)		+= max8925_bl.o
>  obj-$(CONFIG_BACKLIGHT_MP3309C)		+= mp3309c.o
>  obj-$(CONFIG_BACKLIGHT_MT6370)		+= mt6370-backlight.o
> diff --git a/drivers/video/backlight/max25014.c b/drivers/video/backlight/max25014.c
> new file mode 100644
> index 000000000000..36bae508697e
> --- /dev/null
...
> +
> +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)

if (ret), check others regmap_*()

> +		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) {

uint32 always >= 0

So
	if (val)

> +		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)

BIT(0)

> +			dev_err(&maxim->client->dev,
> +				"Overtemperature shutdown\n");
> +		if (val & 0b10)
> +			dev_err(&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;
> +}
> +
...
> +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;
> +	struct fwnode_handle *child;
> +	uint32_t strings[4];
> +	int res, i;
> +
> +	if (!node) {
> +		dev_err(dev, "no platform data\n");
> +		return -EINVAL;
> +	}

call from probe, check other place

	return dev_err_probe()

> +
> +	child = device_get_next_child_node(dev, NULL);
> +	if (child) {
> +		res = fwnode_property_count_u32(child, "led-sources");
> +		if (res > 0) {
> +			fwnode_property_read_u32_array(child, "led-sources",
> +						       strings, res);
> +
> +			/* set all strings as disabled, then enable those in led-sources*/
> +			maxim->strings_mask = 0xf;
> +			for (i = 0; i < res; i++) {
> +				if (strings[i] <= 4)
> +					maxim->strings_mask &= ~BIT(strings[i]);
> +			}
> +		}
> +
> +		fwnode_property_read_u32(child, "default-brightness",
> +					 initial_brightness);
> +
> +		fwnode_handle_put(child);
> +	}
> +
> +	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 = 50;

try keep reverise christmas order

> +
> +	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_optional(&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;
> +		}
> +	}

use devm_regulator_get_enable_optional() to combine devm_regulator_get_optional()
and regulator_enable() to one call.

> +
> +	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);

gpiod_set_value_cansleep() tolerate NULL, so needn't if check here

and if you pass GPIOD_OUT_HIGH at devm_gpiod_get_optional(), needn't call
this function.

> +
> +	/* Enable can be tied to vin rail wait if either is available */
> +	if (maxim->enable || maxim->vin) {
> +		/* Datasheet Electrical Characteristics tSTARTUP 2ms */
> +		usleep_range(2000, 2500);

now perfer use fsleep()

Frank
> +	}
> +
> +	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);
> +	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;
> +	props.scale = BACKLIGHT_SCALE_LINEAR;
> +
> +	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");
>
> --
> 2.51.2
>
>

On 11/7/25 16:51, Frank Li wrote:
> On Fri, Nov 07, 2025 at 01:49:59PM +0100, Maud Spierings via B4 Relay wrote:
>> From: Maud Spierings <maudspierings@gocontroll.com>
>>
>> The Maxim MAX25014 is a 4-channel automotive grade backlight driver IC
>> with integrated boost controller.
>>
>> Signed-off-by: Maud Spierings <maudspierings@gocontroll.com>
>> ---
>>   MAINTAINERS                        |   1 +
>>   drivers/video/backlight/Kconfig    |   7 +
>>   drivers/video/backlight/Makefile   |   1 +
>>   drivers/video/backlight/max25014.c | 409 +++++++++++++++++++++++++++++++++++++
>>   4 files changed, 418 insertions(+)
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 606ce086f758..d082d3f8cfae 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -15265,6 +15265,7 @@ MAX25014 BACKLIGHT DRIVER
>>   M:	Maud Spierings <maudspierings@gocontroll.com>
>>   S:	Maintained
>>   F:	Documentation/devicetree/bindings/leds/backlight/maxim,max25014.yaml
>> +F:	drivers/video/backlight/max25014.c
>>
>>   MAX31335 RTC DRIVER
>>   M:	Antoniu Miclaus <antoniu.miclaus@analog.com>
>> diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
>> index d9374d208cee..d3bb6ccd4185 100644
>> --- a/drivers/video/backlight/Kconfig
>> +++ b/drivers/video/backlight/Kconfig
>> @@ -262,6 +262,13 @@ config BACKLIGHT_DA9052
>>   	help
>>   	  Enable the Backlight Driver for DA9052-BC and DA9053-AA/Bx PMICs.
>>
>> +config BACKLIGHT_MAX25014
>> +	tristate "Backlight driver for the Maxim MAX25014 chip"
>> +	depends on I2C
>> +	select REGMAP_I2C
>> +	help
>> +	  If you are using a MAX25014 chip as a backlight driver say Y to enable it.
>> +
>>   config BACKLIGHT_MAX8925
>>   	tristate "Backlight driver for MAX8925"
>>   	depends on MFD_MAX8925
>> diff --git a/drivers/video/backlight/Makefile b/drivers/video/backlight/Makefile
>> index dfbb169bf6ea..1170d9ec40b8 100644
>> --- a/drivers/video/backlight/Makefile
>> +++ b/drivers/video/backlight/Makefile
>> @@ -45,6 +45,7 @@ obj-$(CONFIG_BACKLIGHT_LOCOMO)		+= locomolcd.o
>>   obj-$(CONFIG_BACKLIGHT_LP855X)		+= lp855x_bl.o
>>   obj-$(CONFIG_BACKLIGHT_LP8788)		+= lp8788_bl.o
>>   obj-$(CONFIG_BACKLIGHT_LV5207LP)	+= lv5207lp.o
>> +obj-$(CONFIG_BACKLIGHT_MAX25014)	+= max25014.o
>>   obj-$(CONFIG_BACKLIGHT_MAX8925)		+= max8925_bl.o
>>   obj-$(CONFIG_BACKLIGHT_MP3309C)		+= mp3309c.o
>>   obj-$(CONFIG_BACKLIGHT_MT6370)		+= mt6370-backlight.o
>> diff --git a/drivers/video/backlight/max25014.c b/drivers/video/backlight/max25014.c
>> new file mode 100644
>> index 000000000000..36bae508697e
>> --- /dev/null
> ...
>> +
>> +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)
> 
> if (ret), check others regmap_*()
> 
>> +		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) {
> 
> uint32 always >= 0
> 
> So
> 	if (val)
> 
>> +		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)
> 
> BIT(0)
> 
>> +			dev_err(&maxim->client->dev,
>> +				"Overtemperature shutdown\n");
>> +		if (val & 0b10)
>> +			dev_err(&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;
>> +}
>> +
> ...
>> +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;
>> +	struct fwnode_handle *child;
>> +	uint32_t strings[4];
>> +	int res, i;
>> +
>> +	if (!node) {
>> +		dev_err(dev, "no platform data\n");
>> +		return -EINVAL;
>> +	}
> 
> call from probe, check other place
> 
> 	return dev_err_probe()
> 
>> +
>> +	child = device_get_next_child_node(dev, NULL);
>> +	if (child) {
>> +		res = fwnode_property_count_u32(child, "led-sources");
>> +		if (res > 0) {
>> +			fwnode_property_read_u32_array(child, "led-sources",
>> +						       strings, res);
>> +
>> +			/* set all strings as disabled, then enable those in led-sources*/
>> +			maxim->strings_mask = 0xf;
>> +			for (i = 0; i < res; i++) {
>> +				if (strings[i] <= 4)
>> +					maxim->strings_mask &= ~BIT(strings[i]);
>> +			}
>> +		}
>> +
>> +		fwnode_property_read_u32(child, "default-brightness",
>> +					 initial_brightness);
>> +
>> +		fwnode_handle_put(child);
>> +	}
>> +
>> +	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 = 50;
> 
> try keep reverise christmas order
> 
>> +
>> +	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_optional(&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;
>> +		}
>> +	}
> 
> use devm_regulator_get_enable_optional() to combine devm_regulator_get_optional()
> and regulator_enable() to one call.

This however does not return the regulator and will not allow further 
potential power management, I did look into using that one but decided 
against it. There is no runtime PM implemented right now so it wouldn't 
really matter at this point. If it is desirable I will switch it, and it 
will have to be switched back when PM gets implemented.

>> +
>> +	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);
> 
> gpiod_set_value_cansleep() tolerate NULL, so needn't if check here
> 
> and if you pass GPIOD_OUT_HIGH at devm_gpiod_get_optional(), needn't call
> this function.

got it, changed.

>> +
>> +	/* Enable can be tied to vin rail wait if either is available */
>> +	if (maxim->enable || maxim->vin) {
>> +		/* Datasheet Electrical Characteristics tSTARTUP 2ms */
>> +		usleep_range(2000, 2500);
> 
> now perfer use fsleep()

Ah didn't know of that, thanks!

Other small remarks have also been resolved.

Kind regards,
Maud

>> +	}
>> +
>> +	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);
>> +	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;
>> +	props.scale = BACKLIGHT_SCALE_LINEAR;
>> +
>> +	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");
>>
>> --
>> 2.51.2
>>
>>

On Fri, Nov 07, 2025 at 10:51:11AM -0500, Frank Li wrote:
> On Fri, Nov 07, 2025 at 01:49:59PM +0100, Maud Spierings via B4 Relay wrote:
> > From: Maud Spierings <maudspierings@gocontroll.com>
> >
> > The Maxim MAX25014 is a 4-channel automotive grade backlight driver IC
> > with integrated boost controller.
> >
> > Signed-off-by: Maud Spierings <maudspierings@gocontroll.com>

<snip>

> > +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 = 50;
>
> try keep reverise christmas order

I thought reverse christmas tree order only applied to code where the
maintainers called it out in Development/process (e.g. netdev and tip).


Daniel.

On Fri, Nov 07, 2025 at 04:22:33PM +0000, Daniel Thompson wrote:
> On Fri, Nov 07, 2025 at 10:51:11AM -0500, Frank Li wrote:
> > On Fri, Nov 07, 2025 at 01:49:59PM +0100, Maud Spierings via B4 Relay wrote:
> > > From: Maud Spierings <maudspierings@gocontroll.com>
> > >
> > > The Maxim MAX25014 is a 4-channel automotive grade backlight driver IC
> > > with integrated boost controller.
> > >
> > > Signed-off-by: Maud Spierings <maudspierings@gocontroll.com>
>
> <snip>
>
> > > +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 = 50;
> >
> > try keep reverise christmas order
>
> I thought reverse christmas tree order only applied to code where the
> maintainers called it out in Development/process (e.g. netdev and tip).

But, but it is small change when you update next version.

Frank
>
>
> Daniel.