[edk2-platforms][PATCH 2/4] Platform/RPi: Add serial lib for runtime PL011 vs miniUART detection

["Pete Batard" <pete@akeo.ie>]

The Raspberry Pi platform contains two UARTs, one PL011-based and the
other (called miniUART) 16650-compatible, that are pinmuxed to the GPIO
serial port according to whether a Device Tree overlay is present in
config.txt or not. In most cases, it takes only the user commenting or
uncommenting an overlay line in config.txt to switch between PL011 and
miniUART.

As such, the use of a build time option to select the UART should be
avoided when it is effectively possible to detect which of the UART is
in use at runtime, through a simple MMIO call.

This patch does just this by adding a new DualSerialPortLib that
directs the SerialPortLib implementation to use either 16650 or PL011
according to the GPIO pinmuxing.

It should be noted that this code mostly a merge of
* MdeModulePkg/Library/BaseSerialPortLib16550
* ArmPlatformPkg/Library/PL011SerialPortLib
with non-relevant elements stripped from BaseSerialPortLib16550 (such
as PCI support) and a new call added to retreive the 16650 baudrate
divisor, since it is dependent on the platform's VPU's clock divisor.

Signed-off-by: Pete Batard <pete@akeo.ie>
---
 Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.c   | 836 ++++++++++++++++++++
 Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.inf |  55 ++
 2 files changed, 891 insertions(+)

diff --git a/Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.c b/Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.c
new file mode 100644
index 000000000000..05e12f383785
--- /dev/null
+++ b/Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.c
@@ -0,0 +1,836 @@
+/** @file
+  16550 and PL011 Serial Port library functions for Raspberry Pi
+
+  Copyright (c) 2020, Pete Batard <pete@akeo.ie>
+  Copyright (c) 2018, AMD Incorporated. All rights reserved.<BR>
+  Copyright (c) 2014, Hewlett-Packard Development Company, L.P.<BR>
+  Copyright (c) 2012 - 2016, ARM Ltd. All rights reserved.<BR>
+  Copyright (c) 2008 - 2010, Apple Inc. All rights reserved.<BR>
+  Copyright (c) 2006 - 2019, Intel Corporation. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#include <Base.h>
+#include <IndustryStandard/Bcm2836.h>
+#include <IndustryStandard/Bcm2836Gpio.h>
+#include <Library/BaseLib.h>
+#include <Library/IoLib.h>
+#include <Library/PcdLib.h>
+#include <Library/PL011UartClockLib.h>
+#include <Library/PL011UartLib.h>
+#include <Library/SerialPortLib.h>
+
+BOOLEAN UsePl011Uart          = FALSE;
+BOOLEAN UsePl011UartSet       = FALSE;
+
+#define PL011_UART_REGISTER_BASE      BCM2836_PL011_UART_BASE_ADDRESS
+#define MINI_UART_REGISTER_BASE       (BCM2836_MINI_UART_BASE_ADDRESS + 0x40)
+
+//
+// 16550 UART register offsets and bitfields
+//
+#define R_UART_RXBUF          0   // LCR_DLAB = 0
+#define R_UART_TXBUF          0   // LCR_DLAB = 0
+#define R_UART_BAUD_LOW       0   // LCR_DLAB = 1
+#define R_UART_BAUD_HIGH      1   // LCR_DLAB = 1
+#define R_UART_IER            1   // LCR_DLAB = 0
+#define R_UART_FCR            2
+#define   B_UART_FCR_FIFOE    BIT0
+#define   B_UART_FCR_FIFO64   BIT5
+#define R_UART_LCR            3
+#define   B_UART_LCR_DLAB     BIT7
+#define R_UART_MCR            4
+#define   B_UART_MCR_DTRC     BIT0
+#define   B_UART_MCR_RTS      BIT1
+#define R_UART_LSR            5
+#define   B_UART_LSR_RXRDY    BIT0
+#define   B_UART_LSR_TXRDY    BIT5
+#define   B_UART_LSR_TEMT     BIT6
+#define R_UART_MSR            6
+#define   B_UART_MSR_CTS      BIT4
+#define   B_UART_MSR_DSR      BIT5
+#define   B_UART_MSR_RI       BIT6
+#define   B_UART_MSR_DCD      BIT7
+
+/**
+  Read an 8-bit 16550 register.
+
+  @param  Base    The base address register of UART device.
+  @param  Offset  The offset of the 16550 register to read.
+
+  @return The value read from the 16550 register.
+
+**/
+UINT8
+SerialPortReadRegister (
+  UINTN  Base,
+  UINTN  Offset
+  )
+{
+  return MmioRead8 (Base + Offset * PcdGet32 (PcdSerialRegisterStride));
+}
+
+/**
+  Write an 8-bit 16550 register.
+
+  @param  Base    The base address register of UART device.
+  @param  Offset  The offset of the 16550 register to write.
+  @param  Value   The value to write to the 16550 register specified by Offset.
+
+  @return The value written to the 16550 register.
+
+**/
+UINT8
+SerialPortWriteRegister (
+  UINTN  Base,
+  UINTN  Offset,
+  UINT8  Value
+  )
+{
+  return MmioWrite8 (Base + Offset * PcdGet32 (PcdSerialRegisterStride), Value);
+}
+
+/**
+  Return whether the hardware flow control signal allows writing.
+
+  @param  SerialRegisterBase The base address register of UART device.
+
+  @retval TRUE  The serial port is writable.
+  @retval FALSE The serial port is not writable.
+**/
+BOOLEAN
+SerialPortWritable (
+  UINTN  SerialRegisterBase
+  )
+{
+  if (PcdGetBool (PcdSerialUseHardwareFlowControl)) {
+    if (PcdGetBool (PcdSerialDetectCable)) {
+      //
+      // Wait for both DSR and CTS to be set
+      //   DSR is set if a cable is connected.
+      //   CTS is set if it is ok to transmit data
+      //
+      //   DSR  CTS  Description                               Action
+      //   ===  ===  ========================================  ========
+      //    0    0   No cable connected.                       Wait
+      //    0    1   No cable connected.                       Wait
+      //    1    0   Cable connected, but not clear to send.   Wait
+      //    1    1   Cable connected, and clear to send.       Transmit
+      //
+      return (BOOLEAN) ((SerialPortReadRegister (SerialRegisterBase, R_UART_MSR) & (B_UART_MSR_DSR | B_UART_MSR_CTS)) == (B_UART_MSR_DSR | B_UART_MSR_CTS));
+    } else {
+      //
+      // Wait for both DSR and CTS to be set OR for DSR to be clear.
+      //   DSR is set if a cable is connected.
+      //   CTS is set if it is ok to transmit data
+      //
+      //   DSR  CTS  Description                               Action
+      //   ===  ===  ========================================  ========
+      //    0    0   No cable connected.                       Transmit
+      //    0    1   No cable connected.                       Transmit
+      //    1    0   Cable connected, but not clear to send.   Wait
+      //    1    1   Cable connected, and clar to send.        Transmit
+      //
+      return (BOOLEAN) ((SerialPortReadRegister (SerialRegisterBase, R_UART_MSR) & (B_UART_MSR_DSR | B_UART_MSR_CTS)) != (B_UART_MSR_DSR));
+    }
+  }
+
+  return TRUE;
+}
+
+/**
+  Return the baud generator divisor to use for 16650 setup.
+
+  @param  SerialBaudRate The desired baud rate.
+
+  @return The baud generator divisor.
+**/
+UINT32
+SerialPortGetDivisor (
+  UINT32  SerialBaudRate
+)
+{
+  UINT64              BaseClockRate;
+  UINT32              Divisor;
+
+  //
+  // On the Raspberry Pi, the clock to use for the 16650-compatible UART
+  // is the base clock divided by the 12.12 fixed point VPU clock divisor.
+  //
+  BaseClockRate = (UINT64)PcdGet32 (PcdSerialClockRate) * 4;
+  Divisor = MmioRead32(BCM2836_CM_BASE + BCM2836_CM_VPU_CLOCK_DIVISOR) & 0xFFFFFF;
+  if (Divisor != 0)
+    BaseClockRate = (BaseClockRate << 12) / Divisor;
+
+  //
+  // Now calculate divisor for baud generator
+  //    Ref_Clk_Rate / Baud_Rate / 16
+  //
+  Divisor = (UINT32)BaseClockRate / (SerialBaudRate * 16);
+  if (((UINT32)BaseClockRate % (SerialBaudRate * 16)) >= SerialBaudRate * 8) {
+    Divisor++;
+  }
+  return Divisor;
+}
+
+/**
+  Initialize the serial device hardware.
+
+  If no initialization is required, then return RETURN_SUCCESS.
+  If the serial device was successfully initialized, then return RETURN_SUCCESS.
+  If the serial device could not be initialized, then return RETURN_DEVICE_ERROR.
+
+  @retval RETURN_SUCCESS        The serial device was initialized.
+  @retval RETURN_DEVICE_ERROR   The serial device could not be initialized.
+
+**/
+RETURN_STATUS
+EFIAPI
+SerialPortInitialize (
+  VOID
+  )
+{
+  UINTN               SerialRegisterBase;
+  UINT32              Divisor;
+  UINT32              CurrentDivisor;
+  BOOLEAN             Initialized;
+  UINT64              BaudRate;
+  UINT32              ReceiveFifoDepth;
+  EFI_PARITY_TYPE     Parity;
+  UINT8               DataBits;
+  EFI_STOP_BITS_TYPE  StopBits;
+
+  //
+  // First thing we need to do is determine which of PL011 or miniUART is selected
+  //
+  if (!UsePl011UartSet) {
+    UsePl011Uart = ((MmioRead32(GPIO_BASE_ADDRESS + 4) & 0x0003F000) == 0x00024000);
+    UsePl011UartSet = TRUE;
+  }
+
+  if (UsePl011Uart) {
+    BaudRate = FixedPcdGet64 (PcdUartDefaultBaudRate);
+    ReceiveFifoDepth = 0;         // Use default FIFO depth
+    Parity = (EFI_PARITY_TYPE)FixedPcdGet8 (PcdUartDefaultParity);
+    DataBits = FixedPcdGet8 (PcdUartDefaultDataBits);
+    StopBits = (EFI_STOP_BITS_TYPE) FixedPcdGet8 (PcdUartDefaultStopBits);
+
+    return PL011UartInitializePort (
+             PL011_UART_REGISTER_BASE,
+             PL011UartClockGetFreq(),
+             &BaudRate,
+             &ReceiveFifoDepth,
+             &Parity,
+             &DataBits,
+             &StopBits
+             );
+  } else {
+    SerialRegisterBase = MINI_UART_REGISTER_BASE;
+    Divisor = SerialPortGetDivisor (PcdGet32 (PcdSerialBaudRate));
+
+    //
+    // See if the serial port is already initialized
+    //
+    Initialized = TRUE;
+    if ((SerialPortReadRegister (SerialRegisterBase, R_UART_LCR) & 0x3F) != (PcdGet8 (PcdSerialLineControl) & 0x3F)) {
+      Initialized = FALSE;
+    }
+    SerialPortWriteRegister (SerialRegisterBase, R_UART_LCR, (UINT8)(SerialPortReadRegister (SerialRegisterBase, R_UART_LCR) | B_UART_LCR_DLAB));
+    CurrentDivisor =  SerialPortReadRegister (SerialRegisterBase, R_UART_BAUD_HIGH) << 8;
+    CurrentDivisor |= (UINT32) SerialPortReadRegister (SerialRegisterBase, R_UART_BAUD_LOW);
+    SerialPortWriteRegister (SerialRegisterBase, R_UART_LCR, (UINT8)(SerialPortReadRegister (SerialRegisterBase, R_UART_LCR) & ~B_UART_LCR_DLAB));
+    if (CurrentDivisor != Divisor) {
+      Initialized = FALSE;
+    }
+    if (Initialized) {
+      return RETURN_SUCCESS;
+    }
+
+    //
+    // Wait for the serial port to be ready.
+    // Verify that both the transmit FIFO and the shift register are empty.
+    //
+    while ((SerialPortReadRegister (SerialRegisterBase, R_UART_LSR) & (B_UART_LSR_TEMT | B_UART_LSR_TXRDY)) != (B_UART_LSR_TEMT | B_UART_LSR_TXRDY));
+
+    //
+    // Configure baud rate
+    //
+    SerialPortWriteRegister (SerialRegisterBase, R_UART_LCR, B_UART_LCR_DLAB);
+    SerialPortWriteRegister (SerialRegisterBase, R_UART_BAUD_HIGH, (UINT8) (Divisor >> 8));
+    SerialPortWriteRegister (SerialRegisterBase, R_UART_BAUD_LOW, (UINT8) (Divisor & 0xff));
+
+    //
+    // Clear DLAB and configure Data Bits, Parity, and Stop Bits.
+    // Strip reserved bits from PcdSerialLineControl
+    //
+    SerialPortWriteRegister (SerialRegisterBase, R_UART_LCR, (UINT8)(PcdGet8 (PcdSerialLineControl) & 0x3F));
+
+    //
+    // Enable and reset FIFOs
+    // Strip reserved bits from PcdSerialFifoControl
+    //
+    SerialPortWriteRegister (SerialRegisterBase, R_UART_FCR, 0x00);
+    SerialPortWriteRegister (SerialRegisterBase, R_UART_FCR, (UINT8)(PcdGet8 (PcdSerialFifoControl) & (B_UART_FCR_FIFOE | B_UART_FCR_FIFO64)));
+
+    //
+    // Set FIFO Polled Mode by clearing IER after setting FCR
+    //
+    SerialPortWriteRegister (SerialRegisterBase, R_UART_IER, 0x00);
+
+    //
+    // Put Modem Control Register(MCR) into its reset state of 0x00.
+    //
+    SerialPortWriteRegister (SerialRegisterBase, R_UART_MCR, 0x00);
+
+    return RETURN_SUCCESS;
+  }
+}
+
+/**
+  Write data from buffer to serial device.
+
+  Writes NumberOfBytes data bytes from Buffer to the serial device.
+  The number of bytes actually written to the serial device is returned.
+  If the return value is less than NumberOfBytes, then the write operation failed.
+
+  If Buffer is NULL, then ASSERT().
+
+  If NumberOfBytes is zero, then return 0.
+
+  @param  Buffer           Pointer to the data buffer to be written.
+  @param  NumberOfBytes    Number of bytes to written to the serial device.
+
+  @retval 0                NumberOfBytes is 0.
+  @retval >0               The number of bytes written to the serial device.
+                           If this value is less than NumberOfBytes, then the write operation failed.
+
+**/
+UINTN
+EFIAPI
+SerialPortWrite (
+  IN UINT8     *Buffer,
+  IN UINTN     NumberOfBytes
+  )
+{
+  UINTN  SerialRegisterBase;
+  UINTN  Result;
+  UINTN  Index;
+  UINTN  FifoSize;
+
+  //
+  // Serial writes may happen *before* the UART has been initialized
+  // and if we use the wrong UART then, all kind of bad things happen.
+  // To alleviate this, we add UART detection in SerialPortWrite and
+  // guard the UART detection with a second boolean.
+  //
+  if (!UsePl011UartSet) {
+    UsePl011Uart = ((MmioRead32(GPIO_BASE_ADDRESS + 4) & 0x0003F000) == 0x00024000);
+    UsePl011UartSet = TRUE;
+  }
+
+  if (UsePl011Uart) {
+    return PL011UartWrite (PL011_UART_REGISTER_BASE, Buffer, NumberOfBytes);
+  } else {
+    if (Buffer == NULL) {
+      return 0;
+    }
+
+    SerialRegisterBase = MINI_UART_REGISTER_BASE;
+
+    if (NumberOfBytes == 0) {
+      //
+      // Flush the hardware
+      //
+
+      //
+      // Wait for both the transmit FIFO and shift register empty.
+      //
+      while ((SerialPortReadRegister (SerialRegisterBase, R_UART_LSR) & (B_UART_LSR_TEMT | B_UART_LSR_TXRDY)) != (B_UART_LSR_TEMT | B_UART_LSR_TXRDY));
+
+      //
+      // Wait for the hardware flow control signal
+      //
+      while (!SerialPortWritable (SerialRegisterBase));
+      return 0;
+    }
+
+    //
+    // Compute the maximum size of the Tx FIFO
+    //
+    FifoSize = 1;
+    if ((PcdGet8 (PcdSerialFifoControl) & B_UART_FCR_FIFOE) != 0) {
+      if ((PcdGet8 (PcdSerialFifoControl) & B_UART_FCR_FIFO64) == 0) {
+        FifoSize = 16;
+      } else {
+        FifoSize = PcdGet32 (PcdSerialExtendedTxFifoSize);
+      }
+    }
+
+    Result = NumberOfBytes;
+    while (NumberOfBytes != 0) {
+      //
+      // Wait for the serial port to be ready, to make sure both the transmit FIFO
+      // and shift register empty.
+      //
+      while ((SerialPortReadRegister (SerialRegisterBase, R_UART_LSR) & (B_UART_LSR_TEMT | B_UART_LSR_TXRDY)) != (B_UART_LSR_TEMT | B_UART_LSR_TXRDY));
+
+      //
+      // Fill then entire Tx FIFO
+      //
+      for (Index = 0; Index < FifoSize && NumberOfBytes != 0; Index++, NumberOfBytes--, Buffer++) {
+        //
+        // Wait for the hardware flow control signal
+        //
+        while (!SerialPortWritable (SerialRegisterBase));
+
+        //
+        // Write byte to the transmit buffer.
+        //
+        SerialPortWriteRegister (SerialRegisterBase, R_UART_TXBUF, *Buffer);
+      }
+    }
+    return Result;
+  }
+}
+
+/**
+  Reads data from a serial device into a buffer.
+
+  @param  Buffer           Pointer to the data buffer to store the data read from the serial device.
+  @param  NumberOfBytes    Number of bytes to read from the serial device.
+
+  @retval 0                NumberOfBytes is 0.
+  @retval >0               The number of bytes read from the serial device.
+                           If this value is less than NumberOfBytes, then the read operation failed.
+
+**/
+UINTN
+EFIAPI
+SerialPortRead (
+  OUT UINT8     *Buffer,
+  IN  UINTN     NumberOfBytes
+  )
+{
+  UINTN  SerialRegisterBase;
+  UINTN  Result;
+  UINT8  Mcr;
+
+  if (UsePl011Uart) {
+    return PL011UartRead (PL011_UART_REGISTER_BASE, Buffer, NumberOfBytes);
+  } else {
+    if (NULL == Buffer) {
+      return 0;
+    }
+
+    SerialRegisterBase = MINI_UART_REGISTER_BASE;
+
+    Mcr = (UINT8)(SerialPortReadRegister (SerialRegisterBase, R_UART_MCR) & ~B_UART_MCR_RTS);
+
+    for (Result = 0; NumberOfBytes-- != 0; Result++, Buffer++) {
+      //
+      // Wait for the serial port to have some data.
+      //
+      while ((SerialPortReadRegister (SerialRegisterBase, R_UART_LSR) & B_UART_LSR_RXRDY) == 0) {
+        if (PcdGetBool (PcdSerialUseHardwareFlowControl)) {
+          //
+          // Set RTS to let the peer send some data
+          //
+          SerialPortWriteRegister (SerialRegisterBase, R_UART_MCR, (UINT8)(Mcr | B_UART_MCR_RTS));
+        }
+      }
+      if (PcdGetBool (PcdSerialUseHardwareFlowControl)) {
+        //
+        // Clear RTS to prevent peer from sending data
+        //
+        SerialPortWriteRegister (SerialRegisterBase, R_UART_MCR, Mcr);
+      }
+
+      //
+      // Read byte from the receive buffer.
+      //
+      *Buffer = SerialPortReadRegister (SerialRegisterBase, R_UART_RXBUF);
+    }
+
+    return Result;
+  }
+}
+
+/**
+  Polls a serial device to see if there is any data waiting to be read.
+
+  Polls aserial device to see if there is any data waiting to be read.
+  If there is data waiting to be read from the serial device, then TRUE is returned.
+  If there is no data waiting to be read from the serial device, then FALSE is returned.
+
+  @retval TRUE             Data is waiting to be read from the serial device.
+  @retval FALSE            There is no data waiting to be read from the serial device.
+
+**/
+BOOLEAN
+EFIAPI
+SerialPortPoll (
+  VOID
+  )
+{
+  UINTN  SerialRegisterBase;
+
+  if (UsePl011Uart) {
+    return PL011UartPoll (PL011_UART_REGISTER_BASE);
+  } else {
+    SerialRegisterBase = MINI_UART_REGISTER_BASE;
+
+    //
+    // Read the serial port status
+    //
+    if ((SerialPortReadRegister (SerialRegisterBase, R_UART_LSR) & B_UART_LSR_RXRDY) != 0) {
+      if (PcdGetBool (PcdSerialUseHardwareFlowControl)) {
+        //
+        // Clear RTS to prevent peer from sending data
+        //
+        SerialPortWriteRegister (SerialRegisterBase, R_UART_MCR, (UINT8)(SerialPortReadRegister (SerialRegisterBase, R_UART_MCR) & ~B_UART_MCR_RTS));
+      }
+      return TRUE;
+    }
+
+    if (PcdGetBool (PcdSerialUseHardwareFlowControl)) {
+      //
+      // Set RTS to let the peer send some data
+      //
+      SerialPortWriteRegister (SerialRegisterBase, R_UART_MCR, (UINT8)(SerialPortReadRegister (SerialRegisterBase, R_UART_MCR) | B_UART_MCR_RTS));
+    }
+
+    return FALSE;
+  }
+}
+
+/**
+  Sets the control bits on a serial device.
+
+  @param Control                Sets the bits of Control that are settable.
+
+  @retval RETURN_SUCCESS        The new control bits were set on the serial device.
+  @retval RETURN_UNSUPPORTED    The serial device does not support this operation.
+  @retval RETURN_DEVICE_ERROR   The serial device is not functioning correctly.
+
+**/
+RETURN_STATUS
+EFIAPI
+SerialPortSetControl (
+  IN UINT32 Control
+  )
+{
+  UINTN SerialRegisterBase;
+  UINT8 Mcr;
+
+  if (UsePl011Uart) {
+    return PL011UartSetControl (PL011_UART_REGISTER_BASE, Control);
+  } else {
+    //
+    // First determine the parameter is invalid.
+    //
+    if ((Control & (~(EFI_SERIAL_REQUEST_TO_SEND | EFI_SERIAL_DATA_TERMINAL_READY |
+                      EFI_SERIAL_HARDWARE_FLOW_CONTROL_ENABLE))) != 0) {
+      return RETURN_UNSUPPORTED;
+    }
+
+    SerialRegisterBase = MINI_UART_REGISTER_BASE;
+
+    //
+    // Read the Modem Control Register.
+    //
+    Mcr = SerialPortReadRegister (SerialRegisterBase, R_UART_MCR);
+    Mcr &= (~(B_UART_MCR_DTRC | B_UART_MCR_RTS));
+
+    if ((Control & EFI_SERIAL_DATA_TERMINAL_READY) == EFI_SERIAL_DATA_TERMINAL_READY) {
+      Mcr |= B_UART_MCR_DTRC;
+    }
+
+    if ((Control & EFI_SERIAL_REQUEST_TO_SEND) == EFI_SERIAL_REQUEST_TO_SEND) {
+      Mcr |= B_UART_MCR_RTS;
+    }
+
+    //
+    // Write the Modem Control Register.
+    //
+    SerialPortWriteRegister (SerialRegisterBase, R_UART_MCR, Mcr);
+
+    return RETURN_SUCCESS;
+  }
+}
+
+/**
+  Retrieve the status of the control bits on a serial device.
+
+  @param Control                A pointer to return the current control signals from the serial device.
+
+  @retval RETURN_SUCCESS        The control bits were read from the serial device.
+  @retval RETURN_UNSUPPORTED    The serial device does not support this operation.
+  @retval RETURN_DEVICE_ERROR   The serial device is not functioning correctly.
+
+**/
+RETURN_STATUS
+EFIAPI
+SerialPortGetControl (
+  OUT UINT32 *Control
+  )
+{
+  UINTN SerialRegisterBase;
+  UINT8 Msr;
+  UINT8 Mcr;
+  UINT8 Lsr;
+
+  if (UsePl011Uart) {
+    return PL011UartGetControl (PL011_UART_REGISTER_BASE, Control);
+  } else {
+    SerialRegisterBase = MINI_UART_REGISTER_BASE;
+
+    *Control = 0;
+
+    //
+    // Read the Modem Status Register.
+    //
+    Msr = SerialPortReadRegister (SerialRegisterBase, R_UART_MSR);
+
+    if ((Msr & B_UART_MSR_CTS) == B_UART_MSR_CTS) {
+      *Control |= EFI_SERIAL_CLEAR_TO_SEND;
+    }
+
+    if ((Msr & B_UART_MSR_DSR) == B_UART_MSR_DSR) {
+      *Control |= EFI_SERIAL_DATA_SET_READY;
+    }
+
+    if ((Msr & B_UART_MSR_RI) == B_UART_MSR_RI) {
+      *Control |= EFI_SERIAL_RING_INDICATE;
+    }
+
+    if ((Msr & B_UART_MSR_DCD) == B_UART_MSR_DCD) {
+      *Control |= EFI_SERIAL_CARRIER_DETECT;
+    }
+
+    //
+    // Read the Modem Control Register.
+    //
+    Mcr = SerialPortReadRegister (SerialRegisterBase, R_UART_MCR);
+
+    if ((Mcr & B_UART_MCR_DTRC) == B_UART_MCR_DTRC) {
+      *Control |= EFI_SERIAL_DATA_TERMINAL_READY;
+    }
+
+    if ((Mcr & B_UART_MCR_RTS) == B_UART_MCR_RTS) {
+      *Control |= EFI_SERIAL_REQUEST_TO_SEND;
+    }
+
+    if (PcdGetBool (PcdSerialUseHardwareFlowControl)) {
+      *Control |= EFI_SERIAL_HARDWARE_FLOW_CONTROL_ENABLE;
+    }
+
+    //
+    // Read the Line Status Register.
+    //
+    Lsr = SerialPortReadRegister (SerialRegisterBase, R_UART_LSR);
+
+    if ((Lsr & (B_UART_LSR_TEMT | B_UART_LSR_TXRDY)) == (B_UART_LSR_TEMT | B_UART_LSR_TXRDY)) {
+      *Control |= EFI_SERIAL_OUTPUT_BUFFER_EMPTY;
+    }
+
+    if ((Lsr & B_UART_LSR_RXRDY) == 0) {
+      *Control |= EFI_SERIAL_INPUT_BUFFER_EMPTY;
+    }
+
+    return RETURN_SUCCESS;
+  }
+}
+
+/**
+  Sets the baud rate, receive FIFO depth, transmit/receice time out, parity,
+  data bits, and stop bits on a serial device.
+
+  @param BaudRate           The requested baud rate. A BaudRate value of 0 will use the
+                            device's default interface speed.
+                            On output, the value actually set.
+  @param ReveiveFifoDepth   The requested depth of the FIFO on the receive side of the
+                            serial interface. A ReceiveFifoDepth value of 0 will use
+                            the device's default FIFO depth.
+                            On output, the value actually set.
+  @param Timeout            The requested time out for a single character in microseconds.
+                            This timeout applies to both the transmit and receive side of the
+                            interface. A Timeout value of 0 will use the device's default time
+                            out value.
+                            On output, the value actually set.
+  @param Parity             The type of parity to use on this serial device. A Parity value of
+                            DefaultParity will use the device's default parity value.
+                            On output, the value actually set.
+  @param DataBits           The number of data bits to use on the serial device. A DataBits
+                            vaule of 0 will use the device's default data bit setting.
+                            On output, the value actually set.
+  @param StopBits           The number of stop bits to use on this serial device. A StopBits
+                            value of DefaultStopBits will use the device's default number of
+                            stop bits.
+                            On output, the value actually set.
+
+  @retval RETURN_SUCCESS            The new attributes were set on the serial device.
+  @retval RETURN_UNSUPPORTED        The serial device does not support this operation.
+  @retval RETURN_INVALID_PARAMETER  One or more of the attributes has an unsupported value.
+  @retval RETURN_DEVICE_ERROR       The serial device is not functioning correctly.
+
+**/
+RETURN_STATUS
+EFIAPI
+SerialPortSetAttributes (
+  IN OUT UINT64             *BaudRate,
+  IN OUT UINT32             *ReceiveFifoDepth,
+  IN OUT UINT32             *Timeout,
+  IN OUT EFI_PARITY_TYPE    *Parity,
+  IN OUT UINT8              *DataBits,
+  IN OUT EFI_STOP_BITS_TYPE *StopBits
+  )
+{
+  UINTN     SerialRegisterBase;
+  UINT32    SerialBaudRate;
+  UINTN     Divisor;
+  UINT8     Lcr;
+  UINT8     LcrData;
+  UINT8     LcrParity;
+  UINT8     LcrStop;
+
+  if (UsePl011Uart) {
+    return PL011UartInitializePort (
+             PL011_UART_REGISTER_BASE,
+             PL011UartClockGetFreq(),
+             BaudRate,
+             ReceiveFifoDepth,
+             Parity,
+             DataBits,
+             StopBits
+             );
+  } else {
+    SerialRegisterBase = MINI_UART_REGISTER_BASE;
+
+    //
+    // Check for default settings and fill in actual values.
+    //
+    if (*BaudRate == 0) {
+      *BaudRate = PcdGet32 (PcdSerialBaudRate);
+    }
+    SerialBaudRate = (UINT32) *BaudRate;
+
+    if (*DataBits == 0) {
+      LcrData = (UINT8) (PcdGet8 (PcdSerialLineControl) & 0x3);
+      *DataBits = LcrData + 5;
+    } else {
+      if ((*DataBits < 5) || (*DataBits > 8)) {
+        return RETURN_INVALID_PARAMETER;
+      }
+      //
+      // Map 5..8 to 0..3
+      //
+      LcrData = (UINT8) (*DataBits - (UINT8) 5);
+    }
+
+    if (*Parity == DefaultParity) {
+      LcrParity = (UINT8) ((PcdGet8 (PcdSerialLineControl) >> 3) & 0x7);
+      switch (LcrParity) {
+        case 0:
+          *Parity = NoParity;
+          break;
+
+        case 3:
+          *Parity = EvenParity;
+          break;
+
+        case 1:
+          *Parity = OddParity;
+          break;
+
+        case 7:
+          *Parity = SpaceParity;
+          break;
+
+        case 5:
+          *Parity = MarkParity;
+          break;
+
+        default:
+          break;
+      }
+    } else {
+      switch (*Parity) {
+        case NoParity:
+          LcrParity = 0;
+          break;
+
+        case EvenParity:
+          LcrParity = 3;
+          break;
+
+        case OddParity:
+          LcrParity = 1;
+          break;
+
+        case SpaceParity:
+          LcrParity = 7;
+          break;
+
+        case MarkParity:
+          LcrParity = 5;
+          break;
+
+        default:
+          return RETURN_INVALID_PARAMETER;
+      }
+    }
+
+    if (*StopBits == DefaultStopBits) {
+      LcrStop = (UINT8) ((PcdGet8 (PcdSerialLineControl) >> 2) & 0x1);
+      switch (LcrStop) {
+        case 0:
+          *StopBits = OneStopBit;
+          break;
+
+        case 1:
+          if (*DataBits == 5) {
+            *StopBits = OneFiveStopBits;
+          } else {
+            *StopBits = TwoStopBits;
+          }
+          break;
+
+        default:
+          break;
+      }
+    } else {
+      switch (*StopBits) {
+        case OneStopBit:
+          LcrStop = 0;
+          break;
+
+        case OneFiveStopBits:
+        case TwoStopBits:
+          LcrStop = 1;
+          break;
+
+        default:
+          return RETURN_INVALID_PARAMETER;
+      }
+    }
+
+    //
+    // Configure baud rate
+    //
+    Divisor = SerialPortGetDivisor (SerialBaudRate);
+    SerialPortWriteRegister (SerialRegisterBase, R_UART_LCR, B_UART_LCR_DLAB);
+    SerialPortWriteRegister (SerialRegisterBase, R_UART_BAUD_HIGH, (UINT8) (Divisor >> 8));
+    SerialPortWriteRegister (SerialRegisterBase, R_UART_BAUD_LOW, (UINT8) (Divisor & 0xff));
+
+    //
+    // Clear DLAB and configure Data Bits, Parity, and Stop Bits.
+    // Strip reserved bits from line control value
+    //
+    Lcr = (UINT8) ((LcrParity << 3) | (LcrStop << 2) | LcrData);
+    SerialPortWriteRegister (SerialRegisterBase, R_UART_LCR, (UINT8) (Lcr & 0x3F));
+
+    return RETURN_SUCCESS;
+  }
+}
diff --git a/Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.inf b/Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.inf
new file mode 100644
index 000000000000..af1e6b026fe6
--- /dev/null
+++ b/Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.inf
@@ -0,0 +1,55 @@
+## @file
+#
+#  SerialPortLib instance for both PL011 and 16550 UART.
+#
+#  Copyright (c) 2020, Pete Batard <pete@akeo.ie>
+#  Copyright (c) 2006 - 2019, Intel Corporation. All rights reserved.<BR>
+#
+#  SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+[Defines]
+  INF_VERSION                    = 0x0001001A
+  BASE_NAME                      = DualSerialPortLib
+  FILE_GUID                      = FD3EB93E-B59E-42B7-ABA4-ADA4B988B095
+  MODULE_TYPE                    = BASE
+  VERSION_STRING                 = 1.0
+  LIBRARY_CLASS                  = SerialPortLib
+
+[Packages]
+  ArmPlatformPkg/ArmPlatformPkg.dec
+  EmbeddedPkg/EmbeddedPkg.dec
+  MdePkg/MdePkg.dec
+  MdeModulePkg/MdeModulePkg.dec
+  Silicon/Broadcom/Bcm283x/Bcm283x.dec
+
+[LibraryClasses]
+  IoLib
+  PcdLib
+  PL011UartClockLib
+  PL011UartLib
+
+[Sources]
+  DualSerialPortLib.c
+
+[Pcd]
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialRegisterAccessWidth     ## SOMETIMES_CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialUseMmio                 ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialUseHardwareFlowControl  ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialDetectCable             ## SOMETIMES_CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialBaudRate                ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialLineControl             ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialFifoControl             ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialClockRate               ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialPciDeviceInfo           ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialExtendedTxFifoSize      ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialRegisterStride          ## CONSUMES
+
+[FixedPcd]
+  gArmPlatformTokenSpaceGuid.PL011UartClkInHz
+  gBcm283xTokenSpaceGuid.PcdBcm283xRegistersAddress
+  gEfiMdePkgTokenSpaceGuid.PcdUartDefaultBaudRate
+  gEfiMdePkgTokenSpaceGuid.PcdUartDefaultDataBits
+  gEfiMdePkgTokenSpaceGuid.PcdUartDefaultParity
+  gEfiMdePkgTokenSpaceGuid.PcdUartDefaultStopBits
-- 
2.21.0.windows.1