Re: [PATCH v2 1/1] leds: Introduce the multi_max_intensity sysfs attribute

[Jacek Anaszewski]

Hi Armin,

On 3/31/26 9:16 PM, 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/include/linux/led-class-multicolor.h b/include/linux/led-class-multicolor.h
> index db9f34c6736e..6f89d92566b2 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

s/gobal/global/

> + * 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);
>   

Reviewed-by: Jacek Anaszewski <jacek.anaszewski@xxxxxxxxx>

--
Best regards,
Jacek Anaszewski