[edk2-devel] [PATCH v2 25/30] OvmfPkg/LoongArchVirt: Add FdtQemuFwCfgLib

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

This library for PEI phase, and obtains the QemuFwCfg base address by
directly parsing the FDT, reads and writes the data in QemuFwCfg by
operating on the QemuFwCfg base address.

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>
Co-authored-by: Bibo Mao <maobibo@loongson.cn>
---
 .../FdtQemuFwCfgLib/FdtQemuFwCfgPeiLib.c      | 505 ++++++++++++++++++
 .../FdtQemuFwCfgLib/FdtQemuFwCfgPeiLib.inf    |  42 ++
 .../FdtQemuFwCfgLib/QemuFwCfgLibInternal.h    |  73 +++
 .../Library/FdtQemuFwCfgLib/QemuFwCfgPei.c    | 117 ++++
 4 files changed, 737 insertions(+)
 create mode 100644 OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/FdtQemuFwCfgPeiLib.c
 create mode 100644 OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/FdtQemuFwCfgPeiLib.inf
 create mode 100644 OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/QemuFwCfgLibInternal.h
 create mode 100644 OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/QemuFwCfgPei.c

diff --git a/OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/FdtQemuFwCfgPeiLib.c b/OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/FdtQemuFwCfgPeiLib.c
new file mode 100644
index 0000000000..4009a76a80
--- /dev/null
+++ b/OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/FdtQemuFwCfgPeiLib.c
@@ -0,0 +1,505 @@
+/** @file
+
+  Copyright (c) 2023 Loongson Technology Corporation Limited. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+  @par Glossary:
+    - FwCfg   - firmWare  Configure
+    - CTL   - Control
+**/
+
+#include "Uefi.h"
+#include <Base.h>
+#include <PiPei.h>
+#include <Library/BaseLib.h>
+#include <Library/BaseMemoryLib.h>
+#include <Library/DebugLib.h>
+#include <Library/IoLib.h>
+#include <Library/QemuFwCfgLib.h>
+#include <Library/MemoryAllocationLib.h>
+#include <Library/UefiBootServicesTableLib.h>
+#include <Uefi/UefiBaseType.h>
+#include <Library/HobLib.h>
+#include <libfdt.h>
+#include "QemuFwCfgLibInternal.h"
+
+EFI_GUID  mFwCfgSelectorAddressGuid = FW_CONFIG_SELECTOR_ADDRESS_HOB_GUID;
+EFI_GUID  mFwCfgDataAddressGuid     = FW_CONFIG_DATA_ADDRESS_HOB_GUID;
+
+STATIC UINTN  mFwCfgSelectorAddress;
+STATIC UINTN  mFwCfgDataAddress;
+
+/**
+  To get firmware configure selector address.
+
+  @param VOID
+
+  @retval  firmware configure selector address
+**/
+UINTN
+EFIAPI
+QemuGetFwCfgSelectorAddress (
+  VOID
+  )
+{
+  UINTN              FwCfgSelectorAddress;
+  EFI_HOB_GUID_TYPE  *GuidHob;
+  VOID               *DataInHob;
+
+  FwCfgSelectorAddress = mFwCfgSelectorAddress;
+  GuidHob              = NULL;
+  DataInHob            = NULL;
+
+  if (FwCfgSelectorAddress == 0) {
+    GuidHob              = GetFirstGuidHob (&mFwCfgSelectorAddressGuid);
+    DataInHob            = GET_GUID_HOB_DATA (GuidHob);
+    FwCfgSelectorAddress = (UINT64)(*(UINTN *)DataInHob);
+  }
+
+  return FwCfgSelectorAddress;
+}
+
+/**
+  To get firmware configure Data address.
+
+  @param VOID
+
+  @retval  firmware configure data address
+**/
+UINTN
+EFIAPI
+QemuGetFwCfgDataAddress (
+  VOID
+  )
+{
+  UINTN              FwCfgDataAddress;
+  EFI_HOB_GUID_TYPE  *GuidHob;
+  VOID               *DataInHob;
+
+  FwCfgDataAddress = mFwCfgDataAddress;
+  GuidHob          = NULL;
+  DataInHob        = NULL;
+
+  if (FwCfgDataAddress == 0) {
+    GuidHob          = GetFirstGuidHob (&mFwCfgDataAddressGuid);
+    DataInHob        = GET_GUID_HOB_DATA (GuidHob);
+    FwCfgDataAddress = (UINT64)(*(UINTN *)DataInHob);
+  }
+
+  return FwCfgDataAddress;
+}
+
+/**
+  Selects a firmware configuration item for reading.
+
+  Following this call, any data read from this item will start from
+  the beginning of the configuration item's data.
+
+  @param[in] QemuFwCfgItem - Firmware Configuration item to read
+**/
+VOID
+EFIAPI
+QemuFwCfgSelectItem (
+  IN FIRMWARE_CONFIG_ITEM  QemuFwCfgItem
+  )
+{
+  UINTN  FwCfgSelectorAddress;
+
+  FwCfgSelectorAddress = QemuGetFwCfgSelectorAddress ();
+  MmioWrite16 (FwCfgSelectorAddress, SwapBytes16 ((UINT16)(UINTN)QemuFwCfgItem));
+}
+
+/**
+  Slow READ_BYTES_FUNCTION.
+
+  @param[in]  The size of the data to be read.
+  @param[in]  Buffer    The buffer that stores the readout data.
+**/
+VOID
+EFIAPI
+MmioReadBytes (
+  IN UINTN  Size,
+  IN VOID   *Buffer OPTIONAL
+  )
+{
+  UINTN  Left;
+  UINT8  *Ptr;
+  UINT8  *End;
+  UINTN  FwCfgDataAddress;
+
+  Left = Size & 7;
+
+  Size -= Left;
+  Ptr   = Buffer;
+  End   = Ptr + Size;
+
+  FwCfgDataAddress = QemuGetFwCfgDataAddress ();
+  while (Ptr < End) {
+    *(UINT64 *)Ptr = MmioRead64 (FwCfgDataAddress);
+    Ptr           += 8;
+  }
+
+  if (Left & 4) {
+    *(UINT32 *)Ptr = MmioRead32 (FwCfgDataAddress);
+    Ptr           += 4;
+  }
+
+  if (Left & 2) {
+    *(UINT16 *)Ptr = MmioRead16 (FwCfgDataAddress);
+    Ptr           += 2;
+  }
+
+  if (Left & 1) {
+    *Ptr = MmioRead8 (FwCfgDataAddress);
+  }
+}
+
+/**
+  Slow WRITE_BYTES_FUNCTION.
+
+  @param[in]  The size of the data to be write.
+  @param[in]  Buffer    The buffer that stores the writein data.
+**/
+VOID
+EFIAPI
+MmioWriteBytes (
+  IN UINTN  Size,
+  IN VOID   *Buffer OPTIONAL
+  )
+{
+  UINTN  Idx;
+  UINTN  FwCfgDataAddress;
+
+  FwCfgDataAddress = QemuGetFwCfgDataAddress ();
+  for (Idx = 0; Idx < Size; ++Idx) {
+    MmioWrite8 (FwCfgDataAddress, ((UINT8 *)Buffer)[Idx]);
+  }
+}
+
+/**
+  Reads firmware configuration bytes into a buffer
+
+  @param[in] Size - Size in bytes to read
+  @param[in] Buffer - Buffer to store data into  (OPTIONAL if Size is 0)
+**/
+VOID
+EFIAPI
+InternalQemuFwCfgReadBytes (
+  IN UINTN  Size,
+  IN VOID   *Buffer  OPTIONAL
+  )
+{
+  if ((InternalQemuFwCfgDmaIsAvailable ()) &&
+      (Size <= MAX_UINT32))
+  {
+    InternalQemuFwCfgDmaBytes ((UINT32)Size, Buffer, FW_CFG_DMA_CTL_READ);
+    return;
+  }
+
+  MmioReadBytes (Size, Buffer);
+}
+
+/**
+  Reads firmware configuration bytes into a buffer
+
+  If called multiple times, then the data read will
+  continue at the offset of the firmware configuration
+  item where the previous read ended.
+
+  @param[in] Size - Size in bytes to read
+  @param[in] Buffer - Buffer to store data into
+**/
+VOID
+EFIAPI
+QemuFwCfgReadBytes (
+  IN UINTN  Size,
+  IN VOID   *Buffer
+  )
+{
+  if (InternalQemuFwCfgIsAvailable ()) {
+    InternalQemuFwCfgReadBytes (Size, Buffer);
+  } else {
+    ZeroMem (Buffer, Size);
+  }
+}
+
+/**
+  Write firmware configuration bytes from a buffer
+
+  If called multiple times, then the data written will
+  continue at the offset of the firmware configuration
+  item where the previous write ended.
+
+  @param[in] Size - Size in bytes to write
+  @param[in] Buffer - Buffer to read data from
+**/
+VOID
+EFIAPI
+QemuFwCfgWriteBytes (
+  IN UINTN  Size,
+  IN VOID   *Buffer
+  )
+{
+  if (InternalQemuFwCfgIsAvailable ()) {
+    if ((InternalQemuFwCfgDmaIsAvailable ()) &&
+        (Size <= MAX_UINT32))
+    {
+      InternalQemuFwCfgDmaBytes ((UINT32)Size, Buffer, FW_CFG_DMA_CTL_WRITE);
+      return;
+    }
+
+    MmioWriteBytes (Size, Buffer);
+  }
+}
+
+/**
+  Skip bytes in the firmware configuration item.
+
+  Increase the offset of the firmware configuration item without transferring
+  bytes between the item and a caller-provided buffer. Subsequent read, write
+  or skip operations will commence at the increased offset.
+
+  @param[in] Size  Number of bytes to skip.
+**/
+VOID
+EFIAPI
+QemuFwCfgSkipBytes (
+  IN UINTN  Size
+  )
+{
+  UINTN  ChunkSize;
+  UINT8  SkipBuffer[256];
+
+  if (!InternalQemuFwCfgIsAvailable ()) {
+    return;
+  }
+
+  if ((InternalQemuFwCfgDmaIsAvailable ()) &&
+      (Size <= MAX_UINT32))
+  {
+    InternalQemuFwCfgDmaBytes ((UINT32)Size, NULL, FW_CFG_DMA_CTL_SKIP);
+    return;
+  }
+
+  //
+  // Emulate the skip by reading data in chunks, and throwing it away. The
+  // implementation below is suitable even for phases where RAM or dynamic
+  // allocation is not available or appropriate. It also doesn't affect the
+  // static data footprint for client modules. Large skips are not expected,
+  // therefore this fallback is not performance critical. The size of
+  // SkipBuffer is thought not to exert a large pressure on the stack in any
+  // phase.
+  //
+  while (Size > 0) {
+    ChunkSize = MIN (Size, sizeof SkipBuffer);
+    MmioReadBytes (ChunkSize, SkipBuffer);
+    Size -= ChunkSize;
+  }
+}
+
+/**
+  Reads a UINT8 firmware configuration value
+
+  @return    Value of Firmware Configuration item read
+**/
+UINT8
+EFIAPI
+QemuFwCfgRead8 (
+  VOID
+  )
+{
+  UINT8  Result;
+
+  QemuFwCfgReadBytes (sizeof (Result), &Result);
+
+  return Result;
+}
+
+/**
+  Reads a UINT16 firmware configuration value
+
+  @return    Value of Firmware Configuration item read
+**/
+UINT16
+EFIAPI
+QemuFwCfgRead16 (
+  VOID
+  )
+{
+  UINT16  Result;
+
+  QemuFwCfgReadBytes (sizeof (Result), &Result);
+
+  return Result;
+}
+
+/**
+  Reads a UINT32 firmware configuration value
+
+  @return    Value of Firmware Configuration item read
+**/
+UINT32
+EFIAPI
+QemuFwCfgRead32 (
+  VOID
+  )
+{
+  UINT32  Result;
+
+  QemuFwCfgReadBytes (sizeof (Result), &Result);
+
+  return Result;
+}
+
+/**
+  Reads a UINT64 firmware configuration value
+
+  @return    Value of Firmware Configuration item read
+**/
+UINT64
+EFIAPI
+QemuFwCfgRead64 (
+  VOID
+  )
+{
+  UINT64  Result;
+
+  QemuFwCfgReadBytes (sizeof (Result), &Result);
+
+  return Result;
+}
+
+/**
+  Find the configuration item corresponding to the firmware configuration file.
+
+  @param[in]  Name - Name of file to look up.
+  @param[out] Item - Configuration item corresponding to the file, to be passed
+                     to QemuFwCfgSelectItem ().
+  @param[out] Size - Number of bytes in the file.
+
+  @return    RETURN_SUCCESS       If file is found.
+             RETURN_NOT_FOUND     If file is not found.
+             RETURN_UNSUPPORTED   If firmware configuration is unavailable.
+**/
+RETURN_STATUS
+EFIAPI
+QemuFwCfgFindFile (
+  IN   CONST CHAR8           *Name,
+  OUT  FIRMWARE_CONFIG_ITEM  *Item,
+  OUT  UINTN                 *Size
+  )
+{
+  UINT32  Count;
+  UINT32  Idx;
+
+  if (!InternalQemuFwCfgIsAvailable ()) {
+    return RETURN_UNSUPPORTED;
+  }
+
+  QemuFwCfgSelectItem (QemuFwCfgItemFileDir);
+  Count = SwapBytes32 (QemuFwCfgRead32 ());
+
+  for (Idx = 0; Idx < Count; ++Idx) {
+    UINT32  FileSize;
+    UINT16  FileSelect;
+    CHAR8   FileName[QEMU_FW_CFG_FNAME_SIZE];
+
+    FileSize   = QemuFwCfgRead32 ();
+    FileSelect = QemuFwCfgRead16 ();
+    QemuFwCfgRead16 (); // skip the field called "reserved"
+    InternalQemuFwCfgReadBytes (sizeof (FileName), FileName);
+
+    if (AsciiStrCmp (Name, FileName) == 0) {
+      *Item = SwapBytes16 (FileSelect);
+      *Size = SwapBytes32 (FileSize);
+      return RETURN_SUCCESS;
+    }
+  }
+
+  return RETURN_NOT_FOUND;
+}
+
+/**
+  firmware config initialize.
+
+  @param  VOID
+
+  @return    RETURN_SUCCESS  Initialization succeeded.
+**/
+RETURN_STATUS
+EFIAPI
+FdtQemuFwCfgInitialize (
+  VOID
+  )
+{
+  VOID          *DeviceTreeBase;
+  INT32         Node;
+  INT32         Prev;
+  CONST CHAR8   *Type;
+  INT32         Len;
+  CONST UINT64  *RegProp;
+  UINT64        FwCfgSelectorAddress;
+  UINT64        FwCfgDataAddress;
+  UINT64        FwCfgDataSize;
+
+  DeviceTreeBase = (VOID *)(UINTN)PcdGet64 (PcdDeviceTreeInitialBaseAddress);
+  ASSERT (DeviceTreeBase != NULL);
+  //
+  // Make sure we have a valid device tree blob
+  //
+  ASSERT (fdt_check_header (DeviceTreeBase) == 0);
+
+  for (Prev = 0; ; Prev = Node) {
+    Node = fdt_next_node (DeviceTreeBase, Prev, NULL);
+    if (Node < 0) {
+      break;
+    }
+
+    //
+    // Check for memory node
+    //
+    Type = fdt_getprop (DeviceTreeBase, Node, "compatible", &Len);
+    if ((Type) &&
+        (AsciiStrnCmp (Type, "qemu,fw-cfg-mmio", Len) == 0))
+    {
+      //
+      // Get the 'reg' property of this node. For now, we will assume
+      // two 8 byte quantities for base and size, respectively.
+      //
+      RegProp = fdt_getprop (DeviceTreeBase, Node, "reg", &Len);
+      if ((RegProp != 0) &&
+          (Len == (2 * sizeof (UINT64))))
+      {
+        FwCfgDataAddress     = SwapBytes64 (RegProp[0]);
+        FwCfgDataSize        = 8;
+        FwCfgSelectorAddress = FwCfgDataAddress + FwCfgDataSize;
+
+        mFwCfgSelectorAddress = FwCfgSelectorAddress;
+        mFwCfgDataAddress     = FwCfgDataAddress;
+
+        BuildGuidDataHob (
+          &mFwCfgSelectorAddressGuid,
+          (VOID *)&FwCfgSelectorAddress,
+          sizeof (UINT64)
+          );
+
+        BuildGuidDataHob (
+          &mFwCfgDataAddressGuid,
+          (VOID *)&FwCfgDataAddress,
+          sizeof (UINT64)
+          );
+        break;
+      } else {
+        DEBUG ((
+          DEBUG_ERROR,
+          "%a: Failed to parse FDT QemuCfg node\n",
+          __FUNCTION__
+          ));
+        break;
+      }
+    }
+  }
+
+  return RETURN_SUCCESS;
+}
diff --git a/OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/FdtQemuFwCfgPeiLib.inf b/OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/FdtQemuFwCfgPeiLib.inf
new file mode 100644
index 0000000000..4c9d4bcd81
--- /dev/null
+++ b/OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/FdtQemuFwCfgPeiLib.inf
@@ -0,0 +1,42 @@
+## @file
+#  initialized fw_cfg library.
+#
+#  Copyright (c) 2023 Loongson Technology Corporation Limited. All rights reserved.<BR>
+#
+#  SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+[Defines]
+  INF_VERSION                    = 0x00010005
+  BASE_NAME                      = FdtQemuFwCfgPeiLib
+  FILE_GUID                      = cdf9a9d5-7422-4dcb-b41d-607151ad320b
+  MODULE_TYPE                    = BASE
+  VERSION_STRING                 = 1.0
+  LIBRARY_CLASS                  = FtdQemuFwCfgLib|PEIM
+  CONSTRUCTOR                    = FdtQemuFwCfgInitialize
+
+#
+#  VALID_ARCHITECTURES           = LOONGARCH64
+#
+
+[Sources]
+  FdtQemuFwCfgPeiLib.c
+  QemuFwCfgPei.c
+
+[Packages]
+  EmbeddedPkg/EmbeddedPkg.dec
+  MdePkg/MdePkg.dec
+  OvmfPkg/OvmfPkg.dec
+
+[LibraryClasses]
+  BaseLib
+  BaseMemoryLib
+  HobLib
+  DebugLib
+  IoLib
+  MemoryAllocationLib
+  FdtLib
+
+[Pcd]
+  gUefiOvmfPkgTokenSpaceGuid.PcdDeviceTreeInitialBaseAddress
diff --git a/OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/QemuFwCfgLibInternal.h b/OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/QemuFwCfgLibInternal.h
new file mode 100644
index 0000000000..17866cb9d5
--- /dev/null
+++ b/OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/QemuFwCfgLibInternal.h
@@ -0,0 +1,73 @@
+/** @file
+  fw_cfg library implementation.
+
+  Copyright (c) 2023 Loongson Technology Corporation Limited. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+  @par Glossary:
+    - FwCfg   - firmWare  Configure
+**/
+
+#ifndef QEMU_FW_CFG_LIB_INTERNAL_H_
+#define QEMU_FW_CFG_LIB_INTERNAL_H_
+
+#define FW_CONFIG_SELECTOR_ADDRESS_HOB_GUID \
+  { \
+    0x3cc47b04, 0x0d3e, 0xaa64, { 0x06, 0xa6, 0x4b, 0xdc, 0x9a, 0x2c, 0x61, 0x19 } \
+  }
+
+#define FW_CONFIG_DATA_ADDRESS_HOB_GUID \
+  { \
+    0xef854788, 0x10f3, 0x8e7a, { 0x3e, 0xd0, 0x4d, 0x16, 0xc1, 0x79, 0x55, 0x2f } \
+  }
+
+/**
+  Returns a boolean indicating if the firmware configuration interface is
+  available for library-internal purposes.
+
+  This function never changes fw_cfg state.
+
+  @retval    TRUE   The interface is available internally.
+  @retval    FALSE  The interface is not available internally.
+**/
+BOOLEAN
+InternalQemuFwCfgIsAvailable (
+  VOID
+  );
+
+/**
+  Returns a boolean indicating whether QEMU provides the DMA-like access method
+  for fw_cfg.
+
+  @retval    TRUE   The DMA-like access method is available.
+  @retval    FALSE  The DMA-like access method is unavailable.
+**/
+BOOLEAN
+InternalQemuFwCfgDmaIsAvailable (
+  VOID
+  );
+
+/**
+  Transfer an array of bytes, or skip a number of bytes, using the DMA
+  interface.
+
+  @param[in]     Size     Size in bytes to transfer or skip.
+
+  @param[in,out] Buffer   Buffer to read data into or write data from. Ignored,
+                          and may be NULL, if Size is zero, or Control is
+                          FW_CFG_DMA_CTL_SKIP.
+
+  @param[in]     Control  One of the following:
+                          FW_CFG_DMA_CTL_WRITE - write to fw_cfg from Buffer.
+                          FW_CFG_DMA_CTL_READ  - read from fw_cfg into Buffer.
+                          FW_CFG_DMA_CTL_SKIP  - skip bytes in fw_cfg.
+**/
+VOID
+InternalQemuFwCfgDmaBytes (
+  IN     UINT32  Size,
+  IN OUT VOID    *Buffer OPTIONAL,
+  IN     UINT32  Control
+  );
+
+#endif // QEMU_FW_CFG_LIB_INTERNAL_H_
diff --git a/OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/QemuFwCfgPei.c b/OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/QemuFwCfgPei.c
new file mode 100644
index 0000000000..07dc3d1c23
--- /dev/null
+++ b/OvmfPkg/LoongArchVirt/Library/FdtQemuFwCfgLib/QemuFwCfgPei.c
@@ -0,0 +1,117 @@
+/** @file
+  fw_cfg library implementation.
+
+  Copyright (c) 2023 Loongson Technology Corporation Limited. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+  @par Glossary:
+    - FwCfg   - firmWare  Configure
+**/
+
+#include <Library/BaseLib.h>
+#include <Library/DebugLib.h>
+#include <Library/QemuFwCfgLib.h>
+
+#include "QemuFwCfgLibInternal.h"
+
+/**
+  Returns a boolean indicating if the firmware configuration interface
+  is available or not.
+
+  This function may change fw_cfg state.
+
+  @retval    TRUE   The interface is available
+  @retval    FALSE  The interface is not available
+**/
+BOOLEAN
+EFIAPI
+QemuFwCfgIsAvailable (
+  VOID
+  )
+{
+  UINT32  Signature;
+  UINT32  Revision;
+
+  QemuFwCfgSelectItem (QemuFwCfgItemSignature);
+  Signature = QemuFwCfgRead32 ();
+  DEBUG ((DEBUG_INFO, "FW CFG Signature: 0x%x\n", Signature));
+  QemuFwCfgSelectItem (QemuFwCfgItemInterfaceVersion);
+  Revision = QemuFwCfgRead32 ();
+  DEBUG ((DEBUG_INFO, "FW CFG Revision: 0x%x\n", Revision));
+  if ((Signature != SIGNATURE_32 ('Q', 'E', 'M', 'U')) ||
+      (Revision < 1))
+  {
+    DEBUG ((DEBUG_INFO, "QemuFwCfg interface not supported.\n"));
+    return FALSE;
+  }
+
+  DEBUG ((DEBUG_INFO, "QemuFwCfg interface is supported.\n"));
+  return TRUE;
+}
+
+/**
+  Returns a boolean indicating if the firmware configuration interface is
+  available for library-internal purposes.
+
+  This function never changes fw_cfg state.
+
+  @retval    TRUE   The interface is available internally.
+  @retval    FALSE  The interface is not available internally.
+**/
+BOOLEAN
+InternalQemuFwCfgIsAvailable (
+  VOID
+  )
+{
+  //
+  // We always return TRUE, because the consumer of this library ought to have
+  // called QemuFwCfgIsAvailable before making other calls which would hit this
+  // path.
+  //
+  return TRUE;
+}
+
+/**
+  Returns a boolean indicating whether QEMU provides the DMA-like access method
+  for fw_cfg.
+
+  @retval    TRUE   The DMA-like access method is available.
+  @retval    FALSE  The DMA-like access method is unavailable.
+**/
+BOOLEAN
+InternalQemuFwCfgDmaIsAvailable (
+  VOID
+  )
+{
+  return FALSE;
+}
+
+/**
+  Transfer an array of bytes, or skip a number of bytes, using the DMA
+  interface.
+
+  @param[in]     Size     Size in bytes to transfer or skip.
+
+  @param[in, out] Buffer   Buffer to read data into or write data from. Ignored,
+                          and may be NULL, if Size is zero, or Control is
+                          FW_CFG_DMA_CTL_SKIP.
+
+  @param[in]     Control  One of the following:
+                          FW_CFG_DMA_CTL_WRITE - write to fw_cfg from Buffer.
+                          FW_CFG_DMA_CTL_READ  - read from fw_cfg into Buffer.
+                          FW_CFG_DMA_CTL_SKIP  - skip bytes in fw_cfg.
+**/
+VOID
+InternalQemuFwCfgDmaBytes (
+  IN     UINT32  Size,
+  IN OUT VOID    *Buffer OPTIONAL,
+  IN     UINT32  Control
+  )
+{
+  //
+  // We should never reach here
+  //
+  ASSERT (FALSE);
+  CpuDeadLoop ();
+}
-- 
2.27.0



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