RE: [PATCH v9 2/2] leds: ltc3208: Add driver for LTC3208 Multidisplay LED Driver

[Roleda, Jan carlo]

Hello Jones.

Thank you again for the review.

> -----Original Message-----
> From: Lee Jones <lee@xxxxxxxxxx>
> Sent: Wednesday, August 12, 2026 7:41 PM
> To: Roleda, Jan carlo <Jancarlo.Roleda@xxxxxxxxxx>
> Cc: Pavel Machek <pavel@xxxxxxxxxx>; Rob Herring <robh@xxxxxxxxxx>;
> Krzysztof Kozlowski <krzk+dt@xxxxxxxxxx>; Conor Dooley
> <conor+dt@xxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; linux-
> leds@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; Uwe Kleine König
> <u.kleine-koenig@xxxxxxxxxxxx>
> Subject: Re: [PATCH v9 2/2] leds: ltc3208: Add driver for LTC3208 Multidisplay
> LED Driver
> 
> [External]
> 
> On Thu, 06 Aug 2026, Jan Carlo Roleda wrote:
> 
> > Kernel driver implementation for LTC3208 Multidisplay LED Driver.
> >
> > The LTC3208 is a Multi-display LED driver, designed to control up to
> > 7 distinct LED channels (MAIN, SUB, AUX, CAMHI, CAMLO, RED, GREEN,
> > BLUE), each configurable with its own current level that is equally
> > set to its respective output current source pins for external LEDs.
> >
> > It is programmed via the I2C serial interface.
> > MAIN and SUB support 8-bit current level resolution, while AUX,
> > CAMHI/LO, RED, GREEN, and BLUE support 4-bit levels.
> >
> > The AUX LED channel can be configured to mirror the CAM, SUB, and MAIN
> > channel current levels, or as its own independent AUX channel.
> >
> > The CAM LED channel is configured as 2 separate CAMHI and CAMLO
> > register sub-channels, which current is selected via the CAMHL pin, or
> > set to CAMHI register only via setting the S_CAMHILO bit high in register G
> (0x7).
> >
> > Signed-off-by: Jan Carlo Roleda <jancarlo.roleda@xxxxxxxxxx>
> > ---
> >  MAINTAINERS                 |   1 +
> >  drivers/leds/Kconfig        |  12 +++
> >  drivers/leds/Makefile       |   1 +
> >  drivers/leds/leds-ltc3208.c | 231
> > ++++++++++++++++++++++++++++++++++++++++++++
> >  4 files changed, 245 insertions(+)
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS index
> > 2fd6ffdaaf04..e3b59485ecb3 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -15229,6 +15229,7 @@ L:	linux-leds@xxxxxxxxxxxxxxx
> >  S:	Maintained
> >  W:	https://ez.analog.com/linux-software-drivers
> >  F:	Documentation/devicetree/bindings/leds/adi,ltc3208.yaml
> > +F:	drivers/leds/leds-ltc3208.c
> >
> >  LTC4282 HARDWARE MONITOR DRIVER
> >  M:	Nuno Sa <nuno.sa@xxxxxxxxxx>
> > diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig index
> > f4a0a3c8c870..d917ce3b72f4 100644
> > --- a/drivers/leds/Kconfig
> > +++ b/drivers/leds/Kconfig
> > @@ -1028,6 +1028,18 @@ config LEDS_ACER_A500
> >  	  This option enables support for the Power Button LED of
> >  	  Acer Iconia Tab A500.
> >
> > +config LEDS_LTC3208
> > +	tristate "LED Driver for Analog Devices LTC3208"
> > +	depends on LEDS_CLASS && I2C
> > +	select REGMAP_I2C
> > +	help
> > +	  Say Y to enable the LTC3208 LED driver.
> > +	  This enables the LED device LTC3208, a 7-channel, 17-current source
> > +	  multidisplay high-current LED driver, configured via I2C.
> 
> multi-display ?
> 

This is how the device is described in the datasheet;
It refers to it capable of driving multiple LED channels, thus "multi-display".

> > +
> > +	  To compile this driver as a module, choose M here: the module will
> > +	  be called ltc3208.
> > +
> >  source "drivers/leds/blink/Kconfig"
> >
> >  comment "Flash and Torch LED drivers"
> > diff --git a/drivers/leds/Makefile b/drivers/leds/Makefile index
> > 7db3768912ca..0148b87e16ba 100644
> > --- a/drivers/leds/Makefile
> > +++ b/drivers/leds/Makefile
> > @@ -61,6 +61,7 @@ obj-$(CONFIG_LEDS_LP8788)		+= leds-
> lp8788.o
> >  obj-$(CONFIG_LEDS_LP8860)		+= leds-lp8860.o
> >  obj-$(CONFIG_LEDS_LP8864)		+= leds-lp8864.o
> >  obj-$(CONFIG_LEDS_LT3593)		+= leds-lt3593.o
> > +obj-$(CONFIG_LEDS_LTC3208)		+= leds-ltc3208.o
> >  obj-$(CONFIG_LEDS_MAX5970)		+= leds-max5970.o
> >  obj-$(CONFIG_LEDS_MAX77650)		+= leds-max77650.o
> >  obj-$(CONFIG_LEDS_MAX77705)		+= leds-max77705.o
> > diff --git a/drivers/leds/leds-ltc3208.c b/drivers/leds/leds-ltc3208.c
> > new file mode 100644 index 000000000000..25b49e24ca08
> > --- /dev/null
> > +++ b/drivers/leds/leds-ltc3208.c
> > @@ -0,0 +1,231 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * LED driver for Analog Devices LTC3208 Multi-Display Driver
> > + *
> > + * Copyright 2026 Analog Devices Inc.
> > + *
> > + * Author: Jan Carlo Roleda <jancarlo.roleda@xxxxxxxxxx>
> > + *
> 
> Remove this line.
> 

Noted.

> > + */
> > +
> > +#include <linux/bitfield.h>
> > +#include <linux/bitmap.h>
> > +#include <linux/errno.h>
> > +#include <linux/i2c.h>
> > +#include <linux/leds.h>
> > +#include <linux/module.h>
> > +#include <linux/property.h>
> > +#include <linux/regmap.h>
> > +#include <linux/types.h>
> > +
> > +/* Registers */
> > +#define LTC3208_REG_A_GRNRED		0x1 /* Green and Red current
> DAC */
> 
> I'm not agasint the comments, but can we tab them out beyond the values.
> 

Noted.

> > +#define LTC3208_REG_B_AUXBLU		0x2 /* AUX and Blue current
> DAC */
> > +#define LTC3208_REG_C_MAIN		0x3 /* Main current DAC */
> 
> Is this the nomenclature used in the datasheet or can me improve them?
> 

The registers are labelled from A-G in the datasheet, the phrase after each register
for A-D refers to the target LED channel current setting of each register's fields.

I can update these registers to be more descriptive by appending a "_CURRENT":

LTC3208_REG_A_GRNRED_CURRENT
LTC3208_REG_B_AUXBLU_CURRENT
LTC3208_REG_C_MAIN_CURRENT
LTC3208_REG_D_SUB_CURRENT

> > +#define LTC3208_REG_D_SUB		0x4 /* Sub current DAC */
> > +#define LTC3208_REG_E_AUX_SELECT	0x5 /* AUX DAC Select */
> > +#define  LTC3208_AUX1_MASK		GENMASK(1, 0)
> > +#define  LTC3208_AUX2_MASK		GENMASK(3, 2)
> > +#define  LTC3208_AUX3_MASK		GENMASK(5, 4)
> > +#define  LTC3208_AUX4_MASK		GENMASK(7, 6)
> > +#define LTC3208_REG_F_CAM		0x6 /* CAM (High and Low)
> current DAC */
> > +#define LTC3208_REG_G_OPT		0x7 /* Device Options */
> > +#define  LTC3208_OPT_CPO_MASK		GENMASK(7, 6)
> > +#define  LTC3208_OPT_DIS_RGBDROP	BIT(3)
> > +#define  LTC3208_OPT_DIS_CAMHILO	BIT(2)
> > +#define  LTC3208_OPT_EN_RGBS		BIT(1)
> > +
> > +#define LTC3208_MAX_BRIGHTNESS_4BIT	0xF
> > +#define LTC3208_MAX_BRIGHTNESS_8BIT	0xFF
> > +
> > +#define LTC3208_NUM_AUX_LEDS		4 /* Number of configurable
> aux channels */
> > +
> > +enum ltc3208_aux_channel {
> > +	LTC3208_AUX_CHAN_AUX = 0,
> > +	LTC3208_AUX_CHAN_MAIN,
> > +	LTC3208_AUX_CHAN_SUB,
> > +	LTC3208_AUX_CHAN_CAM
> > +};
> > +
> > +enum ltc3208_channel {
> > +	LTC3208_CHAN_MAIN = 0,
> > +	LTC3208_CHAN_SUB,
> > +	LTC3208_CHAN_AUX,
> > +	LTC3208_CHAN_CAML,
> > +	LTC3208_CHAN_CAMH,
> > +	LTC3208_CHAN_RED,
> > +	LTC3208_CHAN_BLUE,
> > +	LTC3208_CHAN_GREEN,
> > +	LTC3208_CHAN_N_COUNT,
> > +};
> > +
> > +static const char *const ltc3208_dt_aux_channels[] = {
> > +	"adi,aux1-channel",
> > +	"adi,aux2-channel",
> > +	"adi,aux3-channel",
> > +	"adi,aux4-channel"
> > +};
> > +
> > +static const char *const ltc3208_aux_opt[] = { "aux", "main", "sub",
> > +"cam" };
> > +
> > +struct ltc3208_led {
> > +	struct led_classdev cdev;
> > +	struct regmap_field *rfield;
> > +};
> > +
> > +static const struct reg_default
> > +ltc3208_reg_defaults[LTC3208_REG_G_OPT] = {
> 
> Since these are already populated, what's the point in specifying a size?
> 

I have no real reason for this. Will update this to remain blank.

> > +	{ LTC3208_REG_A_GRNRED, 0 },
> > +	{ LTC3208_REG_B_AUXBLU, 0 },
> > +	{ LTC3208_REG_C_MAIN, 0 },
> > +	{ LTC3208_REG_D_SUB, 0 },
> > +	{ LTC3208_REG_E_AUX_SELECT, 0 },
> > +	{ LTC3208_REG_F_CAM, 0 },
> > +	{ LTC3208_REG_G_OPT, 0 }
> > +};
> > +
> > +static const struct regmap_config ltc3208_regmap_cfg = {
> > +	.reg_bits = 8,
> > +	.val_bits = 8,
> > +	.max_register = LTC3208_REG_G_OPT,
> > +	.cache_type = REGCACHE_FLAT_S,
> > +	.reg_defaults = ltc3208_reg_defaults,
> > +	.num_reg_defaults = LTC3208_REG_G_OPT, };
> > +
> > +static const struct reg_field
> ltc3208_led_reg_field[LTC3208_CHAN_N_COUNT] = {
> > +	[LTC3208_CHAN_MAIN]  = REG_FIELD(LTC3208_REG_C_MAIN, 0, 7),
> > +	[LTC3208_CHAN_SUB]   = REG_FIELD(LTC3208_REG_D_SUB, 0, 7),
> > +	[LTC3208_CHAN_BLUE]  = REG_FIELD(LTC3208_REG_B_AUXBLU, 0, 3),
> > +	[LTC3208_CHAN_AUX]   = REG_FIELD(LTC3208_REG_B_AUXBLU, 4, 7),
> > +	[LTC3208_CHAN_CAML]  = REG_FIELD(LTC3208_REG_F_CAM, 0, 3),
> > +	[LTC3208_CHAN_CAMH]  = REG_FIELD(LTC3208_REG_F_CAM, 4, 7),
> > +	[LTC3208_CHAN_RED]   = REG_FIELD(LTC3208_REG_A_GRNRED, 0, 3),
> > +	[LTC3208_CHAN_GREEN] = REG_FIELD(LTC3208_REG_A_GRNRED, 4,
> 7), };
> > +
> > +static int ltc3208_led_set_brightness(struct led_classdev *led_cdev,
> > +enum led_brightness brightness) {
> > +	struct ltc3208_led *led = container_of(led_cdev, struct ltc3208_led,
> cdev);
> > +	u8 current_level = brightness;
> > +
> > +	return regmap_field_write(led->rfield, current_level); }
> > +
> > +static int ltc3208_probe(struct i2c_client *client) {
> > +	enum ltc3208_aux_channel
> aux_channels[LTC3208_NUM_AUX_LEDS];
> > +	DECLARE_BITMAP(registered_chans, LTC3208_CHAN_N_COUNT) = { };
> > +	struct regmap *regmap;
> > +	bool disable_rgb_aux4_dropout_signal;
> > +	bool disable_camhl_pin;
> > +	bool set_sub_control_pin;
> > +	int ret;
> > +	u8 dev_options;
> > +
> > +	regmap = devm_regmap_init_i2c(client, &ltc3208_regmap_cfg);
> > +	if (IS_ERR(regmap))
> > +		return dev_err_probe(&client->dev, PTR_ERR(regmap),
> "Failed to
> > +initialize regmap.");
> > +
> > +	regcache_mark_dirty(regmap);
> > +	ret = regcache_sync(regmap);
> > +	if (ret)
> > +		return dev_err_probe(&client->dev, ret, "Failed to sync
> register
> > +cache.");
> > +
> > +	disable_camhl_pin = device_property_read_bool(&client->dev,
> "adi,disable-camhl-pin");
> > +	set_sub_control_pin = device_property_read_bool(&client->dev,
> "adi,cfg-enrgbs-pin");
> > +	disable_rgb_aux4_dropout_signal =
> > +		device_property_read_bool(&client->dev,
> > +"adi,disable-rgb-aux4-dropout");
> > +
> > +	dev_options = FIELD_PREP(LTC3208_OPT_EN_RGBS,
> set_sub_control_pin) |
> > +		      FIELD_PREP(LTC3208_OPT_DIS_CAMHILO,
> disable_camhl_pin) |
> > +		      FIELD_PREP(LTC3208_OPT_CPO_MASK, 0) |
> > +		      FIELD_PREP(LTC3208_OPT_DIS_RGBDROP,
> > +disable_rgb_aux4_dropout_signal);
> > +
> > +	ret = regmap_write(regmap, LTC3208_REG_G_OPT, dev_options);
> > +	if (ret)
> > +		return dev_err_probe(&client->dev, ret, "failed to set device
> > +options register.");
> 
> The style inconsistencies are making me \twitch\.
> 
> I suggest an upper-case char to start and drop the full-stop.
> 

Noted.

> > +
> > +	/* Initialize aux channel configurations */
> > +	for (int i = 0; i < LTC3208_NUM_AUX_LEDS; i++) {
> > +		/* default value (AUX) if property is not present in dt */
> 
> Definitely capitalise comments and it's "DT".
> 
> > +		if (!device_property_present(&client->dev,
> ltc3208_dt_aux_channels[i])) {
> > +			aux_channels[i] = LTC3208_AUX_CHAN_AUX;
> > +			continue;
> > +		}
> > +
> > +		ret = device_property_match_property_string(&client->dev,
> > +
> ltc3208_dt_aux_channels[i],
> > +							    ltc3208_aux_opt,
> LTC3208_NUM_AUX_LEDS);
> > +		if (ret < 0)
> > +			return dev_err_probe(&client->dev, ret, "Error
> reading AUX Channel
> > +%d", i);
> > +
> > +		aux_channels[i] = ret;
> > +	}
> > +
> > +	dev_options = FIELD_PREP(LTC3208_AUX1_MASK, aux_channels[0]) |
> > +		      FIELD_PREP(LTC3208_AUX2_MASK, aux_channels[1]) |
> > +		      FIELD_PREP(LTC3208_AUX3_MASK, aux_channels[2]) |
> > +		      FIELD_PREP(LTC3208_AUX4_MASK, aux_channels[3]);
> > +
> > +	ret = regmap_write(regmap, LTC3208_REG_E_AUX_SELECT,
> dev_options);
> > +	if (ret)
> > +		return dev_err_probe(&client->dev, ret, "error writing to aux
> > +channel register.");
> > +
> > +	device_for_each_child_node_scoped(&client->dev, child) {
> > +		struct ltc3208_led *led;
> > +		struct led_init_data init_data = { };
> > +		u32 chan;
> > +
> > +		ret = fwnode_property_read_u32(child, "reg", &chan);
> > +		if (ret)
> > +			return dev_err_probe(&client->dev, ret, "Failed to get
> reg value
> > +of LED.");
> 
> This is user facing, so "register" would be better.
> 

Noted.

> > +		if (chan >= LTC3208_CHAN_N_COUNT)
> > +			return dev_err_probe(&client->dev, -EINVAL, "%u is
> an invalid LED ID.",
> > +					     chan);
> > +		if (test_and_set_bit(chan, registered_chans))
> > +			return dev_err_probe(&client->dev, -EINVAL, "%u is
> already registered.",
> > +					     chan);
> > +
> > +		led = devm_kzalloc(&client->dev, sizeof(*led), GFP_KERNEL);
> > +		if (!led)
> > +			return -ENOMEM;
> > +
> > +		led->rfield = devm_regmap_field_alloc(&client->dev, regmap,
> > +
> ltc3208_led_reg_field[chan]);
> > +		if (IS_ERR(led->rfield))
> > +			return dev_err_probe(&client->dev, PTR_ERR(led-
> >rfield),
> > +					     "cannot allocate regmap field.");
> > +		led->cdev.brightness_set_blocking =
> ltc3208_led_set_brightness;
> > +		led->cdev.max_brightness =
> LTC3208_MAX_BRIGHTNESS_4BIT;
> > +
> > +		if (chan == LTC3208_CHAN_MAIN || chan ==
> LTC3208_CHAN_SUB)
> > +			led->cdev.max_brightness =
> LTC3208_MAX_BRIGHTNESS_8BIT;
> > +
> > +		init_data.fwnode = child;
> > +
> > +		ret = devm_led_classdev_register_ext(&client->dev, &led-
> >cdev, &init_data);
> > +		if (ret)
> > +			return dev_err_probe(&client->dev, ret, "LED %u
> Register failed.",
> > +chan);
> 
> "Failed to register LED %u"
> 

Noted.

> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct of_device_id ltc3208_match_table[] = {
> > +	{ .compatible = "adi,ltc3208" },
> > +	{ }
> > +};
> > +MODULE_DEVICE_TABLE(of, ltc3208_match_table);
> > +
> > +static struct i2c_driver ltc3208_driver = {
> > +	.driver = {
> > +		.name = "ltc3208",
> > +		.of_match_table = ltc3208_match_table,
> > +	},
> > +	.probe = ltc3208_probe,
> > +};
> > +module_i2c_driver(ltc3208_driver);
> > +
> > +MODULE_LICENSE("GPL");
> > +MODULE_AUTHOR("Jan Carlo Roleda <jancarlo.roleda@xxxxxxxxxx>");
> > +MODULE_DESCRIPTION("LTC3208 LED Driver");
> >
> > --
> > 2.43.0
> >
> 
> --
> Lee Jones

If the comments surrounding the register macro names are sufficient, I will submit another patch soon.

Regards,
Carlo