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Message-ID: <a7dffb1f-1545-413b-99ee-421dc6e9f63a@timmermann.space>
Date: Mon, 10 Nov 2025 12:55:02 +0100
From: Lukas Timmermann <linux@...mermann.space>
To: pavel@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
conor+dt@...nel.org, linux-leds@...r.kernel.org, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 2/2] leds: as3668: Driver for the ams Osram 4-channel
i2c LED driver
Am 23.10.25 um 16:18 schrieb Lee Jones:
> On Tue, 14 Oct 2025, Lukas Timmermann wrote:
>
>> 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@...mermann.space>
>> ---
>> MAINTAINERS | 1 +
>> drivers/leds/Kconfig | 13 +++
>> drivers/leds/Makefile | 1 +
>> drivers/leds/leds-as3668.c | 188 +++++++++++++++++++++++++++++++++++++
>> 4 files changed, 203 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@...mermann.space>
>> L: linux-leds@...r.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@...el.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
>
> LEDS_OSRAM_AMS_AS3668
>
>> + tristate "LED support for AMS AS3668"
>
> "Osram"
Thanks. Makes sense.
>> + depends on LEDS_CLASS
>> + depends on I2C
>> + help
>> + This option enables support for the AMS AS3668 LED controller.
>
> "Osram"
Same.>> + 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..2b7b776fe2f5
>> --- /dev/null
>> +++ b/drivers/leds/leds-as3668.c
>> @@ -0,0 +1,188 @@
>> +// SPDX-License-Identifier: GPL-2.0-or-later
>> +/*
>> + * Osram AMS AS3668 LED Driver IC
>> + *
>> + * Copyright (C) 2025 Lukas Timmermann <linux@...mermann.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
>> +#define AS3668_EXPECTED_I2C_ADDR 0x42
>> +
>> +/* Chip Ident */
>> +
>> +#define AS3668_CHIP_ID1_REG 0x3e
>> +#define AS3668_CHIP_ID 0xa5
>> +
>> +/* Current Control */
>> +
>> +#define AS3668_CURRX_CONTROL_REG 0x01
>> +#define AS3668_CURR1_REG 0x02
>> +#define AS3668_CURR2_REG 0x03
>> +#define AS3668_CURR3_REG 0x04
>> +#define AS3668_CURR4_REG 0x05
>> +#define AS3668_CURRX_MODE_ON 0x1
>> +#define AS3668_CURRX_CURR1_MASK GENMASK(1, 0)
>> +#define AS3668_CURRX_CURR2_MASK GENMASK(3, 2)
>> +#define AS3668_CURRX_CURR3_MASK GENMASK(5, 4)
>> +#define AS3668_CURRX_CURR4_MASK GENMASK(7, 6)
>> +
>> +struct as3668_led {
>> + struct led_classdev cdev;
>> + struct as3668 *chip;
>> + struct fwnode_handle *fwnode;
>> + int led_id;
>> +};
>> +
>> +struct as3668 {
>> + struct i2c_client *client;
>> + struct as3668_led leds[AS3668_MAX_LEDS];
>> +};
>> +
>> +static enum led_brightness as3668_brightness_get(struct led_classdev *cdev)
>> +{
>> + struct as3668_led *led = container_of(cdev, struct as3668_led, cdev);
>> +
>> + return i2c_smbus_read_byte_data(led->chip->client, AS3668_CURR1_REG + led->led_id);
>> +}
>> +
>> +static void as3668_brightness_set(struct led_classdev *cdev, enum led_brightness brightness)
>> +{
>> + struct as3668_led *led = container_of(cdev, struct as3668_led, cdev);
>> +
>> + int err = i2c_smbus_write_byte_data(led->chip->client,
>> + AS3668_CURR1_REG + led->led_id,
>> + brightness);
>> +
>> + if (err)
>> + dev_err(&led->chip->client->dev, "error writing to reg 0x%02x, returned %d\n",
>
> The user isn't going to care about this stuff.
>
> "Failed to set brightness: %d"
>
>> + AS3668_CURR1_REG + led->led_id, err);
>> +}
>> +
>> +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", ®);
>> + if (err)
>> + return dev_err_probe(dev, err, "'reg' property missing from %s\n",
>
> "Failed to read 'reg' property"
>
Thanks
>> + child->name);
>> +
>> + if (reg < 0 || reg > AS3668_MAX_LEDS)
>> + return dev_err_probe(dev, -EOPNOTSUPP,
>> + "'reg' property in %s is out of scope: %d\n",
>
> "Unsupported LED: %d"
>
I understand now that should be user facing messages... Thanks.
>> + child->name, reg);
>> +
>> + led = &as3668->leds[reg];
>> + led->fwnode = of_fwnode_handle(child);
>> +
>> + led->led_id = 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)
>> + return dev_err_probe(dev, err, "failed to register LED %d\n", reg);
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static int as3668_probe(struct i2c_client *client)
>> +{
>> + struct as3668 *as3668;
>> + int err;
>> + u8 chip_id;
>> +
>> + if (client->addr != AS3668_EXPECTED_I2C_ADDR)
>
> Expected is weird.
>
> Why are we trying to catch-out the consumer?
>
> If you already know what the I2C address is, just use that.
>
Okay, I will do that instead.
I aim to fail early in my code and double check everything.
Drivers shouldn't error check the device tree, if I understand you
correctly.
>> + return dev_err_probe(&client->dev, -EFAULT,
>> + "expected i2c address 0x%02x, got 0x%02x\n",
>> + AS3668_EXPECTED_I2C_ADDR, client->addr);
>> +
>> + /* Read identifier from chip */
>
> This comment is superfluous IMHO.
>
> The register name should tell us everything.
>
>> + chip_id = i2c_smbus_read_byte_data(client, AS3668_CHIP_ID1_REG);
>> +
>
> Remove this line.
>
>> + if (chip_id != AS3668_CHIP_ID)
>> + return dev_err_probe(&client->dev, -ENODEV,
>> + "expected chip id 0x%02x, got 0x%02x\n",
>
> "ID"
>
>> + AS3668_CHIP_ID, chip_id);
>> +
>> + as3668 = devm_kzalloc(&client->dev, sizeof(*as3668), GFP_KERNEL);
>> + if (!as3668)
>> + return -ENOMEM;
>> +
>> + as3668->client = client;
>> +
>> + err = as3668_dt_init(as3668);
>> + if (err)
>> + return err;
>> +
>> + /* Set all four channel modes to 'on' */
>
> Even if a specific LED wasn't requested?
>
> Are you sure that this doesn't have any drawbacks (power perhaps)?
>
After reading through downstream code and it's datasheet, this actually
might result in higher power consumption than switching it off.
I suppose we could enable and disable a specific channel when setting
the brightness. I will add that in my next patch version.
>> + err = i2c_smbus_write_byte_data(client, AS3668_CURRX_CONTROL_REG,
>> + FIELD_PREP(AS3668_CURRX_CURR1_MASK, AS3668_CURRX_MODE_ON) |
>> + FIELD_PREP(AS3668_CURRX_CURR2_MASK, AS3668_CURRX_MODE_ON) |
>> + FIELD_PREP(AS3668_CURRX_CURR3_MASK, AS3668_CURRX_MODE_ON) |
>> + FIELD_PREP(AS3668_CURRX_CURR4_MASK, AS3668_CURRX_MODE_ON));
>> +
>> + /* Set initial currents to 0mA */
>> + err |= i2c_smbus_write_byte_data(client, AS3668_CURR1_REG, 0);
>> + err |= i2c_smbus_write_byte_data(client, AS3668_CURR2_REG, 0);
>> + err |= i2c_smbus_write_byte_data(client, AS3668_CURR3_REG, 0);
>> + err |= i2c_smbus_write_byte_data(client, AS3668_CURR4_REG, 0);
>> +
>> + if (err)
>> + return dev_err_probe(&client->dev, -EIO, "failed to write to the device\n");
>> +
>> + return 0;
>> +}
>> +
>> +static void as3668_remove(struct i2c_client *client)
>> +{
>> + int err;
>
> '\n' here.
>
Okay
>> + err = i2c_smbus_write_byte_data(client, AS3668_CURRX_CONTROL_REG, 0);
>> + if (err)
>> + dev_err(&client->dev, "couldn't remove the device\n");
>
> This does not remove the device.
>
> "Failed to turn off the LEDs"
>
Obviously, now that I see it. Thanks
>> +}
>> +
>> +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@...mermann.space>");
>> +MODULE_DESCRIPTION("AS3668 LED driver");
>> +MODULE_LICENSE("GPL");
>> --
>> 2.51.0
>>
>
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