ARM split - Add support for dfu-util EE_HANDS flashing (qmk#6543)

* Initial stab at some fake dfu-util-split-left behaviour

* Apply suggestions from code review

Co-Authored-By: fauxpark <fauxpark@gmail.com>

* Clang format fixes

* Fake eeprom init for both left and right hand

tmk_core/chibios.mk

@@ -248,6 +248,21 @@ dfu-util: $(BUILD_DIR)/$(TARGET).bin cpfirmware sizeafter
 # Legacy alias
 dfu-util-wait: dfu-util
 
+# TODO: Remove once ARM has a way to configure EECONFIG_HANDEDNESS
+#       within the emulated eeprom via dfu-util or another tool
+ifneq (,$(filter $(MAKECMDGOALS),dfu-util-split-left))
+    OPT_DEFS += -DINIT_EE_HANDS_LEFT
+endif
+
+ifneq (,$(filter $(MAKECMDGOALS),dfu-util-split-right))
+    OPT_DEFS += -DINIT_EE_HANDS_RIGHT
+endif
+
+dfu-util-split-left: dfu-util
+
+dfu-util-split-right: dfu-util
+
+
 st-link-cli: $(BUILD_DIR)/$(TARGET).hex sizeafter
 	$(ST_LINK_CLI) $(ST_LINK_ARGS) -q -c SWD -p $(BUILD_DIR)/$(TARGET).hex -Rst
 

tmk_core/common/eeconfig.c

@@ -48,6 +48,16 @@ void eeconfig_init_quantum(void) {
     eeprom_update_dword(EECONFIG_RGB_MATRIX, 0);
     eeprom_update_byte(EECONFIG_RGB_MATRIX_SPEED, 0);
 
+    // TODO: Remove once ARM has a way to configure EECONFIG_HANDEDNESS
+    //        within the emulated eeprom via dfu-util or another tool
+#if defined INIT_EE_HANDS_LEFT
+    #pragma message "Faking EE_HANDS for left hand"
+    eeprom_update_byte(EECONFIG_HANDEDNESS, 1);
+#elif defined INIT_EE_HANDS_RIGHT
+    #pragma message "Faking EE_HANDS for right hand"
+    eeprom_update_byte(EECONFIG_HANDEDNESS, 0);
+#endif
+
     eeconfig_init_kb();
 }