system76-edk2/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.c

/** @file

  Copyright (c) 2011 - 2013, Intel Corporation. All rights reserved.<BR>
  Copyright (C) 2013, Red Hat, Inc.
  Copyright (c) 2017, AMD Incorporated. All rights reserved.<BR>

  SPDX-License-Identifier: BSD-2-Clause-Patent

**/

#include "Uefi.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 "QemuFwCfgLibInternal.h"

/**
  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
  )
{
  DEBUG ((DEBUG_INFO, "Select Item: 0x%x\n", (UINT16)(UINTN)QemuFwCfgItem));
  IoWrite16 (FW_CFG_IO_SELECTOR, (UINT16)(UINTN)QemuFwCfgItem);
}

/**
  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;
  }

  IoReadFifo8 (FW_CFG_IO_DATA, 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;
    }

    IoWriteFifo8 (FW_CFG_IO_DATA, 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);
    IoReadFifo8 (FW_CFG_IO_DATA, 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;
    UINT16  FileReserved;
    CHAR8   FName[QEMU_FW_CFG_FNAME_SIZE];

    FileSize     = QemuFwCfgRead32 ();
    FileSelect   = QemuFwCfgRead16 ();
    FileReserved = QemuFwCfgRead16 ();
    (VOID)FileReserved;  /* Force a do-nothing reference. */
    InternalQemuFwCfgReadBytes (sizeof (FName), FName);

    if (AsciiStrCmp (Name, FName) == 0) {
      *Item = SwapBytes16 (FileSelect);
      *Size = SwapBytes32 (FileSize);
      return RETURN_SUCCESS;
    }
  }

  return RETURN_NOT_FOUND;
}