Re: [PATCH v7 2/2] leds: as3668: Driver for the ams Osram 4-channel i2c LED driver

[Lee Jones <lee@kernel.org>]

On Tue, 08 Jul 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@timmermann.space>
> ---
>  MAINTAINERS                |   1 +
>  drivers/leds/Kconfig       |  13 +++
>  drivers/leds/Makefile      |   1 +
>  drivers/leds/leds-as3668.c | 195 +++++++++++++++++++++++++++++++++++++
>  4 files changed, 210 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..fbf29a6d0296
> --- /dev/null
> +++ b/drivers/leds/leds-as3668.c
> @@ -0,0 +1,195 @@
> +// 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 */

This should be obvious in the nomenclature.

> +#define AS3668_CHIP_ID1 0x3e

AS3668_CHIP_ID1_REG

> +#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

What's the difference between ID and IDENT?

> +#define AS3668_CHIP_REV1 0x01

How many REVs can one chip have?

> +struct as3668_led {
> +	struct led_classdev cdev;
> +	struct as3668 *chip;
> +	struct fwnode_handle *fwnode;
> +
> +	int num;

We can do better than '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;
> +}

These look like abstractions for the sake of abstractions.

Just use the i2c_smbus_*() calls directly.

> +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)
> +			return dev_err_probe(dev, err, "unable to read device tree led reg\n");

"'reg' property missing from %s\n", child->name

> +
> +		if (reg < 0 || reg > AS3668_MAX_LEDS)
> +			return dev_err_probe(dev, -EOPNOTSUPP, "unsupported led reg %d\n", reg);

"'reg' property in %s is out of scope: %d\n", child->name, reg

> +		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)
> +			return dev_err_probe(dev, err, "failed to register %d LED\n", reg);

Swap "%d" and "LED"

> +	}
> +
> +	return 0;
> +}
> +
> +static int as3668_probe(struct i2c_client *client)
> +{
> +	int err;
> +	u8 chip_id1, chip_id2, chip_serial, chip_rev;
> +	struct as3668 *as3668;

Nit: structs at the top, then filter down in size order.

> +	/* Check for sensible i2c address */
> +	if (client->addr != 0x42)

No magic numbers - define this please.

> +		return dev_err_probe(&client->dev, -EFAULT,
> +				     "unexpected address for as3668 device\n");

Unwrap this - you can use up to 100-chars in LEDs.

"Expected I2C address %x, got %x", <DEFINE>, client->addr"

> +	/* 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);

Unlikely.  This too is unexpected, as above.

> +	/* Check the revision */
> +	chip_id2 = as3668_read_value(client, AS3668_CHIP_ID2);

Is child_id2 not for another chip?

This is ambiguous, please improve the variable nomenclature.

> +	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");

Values please.

> +	/* 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;

\n

> +	err = as3668_dt_init(as3668);
> +	if (err)
> +		return dev_err_probe(&client->dev, err, "failed to initialize device\n");

No need for 2 error messages.

> +	/* Initialize the chip */
> +	as3668_write_value(client, AS3668_CURRX_CONTROL, 0x55);

No magic numbers.

> +	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"},

Spaces after the '{' and before the '}'.

> +	{}
> +};
> +

Remove this line.

> +MODULE_DEVICE_TABLE(i2c, as3668_idtable);
> +
> +static const struct of_device_id as3668_match_table[] = {
> +	{.compatible = "ams,as3668"},

Spaces after the '{' and before the '}'.

> +	{}
> +};
> +

Remove this line.

> +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,

Remove all of the odd tabbing from in here.

A single space is fine.

> +};
> +

Remove.

> +module_i2c_driver(as3668_driver);
> +
> +MODULE_AUTHOR("Lukas Timmermann <linux@timmermann.space>");
> +MODULE_DESCRIPTION("AS3668 LED driver");
> +MODULE_LICENSE("GPL");
> -- 
> 2.50.0
> 

-- 
Lee Jones [李琼斯]