[edk2-devel] [PATCH v5 28/36] OvmfPkg/LoongArchVirt: Add the early serial port output library

["Chao Li" <lichao@loongson.cn>]

Add a early serial port output library into LoongArchVirt that named
EarlyFdtSerialPortLib16550, this library is referenced from
MdeModulePkg.

This library is used in the PEI phase. Since the serial port address can
not be saved in memory of the LoongArch QEMU virtual machine in the PEI
phase, the serial prot base address will be obtained from the FDT before
each output.

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4584

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Chao Li <lichao@loongson.cn>
Co-authored-by: Xianglai Li <lixianglai@loongson.cn>
---
 .../EarlyFdtSerialPortLib16550.c              | 815 ++++++++++++++++++
 .../EarlyFdtSerialPortLib16550.inf            |  46 +
 2 files changed, 861 insertions(+)
 create mode 100644 OvmfPkg/LoongArchVirt/Library/EarlyFdtSerialPortLib16550/EarlyFdtSerialPortLib16550.c
 create mode 100644 OvmfPkg/LoongArchVirt/Library/EarlyFdtSerialPortLib16550/EarlyFdtSerialPortLib16550.inf

diff --git a/OvmfPkg/LoongArchVirt/Library/EarlyFdtSerialPortLib16550/EarlyFdtSerialPortLib16550.c b/OvmfPkg/LoongArchVirt/Library/EarlyFdtSerialPortLib16550/EarlyFdtSerialPortLib16550.c
new file mode 100644
index 0000000000..8cc108501c
--- /dev/null
+++ b/OvmfPkg/LoongArchVirt/Library/EarlyFdtSerialPortLib16550/EarlyFdtSerialPortLib16550.c
@@ -0,0 +1,815 @@
+/** @file
+  16550 UART Serial Port library functions
+
+  Copyright (c) 2024, Loongson Technology Corporation Limited. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#include <Base.h>
+#include <Library/BaseLib.h>
+#include <Library/FdtSerialPortAddressLib.h>
+#include <Library/IoLib.h>
+#include <Library/PcdLib.h>
+#include <Library/SerialPortLib.h>
+
+//
+// PCI Defintions.
+//
+#define PCI_BRIDGE_32_BIT_IO_SPACE  0x01
+
+//
+// 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.  If PcdSerialUseMmio is TRUE, then the value is read from
+  MMIO space.  If PcdSerialUseMmio is FALSE, then the value is read from I/O space.  The
+  parameter Offset is added to the base address of the 16550 registers that is specified
+  by PcdSerialRegisterBase. PcdSerialRegisterAccessWidth specifies the MMIO space access
+  width and defaults to 8 bit access, and supports 8 or 32 bit access.
+
+  @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
+  )
+{
+  if (PcdGetBool (PcdSerialUseMmio)) {
+    if (PcdGet8 (PcdSerialRegisterAccessWidth) == 32) {
+      return (UINT8)MmioRead32 (Base + Offset * PcdGet32 (PcdSerialRegisterStride));
+    }
+
+    return MmioRead8 (Base + Offset * PcdGet32 (PcdSerialRegisterStride));
+  } else {
+    return IoRead8 (Base + Offset * PcdGet32 (PcdSerialRegisterStride));
+  }
+}
+
+/**
+  Write an 8-bit 16550 register.  If PcdSerialUseMmio is TRUE, then the value is written to
+  MMIO space.  If PcdSerialUseMmio is FALSE, then the value is written to I/O space.  The
+  parameter Offset is added to the base address of the 16550 registers that is specified
+  by PcdSerialRegisterBase. PcdSerialRegisterAccessWidth specifies the MMIO space access
+  width and defaults to 8 bit access, and supports 8 or 32 bit access.
+
+  @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
+  )
+{
+  if (PcdGetBool (PcdSerialUseMmio)) {
+    if (PcdGet8 (PcdSerialRegisterAccessWidth) == 32) {
+      return (UINT8)MmioWrite32 (Base + Offset * PcdGet32 (PcdSerialRegisterStride), (UINT8)Value);
+    }
+
+    return MmioWrite8 (Base + Offset * PcdGet32 (PcdSerialRegisterStride), Value);
+  } else {
+    return IoWrite8 (Base + Offset * PcdGet32 (PcdSerialRegisterStride), Value);
+  }
+}
+
+/**
+  Retrieve the I/O or MMIO base address register for the PCI UART device.
+
+  This function assumes Root Bus Numer is Zero, and enables I/O and MMIO in PCI UART
+  Device if they are not already enabled.
+
+  @return  The base address register of the UART device.
+**/
+UINTN
+GetSerialRegisterBase (
+  VOID
+  )
+{
+  VOID           *Base;
+  RETURN_STATUS  Status;
+  UINT64         SerialConsoleAddress;
+
+  Base   = (VOID *)(UINTN)PcdGet64 (PcdDeviceTreeInitialBaseAddress);
+  Status = FdtSerialGetConsolePort (Base, &SerialConsoleAddress);
+  if (RETURN_ERROR (Status)) {
+    return (UINTN)0;
+  }
+
+  return SerialConsoleAddress;
+}
+
+/**
+  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;
+}
+
+/**
+  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;
+
+  //
+  // Calculate divisor for baud generator
+  //    Ref_Clk_Rate / Baud_Rate / 16
+  //
+  Divisor = PcdGet32 (PcdSerialClockRate) / (PcdGet32 (PcdSerialBaudRate) * 16);
+  if ((PcdGet32 (PcdSerialClockRate) % (PcdGet32 (PcdSerialBaudRate) * 16)) >= PcdGet32 (PcdSerialBaudRate) * 8) {
+    Divisor++;
+  }
+
+  //
+  // Get the base address of the serial port in either I/O or MMIO space
+  //
+  SerialRegisterBase = GetSerialRegisterBase ();
+  if (SerialRegisterBase == 0) {
+    return RETURN_DEVICE_ERROR;
+  }
+
+  //
+  // 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;
+
+  if (Buffer == NULL) {
+    return 0;
+  }
+
+  SerialRegisterBase = GetSerialRegisterBase ();
+  if (SerialRegisterBase == 0) {
+    return 0;
+  }
+
+  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 (NULL == Buffer) {
+    return 0;
+  }
+
+  SerialRegisterBase = GetSerialRegisterBase ();
+  if (SerialRegisterBase == 0) {
+    return 0;
+  }
+
+  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;
+
+  SerialRegisterBase = GetSerialRegisterBase ();
+  if (SerialRegisterBase == 0) {
+    return FALSE;
+  }
+
+  //
+  // 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;
+
+  //
+  // 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 = GetSerialRegisterBase ();
+  if (SerialRegisterBase == 0) {
+    return RETURN_UNSUPPORTED;
+  }
+
+  //
+  // 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;
+
+  SerialRegisterBase = GetSerialRegisterBase ();
+  if (SerialRegisterBase == 0) {
+    return RETURN_UNSUPPORTED;
+  }
+
+  *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;
+
+  SerialRegisterBase = GetSerialRegisterBase ();
+  if (SerialRegisterBase == 0) {
+    return RETURN_UNSUPPORTED;
+  }
+
+  //
+  // 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;
+    }
+  }
+
+  //
+  // Calculate divisor for baud generator
+  //    Ref_Clk_Rate / Baud_Rate / 16
+  //
+  Divisor = PcdGet32 (PcdSerialClockRate) / (SerialBaudRate * 16);
+  if ((PcdGet32 (PcdSerialClockRate) % (SerialBaudRate * 16)) >= SerialBaudRate * 8) {
+    Divisor++;
+  }
+
+  //
+  // 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 line control value
+  //
+  Lcr = (UINT8)((LcrParity << 3) | (LcrStop << 2) | LcrData);
+  SerialPortWriteRegister (SerialRegisterBase, R_UART_LCR, (UINT8)(Lcr & 0x3F));
+
+  return RETURN_SUCCESS;
+}
diff --git a/OvmfPkg/LoongArchVirt/Library/EarlyFdtSerialPortLib16550/EarlyFdtSerialPortLib16550.inf b/OvmfPkg/LoongArchVirt/Library/EarlyFdtSerialPortLib16550/EarlyFdtSerialPortLib16550.inf
new file mode 100644
index 0000000000..443c92de67
--- /dev/null
+++ b/OvmfPkg/LoongArchVirt/Library/EarlyFdtSerialPortLib16550/EarlyFdtSerialPortLib16550.inf
@@ -0,0 +1,46 @@
+## @file
+#  SerialPortLib instance for 16550 UART.
+#
+#  Copyright (c) 2024, Loongson Technology Corporation Limited. All rights reserved.<BR>
+#
+#  SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+[Defines]
+  INF_VERSION                    = 0x00010005
+  BASE_NAME                      = EarlySerialPortLib16550
+  FILE_GUID                      = f4fb883d-8138-4f29-bb0c-c574e9312c74
+  MODULE_TYPE                    = BASE
+  VERSION_STRING                 = 1.1
+  LIBRARY_CLASS                  = SerialPortLib
+
+[Packages]
+  EmbeddedPkg/EmbeddedPkg.dec
+  MdePkg/MdePkg.dec
+  MdeModulePkg/MdeModulePkg.dec
+  OvmfPkg/OvmfPkg.dec
+
+[LibraryClasses]
+  BaseLib
+  FdtSerialPortAddressLib
+  IoLib
+  PcdLib
+
+[Sources]
+  EarlyFdtSerialPortLib16550.c
+
+[Pcd]
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialRegisterAccessWidth     ## SOMETIMES_CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialUseMmio                 ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialUseHardwareFlowControl  ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialDetectCable             ## SOMETIMES_CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialRegisterBase            ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialBaudRate                ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialLineControl             ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialFifoControl             ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialClockRate               ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialPciDeviceInfo           ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialExtendedTxFifoSize      ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSerialRegisterStride          ## CONSUMES
+  gUefiOvmfPkgTokenSpaceGuid.PcdDeviceTreeInitialBaseAddress      ## CONSUMES
-- 
2.27.0



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