Bug 514062

Summary:	Caps Lock LED indicator does not turn on
Product:	[Applications] systemsettings	Reporter:	tommahu
Component:	kcm_keyboard	Assignee:	Plasma Bugs List <plasma-bugs-null>
Status:	RESOLVED UPSTREAM
Severity:	minor	CC:	butirsky, duha.bugs, kde, natalie_clarius
Priority:	NOR
Version First Reported In:	6.5.4
Target Milestone:	---
Platform:	Arch Linux
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description tommahu 2026-01-02 00:51:34 UTC

SUMMARY

Caps Lock LED indicator does not turn on with a proprietary keyboard under KDE Plasma/Wayland.


STEPS TO REPRODUCE

Keyboard used: Logitech MX Keys
 
Registered in kcm_keyboard as
Model: Generic | Generic 105-key PC
Num Lock on startup: Turn on
Key repeat [v] Delay 600ms Rate: 25 repeats/s.
Layout: French


OBSERVED RESULT

Issue: the caps lock LED does not turn on when the key is pressed. It works in TTY/console mode though. But it does not work under KDE Plasma 6.5.4/Wayland (and prior versions).

Unstable workaround: 
kbd_mode -f -u reinstates the LED but such a command tampers with KDE Plasma which ends up crashing.


Tested alternatives:
I explorer the 'Key Bindings' section but did not identify any setting.


EXPECTED RESULT

Caps Lock LED shall be turned on when enabled


SOFTWARE/OS VERSIONS

OS: Arch Linux (fully updated on 2026-01-02)  
KDE Plasma Version: 6.5.4
KDE Frameworks Version: 6.21.0
Qt Version: 6.10.1


ADDITIONAL INFORMATION
n/a

Comment 1 tommahu 2026-01-02 00:56:17 UTC

1. The kernel LED state is correctly updated:
   - /sys/class/leds/input32::capslock/brightness correctly shows 1/0
   - Verified with: cat /sys/class/leds/input32::capslock/brightness

2. Writing to sysfs succeeds but doesn't update the physical LED:
   - echo 1 > /sys/class/leds/input32::capslock/brightness (no error)
   - Kernel state changes but LED remains off
   
3. Device identification:
   - Event device: /dev/input/event23
   - Vendor ID: 16d0
   - Model ID: 0d3c
   - HID device: /dev/hidraw16

4. Hypothesis: MX Keys uses Logitech HID++ protocol for LED control,
   which KDE Wayland compositor doesn't implement. The keyboard firmware
   doesn't respond to standard Linux LED control mechanisms.

Comment 2 David Edmundson 2026-01-02 10:13:30 UTC

>1. The kernel LED state is correctly updated:

There's not much more we should do at our level.
We update via xkb, which in turn presumably goes down into libinput.

I found a libinput ticket on LEDs and they push it down further to being a kernel problem.

If you're in a position to confirm if it works on Gnome (even via a live USB stick) that would be super useful, please reopen this if it does work there. Otherwise lets file a bug on the kernel.