fix -wconversion-int and add minor comment

Author: hathach

src/common/tusb_types.h

@@ -513,15 +513,19 @@ TU_ATTR_ALWAYS_INLINE static inline uint16_t tu_edpt_packet_size(tusb_desc_endpo
   return tu_le16toh(desc_ep->wMaxPacketSize) & TU_GENMASK(10, 0);
 }
 
-static inline const char *tu_edpt_dir_str(tusb_dir_t dir) {
+#if CFG_TUSB_DEBUG
+TU_ATTR_ALWAYS_INLINE static inline const char *tu_edpt_dir_str(tusb_dir_t dir)
+{
   static const char *str[] = {"out", "in"};
   return str[dir];
 }
 
-static inline const char *tu_edpt_type_str(tusb_xfer_type_t t) {
+TU_ATTR_ALWAYS_INLINE static inline const char *tu_edpt_type_str(tusb_xfer_type_t t)
+{
   static const char *str[] = {"control", "isochronous", "bulk", "interrupt"};
   return str[t];
 }
+#endif
 
 //--------------------------------------------------------------------+
 // Descriptor helper

src/portable/raspberrypi/rp2040/hcd_rp2040.c

@@ -138,18 +138,19 @@ static void __tusb_irq_path_func(hw_handle_buff_status)(void)
         _handle_buff_status_bit(bit, ep);
     }
 
-    // Check interrupt endpoints
+    // Check "interrupt" (asynchronous) endpoints for both IN and OUT
     for (uint i = 1; i <= USB_HOST_INTERRUPT_ENDPOINTS && remaining_buffers; i++)
     {
-        // EPX is bit 0
+        // EPX is bit 0 & 1
         // IEP1 IN  is bit 2
         // IEP1 OUT is bit 3
         // IEP2 IN  is bit 4
         // IEP2 OUT is bit 5
         // IEP3 IN  is bit 6
         // IEP3 OUT is bit 7
         // etc
-        for(int j = 0; j < 2; j++){
+        for(uint j = 0; j < 2; j++)
+        {
             bit = 1 << (i*2+j);
             if (remaining_buffers & bit)
             {
@@ -279,6 +280,8 @@ static struct hw_endpoint *_hw_endpoint_allocate(uint8_t transfer_type)
 
     if (transfer_type != TUSB_XFER_CONTROL)
     {
+        // Note: even though datasheet name these "Interrupt" endpoints. These are actually
+        // "Asynchronous" endpoints and can be used for other type such as: Bulk  (ISO need confirmation)
         ep = _next_free_interrupt_ep();
         pico_info("Allocate %s ep %d\n", tu_edpt_type_str(transfer_type), ep->interrupt_num);
         assert(ep);
@@ -344,11 +347,10 @@ static void _hw_endpoint_init(struct hw_endpoint *ep, uint8_t dev_addr, uint8_t
     if (ep != &epx)
     {
         // Endpoint has its own addr_endp and interrupt bits to be setup!
-        // This is an interrupt endpoint
-        // so need to set up interrupt endpoint address control register with:
-        // device address
-        // endpoint number / direction
-        // preamble
+        // This is an interrupt/async endpoint. so need to set up ADDR_ENDP register with:
+        // - device address
+        // - endpoint number / direction
+        // - preamble
         uint32_t reg = (uint32_t) (dev_addr | (num << USB_ADDR_ENDP1_ENDPOINT_LSB));
 
         if (dir == TUSB_DIR_OUT)