Backlight - New option : BACKLIGHT_CAPS_LOCK (#4769)

* [BACKLIGHT_CAPS_LOCK_INDICATOR] Use backlight toggling as Caps Lock LED

I've implemented this feature because S65-X doesn't have LED indicators
and the existing led_set_kb(usb_led) function try to use backlight as
indicator but that creates an inconsistency with backlight_config state.

- define `BACKLIGHT_CAPS_LOCK_INDICATOR` to enable Caps Lock indicator
  using backlight (for keyboards without dedicated LED)

- Don't turn off LED indicators when suspend because backlight is
  already turned off. Else led_set(0) will turn back on backlight.

- Documentation has been updated

* [BACKLIGHT_CAPS_LOCK_INDICATOR] Turn off all LED indicators except Caps Lock if BACKLIGHT_CAPS_LOCK_INDICATOR

* [BACKLIGHT_CAPS_LOCK] Rename BACKLIGHT_CAPS_LOCK_INDICATOR

* [BACKLIGHT_CAPS_LOCK] Use new IS_LED_ON method

3 files changed, 51 insertions, 25 deletions

diff --git a/docs/feature_backlight.md b/docs/feature_backlight.md
index f7a35406c..c7a1f131e 100644
--- a/docs/feature_backlight.md
+++ b/docs/feature_backlight.md
@@ -40,6 +40,7 @@ To change the behaviour of the backlighting, `#define` these in your `config.h`:
 |---------------------|-------------|-------------------------------------------------------------------------------------------------------------|
 |`BACKLIGHT_PIN`      |`B7`         |The pin that controls the LEDs. Unless you are designing your own keyboard, you shouldn't need to change this|
 |`BACKLIGHT_LEVELS`   |`3`          |The number of brightness levels (maximum 15 excluding off)                                                   |
+|`BACKLIGHT_CAPS_LOCK`|*Not defined*|Enable Caps Lock indicator using backlight (for keyboards without dedicated LED)                             |
 |`BACKLIGHT_BREATHING`|*Not defined*|Enable backlight breathing, if hardware PWM is used                                                          |
 |`BREATHING_PERIOD`   |`6`          |The length of one backlight "breath" in seconds                                                              |
 
diff --git a/quantum/quantum.c b/quantum/quantum.c
index 5d8ffe34e..c1829c768 100644
--- a/quantum/quantum.c
+++ b/quantum/quantum.c
@@ -1448,6 +1448,24 @@ void led_set(uint8_t usb_led)
     //     PORTE &= ~(1<<6);
     // }
 
+#if defined(BACKLIGHT_CAPS_LOCK) && defined(BACKLIGHT_ENABLE)
+  // Use backlight as Caps Lock indicator
+  uint8_t bl_toggle_lvl = 0;
+
+  if (IS_LED_ON(usb_led, USB_LED_CAPS_LOCK) && !backlight_config.enable) {
+    // Turning Caps Lock ON and backlight is disabled in config
+    // Toggling backlight to the brightest level
+    bl_toggle_lvl = BACKLIGHT_LEVELS;
+  } else if (IS_LED_OFF(usb_led, USB_LED_CAPS_LOCK) && backlight_config.enable) {
+    // Turning Caps Lock OFF and backlight is enabled in config
+    // Toggling backlight and restoring config level
+    bl_toggle_lvl = backlight_config.level;
+  }
+
+  // Set level without modify backlight_config to keep ability to restore state
+  backlight_set(bl_toggle_lvl);
+#endif
+
   led_set_kb(usb_led);
 }
 
diff --git a/tmk_core/common/avr/suspend.c b/tmk_core/common/avr/suspend.c
index 28219f4dd..1194a040e 100644
--- a/tmk_core/common/avr/suspend.c
+++ b/tmk_core/common/avr/suspend.c
@@ -102,24 +102,31 @@ static uint8_t wdt_timeout = 0;
  */
 static void power_down(uint8_t wdto) {
 #ifdef PROTOCOL_LUFA
-    if (USB_DeviceState == DEVICE_STATE_Configured) return;
+  if (USB_DeviceState == DEVICE_STATE_Configured) return;
 #endif
-    wdt_timeout = wdto;
+  wdt_timeout = wdto;
 
-    // Watchdog Interrupt Mode
-    wdt_intr_enable(wdto);
+  // Watchdog Interrupt Mode
+  wdt_intr_enable(wdto);
 
 #ifdef BACKLIGHT_ENABLE
-        backlight_set(0);
+  backlight_set(0);
 #endif
 
-        // Turn off LED indicators
-        led_set(0);
+  // Turn off LED indicators
+  uint8_t leds_off = 0;
+#if defined(BACKLIGHT_CAPS_LOCK) && defined(BACKLIGHT_ENABLE)
+  if (is_backlight_enabled()) {
+    // Don't try to turn off Caps Lock indicator as it is backlight and backlight is already off
+    leds_off |= (1<<USB_LED_CAPS_LOCK);
+  }
+#endif
+  led_set(leds_off);
 
-        #ifdef AUDIO_ENABLE
-        // This sometimes disables the start-up noise, so it's been disabled
-                // stop_all_notes();
-        #endif /* AUDIO_ENABLE */
+#ifdef AUDIO_ENABLE
+  // This sometimes disables the start-up noise, so it's been disabled
+  // stop_all_notes();
+#endif /* AUDIO_ENABLE */
 #if defined(RGBLIGHT_SLEEP) && defined(RGBLIGHT_ENABLE)
 #ifdef RGBLIGHT_ANIMATIONS
   rgblight_timer_disable();
@@ -135,20 +142,20 @@ static void power_down(uint8_t wdto) {
 #endif
   suspend_power_down_kb();
 
-    // TODO: more power saving
-    // See PicoPower application note
-    // - I/O port input with pullup
-    // - prescale clock
-    // - BOD disable
-    // - Power Reduction Register PRR
-    set_sleep_mode(SLEEP_MODE_PWR_DOWN);
-    sleep_enable();
-    sei();
-    sleep_cpu();
-    sleep_disable();
-
-    // Disable watchdog after sleep
-    wdt_disable();
+  // TODO: more power saving
+  // See PicoPower application note
+  // - I/O port input with pullup
+  // - prescale clock
+  // - BOD disable
+  // - Power Reduction Register PRR
+  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
+  sleep_enable();
+  sei();
+  sleep_cpu();
+  sleep_disable();
+
+  // Disable watchdog after sleep
+  wdt_disable();
 }
 #endif