diff --git a/MdePkg/Library/PeiIoLibCpuIo/IoHighLevel.c b/MdePkg/Library/PeiIoLibCpuIo/IoHighLevel.c
index 75dc1f8aa4..134aae01bb 100644
--- a/MdePkg/Library/PeiIoLibCpuIo/IoHighLevel.c
+++ b/MdePkg/Library/PeiIoLibCpuIo/IoHighLevel.c
@@ -13,12 +13,6 @@
   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
 
-  The following IoLib instances share the same version of this file:
-
-    BaseIoLibIntrinsic
-    DxeIoLibCpuIo
-    PeiIoLibCpuIo
-
 **/
 
 
diff --git a/MdePkg/Library/PeiIoLibCpuIo/IoLib.c b/MdePkg/Library/PeiIoLibCpuIo/IoLib.c
index e3622e6329..9130921937 100644
--- a/MdePkg/Library/PeiIoLibCpuIo/IoLib.c
+++ b/MdePkg/Library/PeiIoLibCpuIo/IoLib.c
@@ -1,5 +1,5 @@
 /** @file
-  I/O Library.
+  I/O Library. The implementations are based on EFI_PEI_SERVICE->CpuIo interface.
 
   Copyright (c) 2006, Intel Corporation<BR>
   All rights reserved. This program and the accompanying materials
@@ -521,7 +521,7 @@ MmioRead64 (
   //
   // Make sure Address is aligned on a 64-bit boundary.
   //
-  ASSERT ((Address & 7) == 0);
+  ASSERT ((Address & 7) == (sizeof (UINT64) - 1));
   return CpuIo->MemRead64 (PeiServices, CpuIo, (UINT64) Address);
 
 }
diff --git a/MdePkg/Library/PeiIoLibCpuIo/IoLibMmioBuffer.c b/MdePkg/Library/PeiIoLibCpuIo/IoLibMmioBuffer.c
index bc81ca2243..20d926f9f0 100644
--- a/MdePkg/Library/PeiIoLibCpuIo/IoLibMmioBuffer.c
+++ b/MdePkg/Library/PeiIoLibCpuIo/IoLibMmioBuffer.c
@@ -1,5 +1,6 @@
 /** @file
   I/O Library MMIO Buffer Functions.
+  The implementations are based on EFI_PEI_SERVICE->CpuIo interface.
 
   Copyright (c) 2007, Intel Corporation<BR>
   All rights reserved. This program and the accompanying materials
@@ -35,7 +36,7 @@
   @param  Length          Size in bytes of the copy.
   @param  Buffer          Pointer to a system memory buffer receiving the data read.
 
-  @return Buffer
+  @return Pointer to a system memory buffer receiving the data read.
 
 **/
 UINT8 *
@@ -79,7 +80,7 @@ MmioReadBuffer8 (
   @param  Length          Size in bytes of the copy.
   @param  Buffer          Pointer to a system memory buffer receiving the data read.
 
-  @return Buffer
+  @return Pointer to a system memory buffer receiving the data read.
 
 **/
 UINT16 *
@@ -130,7 +131,7 @@ MmioReadBuffer16 (
   @param  Length          Size in bytes of the copy.
   @param  Buffer          Pointer to a system memory buffer receiving the data read.
 
-  @return Buffer
+  @return Pointer to a system memory buffer receiving the data read.
 
 **/
 UINT32 *
@@ -181,7 +182,7 @@ MmioReadBuffer32 (
   @param  Length          Size in bytes of the copy.
   @param  Buffer          Pointer to a system memory buffer receiving the data read.
 
-  @return Buffer
+  @return Pointer to a system memory buffer receiving the data read.
 
 **/
 UINT64 *
@@ -226,10 +227,10 @@ MmioReadBuffer64 (
 
 
   @param  StartAddress    Starting address for the MMIO region to be copied to.
-  @param  Length     Size in bytes of the copy.
+  @param  Length          Size in bytes of the copy.
   @param  Buffer          Pointer to a system memory buffer containing the data to write.
 
-  @return Size in bytes of the copy.
+  @return Pointer to a system memory buffer containing the data to write.
 
 **/
 UINT8 *
@@ -272,10 +273,10 @@ MmioWriteBuffer8 (
   If Buffer is not aligned on a 16-bit boundary, then ASSERT().
 
   @param  StartAddress    Starting address for the MMIO region to be copied to.
-  @param  Length     Size in bytes of the copy.
+  @param  Length          Size in bytes of the copy.
   @param  Buffer          Pointer to a system memory buffer containing the data to write.
 
-  @return Size in bytes of the copy.
+  @return Pointer to a system memory buffer containing the data to write.
 
 **/
 UINT16 *
@@ -326,10 +327,10 @@ MmioWriteBuffer16 (
   If Buffer is not aligned on a 32-bit boundary, then ASSERT().
 
   @param  StartAddress    Starting address for the MMIO region to be copied to.
-  @param  Length     Size in bytes of the copy.
+  @param  Length          Size in bytes of the copy.
   @param  Buffer          Pointer to a system memory buffer containing the data to write.
 
-  @return Size in bytes of the copy.
+  @return Pointer to a system memory buffer containing the data to write.
 
 **/
 UINT32 *
@@ -379,10 +380,10 @@ MmioWriteBuffer32 (
   If Buffer is not aligned on a 64-bit boundary, then ASSERT().
 
   @param  StartAddress    Starting address for the MMIO region to be copied to.
-  @param  Length     Size in bytes of the copy.
+  @param  Length          Size in bytes of the copy.
   @param  Buffer          Pointer to a system memory buffer containing the data to write.
 
-  @return Size in bytes of the copy.
+  @return Pointer to a system memory buffer containing the data to write.
 
 **/
 UINT64 *