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

[Armin Wolf <W_Armin@gmx.de>]

Am 23.04.26 um 15:44 schrieb Lee Jones:
> On Thu, 23 Apr 2026, Armin Wolf wrote:
> 
>> 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?
> 
> This already has Jacek's Rb, so you're half way there.
> 
> However, the merge-window is open, which is when a lot of maintainers
> (including myself) take a breather.  Seeing as I triage submissions in
> chronological order, unfortunately you just bumped yourself to the back
> of the queue.

Alright, just wanted to check that this patch was not forgoten.

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);
>>
>>
>