[libretiny] Disable BLE stack on BK7231N to save ~21KB RAM (#13131)

esphome/components/libretiny/__init__.py

@@ -32,6 +32,7 @@ from .const import (
     CONF_SDK_SILENT,
     CONF_UART_PORT,
     FAMILIES,
+    FAMILY_BK7231N,
     FAMILY_COMPONENT,
     FAMILY_FRIENDLY,
     KEY_BOARD,
@@ -50,6 +51,22 @@ CODEOWNERS = ["@kuba2k2"]
 AUTO_LOAD = ["preferences"]
 IS_TARGET_PLATFORM = True
 
+# BK7231N SDK options to disable unused features.
+# Disabling BLE saves ~21KB RAM and ~200KB Flash because BLE init code is
+# called unconditionally by the SDK. ESPHome doesn't use BLE on LibreTiny.
+#
+# This only works on BK7231N (BLE 5.x). Other BK72XX chips using BLE 4.2
+# (BK7231T, BK7231Q, BK7251; BK7252 boards use the BK7251 family) have a bug
+# where the BLE library still links and references undefined symbols when
+# CFG_SUPPORT_BLE=0.
+#
+# Other options like CFG_TX_EVM_TEST, CFG_RX_SENSITIVITY_TEST, CFG_SUPPORT_BKREG,
+# CFG_SUPPORT_OTA_HTTP, and CFG_USE_SPI_SLAVE were evaluated but provide no  # NOLINT
+# measurable benefit - the linker already strips unreferenced code via -gc-sections.
+_BK7231N_SYS_CONFIG_OPTIONS = [
+    "CFG_SUPPORT_BLE=0",
+]
+
 
 def _detect_variant(value):
     if KEY_LIBRETINY not in CORE.data:
@@ -346,4 +363,10 @@ async def component_to_code(config):
         cg.add_platformio_option("custom_fw_name", "esphome")
         cg.add_platformio_option("custom_fw_version", __version__)
 
+    # Apply chip-specific SDK options to save RAM/Flash
+    if config[CONF_FAMILY] == FAMILY_BK7231N:
+        cg.add_platformio_option(
+            "custom_options.sys_config#h", _BK7231N_SYS_CONFIG_OPTIONS
+        )
+
     await cg.register_component(var, config)