MdePkg: add SBI-based SerialPortLib for RISC-V

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>
Signed-off-by: Andrei Warkentin <andrei.warkentin@intel.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>

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;
+}