Re: [RFC PATCH 0/1] leds: Introduce the multi_max_intensity sysfs attribute

[Werner Sembach <wse@tuxedocomputers.com>]

Hi,

Am 15.03.26 um 00:01 schrieb Armin Wolf:
> This patch series was born out of of a mailing list thread [1] where
> i asked how to properly model a RGB LED as a multicolor LED. Said
> LED has some exotic properties:
>
> 1. 5 global brightness levels.
> 2. 50 intensity levels for each R/G/B color components.
>
> The current sysfs interface mandates that the maximum intensity value
> for each color component should be the same as the maximum global
> brightness. This makes sense for LEDs that only emulate global
> brightness using led_mc_calc_color_components(), but causes problems
> for LEDs that perform global brightness control in hardware.
>
> Faking a maximum global brightness of 50 will not work in this case,
> as the hardware can change the global brightness on its own. Userspace
> applications might also prefer to know the true maximum brightness
> value.
+1 from me for this change, found it strange that it wasn't already the case.
>
> Because of this i decided to add a new sysfs attribute called
> "multi_max_intensity". This attribute is similar to the
> "max_brightness" sysfs attribute, except that it targets the intensity
> values inside the "multi_intensity" sysfs atribute. I also decided to
> cap intensity values comming from userspace to said maximum intensity
> values to relieve drivers from doing it themself. This was already
> proposed in a unrelated patch [2] and might break some misbehaving
> userspace applications that do not respect max_brightness.

Also +1, max_brightness is checked too in the generic part of the code, 
multi_max_intensity should behave the same.

Since writing a wrong intensity does not return an error but just caps the 
value, the risk of breakage should be minimal i think? It might even repair some 
misbehaving userspace applications by avoiding undefined behavior.

Best regards,

Werner

>
> [1] https://lore.kernel.org/linux-leds/2d91a44e-fce2-42dc-b529-133ab4a191f0@gmx.de/
> [2] https://lore.kernel.org/linux-leds/20260123-leds-multicolor-limit-intensity-v1-1-b37761c2fdfd@pengutronix.de/
>
> Armin Wolf (1):
>    leds: Introduce the multi_max_intensity sysfs attribute
>
>   .../ABI/testing/sysfs-class-led-multicolor    | 16 +++++++--
>   Documentation/leds/leds-class-multicolor.rst  | 21 ++++++++++-
>   drivers/hid/hid-lg-g15.c                      |  3 ++
>   drivers/hid/hid-playstation.c                 |  3 ++
>   drivers/leds/flash/leds-mt6360.c              |  8 ++---
>   drivers/leds/led-class-multicolor.c           | 36 +++++++++++++++++--
>   drivers/leds/leds-blinkm.c                    |  3 ++
>   drivers/leds/leds-cros_ec.c                   |  1 +
>   drivers/leds/leds-lp50xx.c                    |  1 +
>   drivers/leds/leds-lp55xx-common.c             |  7 ++--
>   drivers/leds/leds-max77705.c                  |  1 +
>   drivers/leds/leds-sun50i-a100.c               |  3 ++
>   drivers/leds/leds-turris-omnia.c              |  1 +
>   drivers/leds/rgb/leds-group-multicolor.c      |  1 +
>   drivers/leds/rgb/leds-ktd202x.c               |  1 +
>   drivers/leds/rgb/leds-lp5812.c                |  1 +
>   drivers/leds/rgb/leds-mt6370-rgb.c            |  8 ++---
>   drivers/leds/rgb/leds-ncp5623.c               |  4 +--
>   drivers/leds/rgb/leds-pwm-multicolor.c        |  1 +
>   drivers/leds/rgb/leds-qcom-lpg.c              |  1 +
>   drivers/platform/x86/silicom-platform.c       | 30 ++++++++++++++++
>   drivers/platform/x86/uniwill/uniwill-acpi.c   |  4 +--
>   include/linux/led-class-multicolor.h          | 32 ++++++++++++++++-
>   23 files changed, 164 insertions(+), 23 deletions(-)
>