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

Armin Wolf
2026-04-09T21:06:37Z

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.

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);

--
2.39.5