1) Add in Doxygen comment.

2) Update package dependency list.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@5231 6f19259b-4bc3-4df7-8a09-765794883524

EdkCompatibilityPkg/Compatibility/PciCfg2ToPciCfgThunk/PciCfg2ToPciCfgThunk.inf

@@ -1,5 +1,29 @@
 #/** @file
-# Component description file for PeiVariable module.
+# Module produces PciCfgPpi2 on top of PciCfgPpi. It also updates the 
+# PciCfg2Ppi pointer in the EFI_PEI_SERVICES upon a installation of
+# EcpPeiPciCfgPpi. EcpPeiPciCfgPpi is installed in a framework module which
+# produce PciCfgPpi originally. This framework module is updated based on the 
+# following rule:
+# Search pattern:
+# 	   PeiServices->PciCfg = <*>;
+# Replace pattern:
+#         {
+#           static EFI_PEI_PPI_DESCRIPTOR gEcpPeiPciCfgPpiList = {
+#             (EFI_PEI_PPI_DESCRIPTOR_PPI | EFI_PEI_PPI_DESCRIPTOR_TERMINATE_LIST),
+#             &gEcpPeiPciCfgPpiGuid,
+#             <*>
+#           };
+#           (**PeiServices).InstallPpi (PeiServices, gEcpPeiPciCfgPpiList);
+#         }
+
+# 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 present that produces PCI CFG PPI  AND
+# 2) PI module that produces PCI CFG2 is not present
+
 #
 # PEIM to provide the Variable functionality.
 # Copyright (c) 2006 - 2007, Intel Corporation
@@ -50,4 +74,3 @@
 
 [Depex]
   TRUE
-#  gEcpPeiPciCfgPpiGuid