moved ethernet interface choice entirely to config

verified that default choices that were made in C++
are still made now, in config.
that is, c3, c6, s2 and s3 variants choose spi2
and everything else (h2) chooses spi3.
these default choices can be overridden by explicit config

grep -H board idf.*
idf.c3.yaml:  board: esp32-c3-devkitm-1
idf.c6.yaml:  board: esp32-c6-devkitc-1
idf.h2.yaml:  board: esp32-h2-devkitm-1
idf.s2.yaml:  board: esp32-s2-saola-1
idf.s3.yaml:  board: esp32-s3-devkitc-1

for y in idf.*; do esphome config $y 2>/dev/null | grep ' interface'; echo $y; done
  interface: spi2
idf.c3.yaml
  interface: spi2
idf.c6.yaml
  interface: spi3
idf.h2.yaml
  interface: spi2
idf.s2.yaml
  interface: spi2
idf.s3.yaml

esphome/components/ethernet/__init__.py

@@ -13,6 +13,7 @@ from esphome.components.esp32.const import (
     VARIANT_ESP32P4,
     VARIANT_ESP32S2,
     VARIANT_ESP32S3,
+    VARIANT_ESP32C6,
 )
 from esphome.components.network import IPAddress
 from esphome.components.spi import CONF_INTERFACE_INDEX, get_spi_interface
@@ -174,6 +175,12 @@ def _validate(config):
                     f"({CORE.target_framework} {CORE.data[KEY_CORE][KEY_FRAMEWORK_VERSION]}), "
                     f"'{CONF_INTERRUPT_PIN}' is a required option for [ethernet]."
                 )
+        if CORE.using_esp_idf and CONF_INTERFACE not in config:
+            variant = get_esp32_variant()
+            if variant in (VARIANT_ESP32C3, VARIANT_ESP32S2, VARIANT_ESP32S3, VARIANT_ESP32C6):
+                config[CONF_INTERFACE] = "spi2"
+            else:
+                config[CONF_INTERFACE] = "spi3"
     elif config[CONF_TYPE] != "OPENETH":
         if CONF_CLK_MODE in config:
             LOGGER.warning(
@@ -357,11 +364,7 @@ async def to_code(config):
                     "spi2": spi_host_device_t.SPI2_HOST,
                     "spi3": spi_host_device_t.SPI3_HOST,
                 }
-                cg.add(
-                    var.set_interface(
-                        map[config[CONF_INTERFACE]]
-                    )
-                )
+                cg.add(var.set_interface(map[config[CONF_INTERFACE]]))
             add_idf_sdkconfig_option("CONFIG_ETH_USE_SPI_ETHERNET", True)
             add_idf_sdkconfig_option(
                 f"CONFIG_ETH_SPI_ETHERNET_{config[CONF_TYPE]}", True

esphome/components/ethernet/ethernet_component.cpp

@@ -87,17 +87,7 @@ void EthernetComponent::setup() {
       .intr_flags = 0,
   };
 
-#if defined(USE_ESP32_VARIANT_ESP32C3) || defined(USE_ESP32_VARIANT_ESP32S2) || defined(USE_ESP32_VARIANT_ESP32S3) || \
-    defined(USE_ESP32_VARIANT_ESP32C6)
-  auto host = SPI2_HOST;
-#else
-  auto host = SPI3_HOST;
-#endif
-#ifdef USE_ESP_IDF
-  if (this->interface_ != SPI_HOST_MAX) {
-    host = this->interface_;
-  }
-#endif
+  auto host = this->interface_;
 
   err = spi_bus_initialize(host, &buscfg, SPI_DMA_CH_AUTO);
   ESPHL_ERROR_CHECK(err, "SPI bus initialize error");