Remove STM32-specific RX flow control logic from the upper level serial driver to the lower level STM32 serial driver

arch/arm/src/stm32/stm32_serial.c

@@ -2151,23 +2151,39 @@ static bool up_rxflowcontrol(struct uart_dev_s *dev,
 
   if (priv->iflow)
     {
-      /* Disable Rx interrupt to prevent more data being from peripheral.
+      /* Is the RX buffer full? */
-       * When hardware RTS is enabled, this will prevent more data from
-       * coming in.
-       *
-       * This function is only called when UART recv buffer is full, that
-       * is: "dev->recv.head + 1 == dev->recv.tail".
-       *
-       * Logic in "uart_read" will automatically toggle Rx interrupts when
-       * buffer is read empty and thus we do not have to re-enable Rx
-       * interrupts in any other place.
-       */
 
-      ie = priv->ie;
+      if (upper)
-      ie &= ~USART_CR1_RXNEIE;
+        {
-      up_restoreusartint(priv, ie);
+          /* Disable Rx interrupt to prevent more data being from
+           * peripheral.  When hardware RTS is enabled, this will
+           * prevent more data from coming in.
+           *
+           * This function is only called when UART recv buffer is full,
+           * that is: "dev->recv.head + 1 == dev->recv.tail".
+           *
+           * Logic in "uart_read" will automatically toggle Rx interrupts
+           * when buffer is read empty and thus we do not have to re-
+           * enable Rx interrupts.
+           */
 
-      return true;
+          ie = priv->ie;
+          ie &= ~USART_CR1_RXNEIE;
+          up_restoreusartint(priv, ie);
+          return true;
+        }
+
+      /* No.. The RX buffer is empty */
+
+      else
+        {
+          /* We might leave Rx interrupt disabled if full recv buffer was
+           * read empty.  Enable Rx interrupt to make sure that more input is
+           * received.
+           */
+
+          up_rxint(dev, true);
+        }
     }
 
   return false;

drivers/serial/serial.c

@@ -798,19 +798,19 @@ static ssize_t uart_read(FAR struct file *filep, FAR char *buffer, size_t buflen
   if (nbuffered <= watermark)
     {
       /* Let the lower level driver know that the watermark level has been
-       * crossed.
+       * crossed.  It will probably deactivate RX flow control.
        */
 
       (void)uart_rxflowcontrol(dev, nbuffered, false);
     }
 #else
+  /* If the RX  buffer empty */
+
   if (rxbuf->head == rxbuf->tail)
     {
-      /* We might leave Rx interrupt disabled if full recv buffer was read
+      /* Deactivate RX flow control. */
-       * empty. Enable Rx interrupt to make sure that more input is received.
-       */
 
-      uart_enablerxint(dev);
+      (void)uart_rxflowcontrol(dev, 0, false);
     }
 #endif
 #endif

drivers/serial/serialirq.c

@@ -186,7 +186,7 @@ void uart_recvchars(FAR uart_dev_t *dev)
       if (nbuffered >= watermark)
         {
           /* Let the lower level driver know that the watermark level has been
-           * crossed.
+           * crossed.  It will probably activate RX flow control.
            */
 
           if (uart_rxflowcontrol(dev, nbuffered, true))