X-Git-Url: https://git.proxmox.com/?p=mirror_edk2.git;a=blobdiff_plain;f=MdeModulePkg%2FInclude%2FLibrary%2FPciHostBridgeLib.h;h=1606589354e3cd002b13d9eabaa8dd7882991257;hp=d42e9ecdd76306db9aec1ca6485bf5569b1eca44;hb=9d510e61fceee7b92955ef9a3c20343752d8ce3f;hpb=070827be5a5727c736acf5d645722be073640952

diff --git a/MdeModulePkg/Include/Library/PciHostBridgeLib.h b/MdeModulePkg/Include/Library/PciHostBridgeLib.h
index d42e9ecdd7..1606589354 100644
--- a/MdeModulePkg/Include/Library/PciHostBridgeLib.h
+++ b/MdeModulePkg/Include/Library/PciHostBridgeLib.h
@@ -3,14 +3,7 @@
   the platform specific information about the PCI Host Bridge.
 
   Copyright (c) 2016, 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
-  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.
+  SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
 #ifndef __PCI_HOST_BRIDGE_LIB_H__
@@ -20,8 +13,27 @@
 // (Base > Limit) indicates an aperture is not available.
 //
 typedef struct {
+  //
+  // Base and Limit are the device address instead of host address when
+  // Translation is not zero
+  //
   UINT64 Base;
   UINT64 Limit;
+  //
+  // According to UEFI 2.7, Device Address = Host Address + Translation,
+  // so Translation = Device Address - Host Address.
+  // On platforms where Translation is not zero, the subtraction is probably to
+  // be performed with UINT64 wrap-around semantics, for we may translate an
+  // above-4G host address into a below-4G device address for legacy PCIe device
+  // compatibility.
+  //
+  // NOTE: The alignment of Translation is required to be larger than any BAR
+  // alignment in the same root bridge, so that the same alignment can be
+  // applied to both device address and host address, which simplifies the
+  // situation and makes the current resource allocation code in generic PCI
+  // host bridge driver still work.
+  //
+  UINT64 Translation;
 } PCI_ROOT_BRIDGE_APERTURE;
 
 typedef struct {