leds: Introduce the multi_max_intensity sysfs attribute

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>
Link: https://patch.msgid.link/20260509214603.262368-2-W_Armin@gmx.de
Signed-off-by: Lee Jones <lee@kernel.org>

1 files changed, 20 insertions, 1 deletions

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
+
+..