Re: [PATCH v3 1/1] leds: Introduce the multi_max_intensity sysfs attribute

Armin Wolf
2026-04-23T13:36:17Z

Am 09.04.26 um 23:06 schrieb Armin Wolf:
> 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.

WHat is you opinion on this, Pavel? Is it ok to extend the multicolor
LED interface this way?

Thanks,
Armin Wolf

> Reviewed-by: Werner Sembach <wse@tuxedocomputers.com>
> Reviewed-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
> Signed-off-by: Armin Wolf <W_Armin@gmx.de>
> ---
> .../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@ti.com>
> 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@gmx.de>
> +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..68340644f80b 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
>
> ..
>
> @@ -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..8d763b1ae76f 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 += sysfs_emit_at(buf, len, "%u", max_intensity);
> + if (i < mcled_cdev->num_colors - 1)
> + len += sprintf(buf + len, " ");
> + }
> +
> + 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..45469388bb1a 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 global 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.
> + * @brightness - Global brightness of the LED cluster.
> + *
> + * 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);
>