[wifi] Defer esp_wifi_init() to lazy-init so enable_on_boot: false actually saves RAM (#16606)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

esphome/components/wifi/wifi_component.cpp

@@ -632,6 +632,9 @@ void WiFiComponent::setup() {
 #endif
 
   if (this->enable_on_boot_) {
+#ifdef USE_ESP32
+    this->wifi_lazy_init_();
+#endif
     this->start();
   } else {
     this->state_ = WIFI_COMPONENT_STATE_DISABLED;
@@ -1275,6 +1278,11 @@ void WiFiComponent::enable() {
 
   ESP_LOGD(TAG, "Enabling");
   this->state_ = WIFI_COMPONENT_STATE_OFF;
+#ifdef USE_ESP32
+  // Idempotent — only allocates DMA buffers + netifs on the first call. After this,
+  // start() can safely run.
+  this->wifi_lazy_init_();
+#endif
   this->start();
 }
 

esphome/components/wifi/wifi_component.h

@@ -694,6 +694,12 @@ class WiFiComponent final : public Component {
   bool wifi_apply_hostname_();
   bool wifi_sta_connect_(const WiFiAP &ap);
   void wifi_pre_setup_();
+#ifdef USE_ESP32
+  // ESP-IDF only: defers esp_wifi_init() + netif creation (which allocate ~15-30KB of
+  // DMA-capable internal SRAM) until wifi actually needs to come up. Idempotent.
+  // Called from setup() only when enable_on_boot_=true, and from enable() on first use.
+  void wifi_lazy_init_();
+#endif
   WiFiSTAConnectStatus wifi_sta_connect_status_() const;
   bool is_connected_() const {
     return this->state_ == WIFI_COMPONENT_STATE_STA_CONNECTED &&
@@ -889,6 +895,12 @@ class WiFiComponent final : public Component {
   bool rrm_{false};
 #endif
   bool enable_on_boot_{true};
+#ifdef USE_ESP32
+  // Tracks whether esp_wifi_init() + netif creation has happened. Allows enable()
+  // to be called at runtime without re-allocating, and ensures the heavy init is
+  // skipped entirely when enable_on_boot_ is false until first enable().
+  bool wifi_initialized_{false};
+#endif
   bool got_ipv4_address_{false};
   bool keep_scan_results_{false};
   bool has_completed_scan_after_captive_portal_start_{

esphome/components/wifi/wifi_component_esp_idf.cpp

@@ -163,11 +163,26 @@ void WiFiComponent::wifi_pre_setup_() {
     ESP_LOGE(TAG, "esp_event_handler_instance_register failed: %s", esp_err_to_name(err));
     return;
   }
+  // NOTE: netif creation + esp_wifi_init() used to live here. They allocate ~15-30KB of
+  // DMA-capable internal SRAM, which competes with W5500 SPI DMA and I2S DMA on
+  // memory-tight devices. They are now deferred to wifi_lazy_init_(), called from
+  // setup() when enable_on_boot_ is true, or from enable() on first runtime enable.
+  // This makes enable_on_boot:false genuinely skip the wifi DMA allocation.
+}
 
-  s_sta_netif = esp_netif_create_default_wifi_sta();
+void WiFiComponent::wifi_lazy_init_() {
+  if (this->wifi_initialized_)
+    return;
+
+  // Guard each creation so partial init (e.g. a failed esp_wifi_init() below)
+  // followed by a retry via enable() does not leak the existing netif handle
+  // nor re-register the default WiFi handlers.
+  if (s_sta_netif == nullptr)
+    s_sta_netif = esp_netif_create_default_wifi_sta();
 
 #ifdef USE_WIFI_AP
-  s_ap_netif = esp_netif_create_default_wifi_ap();
+  if (s_ap_netif == nullptr)
+    s_ap_netif = esp_netif_create_default_wifi_ap();
 #endif  // USE_WIFI_AP
 
   wifi_init_config_t cfg = WIFI_INIT_CONFIG_DEFAULT();
@@ -175,7 +190,7 @@ void WiFiComponent::wifi_pre_setup_() {
     ESP_LOGW(TAG, "starting wifi without nvs");
     cfg.nvs_enable = false;
   }
-  err = esp_wifi_init(&cfg);
+  esp_err_t err = esp_wifi_init(&cfg);
   if (err != ERR_OK) {
     ESP_LOGE(TAG, "esp_wifi_init failed: %s", esp_err_to_name(err));
     return;
@@ -185,6 +200,7 @@ void WiFiComponent::wifi_pre_setup_() {
     ESP_LOGE(TAG, "esp_wifi_set_storage failed: %s", esp_err_to_name(err));
     return;
   }
+  this->wifi_initialized_ = true;
 }
 
 bool WiFiComponent::wifi_mode_(optional<bool> sta, optional<bool> ap) {

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

@@ -0,0 +1,15 @@
+wifi:
+  ssid: MySSID
+  password: password1
+  enable_on_boot: false
+
+esphome:
+  on_boot:
+    priority: 200
+    then:
+      - if:
+          condition:
+            not:
+              wifi.enabled:
+          then:
+            - wifi.enable: