🔧 Remove LCD_SERIAL_PORT defaults, warn on auto-assign (#24170)

Marlin/Configuration.h

 // Touch-screen LCD for Malyan M200/M300 printers
 //
 //#define MALYAN_LCD
-#if ENABLED(MALYAN_LCD)
-  #define LCD_SERIAL_PORT 1  // Default is 1 for Malyan M200
-#endif
 
 //
 // Touch UI for FTDI EVE (FT800/FT810) displays
 //#define ANYCUBIC_LCD_I3MEGA
 //#define ANYCUBIC_LCD_CHIRON
 #if EITHER(ANYCUBIC_LCD_I3MEGA, ANYCUBIC_LCD_CHIRON)
-  #define LCD_SERIAL_PORT 3  // Default is 3 for Anycubic
   //#define ANYCUBIC_LCD_DEBUG
 #endif
 
 // 320x240 Nextion 2.8" serial TFT Resistive Touch Screen NX3224T028
 //
 //#define NEXTION_TFT
-#if ENABLED(NEXTION_TFT)
-  #define LCD_SERIAL_PORT 1  // Default is 1 for Nextion
-#endif
 
 //
 // Third-party or vendor-customized controller interfaces.

Marlin/Configuration_adv.h

 // Additional options for DGUS / DWIN displays
 //
 #if HAS_DGUS_LCD
-  #define LCD_SERIAL_PORT 3
   #define LCD_BAUDRATE 115200
 
   #define DGUS_RX_BUFFER_SIZE 128

Marlin/src/inc/Conditionals_LCD.h

 // E3V2 extras
 #if HAS_DWIN_E3V2 || IS_DWIN_MARLINUI
   #define SERIAL_CATCHALL 0
-  #ifndef LCD_SERIAL_PORT
-    #if MB(BTT_SKR_MINI_E3_V1_0, BTT_SKR_MINI_E3_V1_2, BTT_SKR_MINI_E3_V2_0, BTT_SKR_MINI_E3_V3_0, BTT_SKR_E3_TURBO)
-      #define LCD_SERIAL_PORT 1
-    #elif MB(CREALITY_V24S1_301, CREALITY_V24S1_301F4, CREALITY_V423)
-      #define LCD_SERIAL_PORT 2 // Creality Ender3S1 board
-    #else
-      #define LCD_SERIAL_PORT 3 // Creality 4.x board
-    #endif
-  #endif
   #define HAS_LCD_BRIGHTNESS 1
   #define LCD_BRIGHTNESS_MAX 250
   #if ENABLED(DWIN_LCD_PROUI)

Marlin/src/inc/Conditionals_adv.h

   #define HAS_USER_ITEM(N) 0
 #endif
 
+/**
+ * LCD_SERIAL_PORT must be defined ahead of HAL.h
+ */
+#ifndef LCD_SERIAL_PORT
+  #if HAS_DWIN_E3V2 || IS_DWIN_MARLINUI
+    #if MB(BTT_SKR_MINI_E3_V1_0, BTT_SKR_MINI_E3_V1_2, BTT_SKR_MINI_E3_V2_0, BTT_SKR_MINI_E3_V3_0, BTT_SKR_E3_TURBO)
+      #define LCD_SERIAL_PORT 1
+    #elif MB(CREALITY_V24S1_301, CREALITY_V24S1_301F4, CREALITY_V423)
+      #define LCD_SERIAL_PORT 2 // Creality Ender3S1 board
+    #else
+      #define LCD_SERIAL_PORT 3 // Creality 4.x board
+    #endif
+  #endif
+  #ifdef LCD_SERIAL_PORT
+    #define AUTO_ASSIGNED_LCD_SERIAL 1
+  #endif
+#endif
+
 #if !HAS_MULTI_SERIAL
   #undef MEATPACK_ON_SERIAL_PORT_2
 #endif

Marlin/src/inc/SanityCheck.h

     #error "The ANYCUBIC LCD requires LCD_SERIAL_PORT to be defined."
   #elif ENABLED(MALYAN_LCD)
     #error "MALYAN_LCD requires LCD_SERIAL_PORT to be defined."
+  #elif ENABLED(NEXTION_LCD)
+    #error "NEXTION_LCD requires LCD_SERIAL_PORT to be defined."
   #endif
 #endif
 

Marlin/src/inc/Warnings.cpp

 
 #ifndef NO_AUTO_ASSIGN_WARNING
 
+  #if AUTO_ASSIGNED_LCD_SERIAL
+    #warning "Note: Auto-assigned LCD_SERIAL_PORT. (Define NO_AUTO_ASSIGN_WARNING to suppress this warning.)"
+  #endif
+
   #if AUTO_ASSIGNED_X2_STEPPER
     #warning "Note: Auto-assigned X2 STEP/DIR/ENABLE_PINs to unused En_STEP/DIR/ENABLE_PINs. (Define NO_AUTO_ASSIGN_WARNING to suppress this warning.)"
   #endif