Stability fix for IRQ-based Ethernet

Under heavy load it is possible for a "packet available" interrupt to
happen while another LWIP call is underway.  In that case it is not
safe to inject a packet at IRQ time.

When that happens, now set a flag and disable IRQs and wait until
the LWIP call is done.  When the call finishes, it will re-enable
IRQs and the IRQ callback will be called again, but this time the
inlwip flag will be unset and the ethernet packet inject safe.

I've run over 9000 W5100::begin/WiFiCliet read fortune/W5100::::end
stress (no delays anywhere) cycles without incident.  W/o this patch,
LWIP state got corrupted in a matter of minutes.

Author: earlephilhower

cores/rp2040/lwip_wrap.cpp

@@ -39,6 +39,11 @@
 //auto_init_recursive_mutex(__lwipMutex); // Only for case with no Ethernet or PicoW, but still doing LWIP (PPP?)
 recursive_mutex_t __lwipMutex;
 
+// When we have a GPIO IRQ for packet reception, the IntfDev will check if we're already doing lwip.
+// If so, it'll disable the IRQ and flag that we need to re-enable it as soon as the current LWIP call ends
+volatile int __inLWIP = 0;
+volatile bool __needsIRQEN = false;
+
 extern "C" {
 
     extern void __lwip(__lwip_op op, void *req, bool fromISR = false);

cores/rp2040/lwip_wrap.h

@@ -38,6 +38,10 @@ extern void ethernet_arch_lwip_gpio_unmask() __attribute__((weak));
 //auto_init_recursive_mutex(__lwipMutex); // Only for case with no Ethernet or PicoW, but still doing LWIP (PPP?)
 extern recursive_mutex_t __lwipMutex;
 
+// When we have a GPIO IRQ for packet reception, the IntfDev will check if we're already doing lwip.
+// If so, it'll disable the IRQ and flag that we need to re-enable it as soon as the current LWIP call ends
+extern volatile int __inLWIP;
+extern volatile bool __needsIRQEN;
 
 // LWIPMutex is a no-op under FreeRTOS because we wrap all calls and just send a request message to
 // the LWIP task.  No locking needed, many people can call LWIP in parallel but the messages will be
@@ -49,6 +53,7 @@ class LWIPMutex {
 public:
     LWIPMutex() {
 #if !defined(__FREERTOS)
+        __inLWIP++;
         if (ethernet_arch_lwip_begin) {
             ethernet_arch_lwip_begin();
         } else {
@@ -64,6 +69,11 @@ class LWIPMutex {
         } else {
             recursive_mutex_exit(&__lwipMutex);
         }
+        __inLWIP--;
+        if (__needsIRQEN && !__inLWIP) {
+            __needsIRQEN = false;
+            ethernet_arch_lwip_gpio_unmask();
+        }
 #endif
     }
 };

libraries/lwIP_Ethernet/src/LwipEthernet.cpp

@@ -58,7 +58,6 @@ static async_context_t *_context = nullptr;
 
 bool __ethernetContextInitted = false;
 
-
 // Theoretically support multiple interfaces
 static std::map<int, std::function<void(void)>> _handlePacketList;
 

libraries/lwIP_Ethernet/src/LwipIntfDev.h

@@ -75,7 +75,6 @@ enum EthernetLinkStatus {
 
 #include <lwip_wrap.h>
 
-
 template<class RawDev>
 class LwipIntfDev: public LwipIntf, public RawDev {
 public:
@@ -496,6 +495,10 @@ template<class RawDev>
 void LwipIntfDev<RawDev>::_irq(void *param) {
     LwipIntfDev *d = static_cast<LwipIntfDev*>(param);
     ethernet_arch_lwip_gpio_mask(); // Disable other IRQs until we're done processing this one
+    if (__inLWIP) {
+        __needsIRQEN = true;
+        return; // We'll get this same IRQ once the current LWIP call is done
+    }
     lwip_callback(_lwipCallback, param, &d->_irqBuffer);
 }