hwdb: Add property for keyboards without LEDs

It is useful for desktop environments to be able to show Caps-Lock or
Num-Lock status changes as an on-screen display when using a keyboard
that doesn't have LEDs for this.

Closes: #5559

hwdb/60-keyboard.hwdb

@@ -1304,3 +1304,16 @@ evdev:input:b0003v1050p0116*
 evdev:input:b0003v05FEp1010*
  XKB_FIXED_LAYOUT="us"
  XKB_FIXED_VARIANT=""
+
+######################### LACK OF MODIFIER LEDS ############################
+# This section lists keyboard which do not have their own LEDs for some
+# modifiers. Only Caps-Lock (KEYBOARD_LED_CAPSLOCK) and Num-Lock
+# (KEYBOARD_LED_CAPSLOCK) are currently handled and need their values set
+# to "0" to indicate the absence of LED.
+#
+# Presence of a LED is implicit when the property is absent.
+
+# Logitech K750
+evdev:input:b0003v046Dp4002*
+ KEYBOARD_LED_NUMLOCK=0
+ KEYBOARD_LED_CAPSLOCK=0

hwdb/parse_hwdb.py

@@ -112,6 +112,8 @@ def property_grammar():
              ('ID_INPUT_TOUCHPAD_INTEGRATION', Or(('internal', 'external'))),
              ('XKB_FIXED_LAYOUT', STRING),
              ('XKB_FIXED_VARIANT', STRING),
+             ('KEYBOARD_LED_NUMLOCK', Literal('0')),
+             ('KEYBOARD_LED_CAPSLOCK', Literal('0')),
              ('ACCEL_MOUNT_MATRIX', mount_matrix),
             )
     fixed_props = [Literal(name)('NAME') - Suppress('=') - val('VALUE')