stm32f7: serial: add interface to get uart_dev_t by USART number, stm32_serial_get_uart

arch/arm/src/stm32f7/stm32_serial.c

@@ -228,6 +228,10 @@ struct up_dev_s
   uint16_t          ie;        /* Saved interrupt mask bits value */
   uint16_t          sr;        /* Saved status bits */
 
+  /* Has been initialized and HW is setup. */
+
+  bool              initialized;
+
   /* If termios are supported, then the following fields may vary at
    * runtime.
    */
@@ -1460,6 +1464,11 @@ static int up_setup(struct uart_dev_s *dev)
   /* Set up the cached interrupt enables value */
 
   priv->ie    = 0;
+
+  /* Mark device as initialized. */
+
+  priv->initialized = true;
+
   return OK;
 }
 
@@ -1539,6 +1548,10 @@ static void up_shutdown(struct uart_dev_s *dev)
   struct up_dev_s *priv = (struct up_dev_s *)dev->priv;
   uint32_t regval;
 
+  /* Mark device as uninitialized. */
+
+  priv->initialized = false;
+
   /* Disable all interrupts */
 
   up_disableusartint(priv, NULL);
@@ -2529,6 +2542,31 @@ static int up_pm_prepare(struct pm_callback_s *cb, int domain,
 
 #ifdef USE_SERIALDRIVER
 
+/****************************************************************************
+ * Name: stm32_serial_get_uart
+ *
+ * Description:
+ *   Get serial driver structure for STM32 USART
+ *
+ ****************************************************************************/
+
+FAR uart_dev_t *stm32_serial_get_uart(int uart_num)
+{
+  int uart_idx = uart_num - 1;
+
+  if (uart_idx < 0 || uart_idx >= STM32_NSERIAL || !uart_devs[uart_idx])
+    {
+      return NULL;
+    }
+
+  if (!uart_devs[uart_idx]->initialized)
+    {
+      return NULL;
+    }
+
+  return &uart_devs[uart_idx]->dev;
+}
+
 /****************************************************************************
  * Name: up_earlyserialinit
  *

arch/arm/src/stm32f7/stm32_uart.h

@@ -41,6 +41,7 @@
  ************************************************************************************/
 
 #include <nuttx/config.h>
+#include <nuttx/serial/serial.h>
 
 #include "chip/stm32_uart.h"
 
@@ -319,6 +320,16 @@ extern "C"
  * Public Functions
  ************************************************************************************/
 
+/************************************************************************************
+ * Name: stm32_serial_get_uart
+ *
+ * Description:
+ *   Get serial driver structure for STM32 USART
+ *
+ ************************************************************************************/
+
+FAR uart_dev_t *stm32_serial_get_uart(int uart_num);
+
 /************************************************************************************
  * Name: stm32_serial_dma_poll
  *