diff --git a/MdePkg/Include/Protocol/SimpleTextInEx.h b/MdePkg/Include/Protocol/SimpleTextInEx.h
index 436ff37b14..4591bd4779 100644
--- a/MdePkg/Include/Protocol/SimpleTextInEx.h
+++ b/MdePkg/Include/Protocol/SimpleTextInEx.h
@@ -5,7 +5,7 @@
   which exposes much more state and modifier information from the input device,
   also allows one to register a notification for a particular keystroke.
 
-  Copyright (c) 2006 - 2012, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2006 - 2017, Intel Corporation. All rights reserved.<BR>
   This program and the accompanying materials
   are licensed and made available under the terms and conditions of the BSD License
   which accompanies this distribution.  The full text of the license may be found at
@@ -251,18 +251,19 @@ EFI_STATUS
 
   @param KeyData                  A pointer to a buffer that is filled in with
                                   the keystroke information for the key that was
-                                  pressed.
+                                  pressed. If KeyData.Key, KeyData.KeyState.KeyToggleState
+                                  and KeyData.KeyState.KeyShiftState are 0, then any incomplete
+                                  keystroke will trigger a notification of the KeyNotificationFunction.
 
-  @param KeyNotificationFunction  Points to the function to be
-                                  called when the key sequence
-                                  is typed specified by KeyData.
+  @param KeyNotificationFunction  Points to the function to be called when the key sequence
+                                  is typed specified by KeyData. This notification function
+                                  should be called at <=TPL_CALLBACK.
 
 
   @param NotifyHandle             Points to the unique handle assigned to
                                   the registered notification.
 
-  @retval EFI_SUCCESS           The device state was set
-                                appropriately.
+  @retval EFI_SUCCESS           Key notify was registered successfully.
 
   @retval EFI_OUT_OF_RESOURCES  Unable to allocate necessary
                                 data structures.
@@ -286,7 +287,7 @@ EFI_STATUS
   @param NotificationHandle The handle of the notification
                             function being unregistered.
 
-  @retval EFI_SUCCESS The device state was set appropriately.
+  @retval EFI_SUCCESS           Key notify was unregistered successfully.
 
   @retval EFI_INVALID_PARAMETER The NotificationHandle is
                                 invalid.