Documentation: leds: leds-class: Document keyboard backlight LED class naming

Document the existing practice of always using 'kbd_backlight' for
the function part of LED class device names for LED class devices which
control single-zone keyboard backlights.

Also extend this existing practice with a new naming scheme for keyboards
with zoned backlight control. There are several drivers in the works (see
the Link:tags below) which offer backlight control for keyboards where
the keyboard backlight is divided in a limited number of zones, e.g.
"main", "cursor" and "numpad" zones.

It is important to agree on a consistent naming scheme for these now,
so that userspace can support multiple different models / vendors through
a single unified naming scheme.

Link: https://lore.kernel.org/platform-driver-x86/20230131235027.36304-1-rishitbansal0@gmail.com/
Link: https://lore.kernel.org/platform-driver-x86/20240719100011.16656-1-carlosmiguelferreira.2003@gmail.com/
Link: https://lore.kernel.org/platform-driver-x86/20260304105831.119349-3-edip@medip.dev/
Link: https://lore.kernel.org/platform-driver-x86/20240806205001.191551-2-mustafa.eskieksi@gmail.com/
Link: https://lore.kernel.org/linux-input/20260402075239.3829699-1-xav@bes.tel/
Signed-off-by: Carlos Ferreira <carlosmiguelferreira.2003@gmail.com>
Co-developed-by: Hans de Goede <johannes.goede@oss.qualcomm.com>
Signed-off-by: Hans de Goede <johannes.goede@oss.qualcomm.com>
Acked-by: Kate Hsuan <hpa@redhat.com>
Link: https://patch.msgid.link/20260504145434.12746-1-johannes.goede@oss.qualcomm.com
Signed-off-by: Lee Jones <lee@kernel.org>

diff --git a/Documentation/leds/leds-class.rst b/Documentation/leds/leds-class.rst
index 5db620ed27aa2e6ad9599b9bcf87b337db79cc4c..3913966cfdac0419ca10bcf629d1dc4419058914 100644 (file)
--- a/Documentation/leds/leds-class.rst
+++ b/Documentation/leds/leds-class.rst
@@ -116,6 +116,69 @@ above leaves scope for further attributes should they be needed. If sections
 of the name don't apply, just leave that section blank.
 
 
+Keyboard backlight control LED Device Naming
+============================================
+
+For backlit keyboards with a single brightness / color settings a single
+(multicolor) LED class device should be used to allow userspace to change
+the backlight brightness (and if possible the color). This LED class device
+must use "kbd_backlight" for the function part of the LED class device name.
+IOW the name must end with ":kbd_backlight".
+
+For backlit keyboards with multiple control zones, one (multicolor) LED class
+device should be used per zone. These LED class devices' name must follow:
+
+       "<devicename>:<color>:kbd_zoned_backlight-<zone_name>"
+
+and <devicename> must be the same for all zones of the same keyboard.
+
+<zone_name> should be descriptive of which part of the keyboard backlight
+the zone covers and should be suitable for userspace to show to an end user
+in an UI for controlling the zones.
+
+Where possible <zone_name> should be a value already used by other
+zoned keyboards with a similar or identical zone layout, e.g.:
+
+<devicename>:<color>:kbd_zoned_backlight-right
+<devicename>:<color>:kbd_zoned_backlight-middle
+<devicename>:<color>:kbd_zoned_backlight-left
+<devicename>:<color>:kbd_zoned_backlight-corners
+<devicename>:<color>:kbd_zoned_backlight-wasd
+
+or:
+
+<devicename>:<color>:kbd_zoned_backlight-main
+<devicename>:<color>:kbd_zoned_backlight-cursor
+<devicename>:<color>:kbd_zoned_backlight-numpad
+<devicename>:<color>:kbd_zoned_backlight-corners
+<devicename>:<color>:kbd_zoned_backlight-wasd
+
+Note that this is intended for keyboards with a limited number of zones,
+keyboards with per key addressable backlighting must not use LED class devices
+since the sysfs API is not suitable for rapidly change multiple LEDs in one
+"commit" as is necessary to do animations / special effects on such keyboards.
+
+An exception to the rule that all zones must follow:
+
+       "<devicename>:<color>:kbd_zoned_backlight-<zone_name>"
+
+is made for the special case where there is a single big zone which controls
+the backlighting of almost all of the keyboard and there are some small areas
+with separate control, like just the 4 cursor keys, or the WASD keys. In this
+case the main zone should use 'kbd_backlight' for the function part of the name
+for compatibility with (older) userspace code which is not aware of
+the "kbd_zoned_backlight-<zone_name>" function naming scheme.
+
+While the smaller zones should use the new zoned naming scheme. Such a setup
+would result in e.g.:
+
+<devicename>:<color>:kbd_backlight
+<devicename>:<color>:kbd_zoned_backlight-wasd
+
+"kbd_zoned_backlight-<zone_name>" aware userspace should be aware of this
+exception and check for a main zone with a "kbd_backlight" function-name.
+
+
 Brightness setting API
 ======================