Re: [PATCH v7 2/3] MdePkg: add SBI-based SerialPortLib for RISC-V

["Sunil V L" <sunilvl@ventanamicro.com>]

Thanks, Andrei. Just one nit comment below.

Otherwise, LGTM.
Reviewed-by: Sunil V L <sunilvl@ventanamicro.com>

On Fri, Apr 07, 2023 at 04:44:24PM -0500, Andrei Warkentin wrote:
> These are implementations of SerialPortLib using SBI console services.
> - BaseSerialPortLibRiscVSbiLib is appropriate for SEC/PEI (XIP) environments
> - BaseSerialPortLibRiscVSbiLibRam is appropriate for PrePI/DXE environments
> 
> Tested with:
> - Qemu RiscVVirt (non-DBCN case, backed by UART)
> - TinyEMU + RiscVVirt (non-DBCN case, HTIF)
> - TinyEMU + RiscVVirt (DBCN case, HTIF)
> 
> Cc: Daniel Schaefer <git@danielschaefer.me>
> Cc: Sunil V L <sunilvl@ventanamicro.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Cc: Liming Gao <gaoliming@byosoft.com.cn>
> Cc: Zhiguang Liu <zhiguang.liu@intel.com>
> Acked-by: Gerd Hoffmann <kraxel@redhat.com>
> Signed-off-by: Andrei Warkentin <andrei.warkentin@intel.com>
> ---
>  MdePkg/MdePkg.dsc                                                               |   2 +
>  MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.inf    |  41 +++
>  MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLibRam.inf |  38 +++
>  MdePkg/Library/BaseSerialPortLibRiscVSbiLib/Common.h                            |  41 +++
>  MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.c      | 208 ++++++++++++++
>  MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLibRam.c   | 289 ++++++++++++++++++++
>  MdePkg/Library/BaseSerialPortLibRiscVSbiLib/Common.c                            | 132 +++++++++
>  MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.uni    |  16 ++
>  8 files changed, 767 insertions(+)
> 
> diff --git a/MdePkg/MdePkg.dsc b/MdePkg/MdePkg.dsc
> index 0ac7618b4623..a810ad0d147d 100644
> --- a/MdePkg/MdePkg.dsc
> +++ b/MdePkg/MdePkg.dsc
> @@ -192,5 +192,7 @@ [Components.ARM, Components.AARCH64]
>  
>  [Components.RISCV64]
>    MdePkg/Library/BaseRiscVSbiLib/BaseRiscVSbiLib.inf
> +  MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.inf
> +  MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLibRam.inf
>  
>  [BuildOptions]
> diff --git a/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.inf b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.inf
> new file mode 100644
> index 000000000000..2340ac6bfe67
> --- /dev/null
> +++ b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.inf
> @@ -0,0 +1,41 @@
> +## @file
> +#  Serial Port Library backed by SBI console.
> +#
> +#  Meant for SEC and PEI (XIP) environments.
> +#
> +#  Due to limitations of SBI console interface and XIP environments
> +#  (on use of globals), this library instance does not implement reading
> +#  and polling the serial port. See PrePiDxeSerialPortLibRiscVSbiRam.inf
> +#  for the full-featured variant meant for PrePi and DXE environments.
> +#
> +#  Copyright (c) 2023, Intel Corporation. All rights reserved.<BR>
> +#
> +#  SPDX-License-Identifier: BSD-2-Clause-Patent
> +#
> +#
> +##
> +
> +[Defines]
> +  INF_VERSION                    = 0x0001001B
> +  BASE_NAME                      = BaseSerialPortLibRiscVSbiLib
> +  MODULE_UNI_FILE                = BaseSerialPortLibRiscVSbiLib.uni
> +  FILE_GUID                      = 639fad38-4bfd-4eb9-9f09-e97c7947d480
> +  MODULE_TYPE                    = BASE
> +  VERSION_STRING                 = 1.0
> +  LIBRARY_CLASS                  = SerialPortLib | SEC PEI_CORE PEIM
> +
> +
> +#
> +#  VALID_ARCHITECTURES           = RISCV64
> +#
> +
> +[Sources]
> +  BaseSerialPortLibRiscVSbiLib.c
> +  Common.c
> +  Common.h
> +
> +[Packages]
> +  MdePkg/MdePkg.dec
> +
> +[LibraryClasses]
> +  RiscVSbiLib
> diff --git a/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLibRam.inf b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLibRam.inf
> new file mode 100644
> index 000000000000..d09573ca5b36
> --- /dev/null
> +++ b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLibRam.inf
> @@ -0,0 +1,38 @@
> +## @file
> +#  Serial Port Library backed by SBI console.
> +#
> +#  Meant for PrePi and DXE environments (where globals are allowed). See
> +#  BaseSerialPortLibRiscVSbiLib.inf for a reduced variant appropriate
> +#  for SEC and PEI (XIP) environments.
> +#
> +#  Copyright (c) 2023, Intel Corporation. All rights reserved.<BR>
> +#
> +#  SPDX-License-Identifier: BSD-2-Clause-Patent
> +#
> +#
> +##
> +
> +[Defines]
> +  INF_VERSION                    = 0x0001001B
> +  BASE_NAME                      = BaseSerialPortLibRiscVSbiLibRam
> +  MODULE_UNI_FILE                = BaseSerialPortLibRiscVSbiLib.uni
> +  FILE_GUID                      = 872af743-ab56-45b4-a065-602567f4820c
> +  MODULE_TYPE                    = BASE
> +  VERSION_STRING                 = 1.0
> +  LIBRARY_CLASS                  = SerialPortLib | SEC DXE_CORE DXE_DRIVER DXE_RUNTIME_DRIVER UEFI_DRIVER UEFI_APPLICATION
> +
> +
> +#
> +#  VALID_ARCHITECTURES           = RISCV64
> +#
> +
> +[Sources]
> +  BaseSerialPortLibRiscVSbiLibRam.c
> +  Common.c
> +  Common.h
> +
> +[Packages]
> +  MdePkg/MdePkg.dec
> +
> +[LibraryClasses]
> +  RiscVSbiLib
> diff --git a/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/Common.h b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/Common.h
> new file mode 100644
> index 000000000000..98c1a5d3865e
> --- /dev/null
> +++ b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/Common.h
> @@ -0,0 +1,41 @@
> +/** @file
> +  Serial Port Library backed by SBI console.
> +
> +  Common functionality shared by PrePiDxeSerialPortLibRiscVSbi and
> +  PrePiDxeSerialPortLibRiscVSbiRam implementations.
> +
> +  Copyright (c) 2023, Intel Corporation. All rights reserved.<BR>
> +  SPDX-License-Identifier: BSD-2-Clause-Patent
> +
> +**/
> +
> +#ifndef SERIAL_PORT_SBI_COMMON_H_
> +#define SERIAL_PORT_SBI_COMMON_H_
> +
> +#include <Base.h>
> +#include <Library/SerialPortLib.h>
> +#include <Library/BaseRiscVSbiLib.h>
> +
> +BOOLEAN
> +SbiImplementsDbcn (
> +  VOID
> +  );
> +
> +BOOLEAN
> +SbiImplementsLegacyPutchar (
> +  VOID
> +  );
> +
> +UINTN
> +SbiLegacyPutchar (
> +  IN  UINT8  *Buffer,
> +  IN  UINTN  NumberOfBytes
> +  );
> +
> +UINTN
> +SbiDbcnWrite (
> +  IN  UINT8  *Buffer,
> +  IN  UINTN  NumberOfBytes
> +  );
> +
> +#endif /* SERIAL_PORT_SBI_COMMON_H_ */
> diff --git a/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.c b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.c
> new file mode 100644
> index 000000000000..f4f2959cf8cc
> --- /dev/null
> +++ b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.c
> @@ -0,0 +1,208 @@
> +/** @file
> +  Serial Port Library backed by SBI console.
> +
> +  Meant for SEC and PEI (XIP) environments.
> +
> +  Due to limitations of SBI console interface and XIP environments
> +  (on use of globals), this library instance does not implement reading
> +  and polling the serial port. See BaseSerialPortLibRiscVSbiLibRam.c for
> +  the full-featured variant meant for PrePi and DXE environments.
> +
> +  Copyright (c) 2023, Intel Corporation. All rights reserved.<BR>
> +  SPDX-License-Identifier: BSD-2-Clause-Patent
> +
> +**/
> +
> +#include "Common.h"
> +
> +/**
> +  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
> +  )
> +{
> +  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 NumberOfBytes is zero, then return 0.
> +
> +  @param  Buffer           The pointer to the data buffer to be written.
> +  @param  NumberOfBytes    The 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
> +  )
> +{
> +  if (NumberOfBytes == 0) {
> +    return 0;
> +  }
> +
> +  if (SbiImplementsDbcn ()) {
> +    return SbiDbcnWrite (Buffer, NumberOfBytes);
> +  }
> +
> +  if (SbiImplementsLegacyPutchar ()) {
> +    return SbiLegacyPutchar (Buffer, NumberOfBytes);
> +  }
> +
> +  /*
> +   * Neither DBCN or legacy extension were present.
> +   */
> +  return 0;
> +}
> +
> +/**
> +  Read data from serial device and save the datas in buffer.
> +
> +  Reads NumberOfBytes data bytes from a serial device into the buffer
> +  specified by Buffer. The number of bytes actually read is returned.
> +  If the return value is less than NumberOfBytes, then the rest operation failed.
> +  If NumberOfBytes is zero, then return 0.
> +
> +  @param  Buffer           The pointer to the data buffer to store the data read from the serial device.
> +  @param  NumberOfBytes    The number of bytes which will be read.
> +
> +  @retval 0                Read data failed; No data is to be read.
> +  @retval >0               The actual number of bytes read from serial device.
> +
> +**/
> +UINTN
> +EFIAPI
> +SerialPortRead (
> +  OUT UINT8  *Buffer,
> +  IN  UINTN  NumberOfBytes
> +  )
> +{
> +  return 0;
> +}
> +
> +/**
> +  Polls a serial device to see if there is any data waiting to be read.
> +
> +  Polls a serial 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
> +  )
> +{
> +  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
> +  )
> +{
> +  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
> +  )
> +{
> +  *Control = 0;
> +  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
> +  )
> +{
> +  return RETURN_SUCCESS;
> +}
> diff --git a/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLibRam.c b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLibRam.c
> new file mode 100644
> index 000000000000..fafba87b7cd1
> --- /dev/null
> +++ b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLibRam.c
> @@ -0,0 +1,289 @@
> +/** @file
> +  Serial Port Library backed by SBI console.
> +
> +  Meant for PrePi and DXE environments (where globals are allowed). See
> +  BaseSerialPortLibRiscVSbiLib.c for a reduced variant appropriate for
> +  SEC and PEI (XIP) environments.
> +
> +  Copyright (c) 2023, Intel Corporation. All rights reserved.<BR>
> +  SPDX-License-Identifier: BSD-2-Clause-Patent
> +
> +**/
> +
> +#include <Base.h>
> +#include <Library/SerialPortLib.h>
> +#include <Library/BaseRiscVSbiLib.h>
> +#include "Common.h"
> +
> +STATIC BOOLEAN  mHaveDbcn          = FALSE;
> +STATIC BOOLEAN  mHaveLegacyPutchar = FALSE;
> +STATIC BOOLEAN  mHaveLegacyGetchar = FALSE;
> +STATIC INT64    mLastGetChar       = -1;
> +
> +/**
> +  Return whether the legacy console getchar extension is implemented.
> +
> +  @retval TRUE                  Extension is implemented.
> +  @retval FALSE                 Extension is not implemented.
> +
> +**/
> +STATIC
> +BOOLEAN
> +SbiImplementsLegacyGetchar (
> +  VOID
> +  )
> +{
> +  SBI_RET  Ret;
> +
> +  Ret = SbiCall (SBI_EXT_BASE, SBI_EXT_BASE_PROBE_EXT, 1, SBI_EXT_0_1_CONSOLE_GETCHAR);
> +  if ((TranslateError (Ret.Error) == EFI_SUCCESS) &&
> +      (Ret.Value != 0))
> +  {
> +    return TRUE;
> +  }
> +
> +  return FALSE;
> +}
> +
> +/**
> +  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
> +  )
> +{
> +  if (SbiImplementsDbcn ()) {
> +    mHaveDbcn = TRUE;
> +    return RETURN_SUCCESS;
> +  }
> +
> +  if (SbiImplementsLegacyPutchar ()) {
> +    mHaveLegacyPutchar = TRUE;
> +  }
> +
> +  if (SbiImplementsLegacyGetchar ()) {
> +    mHaveLegacyGetchar = TRUE;
> +  }
> +
> +  return (mHaveLegacyGetchar && mHaveLegacyPutchar) ?
> +         RETURN_SUCCESS :
> +         RETURN_DEVICE_ERROR;
> +}
> +
> +/**
> +  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 NumberOfBytes is zero, then return 0.
> +
> +  @param  Buffer           The pointer to the data buffer to be written.
> +  @param  NumberOfBytes    The 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
> +  )
> +{
> +  if (NumberOfBytes == 0) {
> +    return 0;
> +  }
> +
> +  if (mHaveDbcn) {
> +    return SbiDbcnWrite (Buffer, NumberOfBytes);
> +  } else if (mHaveLegacyPutchar) {
> +    return SbiLegacyPutchar (Buffer, NumberOfBytes);
> +  }
> +
> +  /*
> +   * Neither DBCN or legacy extension were present.
> +   */
> +  return 0;
> +}
> +
> +/**
> +  Read data from serial device and save the datas in buffer.
> +
> +  Reads NumberOfBytes data bytes from a serial device into the buffer
> +  specified by Buffer. The number of bytes actually read is returned.
> +  If the return value is less than NumberOfBytes, then the rest operation failed.
> +  If NumberOfBytes is zero, then return 0.
> +
> +  @param  Buffer           The pointer to the data buffer to store the data read from the serial device.
> +  @param  NumberOfBytes    The number of bytes which will be read.
> +
> +  @retval 0                Read data failed; No data is to be read.
> +  @retval >0               The actual number of bytes read from serial device.
> +
> +**/
> +UINTN
> +EFIAPI
> +SerialPortRead (
> +  OUT UINT8  *Buffer,
> +  IN  UINTN  NumberOfBytes
> +  )
> +{
> +  UINTN  Index;
> +
> +  Index = 0;
> +  while ((Index < NumberOfBytes) && SerialPortPoll ()) {
> +    Buffer[Index++] = (UINT8)mLastGetChar;
> +    mLastGetChar    = -1;
> +  }
> +
> +  return Index;
> +}
> +
> +/**
> +  Polls a serial device to see if there is any data waiting to be read.
> +
> +  Polls a serial 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
> +  )
> +{
> +  /*
> +   * Careful. OpenSBI with HTIF console will return -1 followed by -2
> +   * if there is no character received. So just check for values >= 0.
> +   */
> +
> +  if (mLastGetChar >= 0) {
> +    return TRUE;
> +  }
> +
> +  if (mHaveDbcn) {
> +    UINT8    Buffer;
> +    SBI_RET  Ret;
> +
> +    Ret = SbiCall (
> +            SBI_EXT_DBCN,
> +            SBI_EXT_DBCN_READ,
> +            3,
> +            1,
> +            ((UINTN)&Buffer),
> +            0
> +            );
> +    if ((TranslateError (Ret.Error) == EFI_SUCCESS) &&
> +        (Ret.Value == 1))
> +    {
> +      mLastGetChar = Buffer;
> +    }
> +  } else if (mHaveLegacyGetchar) {
> +    mLastGetChar = (INT64)SbiCall (SBI_EXT_0_1_CONSOLE_GETCHAR, 0, 0).Error;
> +  }
> +
> +  return mLastGetChar >= 0;
> +}
> +
> +/**
> +  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
> +  )
> +{
> +  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
> +  )
> +{
> +  *Control = 0;
> +  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
> +  )
> +{
> +  return RETURN_SUCCESS;
> +}
> diff --git a/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/Common.c b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/Common.c
> new file mode 100644
> index 000000000000..4926ac675b62
> --- /dev/null
> +++ b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/Common.c
> @@ -0,0 +1,132 @@
> +/** @file
> +  Serial Port Library backed by SBI console.
> +
> +  Common functionality shared by PrePiDxeSerialPortLibRiscVSbi and
> +  PrePiDxeSerialPortLibRiscVSbiRam implementations.
> +
> +  Copyright (c) 2023, Intel Corporation. All rights reserved.<BR>
> +  SPDX-License-Identifier: BSD-2-Clause-Patent
> +
> +**/
> +
> +#include "Common.h"
> +
> +/**
> +  Return whether the DBCN extension is implemented.
> +
> +  @retval TRUE                  Extension is implemented.
> +  @retval FALSE                 Extension is not implemented.
> +
> +**/
> +BOOLEAN
> +SbiImplementsDbcn (
> +  VOID
> +  )
> +{
> +  SBI_RET  Ret;
> +
> +  Ret = SbiCall (SBI_EXT_BASE, SBI_EXT_BASE_PROBE_EXT, 1, SBI_EXT_DBCN);
> +  if ((TranslateError (Ret.Error) == EFI_SUCCESS) &&
> +      (Ret.Value != 0))
> +  {
> +    return TRUE;
> +  }
> +
> +  return FALSE;
> +}
> +
> +/**
> +  Return whether the legacy console putchar extension is implemented.
> +
> +  @retval TRUE                  Extension is implemented.
> +  @retval FALSE                 Extension is not implemented.
> +
> +**/
> +BOOLEAN
> +SbiImplementsLegacyPutchar (
> +  VOID
> +  )
> +{
> +  SBI_RET  Ret;
> +
> +  Ret = SbiCall (SBI_EXT_BASE, SBI_EXT_BASE_PROBE_EXT, 1, SBI_EXT_0_1_CONSOLE_PUTCHAR);
> +  if ((TranslateError (Ret.Error) == EFI_SUCCESS) &&
> +      (Ret.Value != 0))
> +  {
> +    return TRUE;
> +  }
> +
> +  return FALSE;
> +}
> +
> +/**
> +  Write data from buffer to console via SBI legacy putchar extension.
> +
> +  The number of bytes actually written to the SBI console is returned.
> +  If the return value is less than NumberOfBytes, then the write operation failed.
> +
> +  @param  Buffer           The pointer to the data buffer to be written.
> +  @param  NumberOfBytes    The number of bytes to written to the serial device.
> +
> +  @retval >=0              The number of bytes written to the serial device.
> +                           If this value is less than NumberOfBytes, then the
> +                           write operation failed.
> +
> +**/
> +UINTN
> +SbiLegacyPutchar (
> +  IN  UINT8  *Buffer,
> +  IN  UINTN  NumberOfBytes
> +  )
> +{
> +  SBI_RET  Ret;
> +  UINTN    Index;
> +
> +  for (Index = 0; Index < NumberOfBytes; Index++) {
> +    Ret =  SbiCall (SBI_EXT_0_1_CONSOLE_PUTCHAR, 0, 1, Buffer[Index]);
> +    if ((INT64)Ret.Error < 0) {
> +      break;
> +    }
> +  }
> +
> +  return Index;
> +}
> +
> +/**
> +  Write data from buffer to console via SBI DBCN.
> +
> +  The number of bytes actually written to the SBI console is returned.
> +  If the return value is less than NumberOfBytes, then the write operation failed.
> +
> +  @param  Buffer           The pointer to the data buffer to be written.
> +  @param  NumberOfBytes    The number of bytes to written to the serial device.
> +
> +  @retval >=0              The number of bytes written to the serial device.
> +                           If this value is less than NumberOfBytes, then the
> +                           write operation failed.
> +
> +**/
> +UINTN
> +SbiDbcnWrite (
> +  IN  UINT8  *Buffer,
> +  IN  UINTN  NumberOfBytes
> +  )
> +{
> +  SBI_RET  Ret;
> +
> +  Ret = SbiCall (
> +          SBI_EXT_DBCN,
> +          SBI_EXT_DBCN_WRITE,
> +          3,
> +          NumberOfBytes,
> +          ((UINTN)Buffer),
> +          0
> +          );
> +
> +  /*
> +   * May do partial writes. Don't bother decoding
> +   * Ret.Error as we're only interested in number of
> +   * bytes written to console.
> +   */
> +  return Ret.Value;
> +}
> diff --git a/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.uni b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.uni
> new file mode 100644
> index 000000000000..7b22caa5a090
> --- /dev/null
> +++ b/MdePkg/Library/BaseSerialPortLibRiscVSbiLib/BaseSerialPortLibRiscVSbiLib.uni
> @@ -0,0 +1,16 @@
> +// /** @file
> +// Serial Port Library backed by SBI console.
> +//
> +// Serial Port Library backed by SBI console.
Duplicate sentence.