Re: [PATCH 1/1] leds: Introduce the multi_max_intensity sysfs attribute

[Lee Jones]

On Tue, 24 Mar 2026, Armin Wolf wrote:

> Some multicolor LEDs support global brightness control in hardware,
> meaning that the maximum intensity of the color components is not
> connected to the maximum global brightness. Such LEDs cannot be
> described properly by the current multicolor LED class interface,
> because it assumes that the maximum intensity of each color component
> is described by the maximum global brightness of the LED.
> 
> Fix this by introducing a new sysfs attribute called
> "multi_max_intensity" holding the maximum intensity values for the
> color components of a multicolor LED class device. Drivers can use
> the new max_intensity field inside struct mc_subled to tell the
> multicolor LED class code about those values. Intensity values written
> by userspace applications will be limited to this maximum value.
> 
> Drivers for multicolor LEDs that do not support global brightness
> control in hardware might still want to use the maximum global LED
> brightness supplied via devicetree as the maximum intensity of each
> individual color component. Such drivers should set max_intensity
> to 0 so that the multicolor LED core can act accordingly.
> 
> The lp50xx and ncp5623 LED drivers already use hardware-based control
> for the global LED brightness. Modify those drivers to correctly
> initalize .max_intensity to avoid being limited to the maximum global
> brightness supplied via devicetree.
> 
> Signed-off-by: Armin Wolf <W_Armin@xxxxxx>
> ---
>  .../ABI/testing/sysfs-class-led-multicolor    | 19 ++++++--
>  Documentation/leds/leds-class-multicolor.rst  | 21 ++++++++-
>  drivers/leds/led-class-multicolor.c           | 47 ++++++++++++++++++-
>  drivers/leds/leds-lp50xx.c                    |  1 +
>  drivers/leds/rgb/leds-ncp5623.c               |  4 +-
>  include/linux/led-class-multicolor.h          | 30 +++++++++++-
>  6 files changed, 113 insertions(+), 9 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-led-multicolor b/Documentation/ABI/testing/sysfs-class-led-multicolor
> index 16fc827b10cb..197da3e775b4 100644
> --- a/Documentation/ABI/testing/sysfs-class-led-multicolor
> +++ b/Documentation/ABI/testing/sysfs-class-led-multicolor
> @@ -16,9 +16,22 @@ Date:		March 2020
>  KernelVersion:	5.9
>  Contact:	Dan Murphy <dmurphy@xxxxxx>
>  Description:	read/write
> -		This file contains array of integers. Order of components is
> -		described by the multi_index array. The maximum intensity should
> -		not exceed /sys/class/leds/<led>/max_brightness.
> +		This file contains an array of integers. The order of components
> +		is described by the multi_index array. The maximum intensity value
> +		supported by each color component is described by the multi_max_intensity
> +		file. Writing intensity values larger than the maximum value of a
> +		given color component will result in those values being clamped.
> +
> +		For additional details please refer to
> +		Documentation/leds/leds-class-multicolor.rst.
> +
> +What:		/sys/class/leds/<led>/multi_max_intensity
> +Date:		March 2026
> +KernelVersion:	7.1
> +Contact:	Armin Wolf <W_Armin@xxxxxx>
> +Description:	read
> +		This file contains an array of integers describing the maximum
> +		intensity value for each intensity component.
>  		For additional details please refer to
>  		Documentation/leds/leds-class-multicolor.rst.
> diff --git a/Documentation/leds/leds-class-multicolor.rst b/Documentation/leds/leds-class-multicolor.rst
> index c6b47b4093c4..8f42f10078ad 100644
> --- a/Documentation/leds/leds-class-multicolor.rst
> +++ b/Documentation/leds/leds-class-multicolor.rst
> @@ -25,10 +25,14 @@ color name to indexed value.
>  The ``multi_index`` file is an array that contains the string list of the colors as
>  they are defined in each ``multi_*`` array file.
>  
> -The ``multi_intensity`` is an array that can be read or written to for the
> +The ``multi_intensity`` file is an array that can be read or written to for the
>  individual color intensities.  All elements within this array must be written in
>  order for the color LED intensities to be updated.
>  
> +The ``multi_max_intensity`` file is an array that contains the maximum intensity
> +value supported by each color intensity. Intensity values above this will be
> +automatically clamped into the supported range.
> +
>  Directory Layout Example
>  ========================
>  .. code-block:: console
> @@ -38,6 +42,7 @@ Directory Layout Example
>      -r--r--r--    1 root     root          4096 Oct 19 16:16 max_brightness
>      -r--r--r--    1 root     root          4096 Oct 19 16:16 multi_index
>      -rw-r--r--    1 root     root          4096 Oct 19 16:16 multi_intensity
> +    -r--r--r--    1 root     root          4096 OCt 19 16:16 multi_max_intensity

Nit: Oct

>  
>  ..
>  
> @@ -104,3 +109,17 @@ the color LED group.
>      128
>  
>  ..
> +
> +Writing intensity values larger than the maximum specified in ``multi_max_intensity``
> +will result in those values being clamped into the supported range.
> +
> +.. code-block:: console
> +
> +   # cat /sys/class/leds/multicolor:status/multi_max_intensity
> +   255 255 255
> +
> +   # echo 512 512 512 > /sys/class/leds/multicolor:status/multi_intensity
> +   # cat /sys/class/leds/multicolor:status/multi_intensity
> +   255 255 255
> +
> +..
> diff --git a/drivers/leds/led-class-multicolor.c b/drivers/leds/led-class-multicolor.c
> index 6b671f3f9c61..13a35e6a28df 100644
> --- a/drivers/leds/led-class-multicolor.c
> +++ b/drivers/leds/led-class-multicolor.c
> @@ -7,10 +7,28 @@
>  #include <linux/init.h>
>  #include <linux/led-class-multicolor.h>
>  #include <linux/math.h>
> +#include <linux/minmax.h>
>  #include <linux/module.h>
>  #include <linux/slab.h>
>  #include <linux/uaccess.h>
>  
> +static unsigned int led_mc_get_max_intensity(struct led_classdev_mc *mcled_cdev, size_t index)
> +{
> +	unsigned int max_intensity;
> +
> +	/* The maximum global brightness value might still be changed by
> +	 * led_classdev_register_ext() using devicetree properties. This
> +	 * prevents us from changing subled_info[X].max_intensity when
> +	 * registering a multicolor LED class device, so we have to do
> +	 * this during runtime.
> +	 */
> +	max_intensity = mcled_cdev->subled_info[index].max_intensity;
> +	if (max_intensity)
> +		return max_intensity;
> +
> +	return mcled_cdev->led_cdev.max_brightness;
> +}
> +
>  int led_mc_calc_color_components(struct led_classdev_mc *mcled_cdev,
>  				 enum led_brightness brightness)
>  {
> @@ -27,6 +45,27 @@ int led_mc_calc_color_components(struct led_classdev_mc *mcled_cdev,
>  }
>  EXPORT_SYMBOL_GPL(led_mc_calc_color_components);
>  
> +static ssize_t multi_max_intensity_show(struct device *dev,
> +					struct device_attribute *intensity_attr, char *buf)
> +{
> +	struct led_classdev *led_cdev = dev_get_drvdata(dev);
> +	struct led_classdev_mc *mcled_cdev = lcdev_to_mccdev(led_cdev);
> +	unsigned int max_intensity;
> +	int len = 0;
> +	int i;
> +
> +	for (i = 0; i < mcled_cdev->num_colors; i++) {
> +		max_intensity = led_mc_get_max_intensity(mcled_cdev, i);
> +		len += sprintf(buf + len, "%u", max_intensity);
> +		if (i < mcled_cdev->num_colors - 1)
> +			len += sprintf(buf + len, " ");
> +	}

This should be 'sysfs_emit_at()'.

> +
> +	buf[len++] = '\n';
> +	return len;
> +}
> +static DEVICE_ATTR_RO(multi_max_intensity);
> +
>  static ssize_t multi_intensity_store(struct device *dev,
>  				struct device_attribute *intensity_attr,
>  				const char *buf, size_t size)
> @@ -35,6 +74,7 @@ static ssize_t multi_intensity_store(struct device *dev,
>  	struct led_classdev_mc *mcled_cdev = lcdev_to_mccdev(led_cdev);
>  	int nrchars, offset = 0;
>  	unsigned int intensity_value[LED_COLOR_ID_MAX];
> +	unsigned int max_intensity;
>  	int i;
>  	ssize_t ret;
>  
> @@ -56,8 +96,10 @@ static ssize_t multi_intensity_store(struct device *dev,
>  		goto err_out;
>  	}
>  
> -	for (i = 0; i < mcled_cdev->num_colors; i++)
> -		mcled_cdev->subled_info[i].intensity = intensity_value[i];
> +	for (i = 0; i < mcled_cdev->num_colors; i++) {
> +		max_intensity = led_mc_get_max_intensity(mcled_cdev, i);
> +		mcled_cdev->subled_info[i].intensity = min(intensity_value[i], max_intensity);
> +	}
>  
>  	if (!test_bit(LED_BLINK_SW, &led_cdev->work_flags))
>  		led_set_brightness(led_cdev, led_cdev->brightness);
> @@ -111,6 +153,7 @@ static ssize_t multi_index_show(struct device *dev,
>  static DEVICE_ATTR_RO(multi_index);
>  
>  static struct attribute *led_multicolor_attrs[] = {
> +	&dev_attr_multi_max_intensity.attr,
>  	&dev_attr_multi_intensity.attr,
>  	&dev_attr_multi_index.attr,
>  	NULL,
> diff --git a/drivers/leds/leds-lp50xx.c b/drivers/leds/leds-lp50xx.c
> index e2a9c8592953..69c3550f1a31 100644
> --- a/drivers/leds/leds-lp50xx.c
> +++ b/drivers/leds/leds-lp50xx.c
> @@ -525,6 +525,7 @@ static int lp50xx_probe_dt(struct lp50xx *priv)
>  			}
>  
>  			mc_led_info[multi_index].color_index = color_id;
> +			mc_led_info[multi_index].max_intensity = 255;
>  			num_colors++;
>  		}
>  
> diff --git a/drivers/leds/rgb/leds-ncp5623.c b/drivers/leds/rgb/leds-ncp5623.c
> index 85d6be6fff2b..f2528f06507d 100644
> --- a/drivers/leds/rgb/leds-ncp5623.c
> +++ b/drivers/leds/rgb/leds-ncp5623.c
> @@ -56,8 +56,7 @@ static int ncp5623_brightness_set(struct led_classdev *cdev,
>  	for (int i = 0; i < mc_cdev->num_colors; i++) {
>  		ret = ncp5623_write(ncp->client,
>  				    NCP5623_PWM_REG(mc_cdev->subled_info[i].channel),
> -				    min(mc_cdev->subled_info[i].intensity,
> -					NCP5623_MAX_BRIGHTNESS));
> +				    mc_cdev->subled_info[i].intensity);
>  		if (ret)
>  			return ret;
>  	}
> @@ -190,6 +189,7 @@ static int ncp5623_probe(struct i2c_client *client)
>  			goto release_led_node;
>  
>  		subled_info[ncp->mc_dev.num_colors].channel = reg;
> +		subled_info[ncp->mc_dev.num_colors].max_intensity = NCP5623_MAX_BRIGHTNESS;
>  		subled_info[ncp->mc_dev.num_colors++].color_index = color_index;
>  	}
>  
> diff --git a/include/linux/led-class-multicolor.h b/include/linux/led-class-multicolor.h
> index db9f34c6736e..26f6d20b887d 100644
> --- a/include/linux/led-class-multicolor.h
> +++ b/include/linux/led-class-multicolor.h
> @@ -9,10 +9,31 @@
>  #include <linux/leds.h>
>  #include <dt-bindings/leds/common.h>
>  
> +/**
> + * struct mc_subled - Color component description.
> + * @color_index: Color ID.
> + * @brightness: Scaled intensity.
> + * @intensity: Current intensity.
> + * @max_intensity: Maximum supported intensity value.
> + * @channel: Channel index.
> + *
> + * Describes a color component of a multicolor LED. Many multicolor LEDs
> + * do no support gobal brightness control in hardware, so they use
> + * the brightness field in connection with led_mc_calc_color_components()
> + * to perform the intensity scaling in software.
> + * Such drivers should set max_intensity to 0 to signal the multicolor LED core
> + * that the maximum global brightness of the LED class device should be used for
> + * limiting incoming intensity values.
> + *
> + * Multicolor LEDs that do support global brightness control in hardware
> + * should instead set max_intensity to the maximum intensity value supported
> + * by the hardware for a given color component.
> + */
>  struct mc_subled {
>  	unsigned int color_index;
>  	unsigned int brightness;
>  	unsigned int intensity;
> +	unsigned int max_intensity;
>  	unsigned int channel;
>  };
>  
> @@ -53,7 +74,14 @@ int led_classdev_multicolor_register_ext(struct device *parent,
>   */
>  void led_classdev_multicolor_unregister(struct led_classdev_mc *mcled_cdev);
>  
> -/* Calculate brightness for the monochrome LED cluster */
> +/**
> + * led_mc_calc_color_components() - Calculates component brightness values of a LED cluster.
> + * @mcled_cdev - Multicolor LED class device of the LED cluster.
> + * @led_brightness - Global brightness of the LED cluster.

The header comment does not match the parameters.

Make sure you compile with W=1 to catch kernel-doc issues.

> + * Calculates the brightness values for each color component of a monochrome LED cluster,
> + * see Documentation/leds/leds-class-multicolor.rst for details.
> + */
>  int led_mc_calc_color_components(struct led_classdev_mc *mcled_cdev,
>  				 enum led_brightness brightness);
>  
> -- 
> 2.39.5
> 
> 

-- 
Lee Jones [李琼斯]