diff --git a/EdkCompatibilityPkg/Compatibility/PciCfgToPciCfg2Thunk/PciCfgToPciCfg2Thunk.c b/EdkCompatibilityPkg/Compatibility/PciCfgToPciCfg2Thunk/PciCfgToPciCfg2Thunk.c
index 9821253fa9..e6592cf1ac 100644
--- a/EdkCompatibilityPkg/Compatibility/PciCfgToPciCfg2Thunk/PciCfgToPciCfg2Thunk.c
+++ b/EdkCompatibilityPkg/Compatibility/PciCfgToPciCfg2Thunk/PciCfgToPciCfg2Thunk.c
@@ -1,4 +1,14 @@
-/*++
+/**
+Module produce PciCfgPpi on top of PciCfgPpi2.
+
+PIWG's PI specification replaces Inte's EFI Specification 1.10.
+EFI_PEI_PCI_CFG_PPI defined in Inte's EFI Specification 1.10 is replaced by
+EFI_PEI_PCI_CFG2_PPI in PI 1.0.
+This module produces PciCfgPpi on top of PciCfgPpi2. This module is used on platform when both of
+these two conditions are true:
+1) Framework module is present that consumes PCI CFG  AND
+2) R9 module is present that produces PCI CFG2 but not PCI CFG
+
 
 Copyright (c) 2006 - 2008 Intel Corporation. <BR>
 All rights reserved. This program and the accompanying materials
@@ -9,14 +19,7 @@ http://opensource.org/licenses/bsd-license.php
 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
 Module Name:
-
-  Variable.c
-
-Abstract:
-
-  PEIM to provide the Variable functionality
-
---*/
+**/
 
 #include <PiPei.h>
 #include <Ppi/PciCfg.h>
@@ -26,6 +29,31 @@ Abstract:
 //
 // Function Prototypes
 //
+
+/**
+  Reads from a given location in the PCI configuration space.
+
+  @param  PeiServices                   An indirect pointer to the PEI Services Table published by the PEI Foundation.
+
+  @param  This                              Pointer to local data for the interface.
+
+  @param  Width                           The width of the access. Enumerated in bytes.
+                                                   See EFI_PEI_PCI_CFG_PPI_WIDTH above.
+
+  @param  Address                       The physical address of the access. The format of
+                                                  the address is described by EFI_PEI_PCI_CFG_PPI_PCI_ADDRESS.
+
+  @param  Buffer                           A pointer to the buffer of data..
+
+
+  @retval EFI_SUCCESS                 The function completed successfully.
+
+  @retval EFI_DEVICE_ERROR        There was a problem with the transaction.
+
+  @retval EFI_DEVICE_NOT_READY  The device is not capable of supporting the operation at this
+                                                    time.
+
+**/
 EFI_STATUS
 EFIAPI
 PciCfgRead (
@@ -36,6 +64,30 @@ PciCfgRead (
   IN OUT VOID                     *Buffer
   );
 
+/**
+  Write to a given location in the PCI configuration space.
+
+  @param  PeiServices                   An indirect pointer to the PEI Services Table published by the PEI Foundation.
+
+  @param  This                              Pointer to local data for the interface.
+
+  @param  Width                            The width of the access. Enumerated in bytes.
+                                                    See EFI_PEI_PCI_CFG_PPI_WIDTH above.
+
+  @param  Address                         The physical address of the access. The format of
+                                                    the address is described by EFI_PEI_PCI_CFG_PPI_PCI_ADDRESS.
+
+  @param  Buffer                            A pointer to the buffer of data..
+
+
+  @retval EFI_SUCCESS                   The function completed successfully.
+
+  @retval EFI_DEVICE_ERROR          There was a problem with the transaction.
+
+  @retval EFI_DEVICE_NOT_READY  The device is not capable of supporting the operation at this
+                                                     time.
+
+**/
 EFI_STATUS
 EFIAPI
 PciCfgWrite (
@@ -46,6 +98,34 @@ PciCfgWrite (
   IN OUT VOID                     *Buffer
   );
 
+/**
+  PCI read-modify-write operation.
+
+  @param  PeiServices                     An indirect pointer to the PEI Services Table
+                                                      published by the PEI Foundation.
+
+  @param  This                                Pointer to local data for the interface.
+
+  @param  Width                             The width of the access. Enumerated in bytes. Type
+                                                      EFI_PEI_PCI_CFG_PPI_WIDTH is defined in Read().
+
+  @param  Address                           The physical address of the access.
+
+  @param  SetBits                            Points to value to bitwise-OR with the read configuration value.
+                                                      The size of the value is determined by Width.
+
+  @param  ClearBits                         Points to the value to negate and bitwise-AND with the read configuration value.
+                                                      The size of the value is determined by Width.
+
+
+  @retval EFI_SUCCESS                   The function completed successfully.
+
+  @retval EFI_DEVICE_ERROR          There was a problem with the transaction.
+
+  @retval EFI_DEVICE_NOT_READY  The device is not capable of supporting
+                                                    the operation at this time.
+
+**/
 EFI_STATUS
 EFIAPI
 PciCfgModify (
@@ -72,36 +152,55 @@ EFI_PEI_PPI_DESCRIPTOR     mPpiListPciCfg = {
   &mPciCfgPpi
 };
 
+/**
+
+  Standard PEIM entry point.
+
+  @param FfsHeadher   The FFS file header
+  @param PeiServices   General purpose services available to every PEIM.
+
+
+  @retval EFI_SUCCESS if the interface could be successfully
+                                    installed
+
+--*/
 EFI_STATUS
 EFIAPI
 PeimInitializePciCfg (
-  IN EFI_FFS_FILE_HEADER     *FfsHeader,
+  IN EFI_PEI_FILE_HANDLE     FfsHeader,
   IN CONST EFI_PEI_SERVICES  **PeiServices
   )
-/*++
-
-Routine Description:
-
-  Provide the functionality of the variable services.
-
-Arguments:
-
-  FfsHeadher  - The FFS file header
-  PeiServices - General purpose services available to every PEIM.
-
-Returns:
-
-  Status -  EFI_SUCCESS if the interface could be successfully
-            installed
-
---*/
 {
   //
-  // Publish the variable capability to other modules
+  // Publish the PciCfgToPciCfg2 Thunk capability to other modules
   //
   return (*PeiServices)->InstallPpi (PeiServices, &mPpiListPciCfg);
 }
 
+/**
+  Reads from a given location in the PCI configuration space.
+
+  @param  PeiServices                   An indirect pointer to the PEI Services Table published by the PEI Foundation.
+
+  @param  This                              Pointer to local data for the interface.
+
+  @param  Width                           The width of the access. Enumerated in bytes.
+                                                   See EFI_PEI_PCI_CFG_PPI_WIDTH above.
+
+  @param  Address                       The physical address of the access. The format of
+                                                  the address is described by EFI_PEI_PCI_CFG_PPI_PCI_ADDRESS.
+
+  @param  Buffer                           A pointer to the buffer of data..
+
+
+  @retval EFI_SUCCESS                 The function completed successfully.
+
+  @retval EFI_DEVICE_ERROR        There was a problem with the transaction.
+
+  @retval EFI_DEVICE_NOT_READY  The device is not capable of supporting the operation at this
+                                                    time.
+
+**/
 EFI_STATUS
 EFIAPI
 PciCfgRead (
@@ -119,6 +218,31 @@ PciCfgRead (
   return PciCfg2->Read ((CONST EFI_PEI_SERVICES **)PeiServices, PciCfg2, Width, Address, Buffer);
 }
 
+
+/**
+  Write to a given location in the PCI configuration space.
+
+  @param  PeiServices                   An indirect pointer to the PEI Services Table published by the PEI Foundation.
+
+  @param  This                              Pointer to local data for the interface.
+
+  @param  Width                            The width of the access. Enumerated in bytes.
+                                                    See EFI_PEI_PCI_CFG_PPI_WIDTH above.
+
+  @param  Address                         The physical address of the access. The format of
+                                                    the address is described by EFI_PEI_PCI_CFG_PPI_PCI_ADDRESS.
+
+  @param  Buffer                            A pointer to the buffer of data..
+
+
+  @retval EFI_SUCCESS                   The function completed successfully.
+
+  @retval EFI_DEVICE_ERROR          There was a problem with the transaction.
+
+  @retval EFI_DEVICE_NOT_READY  The device is not capable of supporting the operation at this
+                                                     time.
+
+**/
 EFI_STATUS
 EFIAPI
 PciCfgWrite (
@@ -136,6 +260,34 @@ PciCfgWrite (
   return PciCfg2->Write ((CONST EFI_PEI_SERVICES **)PeiServices, PciCfg2, Width, Address, Buffer);
 }
 
+/**
+  PCI read-modify-write operation.
+
+  @param  PeiServices                     An indirect pointer to the PEI Services Table
+                                                      published by the PEI Foundation.
+
+  @param  This                                Pointer to local data for the interface.
+
+  @param  Width                             The width of the access. Enumerated in bytes. Type
+                                                      EFI_PEI_PCI_CFG_PPI_WIDTH is defined in Read().
+
+  @param  Address                           The physical address of the access.
+
+  @param  SetBits                            Points to value to bitwise-OR with the read configuration value.
+                                                      The size of the value is determined by Width.
+
+  @param  ClearBits                         Points to the value to negate and bitwise-AND with the read configuration value.
+                                                      The size of the value is determined by Width.
+
+
+  @retval EFI_SUCCESS                   The function completed successfully.
+
+  @retval EFI_DEVICE_ERROR          There was a problem with the transaction.
+
+  @retval EFI_DEVICE_NOT_READY  The device is not capable of supporting
+                                                    the operation at this time.
+
+**/
 EFI_STATUS
 EFIAPI
 PciCfgModify (
diff --git a/EdkCompatibilityPkg/Compatibility/PciCfgToPciCfg2Thunk/PciCfgToPciCfg2Thunk.inf b/EdkCompatibilityPkg/Compatibility/PciCfgToPciCfg2Thunk/PciCfgToPciCfg2Thunk.inf
index a264ab4b93..e1fbae31b6 100644
--- a/EdkCompatibilityPkg/Compatibility/PciCfgToPciCfg2Thunk/PciCfgToPciCfg2Thunk.inf
+++ b/EdkCompatibilityPkg/Compatibility/PciCfgToPciCfg2Thunk/PciCfgToPciCfg2Thunk.inf
@@ -1,5 +1,14 @@
 #/** @file
-# Component description file for PeiVariable module.
+# Module produce PciCfgPpi on top of PciCfgPpi2.
+# 
+# PIWG's PI specification replaces Inte's EFI Specification 1.10.
+# EFI_PEI_PCI_CFG_PPI defined in Inte's EFI Specification 1.10 is replaced by
+# EFI_PEI_PCI_CFG2_PPI in PI 1.0.
+# This module produces PciCfgPpi on top of PciCfgPpi2. This module is used on platform when both of
+# these two conditions are true:
+# 1) Framework module is present that consumes PCI CFG  AND
+# 2) R9 module is present that produces PCI CFG2 but not PCI CFG
+
 #
 # PEIM to provide the Variable functionality.
 # Copyright (c) 2006 - 2007, Intel Corporation