MdePkg: UefiDevicePathLib: Support UefiDevicePathLib under StandaloneMm

[mirror_edk2.git] / PcAtChipsetPkg / Library / AcpiTimerLib / DxeAcpiTimerLib.c

/** @file\r
  ACPI Timer implements one instance of Timer Library.\r
\r
  Copyright (c) 2013 - 2018, Intel Corporation. All rights reserved.<BR>\r
  SPDX-License-Identifier: BSD-2-Clause-Patent\r
\r
**/\r
\r
#include <PiDxe.h>\r
#include <Library/TimerLib.h>\r
#include <Library/BaseLib.h>\r
#include <Library/HobLib.h>\r
\r
extern GUID mFrequencyHobGuid;\r
\r
/**\r
  The constructor function enables ACPI IO space.\r
\r
  If ACPI I/O space not enabled, this function will enable it.\r
  It will always return RETURN_SUCCESS.\r
\r
  @retval EFI_SUCCESS   The constructor always returns RETURN_SUCCESS.\r
\r
**/\r
RETURN_STATUS\r
EFIAPI\r
AcpiTimerLibConstructor (\r
  VOID\r
  );\r
\r
/**\r
  Calculate TSC frequency.\r
\r
  The TSC counting frequency is determined by comparing how far it counts\r
  during a 101.4 us period as determined by the ACPI timer.\r
  The ACPI timer is used because it counts at a known frequency.\r
  The TSC is sampled, followed by waiting 363 counts of the ACPI timer,\r
  or 101.4 us. The TSC is then sampled again. The difference multiplied by\r
  9861 is the TSC frequency. There will be a small error because of the\r
  overhead of reading the ACPI timer. An attempt is made to determine and\r
  compensate for this error.\r
\r
  @return The number of TSC counts per second.\r
\r
**/\r
UINT64\r
InternalCalculateTscFrequency (\r
  VOID\r
  );\r
\r
//\r
// Cached performance counter frequency\r
//\r
UINT64  mPerformanceCounterFrequency = 0;\r
\r
/**\r
  Internal function to retrieves the 64-bit frequency in Hz.\r
\r
  Internal function to retrieves the 64-bit frequency in Hz.\r
\r
  @return The frequency in Hz.\r
\r
**/\r
UINT64\r
InternalGetPerformanceCounterFrequency (\r
  VOID\r
  )\r
{\r
  return  mPerformanceCounterFrequency;\r
}\r
\r
/**\r
  The constructor function enables ACPI IO space, and caches PerformanceCounterFrequency.\r
\r
  @param  ImageHandle   The firmware allocated handle for the EFI image.\r
  @param  SystemTable   A pointer to the EFI System Table.\r
\r
  @retval EFI_SUCCESS   The constructor always returns RETURN_SUCCESS.\r
\r
**/\r
EFI_STATUS\r
EFIAPI\r
DxeAcpiTimerLibConstructor (\r
  IN EFI_HANDLE        ImageHandle,\r
  IN EFI_SYSTEM_TABLE  *SystemTable\r
  )\r
{\r
  EFI_HOB_GUID_TYPE   *GuidHob;\r
\r
  //\r
  // Enable ACPI IO space.\r
  //\r
  AcpiTimerLibConstructor ();\r
\r
  //\r
  // Initialize PerformanceCounterFrequency\r
  //\r
  GuidHob = GetFirstGuidHob (&mFrequencyHobGuid);\r
  if (GuidHob != NULL) {\r
    mPerformanceCounterFrequency = *(UINT64*)GET_GUID_HOB_DATA (GuidHob);\r
  } else {\r
    mPerformanceCounterFrequency = InternalCalculateTscFrequency ();\r
  }\r
\r
  return EFI_SUCCESS;\r
}\r