stm32/eth: Restructure LWIP initialization for static IP support.

This restructures the LWIP network interface initialization to allow
static IP configuration before active(True) is called, improving the
user experience and network configuration workflow.

Changes:
- Split netif initialization into early (eth_init) and late phases
- eth_netif_init_early() sets up netif structure in eth_init()
- eth_lwip_init() adds netif to network stack in eth_start()
- DHCP only starts if no static IP is configured (0.0.0.0)
- eth_stop() removes from stack but preserves netif for reuse

Workflow:
1. eth_init() -> netif structure ready for IP configuration
2. User can set static IP via ipconfig() before active(True)
3. eth_start() -> adds to network stack, starts DHCP if needed
4. eth_stop() -> removes from network stack, preserves config

This allows the common pattern:
  eth = network.LAN()
  eth.ipconfig(addr='192.168.1.100', ...)  # Set static IP
  eth.active(True)                          # Start networking

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>
Signed-off-by: Andrew Leech <[email protected]>

Author: pi-anl

ports/stm32/eth.c

@@ -132,7 +132,7 @@ eth_t eth_instance;
 
 static void eth_mac_deinit(eth_t *self);
 static void eth_process_frame(eth_t *self, size_t len, const uint8_t *buf);
-static void eth_netif_init_early(eth_t *self);
+static void eth_lwip_init(eth_t *self);
 static void eth_phy_link_status_poll(eth_t *self);
 static void eth_phy_configure_autoneg(eth_t *self);
 
@@ -230,8 +230,8 @@ int eth_init(eth_t *self, int mac_idx, uint32_t phy_addr, int phy_type) {
     __HAL_RCC_ETH_CLK_ENABLE();
     #endif
 
-    // Initialize netif structure early so static IP can be configured before active(True)
-    eth_netif_init_early(self);
+    // Initialize netif and register with LWIP
+    eth_lwip_init(self);
 
     return 0;
 }
@@ -791,7 +791,8 @@ static err_t eth_netif_init(struct netif *netif) {
     return ERR_OK;
 }
 
-static void eth_netif_init_early(eth_t *self) {
+static void eth_lwip_init(eth_t *self) {
+    MICROPY_PY_LWIP_ENTER
     // Initialize netif structure but don't add to network stack yet
     struct netif *n = &self->netif;
     n->name[0] = 'e';
@@ -805,48 +806,19 @@ static void eth_netif_init_early(eth_t *self) {
     IP_ADDR4(&ipconfig[2], 192, 168, 0, 1);    // Gateway
     IP_ADDR4(&ipconfig[3], 8, 8, 8, 8);        // DNS
 
-    netif_set_addr(n, ip_2_ip4(&ipconfig[0]), ip_2_ip4(&ipconfig[1]), ip_2_ip4(&ipconfig[2]));
+    netif_add(n, ip_2_ip4(&ipconfig[0]), ip_2_ip4(&ipconfig[1]), ip_2_ip4(&ipconfig[2]), self, eth_netif_init, ethernet_input);
+    netif_set_hostname(n, mod_network_hostname_data);
+
+    ip_addr_t dns_addr;
+    IP_ADDR4(&dns_addr, 8, 8, 8, 8);
+    dns_setserver(0, &dns_addr);
 
     // Initialize DHCP structure
     dhcp_set_struct(n, &self->dhcp_struct);
-}
-
-static void eth_lwip_init(eth_t *self) {
-    MICROPY_PY_LWIP_ENTER
-
-    struct netif *n = &self->netif;
-
-    // Add netif to network stack (only if not already added)
-    if (netif_find(n->name) == NULL) {
-        ip_addr_t dns_addr;
-        IP_ADDR4(&dns_addr, 8, 8, 8, 8);
-
-        netif_add(n, netif_ip4_addr(n), netif_ip4_netmask(n), netif_ip4_gw(n), self, eth_netif_init, ethernet_input);
-        netif_set_hostname(n, mod_network_hostname_data);
-        netif_set_default(n);
-        netif_set_up(n);
-
-        dns_setserver(0, &dns_addr);
-
-        #if LWIP_IPV6
-        netif_create_ip6_linklocal_address(n, 1);
-        #endif
-    }
-
-    MICROPY_PY_LWIP_EXIT
-}
-
-static void eth_start_dhcp_if_needed(eth_t *self) {
-    MICROPY_PY_LWIP_ENTER
-    struct netif *netif = &self->netif;
-
-    // Check if a static IP address has been configured
-    if (ip4_addr_isany_val(*netif_ip4_addr(netif))) {
-        // No static IP configured, start DHCP
-        dhcp_start(netif);
-    }
-    // If static IP is already configured, don't start DHCP
 
+    #if LWIP_IPV6
+    netif_create_ip6_linklocal_address(n, 1);
+    #endif
     MICROPY_PY_LWIP_EXIT
 }
 
@@ -898,25 +870,6 @@ static void eth_phy_link_status_poll(eth_t *self) {
     }
 }
 
-static void eth_lwip_deinit(eth_t *self) {
-    MICROPY_PY_LWIP_ENTER
-    struct netif *netif = &self->netif;
-
-    // Stop DHCP if running
-    if (netif_dhcp_data(netif)) {
-        dhcp_stop(netif);
-    }
-
-    // Remove from network stack but keep netif structure for reuse
-    for (struct netif *n = netif_list; n != NULL; n = n->next) {
-        if (n == netif) {
-            netif_remove(n);
-            break;
-        }
-    }
-    MICROPY_PY_LWIP_EXIT
-}
-
 static void eth_process_frame(eth_t *self, size_t len, const uint8_t *buf) {
     eth_trace(self, len, buf, NETUTILS_TRACE_NEWLINE);
 
@@ -967,11 +920,20 @@ int eth_start(eth_t *self) {
         return ret;
     }
 
-    // Initialize LWIP netif (only once, safe to call multiple times)
-    eth_lwip_init(self);
+    MICROPY_PY_LWIP_ENTER
+    struct netif *n = &self->netif;
+
+    // Enable the interface in LWIP
+    netif_set_default(n);
+    netif_set_up(n);
 
     // Start DHCP if no static IP has been configured
-    eth_start_dhcp_if_needed(self);
+    if (ip4_addr_isany_val(*netif_ip4_addr(n))) {
+        // No static IP configured, start DHCP
+        dhcp_start(n);
+    }
+
+    MICROPY_PY_LWIP_EXIT
 
     // Do an initial link status poll
     eth_phy_link_status_poll(self);
@@ -981,7 +943,12 @@ int eth_start(eth_t *self) {
 }
 
 int eth_stop(eth_t *self) {
-    eth_lwip_deinit(self);
+    // Stop DHCP if running
+    if (netif_dhcp_data(&self->netif)) {
+        dhcp_stop(&self->netif);
+    }
+    netif_set_down(&self->netif);
+
     eth_mac_deinit(self);
     self->enabled = false;
     return 0;