PS/2 mouse absolutely requires the PS/2 connector.

src/device.c

@@ -529,6 +529,8 @@ device_is_valid(const device_t *device, int mflags)
 
     if ((device->flags & DEVICE_AGP) && !(mflags & MACHINE_AGP)) return(0);
 
+    if ((device->flags & DEVICE_PS2) && !(mflags & MACHINE_PS2)) return(0);
+
     return(1);
 }
 

src/mouse_ps2.c

@@ -345,7 +345,7 @@ static const device_config_t ps2_config[] = {
 
 const device_t mouse_ps2_device = {
     "Standard PS/2 Mouse",
-    0,
+    DEVICE_PS2,
     MOUSE_TYPE_PS2,
     mouse_ps2_init, ps2_close, NULL,
     ps2_poll, NULL, NULL,