diff --git a/arch/arm/src/imxrt/hardware/imxrt_lpuart.h b/arch/arm/src/imxrt/hardware/imxrt_lpuart.h
index d3b481d8ed..77d0f51ef2 100644
--- a/arch/arm/src/imxrt/hardware/imxrt_lpuart.h
+++ b/arch/arm/src/imxrt/hardware/imxrt_lpuart.h
@@ -340,7 +340,9 @@
 #  define LPUART_MODIR_TXCTSSRC_CTSB   (0 << 5)  /* Bit nn:  CTS input is CTS_B pin */
 #  define LPUART_MODIR_TXCTSSRC_RXMAT  (1 << 5)  /* Bit nn:  Transmit CTS Source */
                                                  /* Bits 6-7:  Reserved */
-#define LPUART_MODIR_RTSWATER          (8)       /* Bits 8-9: Receive RTS Configuration */
+#define LPUART_MODIR_RTSWATER_SHIFT    (8)       /* Bits 8-9: Receive RTS Configuration */
+#define LPUART_MODIR_RTSWATER_MASK     (3 << LPUART_MODIR_RTSWATER_SHIFT)
+#  define LPUART_MODIR_RTSWATER(n)     ((uint32_t)(n) << LPUART_MODIR_RTSWATER_SHIFT)
                                                  /* Bits 10-15:  Reserved */
 #define LPUART_MODIR_TNP_SHIFT         (16)      /* Bits 16-17: Transmitter narrow pulse */
 #define LPUART_MODIR_TNP_MASK          (3 << LPUART_MODIR_TNP_SHIFT)
@@ -360,6 +362,7 @@
 #  define LPUART_FIFO_RXFIFOSIZE_64    (5 << LPUART_FIFO_RXFIFOSIZE_SHIFT) /* 64 datawords */
 #  define LPUART_FIFO_RXFIFOSIZE_128   (6 << LPUART_FIFO_RXFIFOSIZE_SHIFT) /* 128 datawords */
 #  define LPUART_FIFO_RXFIFOSIZE_256   (7 << LPUART_FIFO_RXFIFOSIZE_SHIFT) /* 256 datawords */
+#define LPUART_FIFO_RXFE               (1 << 3)  /* Bit 3:  Receive FIFO Enable */
 #define LPUART_FIFO_TXFIFOSIZE_SHIFT   (4)       /* Bits 4-6: Transmit FIFO. Buffer Depth */
 #define LPUART_FIFO_TXFIFOSIZE_MASK    (7 << LPUART_FIFO_TXFIFOSIZE_SHIFT)
 #  define LPUART_FIFO_TXFIFOSIZE_1     (0 << LPUART_FIFO_TXFIFOSIZE_SHIFT) /* 1 datawords */
diff --git a/arch/arm/src/imxrt/imxrt_serial.c b/arch/arm/src/imxrt/imxrt_serial.c
index 88e3e812e9..7e7434b71b 100644
--- a/arch/arm/src/imxrt/imxrt_serial.c
+++ b/arch/arm/src/imxrt/imxrt_serial.c
@@ -1643,7 +1643,7 @@ static int up_pm_prepare(struct pm_callback_s *cb, int domain,
  *
  ****************************************************************************/
 
-void up_earlyserialinit(void)
+void imxrt_earlyserialinit(void)
 {
   /* NOTE: This function assumes that low level hardware configuration
    * -- including all clocking and pin configuration -- was performed by the
diff --git a/arch/arm/src/imxrt/imxrt_serial.h b/arch/arm/src/imxrt/imxrt_serial.h
index b9bf4b8288..8b19457a3f 100644
--- a/arch/arm/src/imxrt/imxrt_serial.h
+++ b/arch/arm/src/imxrt/imxrt_serial.h
@@ -33,8 +33,8 @@
  *
  ****************************************************************************/
 
-#ifndef __ARCH_ARM_SRC_IMXRT_IMX_SERIAL_H
-#define __ARCH_ARM_SRC_IMXRT_IMX_SERIAL_H
+#ifndef __ARCH_ARM_SRC_IMXRT_IMXRT_SERIAL_H
+#define __ARCH_ARM_SRC_IMXRT_IMXRT_SERIAL_H
 
 /****************************************************************************
  * Included Files
@@ -90,37 +90,10 @@ extern "C"
 void imxrt_earlyserialinit(void);
 #endif
 
-/****************************************************************************
- * Name: uart_earlyserialinit
- *
- * Description:
- *   Performs the low level UART initialization early in debug so that the
- *   serial console will be available during bootup.  This must be called
- *   before up_serialinit.
- *
- ****************************************************************************/
-
-#if defined(USE_EARLYSERIALINIT) && defined(IMXRT_HAVE_LPUART)
-void uart_earlyserialinit(void);
-#endif
-
-/****************************************************************************
- * Name: uart_serialinit
- *
- * Description:
- *   Register the UART serial console and serial ports.  This assumes that
- *   uart_earlyserialinit was called previously.
- *
- ****************************************************************************/
-
-#ifdef IMXRT_HAVE_LPUART
-void uart_serialinit(void);
-#endif
-
 #undef EXTERN
 #if defined(__cplusplus)
 }
 #endif
 
 #endif /* __ASSEMBLY__ */
-#endif /* __ARCH_ARM_SRC_IMXRT_IMX_SERIAL_H */
+#endif /* __ARCH_ARM_SRC_IMXRT_IMXRT_SERIAL_H */
diff --git a/arch/arm/src/imxrt/imxrt_start.c b/arch/arm/src/imxrt/imxrt_start.c
index 419f928cbc..d4e6cbe66b 100644
--- a/arch/arm/src/imxrt/imxrt_start.c
+++ b/arch/arm/src/imxrt/imxrt_start.c
@@ -381,7 +381,7 @@ void __start(void)
   /* Perform early serial initialization */
 
 #ifdef USE_EARLYSERIALINIT
-  up_earlyserialinit();
+  imxrt_earlyserialinit();
 #endif
 
   /* Then start NuttX */