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Subject: Re: [PATCH v11 04/16] leds: multicolor: Introduce a multicolor class
 definition
To:     Dan Murphy <dmurphy@ti.com>, pavel@ucw.cz
Cc:     linux-leds@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20191008204800.19870-1-dmurphy@ti.com>
 <20191008204800.19870-5-dmurphy@ti.com>
From:   Jacek Anaszewski <jacek.anaszewski@gmail.com>
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Message-ID: <e031ad7d-3191-eddf-ec7e-db9f31b6f05b@gmail.com>
Date:   Wed, 9 Oct 2019 23:47:52 +0200
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Dan,

On 10/8/19 10:47 PM, Dan Murphy wrote:
> Introduce a multicolor class that groups colored LEDs
> within a LED node.
> 
> The multi color class groups monochrome LEDs and allows controlling two
> aspects of the final combined color: hue and lightness. The former is
> controlled via <color>_intensity files and the latter is controlled
> via brightness file.
> 
> Signed-off-by: Dan Murphy <dmurphy@ti.com>
> ---
>  .../ABI/testing/sysfs-class-led-multicolor    |  35 +++
>  Documentation/leds/index.rst                  |   1 +
>  Documentation/leds/leds-class-multicolor.rst  |  96 +++++++
>  drivers/leds/Kconfig                          |  10 +
>  drivers/leds/Makefile                         |   1 +
>  drivers/leds/led-class-multicolor.c           | 271 ++++++++++++++++++
>  include/linux/led-class-multicolor.h          | 143 +++++++++
>  7 files changed, 557 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-class-led-multicolor
>  create mode 100644 Documentation/leds/leds-class-multicolor.rst
>  create mode 100644 drivers/leds/led-class-multicolor.c
>  create mode 100644 include/linux/led-class-multicolor.h
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-led-multicolor b/Documentation/ABI/testing/sysfs-class-led-multicolor
> new file mode 100644
> index 000000000000..65cb43de26e6
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-class-led-multicolor
> @@ -0,0 +1,35 @@
> +What:		/sys/class/leds/<led>/brightness
> +Date:		Sept 2019
> +KernelVersion:	5.5
> +Contact:	Dan Murphy <dmurphy@ti.com>
> +Description:	read/write
> +		Writing to this file will update all LEDs within the group to a
> +		calculated percentage of what each color LED intensity is set
> +		to. The percentage is calculated via the equation below:
> +
> +		led_brightness = brightness * <color>_intensity/<color>_max_intensity

This equation alone incites questions on how it is supposed to work.

It would be better to present the whole algorithm for calculating
combined color here.

> +
> +		For additional details please refer to
> +		Documentation/leds/leds-class-multicolor.rst.
> +
> +		The value of the color is from 0 to
> +		/sys/class/leds/<led>/max_brightness.
> +
> +What:		/sys/class/leds/<led>/colors/<color>_intensity
> +Date:		Sept 2019
> +KernelVersion:	5.5
> +Contact:	Dan Murphy <dmurphy@ti.com>
> +Description:	read/write
> +		The <color>_intensity file is created based on the color
> +		defined by the registrar of the class.
> +		There is one file per color presented.
> +
> +		The value of the color is from 0 to
> +		/sys/class/leds/<led>/colors/<color>_max_intensity.
> +
> +What:		/sys/class/leds/<led>/colors/<color>_max_intensity
> +Date:		Sept 2019
> +KernelVersion:	5.5
> +Contact:	Dan Murphy <dmurphy@ti.com>
> +Description:	read only
> +		Maximum intensity level for the LED color.
> diff --git a/Documentation/leds/index.rst b/Documentation/leds/index.rst
> index 060f4e485897..bc70c6aa7138 100644
> --- a/Documentation/leds/index.rst
> +++ b/Documentation/leds/index.rst
> @@ -9,6 +9,7 @@ LEDs
>  
>     leds-class
>     leds-class-flash
> +   leds-class-multicolor
>     ledtrig-oneshot
>     ledtrig-transient
>     ledtrig-usbport
> diff --git a/Documentation/leds/leds-class-multicolor.rst b/Documentation/leds/leds-class-multicolor.rst
> new file mode 100644
> index 000000000000..7a695a29377e
> --- /dev/null
> +++ b/Documentation/leds/leds-class-multicolor.rst
> @@ -0,0 +1,96 @@
> +====================================
> +Multi Color LED handling under Linux
> +====================================
> +
> +Description
> +===========
> +The multi color class groups monochrome LEDs and allows controlling two
> +aspects of the final combined color: hue and lightness. The former is
> +controlled via <color>_intensity files and the latter is controlled
> +via brightness file.
> +
> +For more details on hue and lightness notions please refer to
> +https://en.wikipedia.org/wiki/CIECAM02.
> +
> +Note that intensity files only cache the written value and the actual
> +change of hardware state occurs upon writing brightness file. This
> +allows for changing many factors of the perceived color in a virtually
> +unnoticeable way for the human observer.
> +
> +Multicolor Class Control
> +========================
> +The multicolor class presents the LED groups under a directory called "colors".
> +This directory is a child under the LED parent node created by the led_class
> +framework.  The led_class framework is documented in led-class.rst within this
> +documentation directory.
> +
> +Each colored LED will have two files created under the colors directory
> +<color>_intensity and <color>_max_intensity. These files will contain
> +one of LED_COLOR_ID_* definitions from the header
> +include/dt-bindings/leds/common.h.
> +
> +Directory Layout Example
> +========================
> +root:/sys/class/leds/rgb:grouped_leds# ls -lR colors/
> +-rw-r--r--    1 root     root          4096 Jul  7 03:10 blue_intensity
> +-r--r--r--    1 root     root          4096 Jul  7 03:10 blue_max_intensity
> +-rw-r--r--    1 root     root          4096 Jul  7 03:10 green_intensity
> +-r--r--r--    1 root     root          4096 Jul  7 03:10 green_max_intensity
> +-rw-r--r--    1 root     root          4096 Jul  7 03:10 red_intensity
> +-r--r--r--    1 root     root          4096 Jul  7 03:10 red_max_intensity
> +
> +Multicolor Class Brightness Control
> +===================================
> +The multiclor class framework will calculate each monochrome LEDs intensity.
> +
> +The brightness level for each LED is calculated based on the color LED
> +intensity setting divided by the color LED max intensity setting multiplied by
> +the requested brightness.
> +
> +led_brightness = brightness * <color>_intensity/<color>_max_intensity
> +
> +Example:
> +Three LEDs are present in the group as defined in "Directory Layout Example"
> +within this document.
> +
> +A user first writes the color LED brightness file with the brightness level that
> +is necessary to achieve a blueish violet output from the RGB LED group.
> +
> +echo 138 > /sys/class/leds/rgb:grouped_leds/red_intensity
> +echo 43 > /sys/class/leds/rgb:grouped_leds/green_intensity
> +echo 226 > /sys/class/leds/rgb:grouped_leds/blue_intensity
> +
> +red -
> +	intensity = 138
> +	max_intensity = 255
> +green -
> +	intensity = 43
> +	max_intensity = 255
> +blue -
> +	intensity = 226
> +	max_intensity = 255
> +
> +The user can control the brightness of that RGB group by writing the parent
> +'brightness' control.  Assuming a parent max_brightness of 255 the user may want
> +to dim the LED color group to half.  The user would write a value of 128 to the
> +parent brightness file then the values written to each LED will be adjusted
> +base on this value
> +
> +cat /sys/class/leds/rgb:grouped_leds/max_brightness
> +255
> +echo 128 > /sys/class/leds/rgb:grouped_leds/brightness
> +
> +adjusted_red_value = 128 * 138/255 = 69
> +adjusted_green_value = 128 * 43/255 = 21
> +adjusted_blue_value = 128 * 226/255 = 113
> +
> +Reading the parent brightness file will return the current brightness value of
> +the color LED group.
> +
> +cat /sys/class/leds/rgb:grouped_leds/max_brightness
> +255
> +
> +echo 128 > /sys/class/leds/rgb:grouped_leds/brightness
> +
> +cat /sys/class/leds/rgb:grouped_leds/brightness
> +128
> diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
> index 4b68520ac251..a1ede89afc9e 100644
> --- a/drivers/leds/Kconfig
> +++ b/drivers/leds/Kconfig
> @@ -30,6 +30,16 @@ config LEDS_CLASS_FLASH
>  	  for the flash related features of a LED device. It can be built
>  	  as a module.
>  
> +config LEDS_CLASS_MULTI_COLOR
> +	tristate "LED Mulit Color LED Class Support"
> +	depends on LEDS_CLASS
> +	help
> +	  This option enables the multicolor LED sysfs class in /sys/class/leds.
> +	  It wraps LED class and adds multicolor LED specific sysfs attributes
> +	  and kernel internal API to it. You'll need this to provide support
> +	  for multicolor LEDs that are grouped together. This class is not
> +	  intended for single color LEDs. It can be built as a module.
> +
>  config LEDS_BRIGHTNESS_HW_CHANGED
>  	bool "LED Class brightness_hw_changed attribute support"
>  	depends on LEDS_CLASS
> diff --git a/drivers/leds/Makefile b/drivers/leds/Makefile
> index 2da39e896ce8..841038cfe35b 100644
> --- a/drivers/leds/Makefile
> +++ b/drivers/leds/Makefile
> @@ -4,6 +4,7 @@
>  obj-$(CONFIG_NEW_LEDS)			+= led-core.o
>  obj-$(CONFIG_LEDS_CLASS)		+= led-class.o
>  obj-$(CONFIG_LEDS_CLASS_FLASH)		+= led-class-flash.o
> +obj-$(CONFIG_LEDS_CLASS_MULTI_COLOR)	+= led-class-multicolor.o
>  obj-$(CONFIG_LEDS_TRIGGERS)		+= led-triggers.o
>  
>  # LED Platform Drivers
> diff --git a/drivers/leds/led-class-multicolor.c b/drivers/leds/led-class-multicolor.c
> new file mode 100644
> index 000000000000..89f4bc9e057c
> --- /dev/null
> +++ b/drivers/leds/led-class-multicolor.c
> @@ -0,0 +1,271 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// LED Multi Color class interface
> +// Copyright (C) 2019 Texas Instruments Incorporated - http://www.ti.com/
> +
> +#include <linux/device.h>
> +#include <linux/init.h>
> +#include <linux/led-class-multicolor.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/uaccess.h>
> +
> +#include "leds.h"
> +
> +#define INTENSITY_NAME		"_intensity"
> +#define MAX_INTENSITY_NAME	"_max_intensity"
> +
> +int led_mc_calc_brightness(struct led_classdev_mc *mcled_cdev,
> +			    enum led_brightness brightness,
> +			    struct led_mc_color_conversion color_component[])

Now the function name doesn't match with the output array name.

How about:

- led_mc_brightness_to_color_components
- led_mc_calc_color_components

Other suggestions?

> +{
> +	struct led_mc_color_entry *priv;
> +	int i = 0;
> +
> +	list_for_each_entry(priv, &mcled_cdev->color_list, list) {
> +		color_component[i].color_id = priv->led_color_id;
> +		color_component[i].brightness = brightness *
> +					  priv->intensity / priv->max_intensity;
> +		i++;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(led_mc_calc_brightness);
> +
> +static ssize_t intensity_store(struct device *dev,
> +				struct device_attribute *intensity_attr,
> +				const char *buf, size_t size)
> +{
> +	struct led_mc_color_entry *priv = container_of(intensity_attr,
> +						    struct led_mc_color_entry,
> +						      intensity_attr);
> +	struct led_classdev *led_cdev = priv->mcled_cdev->led_cdev;
> +	unsigned long value;
> +	ssize_t ret;
> +
> +	mutex_lock(&led_cdev->led_access);
> +
> +	ret = kstrtoul(buf, 10, &value);
> +	if (ret)
> +		goto unlock;
> +
> +	if (value > priv->max_intensity) {
> +		ret = -EINVAL;
> +		goto unlock;
> +	}
> +
> +	priv->intensity = value;
> +	ret = size;
> +
> +unlock:
> +	mutex_unlock(&led_cdev->led_access);
> +	return ret;
> +}
> +
> +static ssize_t intensity_show(struct device *dev,
> +			      struct device_attribute *intensity_attr,
> +			      char *buf)
> +{
> +	struct led_mc_color_entry *priv = container_of(intensity_attr,
> +						    struct led_mc_color_entry,
> +						      intensity_attr);
> +
> +	return sprintf(buf, "%d\n", priv->intensity);
> +}
> +
> +static ssize_t max_intensity_show(struct device *dev,
> +				   struct device_attribute *max_intensity_attr,
> +				   char *buf)
> +{
> +	struct led_mc_color_entry *priv = container_of(max_intensity_attr,
> +						    struct led_mc_color_entry,
> +						      max_intensity_attr);
> +
> +	return sprintf(buf, "%d\n", priv->max_intensity);
> +}
> +
> +static struct attribute *led_color_attrs[] = {
> +	NULL,
> +};
> +
> +static struct attribute_group led_color_group = {
> +	.name = "colors",
> +	.attrs = led_color_attrs,
> +};
> +
> +static int led_multicolor_init_color(struct led_classdev_mc *mcled_cdev,
> +				     int color_id)
> +{
> +	struct led_classdev *led_cdev = mcled_cdev->led_cdev;
> +	struct led_mc_color_entry *mc_priv;
> +	char *intensity_file_name;
> +	char *max_intensity_file_name;
> +	size_t len;
> +	int ret;
> +
> +	mc_priv = devm_kzalloc(led_cdev->dev, sizeof(*mc_priv), GFP_KERNEL);
> +	if (!mc_priv)
> +		return -ENOMEM;
> +
> +	mc_priv->led_color_id = color_id;
> +	mc_priv->mcled_cdev = mcled_cdev;
> +
> +	sysfs_attr_init(&mc_priv->intensity_attr.attr);
> +	len = strlen(led_colors[color_id]) + strlen(INTENSITY_NAME) + 1;
> +	intensity_file_name = kzalloc(len, GFP_KERNEL);
> +	if (!intensity_file_name)
> +		return -ENOMEM;
> +
> +	snprintf(intensity_file_name, len, "%s%s",
> +		 led_colors[color_id], INTENSITY_NAME);
> +	mc_priv->intensity_attr.attr.name = intensity_file_name;
> +	mc_priv->intensity_attr.attr.mode = 0644;
> +	mc_priv->intensity_attr.store = intensity_store;
> +	mc_priv->intensity_attr.show = intensity_show;
> +	ret = sysfs_add_file_to_group(&led_cdev->dev->kobj,
> +				      &mc_priv->intensity_attr.attr,
> +				      led_color_group.name);
> +	if (ret)
> +		goto intensity_err_out;
> +
> +	sysfs_attr_init(&mc_priv->max_intensity_attr.attr);
> +	len = strlen(led_colors[color_id]) + strlen(MAX_INTENSITY_NAME) + 1;
> +	max_intensity_file_name = kzalloc(len, GFP_KERNEL);
> +	if (!max_intensity_file_name) {
> +		ret = -ENOMEM;
> +		goto intensity_err_out;
> +	}
> +
> +	snprintf(max_intensity_file_name, len, "%s%s",
> +		 led_colors[color_id], MAX_INTENSITY_NAME);
> +	mc_priv->max_intensity_attr.attr.name = max_intensity_file_name;
> +	mc_priv->max_intensity_attr.attr.mode = 0444;
> +	mc_priv->max_intensity_attr.show = max_intensity_show;
> +	ret = sysfs_add_file_to_group(&led_cdev->dev->kobj,
> +				      &mc_priv->max_intensity_attr.attr,
> +				      led_color_group.name);
> +	if (ret)
> +		goto max_intensity_err_out;
> +
> +	mc_priv->max_intensity = LED_FULL;
> +	list_add_tail(&mc_priv->list, &mcled_cdev->color_list);
> +
> +max_intensity_err_out:
> +	kfree(max_intensity_file_name);
> +intensity_err_out:
> +	kfree(intensity_file_name);
> +	return ret;
> +}
> +
> +static int led_multicolor_init_color_dir(struct led_classdev_mc *mcled_cdev)
> +{
> +	struct led_classdev *led_cdev = mcled_cdev->led_cdev;
> +	int ret;
> +	int i;
> +
> +	ret = sysfs_create_group(&led_cdev->dev->kobj, &led_color_group);
> +	if (ret)
> +		return ret;
> +
> +	for (i = 0; i < LED_COLOR_ID_MAX; i++) {
> +		if (test_bit(i, &mcled_cdev->available_colors)) {
> +			ret = led_multicolor_init_color(mcled_cdev, i);
> +			if (ret)
> +				break;
> +
> +		}
> +	}
> +
> +	return ret;
> +}
> +
> +int led_classdev_multicolor_register_ext(struct device *parent,
> +				     struct led_classdev_mc *mcled_cdev,
> +				     struct led_init_data *init_data)
> +{
> +	struct led_classdev *led_cdev;
> +	int ret;
> +
> +	if (!mcled_cdev)
> +		return -EINVAL;
> +
> +	led_cdev = mcled_cdev->led_cdev;
> +	INIT_LIST_HEAD(&mcled_cdev->color_list);
> +
> +	/* Register led class device */
> +	ret = led_classdev_register_ext(parent, led_cdev, init_data);
> +	if (ret)
> +		return ret;
> +
> +	return led_multicolor_init_color_dir(mcled_cdev);
> +}
> +EXPORT_SYMBOL_GPL(led_classdev_multicolor_register_ext);
> +
> +void led_classdev_multicolor_unregister(struct led_classdev_mc *mcled_cdev)
> +{
> +	struct led_mc_color_entry *priv, *next;
> +
> +	if (!mcled_cdev)
> +		return;
> +
> +	list_for_each_entry_safe(priv, next, &mcled_cdev->color_list, list)
> +		list_del(&priv->list);
> +
> +	sysfs_remove_group(&mcled_cdev->led_cdev->dev->kobj, &led_color_group);
> +	led_classdev_unregister(mcled_cdev->led_cdev);
> +}
> +EXPORT_SYMBOL_GPL(led_classdev_multicolor_unregister);
> +
> +static void devm_led_classdev_multicolor_release(struct device *dev, void *res)
> +{
> +	led_classdev_multicolor_unregister(*(struct led_classdev_mc **)res);
> +}
> +
> +int devm_led_classdev_multicolor_register_ext(struct device *parent,
> +					     struct led_classdev_mc *mcled_cdev,
> +					      struct led_init_data *init_data)
> +{
> +	struct led_classdev_mc **dr;
> +	int ret;
> +
> +	dr = devres_alloc(devm_led_classdev_multicolor_release,
> +			  sizeof(*dr), GFP_KERNEL);
> +	if (!dr)
> +		return -ENOMEM;
> +
> +	ret = led_classdev_multicolor_register(parent, mcled_cdev);
> +	if (ret) {
> +		devres_free(dr);
> +		return ret;
> +	}
> +
> +	*dr = mcled_cdev;
> +	devres_add(parent, dr);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(devm_led_classdev_multicolor_register_ext);
> +
> +static int devm_led_classdev_multicolor_match(struct device *dev,
> +					      void *res, void *data)
> +{
> +	struct led_classdev_mc **p = res;
> +
> +	if (WARN_ON(!p || !*p))
> +		return 0;
> +
> +	return *p == data;
> +}
> +
> +void devm_led_classdev_multicolor_unregister(struct device *dev,
> +					     struct led_classdev_mc *mcled_cdev)
> +{
> +	WARN_ON(devres_release(dev,
> +			       devm_led_classdev_multicolor_release,
> +			       devm_led_classdev_multicolor_match, mcled_cdev));
> +}
> +EXPORT_SYMBOL_GPL(devm_led_classdev_multicolor_unregister);
> +
> +MODULE_AUTHOR("Dan Murphy <dmurphy@ti.com>");
> +MODULE_DESCRIPTION("Multi Color LED class interface");
> +MODULE_LICENSE("GPL v2");
> diff --git a/include/linux/led-class-multicolor.h b/include/linux/led-class-multicolor.h
> new file mode 100644
> index 000000000000..5d0cdca32223
> --- /dev/null
> +++ b/include/linux/led-class-multicolor.h
> @@ -0,0 +1,143 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* LED Multicolor class interface
> + * Copyright (C) 2019 Texas Instruments Incorporated - http://www.ti.com/
> + */
> +
> +#ifndef __LINUX_MULTICOLOR_LEDS_H_INCLUDED
> +#define __LINUX_MULTICOLOR_LEDS_H_INCLUDED
> +
> +#include <linux/leds.h>
> +#include <dt-bindings/leds/common.h>
> +
> +struct led_classdev_mc;
> +
> +struct led_mc_color_conversion {
> +	int color_id;
> +	int brightness;
> +	int output_num;
> +};
> +
> +struct led_mc_color_entry {
> +	struct led_classdev_mc *mcled_cdev;
> +
> +	struct device_attribute max_intensity_attr;
> +	struct device_attribute intensity_attr;
> +
> +	enum led_brightness max_intensity;
> +	enum led_brightness intensity;
> +
> +	struct list_head list;
> +
> +	int led_color_id;
> +};
> +
> +struct led_classdev_mc {
> +	/* led class device */
> +	struct led_classdev *led_cdev;
> +	struct list_head color_list;
> +
> +	unsigned long available_colors;
> +	int num_leds;
> +};
> +#ifdef CONFIG_LEDS_CLASS_MULTI_COLOR
> +static inline struct led_classdev_mc *lcdev_to_mccdev(
> +						struct led_classdev *lcdev)
> +{
> +	return container_of(lcdev, struct led_classdev_mc, led_cdev);
> +}
> +
> +/**
> + * led_classdev_multicolor_register_ext - register a new object of led_classdev
> + *				      class with support for multicolor LEDs
> + * @parent: the multicolor LED to register
> + * @mcled_cdev: the led_classdev_mc structure for this device
> + * @init_data: the LED class Multi color device initialization data
> + *
> + * Returns: 0 on success or negative error value on failure
> + */
> +int led_classdev_multicolor_register_ext(struct device *parent,
> +					    struct led_classdev_mc *mcled_cdev,
> +					    struct led_init_data *init_data);
> +
> +static inline int led_classdev_multicolor_register(struct device *parent,
> +					    struct led_classdev_mc *mcled_cdev)
> +{
> +	return led_classdev_multicolor_register_ext(parent, mcled_cdev, NULL);
> +}
> +
> +/**
> + * led_classdev_multicolor_unregister - unregisters an object of led_classdev
> + *					class with support for multicolor LEDs
> + * @mcled_cdev: the multicolor LED to unregister
> + *
> + * Unregister a previously registered via led_classdev_multicolor_register
> + * object
> + */
> +void led_classdev_multicolor_unregister(struct led_classdev_mc *mcled_cdev);
> +
> +/* Calculate brightness for the monochrome LED cluster */
> +int led_mc_calc_brightness(struct led_classdev_mc *mcled_cdev,
> +			    enum led_brightness brightness,
> +			    struct led_mc_color_conversion color_component[]);
> +
> +int devm_led_classdev_multicolor_register_ext(struct device *parent,
> +					  struct led_classdev_mc *mcled_cdev,
> +					  struct led_init_data *init_data);
> +
> +static inline int devm_led_classdev_multicolor_register(struct device *parent,
> +				     struct led_classdev_mc *mcled_cdev)
> +{
> +	return devm_led_classdev_multicolor_register_ext(parent, mcled_cdev,
> +							 NULL);
> +}
> +
> +void devm_led_classdev_multicolor_unregister(struct device *parent,
> +					    struct led_classdev_mc *mcled_cdev);
> +#else
> +
> +static inline struct led_classdev_mc *lcdev_to_mccdev(
> +						struct led_classdev *lcdev)
> +{
> +	return NULL;
> +}
> +
> +static inline int led_classdev_multicolor_register_ext(struct device *parent,
> +					    struct led_classdev_mc *mcled_cdev,
> +					    struct led_init_data *init_data)
> +{
> +	return -EINVAL;
> +}
> +
> +static inline int led_classdev_multicolor_register(struct device *parent,
> +					    struct led_classdev_mc *mcled_cdev)
> +{
> +	return -EINVAL;
> +}
> +
> +static inline void led_classdev_multicolor_unregister(struct led_classdev_mc *mcled_cdev) {}
> +
> +static inline int led_mc_calc_brightness(struct led_classdev_mc *mcled_cdev,
> +					 enum led_brightness brightness,
> +			struct led_mc_color_conversion color_component[])
> +{
> +	return -EINVAL;
> +}
> +
> +static inline int devm_led_classdev_multicolor_register_ext(struct device *parent,
> +					  struct led_classdev_mc *mcled_cdev,
> +					  struct led_init_data *init_data)
> +{
> +	return -EINVAL;
> +}
> +
> +static inline int devm_led_classdev_multicolor_register(struct device *parent,
> +				     struct led_classdev_mc *mcled_cdev)
> +{
> +	return -EINVAL;
> +}

Do you have use case for which these no-ops would be useful?
We don't have no-ops for any of current LED API beside triggers,
which are indeed useful.

> +static inline void devm_led_classdev_multicolor_unregister(struct device *parent,
> +				    struct led_classdev_mc *mcled_cdev) {}
> +
> +#endif	/* CONFIG_LEDS_CLASS_MULTI_COLOR */
> +#endif	/* __LINUX_MULTICOLOR_LEDS_H_INCLUDED */
> 

-- 
Best regards,
Jacek Anaszewski