[esp32] Add option to disable libc locks in IRAM, saving ~1.3KB RAM (#10930)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

esphome/components/esp32/__init__.py

@@ -544,6 +544,7 @@ CONF_ENABLE_LWIP_MDNS_QUERIES = "enable_lwip_mdns_queries"
 CONF_ENABLE_LWIP_BRIDGE_INTERFACE = "enable_lwip_bridge_interface"
 CONF_ENABLE_LWIP_TCPIP_CORE_LOCKING = "enable_lwip_tcpip_core_locking"
 CONF_ENABLE_LWIP_CHECK_THREAD_SAFETY = "enable_lwip_check_thread_safety"
+CONF_DISABLE_LIBC_LOCKS_IN_IRAM = "disable_libc_locks_in_iram"
 
 
 def _validate_idf_component(config: ConfigType) -> ConfigType:
@@ -606,6 +607,9 @@ FRAMEWORK_SCHEMA = cv.All(
                     cv.Optional(
                         CONF_ENABLE_LWIP_CHECK_THREAD_SAFETY, default=True
                     ): cv.boolean,
+                    cv.Optional(
+                        CONF_DISABLE_LIBC_LOCKS_IN_IRAM, default=True
+                    ): cv.boolean,
                     cv.Optional(CONF_EXECUTE_FROM_PSRAM): cv.boolean,
                 }
             ),
@@ -864,6 +868,12 @@ async def to_code(config):
     if advanced.get(CONF_ENABLE_LWIP_CHECK_THREAD_SAFETY, True):
         add_idf_sdkconfig_option("CONFIG_LWIP_CHECK_THREAD_SAFETY", True)
 
+    # Disable placing libc locks in IRAM to save RAM
+    # This is safe for ESPHome since no IRAM ISRs (interrupts that run while cache is disabled)
+    # use libc lock APIs. Saves approximately 1.3KB (1,356 bytes) of IRAM.
+    if advanced.get(CONF_DISABLE_LIBC_LOCKS_IN_IRAM, True):
+        add_idf_sdkconfig_option("CONFIG_LIBC_LOCKS_PLACE_IN_IRAM", False)
+
     cg.add_platformio_option("board_build.partitions", "partitions.csv")
     if CONF_PARTITIONS in config:
         add_extra_build_file(

tests/components/esp32/test.esp32-idf.yaml

@@ -5,6 +5,7 @@ esp32:
     advanced:
       enable_lwip_mdns_queries: true
       enable_lwip_bridge_interface: true
+      disable_libc_locks_in_iram: false  # Test explicit opt-out of RAM optimization
 
 wifi:
   ssid: MySSID

tests/components/esp32/test.esp32-s3-idf.yaml

@@ -4,6 +4,7 @@ esp32:
     type: esp-idf
     advanced:
       execute_from_psram: true
+      disable_libc_locks_in_iram: true  # Test default RAM optimization enabled
 
 psram:
   mode: octal