Initial migration of software PWM backlight (#6709)

* Initial migration of software PWM backlight

* First pass at backlight driver docs

* Correct driver name in docs

* Run backlight_task when using BACKLIGHT_PINS

* Resolve backlight docs TODOs

4 files changed, 75 insertions, 6 deletions

diff --git a/quantum/backlight/backlight_avr.c b/quantum/backlight/backlight_avr.c
index 445698f47c..648a37adf3 100644
--- a/quantum/backlight/backlight_avr.c
+++ b/quantum/backlight/backlight_avr.c
@@ -159,7 +159,7 @@
 #        define BACKLIGHT_ON_STATE 0
 #    endif
 
-void backlight_on(uint8_t backlight_pin) {
+void backlight_on(pin_t backlight_pin) {
 #    if BACKLIGHT_ON_STATE == 0
     writePinLow(backlight_pin);
 #    else
@@ -167,7 +167,7 @@ void backlight_on(uint8_t backlight_pin) {
 #    endif
 }
 
-void backlight_off(uint8_t backlight_pin) {
+void backlight_off(pin_t backlight_pin) {
 #    if BACKLIGHT_ON_STATE == 0
     writePinHigh(backlight_pin);
 #    else
@@ -191,16 +191,16 @@ void backlight_off(uint8_t backlight_pin) {
 
 #        define FOR_EACH_LED(x)                                 \
             for (uint8_t i = 0; i < BACKLIGHT_LED_COUNT; i++) { \
-                uint8_t backlight_pin = backlight_pins[i];      \
+                pin_t backlight_pin = backlight_pins[i];      \
                 { x }                                           \
             }
 
-static const uint8_t backlight_pins[BACKLIGHT_LED_COUNT] = BACKLIGHT_PIN_INIT;
+static const pin_t backlight_pins[BACKLIGHT_LED_COUNT] = BACKLIGHT_PIN_INIT;
 
 #    else  // full hardware PWM
 
 // we support only one backlight pin
-static const uint8_t backlight_pin = BACKLIGHT_PIN;
+static const pin_t backlight_pin = BACKLIGHT_PIN;
 #        define FOR_EACH_LED(x) x
 
 #    endif
diff --git a/quantum/backlight/backlight_soft.c b/quantum/backlight/backlight_soft.c
new file mode 100644
index 0000000000..a6aba7782c
--- /dev/null
+++ b/quantum/backlight/backlight_soft.c
@@ -0,0 +1,66 @@
+#include "quantum.h"
+#include "backlight.h"
+
+#if !defined(BACKLIGHT_PIN) && !defined(BACKLIGHT_PINS)
+#    error "Backlight pin/pins not defined. Please configure."
+#endif
+
+#ifdef BACKLIGHT_BREATHING
+#    error "Backlight breathing is not available for software PWM. Please disable."
+#endif
+
+#ifndef BACKLIGHT_ON_STATE
+#    define BACKLIGHT_ON_STATE 0
+#endif
+
+#ifdef BACKLIGHT_PINS
+#    define BACKLIGHT_PIN_INIT BACKLIGHT_PINS
+#else
+#    define BACKLIGHT_PIN_INIT \
+        { BACKLIGHT_PIN }
+#endif
+
+static const pin_t backlight_pins[] = BACKLIGHT_PIN_INIT;
+#define BACKLIGHT_LED_COUNT (sizeof(backlight_pins) / sizeof(pin_t))
+
+#define FOR_EACH_LED(x)                                 \
+    for (uint8_t i = 0; i < BACKLIGHT_LED_COUNT; i++) { \
+        pin_t backlight_pin = backlight_pins[i];        \
+        { x }                                           \
+    }
+
+void backlight_on(pin_t backlight_pin) {
+#if BACKLIGHT_ON_STATE == 0
+    writePinLow(backlight_pin);
+#else
+    writePinHigh(backlight_pin);
+#endif
+}
+
+void backlight_off(pin_t backlight_pin) {
+#if BACKLIGHT_ON_STATE == 0
+    writePinHigh(backlight_pin);
+#else
+    writePinLow(backlight_pin);
+#endif
+}
+
+void backlight_init_ports(void) {
+    // Setup backlight pin as output and output to on state.
+    FOR_EACH_LED(setPinOutput(backlight_pin); backlight_on(backlight_pin);)
+}
+
+void backlight_task(void) {
+    static uint8_t backlight_tick = 0;
+
+    if ((0xFFFF >> (get_backlight_level() * ((BACKLIGHT_LEVELS + 1) / 2))) & (1 << backlight_tick)) {
+        FOR_EACH_LED(backlight_on(backlight_pin);)
+    } else {
+        FOR_EACH_LED(backlight_off(backlight_pin);)
+    }
+    backlight_tick = (backlight_tick + 1) % 16;
+}
+
+void backlight_set(uint8_t level) {
+    // noop as backlight_task uses get_backlight_level()
+}
diff --git a/quantum/quantum.c b/quantum/quantum.c
index 575bf88bbb..248707057d 100644
--- a/quantum/quantum.c
+++ b/quantum/quantum.c
@@ -992,7 +992,7 @@ void matrix_scan_quantum() {
 #if defined(BACKLIGHT_ENABLE)
 #    if defined(LED_MATRIX_ENABLE)
     led_matrix_task();
-#    elif defined(BACKLIGHT_PIN)
+#    elif defined(BACKLIGHT_PIN) || defined(BACKLIGHT_PINS)
     backlight_task();
 #    endif
 #endif
diff --git a/quantum/quantum.h b/quantum/quantum.h
index 759f7712c2..01abe1c0a1 100644
--- a/quantum/quantum.h
+++ b/quantum/quantum.h
@@ -256,6 +256,9 @@ void tap_code16(uint16_t code);
 #ifdef BACKLIGHT_ENABLE
 void backlight_init_ports(void);
 void backlight_task(void);
+void backlight_task_internal(void);
+void backlight_on(pin_t backlight_pin);
+void backlight_off(pin_t backlight_pin);
 
 #    ifdef BACKLIGHT_BREATHING
 void breathing_task(void);