[PATCH v6 2/2] leds: as3668: Driver for the ams Osram 4-channel i2c LED driver

[Lukas Timmermann <linux@timmermann.space>]

Since there were no existing drivers for the AS3668 or related devices,
a new driver was introduced in a separate file. Similar devices were
reviewed, but none shared enough characteristics to justify code reuse.
As a result, this driver is written specifically for the AS3668.

Signed-off-by: Lukas Timmermann <linux@timmermann.space>
---
 MAINTAINERS                |   1 +
 drivers/leds/Kconfig       |  13 +++
 drivers/leds/Makefile      |   1 +
 drivers/leds/leds-as3668.c | 204 +++++++++++++++++++++++++++++++++++++
 4 files changed, 219 insertions(+)
 create mode 100644 drivers/leds/leds-as3668.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 091206c54c63..945d78fef380 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3511,6 +3511,7 @@ M:	Lukas Timmermann <linux@timmermann.space>
 L:	linux-leds@vger.kernel.org
 S:	Maintained
 F:	Documentation/devicetree/bindings/leds/ams,as3668.yaml
+F:	drivers/leds/leds-as3668.c
 
 ASAHI KASEI AK7375 LENS VOICE COIL DRIVER
 M:	Tianshu Qiu <tian.shu.qiu@intel.com>
diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
index a104cbb0a001..8cfb423ddf82 100644
--- a/drivers/leds/Kconfig
+++ b/drivers/leds/Kconfig
@@ -100,6 +100,19 @@ config LEDS_ARIEL
 
 	  Say Y to if your machine is a Dell Wyse 3020 thin client.
 
+config LEDS_AS3668
+	tristate "LED support for AMS AS3668"
+	depends on LEDS_CLASS
+	depends on I2C
+	help
+	  This option enables support for the AMS AS3668 LED controller.
+	  The AS3668 provides up to four LED channels and is controlled via
+	  the I2C bus. This driver offers basic brightness control for each
+	  channel, without support for blinking or other advanced features.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called leds-as3668.
+
 config LEDS_AW200XX
 	tristate "LED support for Awinic AW20036/AW20054/AW20072/AW20108"
 	depends on LEDS_CLASS
diff --git a/drivers/leds/Makefile b/drivers/leds/Makefile
index 2f170d69dcbf..983811384fec 100644
--- a/drivers/leds/Makefile
+++ b/drivers/leds/Makefile
@@ -14,6 +14,7 @@ obj-$(CONFIG_LEDS_ADP5520)		+= leds-adp5520.o
 obj-$(CONFIG_LEDS_AN30259A)		+= leds-an30259a.o
 obj-$(CONFIG_LEDS_APU)			+= leds-apu.o
 obj-$(CONFIG_LEDS_ARIEL)		+= leds-ariel.o
+obj-$(CONFIG_LEDS_AS3668)		+= leds-as3668.o
 obj-$(CONFIG_LEDS_AW200XX)		+= leds-aw200xx.o
 obj-$(CONFIG_LEDS_AW2013)		+= leds-aw2013.o
 obj-$(CONFIG_LEDS_BCM6328)		+= leds-bcm6328.o
diff --git a/drivers/leds/leds-as3668.c b/drivers/leds/leds-as3668.c
new file mode 100644
index 000000000000..cb1b90217ca6
--- /dev/null
+++ b/drivers/leds/leds-as3668.c
@@ -0,0 +1,204 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Osram AMS AS3668 LED Driver IC
+ *
+ *  Copyright (C) 2025 Lukas Timmermann <linux@timmermann.space>
+ */
+
+#include <linux/bitfield.h>
+#include <linux/i2c.h>
+#include <linux/leds.h>
+#include <linux/module.h>
+#include <linux/uleds.h>
+
+#define AS3668_MAX_LEDS 4
+
+/* Chip Registers */
+#define AS3668_CHIP_ID1 0x3e
+#define AS3668_CHIP_ID2 0x3f
+
+#define AS3668_CHIP_ID2_SERIAL_MASK GENMASK(7, 4)
+#define AS3668_CHIP_ID2_REV_MASK GENMASK(3, 0)
+
+#define AS3668_CURRX_CONTROL 0x01
+#define AS3668_CURR1 0x02
+#define AS3668_CURR2 0x03
+#define AS3668_CURR3 0x04
+#define AS3668_CURR4 0x05
+
+/* Constants */
+#define AS3668_CHIP_IDENT 0xa5
+#define AS3668_CHIP_REV1 0x01
+
+struct as3668_led {
+	struct led_classdev cdev;
+	struct as3668 *chip;
+	struct fwnode_handle *fwnode;
+
+	int num;
+};
+
+struct as3668 {
+	struct i2c_client *client;
+	struct as3668_led leds[AS3668_MAX_LEDS];
+};
+
+static int as3668_read_value(struct i2c_client *client, u8 reg)
+{
+	return i2c_smbus_read_byte_data(client, reg);
+}
+
+static int as3668_write_value(struct i2c_client *client, u8 reg, u8 value)
+{
+	int err = i2c_smbus_write_byte_data(client, reg, value);
+
+	if (err)
+		dev_err(&client->dev, "error writing to reg 0x%02x, returned %d\n", reg, err);
+
+	return err;
+}
+
+static enum led_brightness as3668_brightness_get(struct led_classdev *cdev)
+{
+	struct as3668_led *led = container_of(cdev, struct as3668_led, cdev);
+
+	return as3668_read_value(led->chip->client, AS3668_CURR1 + led->num);
+}
+
+static void as3668_brightness_set(struct led_classdev *cdev, enum led_brightness brightness)
+{
+	struct as3668_led *led = container_of(cdev, struct as3668_led, cdev);
+
+	as3668_write_value(led->chip->client, AS3668_CURR1 + led->num, brightness);
+}
+
+static int as3668_dt_init(struct as3668 *as3668)
+{
+	struct device *dev = &as3668->client->dev;
+	struct as3668_led *led;
+	struct led_init_data init_data = {};
+	int err;
+	u32 reg;
+
+	for_each_available_child_of_node_scoped(dev_of_node(dev), child) {
+		err = of_property_read_u32(child, "reg", &reg);
+		if (err) {
+			dev_err(dev, "unable to read device tree led reg, err %d\n", err);
+			return err;
+		}
+
+		if (reg < 0 || reg > AS3668_MAX_LEDS) {
+			dev_err(dev, "unsupported led reg %d\n", reg);
+			return -EOPNOTSUPP;
+		}
+
+		led = &as3668->leds[reg];
+		led->fwnode = of_fwnode_handle(child);
+
+		led->num = reg;
+		led->chip = as3668;
+
+		led->cdev.max_brightness = U8_MAX;
+		led->cdev.brightness_get = as3668_brightness_get;
+		led->cdev.brightness_set = as3668_brightness_set;
+
+		init_data.fwnode = led->fwnode;
+		init_data.default_label = ":";
+
+		err = devm_led_classdev_register_ext(dev, &led->cdev, &init_data);
+		if (err) {
+			dev_err(dev, "failed to register %d LED\n", reg);
+			return err;
+		}
+	}
+
+	return 0;
+}
+
+static int as3668_probe(struct i2c_client *client)
+{
+	u8 chip_id1, chip_id2, chip_serial, chip_rev;
+	struct as3668 *as3668;
+
+	/* Check for sensible i2c address */
+	if (client->addr != 0x42)
+		return dev_err_probe(&client->dev, -EFAULT,
+				     "unexpected address for as3668 device\n");
+
+	/* Read identifier from chip */
+	chip_id1 = as3668_read_value(client, AS3668_CHIP_ID1);
+
+	if (chip_id1 != AS3668_CHIP_IDENT)
+		return dev_err_probe(&client->dev, -ENODEV,
+				"chip reported wrong id: 0x%02x\n", chip_id1);
+
+	/* Check the revision */
+	chip_id2 = as3668_read_value(client, AS3668_CHIP_ID2);
+	chip_serial = FIELD_GET(AS3668_CHIP_ID2_SERIAL_MASK, chip_id2);
+	chip_rev = FIELD_GET(AS3668_CHIP_ID2_REV_MASK, chip_id2);
+
+	if (chip_rev != AS3668_CHIP_REV1)
+		dev_warn(&client->dev, "unexpected chip revision\n");
+
+	/* Print out information about the chip */
+	dev_dbg(&client->dev,
+		"chip_id: 0x%02x | chip_id2: 0x%02x | chip_serial: 0x%02x | chip_rev: 0x%02x\n",
+		chip_id1, chip_id2, chip_serial, chip_rev);
+
+	as3668 = devm_kzalloc(&client->dev, sizeof(*as3668), GFP_KERNEL);
+
+	if (!as3668)
+		return -ENOMEM;
+
+	as3668->client = client;
+	int err = as3668_dt_init(as3668);
+
+	if (err) {
+		dev_err(&client->dev, "failed to initialize device, err %d\n", err);
+		return err;
+	}
+
+	/* Initialize the chip */
+	as3668_write_value(client, AS3668_CURRX_CONTROL, 0x55);
+	as3668_write_value(client, AS3668_CURR1, 0x00);
+	as3668_write_value(client, AS3668_CURR2, 0x00);
+	as3668_write_value(client, AS3668_CURR3, 0x00);
+	as3668_write_value(client, AS3668_CURR4, 0x00);
+
+	return 0;
+}
+
+static void as3668_remove(struct i2c_client *client)
+{
+	as3668_write_value(client, AS3668_CURRX_CONTROL, 0x0);
+}
+
+static const struct i2c_device_id as3668_idtable[] = {
+	{"as3668"},
+	{}
+};
+
+MODULE_DEVICE_TABLE(i2c, as3668_idtable);
+
+static const struct of_device_id as3668_match_table[] = {
+	{.compatible = "ams,as3668"},
+	{}
+};
+
+MODULE_DEVICE_TABLE(of, as3668_match_table);
+
+static struct i2c_driver as3668_driver = {
+	.driver = {
+		.name           = "leds_as3668",
+		.of_match_table = as3668_match_table,
+	},
+	.probe          = as3668_probe,
+	.remove         = as3668_remove,
+	.id_table       = as3668_idtable,
+};
+
+module_i2c_driver(as3668_driver);
+
+MODULE_AUTHOR("Lukas Timmermann <linux@timmermann.space>");
+MODULE_DESCRIPTION("AS3668 LED driver");
+MODULE_LICENSE("GPL");
-- 
2.49.0