Move SPLIT_HAND_PIN setup to split_pre_init (#17271)

* Move SPLIT_HAND_PIN setup to split_pre_init

* doppelganger should use old behaviour

* Add comment for future

Co-authored-by: Joel Challis <git@zvecr.com>

Co-authored-by: Joel Challis <git@zvecr.com>

keyboards/doppelganger/doppelganger.c

@@ -15,25 +15,31 @@
  */
 #include "doppelganger.h"
 
-void keyboard_pre_init_kb (void) {
-  setPinOutput(C6);
-  setPinOutput(B0);
+void keyboard_pre_init_kb(void) {
+    setPinOutput(C6);
+    setPinOutput(B0);
 }
 
 bool led_update_kb(led_t led_state) {
-  bool res = led_update_user(led_state);
-  if(res) {
-    // writePin sets the pin high for 1 and low for 0.
-    // In this example the pins are inverted, setting
-    // it low/0 turns it on, and high/1 turns the LED off.
-    // This behavior depends on whether the LED is between the pin
-    // and VCC or the pin and GND.
-    writePin(C6, !led_state.caps_lock);
-  }
-  return res;
+    bool res = led_update_user(led_state);
+    if (res) {
+        // writePin sets the pin high for 1 and low for 0.
+        // In this example the pins are inverted, setting
+        // it low/0 turns it on, and high/1 turns the LED off.
+        // This behavior depends on whether the LED is between the pin
+        // and VCC or the pin and GND.
+        writePin(C6, !led_state.caps_lock);
+    }
+    return res;
 }
 
 __attribute__((weak)) layer_state_t layer_state_set_user(layer_state_t state) {
-  writePin(B0, !(state & (1UL << 1)));
-  return state;
+    writePin(B0, !(state & (1UL << 1)));
+    return state;
+}
+
+// Override core logic as we reuse SPLIT_HAND_PIN within matrix pins
+bool is_keyboard_left(void) {
+    setPinInput(SPLIT_HAND_PIN);
+    return readPin(SPLIT_HAND_PIN);
 }

quantum/split_common/split_util.c

@@ -94,7 +94,6 @@ static uint8_t peek_matrix_intersection(pin_t out_pin, pin_t in_pin) {
 __attribute__((weak)) bool is_keyboard_left(void) {
 #if defined(SPLIT_HAND_PIN)
     // Test pin SPLIT_HAND_PIN for High/Low, if low it's right hand
-    setPinInput(SPLIT_HAND_PIN);
 #    ifdef SPLIT_HAND_PIN_LOW_IS_LEFT
     return !readPin(SPLIT_HAND_PIN);
 #    else
@@ -133,6 +132,10 @@ __attribute__((weak)) bool is_keyboard_master(void) {
 
 // this code runs before the keyboard is fully initialized
 void split_pre_init(void) {
+#if defined(SPLIT_HAND_PIN)
+    setPinInput(SPLIT_HAND_PIN);
+    wait_us(100);
+#endif
     isLeftHand = is_keyboard_left();
 
 #if defined(RGBLIGHT_ENABLE) && defined(RGBLED_SPLIT)