[Core] Allow customizing PWM frequency (#21717)

* [Core] Allow customizing PWM frequency

Some frequencies can cause audible noise. Changing the frequency
eliminates that.

Signed-off-by: Daniel Schaefer <dhs@frame.work>

* docs/feature-backlight: Mention PWM frequency

Signed-off-by: Daniel Schaefer <dhs@frame.work>

---------

Signed-off-by: Daniel Schaefer <dhs@frame.work>

docs/feature_backlight.md

@@ -39,6 +39,7 @@ Add the following to your `config.h`:
 |`BACKLIGHT_LIMIT_VAL`        |`255`             |The maximum duty cycle of the backlight -- `255` allows for full brightness, any lower will decrease the maximum.|
 |`BACKLIGHT_DEFAULT_LEVEL`    |`BACKLIGHT_LEVELS`|The default backlight level to use upon clearing the EEPROM                                                      |
 |`BACKLIGHT_DEFAULT_BREATHING`|*Not defined*     |Whether to enable backlight breathing upon clearing the EEPROM                                                   |
+|`BACKLIGHT_PWM_PERIOD`       |2048Hz            |Defaults to `BACKLIGHT_PWM_COUNTER_FREQUENCY / 2048`, which results in a PWM frequency of 2048Hz.                |
 
 Unless you are designing your own keyboard, you generally should not need to change the `BACKLIGHT_PIN` or `BACKLIGHT_ON_STATE`.
 

platforms/chibios/chibios_config.h

@@ -37,7 +37,9 @@
 #        define BACKLIGHT_PAL_MODE (PAL_MODE_ALTERNATE_PWM | PAL_RP_PAD_DRIVE12 | PAL_RP_GPIO_OE)
 #    endif
 #    define BACKLIGHT_PWM_COUNTER_FREQUENCY 1000000
-#    define BACKLIGHT_PWM_PERIOD BACKLIGHT_PWM_COUNTER_FREQUENCY / 2048
+#    ifndef BACKLIGHT_PWM_PERIOD
+#        define BACKLIGHT_PWM_PERIOD BACKLIGHT_PWM_COUNTER_FREQUENCY / 2048
+#    endif
 
 #    ifndef AUDIO_PWM_PAL_MODE
 #        define AUDIO_PWM_PAL_MODE (PAL_MODE_ALTERNATE_PWM | PAL_RP_PAD_DRIVE12 | PAL_RP_GPIO_OE)