Re: [edk2-devel] [PATCH v6 28/36] OvmfPkg/LoongArchVirt: Add the early serial port output library

["maobibo" <maobibo@loongson.cn>]

On 2024/1/5 下午5:45, Chao Li wrote:
> 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>
> Cc: Bibo Mao <maobibo@loongson.cn>
> Cc: Dongyan Qian <qiandongyan@loongson.cn>
> 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
> 
Reviewed-by: Bibo Mao <maobibo@loongson.cn>



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