MdeModulePkg: Replace BSD License with BSD+Patent License

[mirror_edk2.git] / MdeModulePkg / Universal / PCD / Dxe / PcdDxe.uni

// /** @file
// PCD DXE driver manage database contains all dynamic PCD entries and produce the implementation of PCD protocol.
//
// This version PCD DXE depends on the external PCD database binary file, not built in PCD data base.
// There are two PCD Protocols as follows:
// 1) PCD_PROTOCOL
// It is EDKII implementation which support Dynamic/DynamicEx type Pcds.
// 2) EFI_PCD_PROTOCOL
// It is defined by PI specification 1.2, Vol 3 which only support dynamicEx
// type Pcd.
//
// For dynamicEx type PCD, it is compatible between PCD_PROTOCOL and EFI_PCD_PROTOCOL.
// PCD DXE driver will produce above two protocols at same time.
//
// PCD database is generated as the separate binary image at build time. The binary image
// will be intergrated into Firmware volume together with PCD driver.
//
// ////////////////////////////////////////////////////////////////////////////////
// //                                                                            //
// //                      Introduction of PCD database                          //
// //                                                                            //
// ////////////////////////////////////////////////////////////////////////////////
//
// 1, Introduction
// PCD database hold all dynamic type PCD information. The structure of PEI PCD
// database is generated by build tools according to dynamic PCD usage for
// specified platform.
//
// 2, Dynamic Type PCD
// Dynamic type PCD is used for the configuration/setting which value is determined
// dynamic. In contrast, the value of static type PCD (FeatureFlag, FixedPcd,
// PatchablePcd) is fixed in final generated FD image in build time.
//
// 2.1 The "dynamic" determination means one of below cases:
// a) The PCD setting value is produced by someone driver and consumed by
// other driver in execution time.
// b) The PCD setting value is set/get by user from FrontPage.
// c) The PCD setting value is produced by platform OEM vendor in specified area.
//
// 2.2 According to module distribution way, dynamic PCD could be classfied as:
// a) Dynamic:
// If module is released in source code and will be built with platform
// DSC, the dynamic PCD used by this module can be accessed as:
// PcdGetxx(PcdSampleDynamicPcd);
// In building platform, build tools will translate PcdSampleDynamicPcd to
// pair of {Token Space Guid: Token Number} for this PCD.
// b) DynamicEx:
// If module is release as binary and will not pariticpate platform building,
// the dynamic PCD used by this module need be accessed as:
// PcdGetxxEx(gEfiMyTokenspaceGuid, PcdSampleDynamicPcd)
// Developer need explicity gives {Token Space Guid:Token Number} as parameter
// in writting source code.
//
// 2.3 According to PCD value's storage method, dynamic PCD could be classfied as:
// a) Default Storage:
// - The PCD value is stored in PCD database maintained by PCD driver in boot
// time memory.
// - This type is used for communication between PEIM/DXE driver, DXE/DXE
// driver. But all set/get value will be losted after boot-time memory
// is turn off.
// - [PcdsDynamicDefault] is used as section name for this type PCD in
// platform DSC file. [PcdsDynamicExDefault] is used for dynamicEx type PCD.
//
// b) Variable Storage:
// - The PCD value is stored in variable area.
// - As default storage type, this type PCD could be used for PEI/DXE driver
// communication. But beside it, this type PCD could also be used to store
// the value associate with a HII setting via variable interface.
// - In PEI phase, the PCD value could only be got but can not be set due
// to variable area is readonly.
// - [PcdsDynamicHii] is used as section name for this type PCD in platform
// DSC file. [PcdsDynamicExHii] is for dynamicEx type PCD.
//
// c) OEM specificed storage area:
// - The PCD value is stored in OEM specified area which base address is
// specified by a FixedAtBuild PCD setting - PcdVpdBaseAddress.
// - The area is read only for PEI and DXE phase.
// - [PcdsDynamicVpd] is used as section name for this type PCD in platform
// DSC file. [PcdsDynamicExVpd] is for dynamicex type PCD.
//
// 2.4 When and how to use dynamic PCD
// Module developer do not care the used PCD is dynamic or static when writting
// source code/INF. Dynamic PCD and dynamic type is pointed by platform integrator
// in platform DSC file. Please ref section 2.3 to get matching between dynamic
// PCD type and section name in DSC file.
//
// 3, PCD database:
// Although dynamic PCD could be in different storage type as above description,
// but the basic information and default value for all dynamic PCD is hold
// by PCD database maintained by PEI/DXE driver.
//
// As the whole EFI BIOS boot path is divided into PEI/DXE phase, the PCD database
// also is divided into Pei/Dxe database maintaied by PcdPeim/PcdDxe driver separatly.
// To make PcdPeim's driver image smaller, PEI PCD database only hold all dynamic
// PCD information used in PEI phase or use in both PEI/DXE phase. And DXE PCD
// database contains all PCDs used in PEI/DXE phase in memory.
//
// Build tool will generate PCD database into the separate binary file for
// PEI/DXE PCD driver according to dynamic PCD section in platform DSC file.
//
// 3.1 PcdPeim and PcdDxe
// PEI PCD database is maintained by PcdPeim driver run from flash. PcdPeim driver
// build guid hob in temporary memory and copy the binary data base from flash
// to temporary memory for PEI PCD database.
// DXE PCD database is maintained by PcdDxe driver.At entry point of PcdDxe driver,
// a new PCD database is allocated in boot-time memory which including all
// PEI PCD and DXE PCD entry.
//
// Pcd driver should run as early as possible before any other driver access
// dynamic PCD's value. PEI/DXE "Apriori File" mechanism make it possible by
// making PcdPeim/PcdDxe as first dispatching driver in PEI/DXE phase.
//
// 3.2 Token space Guid/Token number, Platform token, Local token number
// Dynamic PCD
// +-----------+               +---------+
// |TokenSpace |               |Platform |
// |   Guid    |  build tool   | Token   |
// |    +      +-------------->| Number  |
// |  Token    |               +---------+`._
// |  Number   |                             `.
// +-----------+                               `.  +------+
// `-|Local |
// |Token |
// DynamicEx PCD            ,-|Number|
// +-----------+         ,-'  +------+
// |TokenSpace |      ,-'
// |   Guid    |  _,-'
// |    +      +.'
// |  Token    |
// |  Number   |
// +-----------+
//
//
// 3.2.1 Pair of Token space guid + Token number
// Any type PCD is identified by pair of "TokenSpaceGuid + TokeNumber". But it
// is not easy maintained by PCD driver, and hashed token number will make
// searching slowly.
//
// 3.2.2 Platform Token Number
// "Platform token number" concept is introduced for mapping to a pair of
// "TokenSpaceGuid + TokenNumber". The platform token number is generated by
// build tool in autogen.h and all of them are continual in a platform scope
// started from 1.(0 meaning invalid internal token number)
// With auto-generated "platform token number", PcdGet(PcdSampleDynamicPcd)
// in source code is translated to LibPcdGet(_PCD_TOKEN_PcdSampleDynamicPcd)
// in autogen.h.
// Notes: The mapping between pair of "tokenspace guid + token number" and
// "internal token number" need build tool establish, so "platform token number"
// mechanism is not suitable for binary module which use DynamicEx type PCD.
// To access a dynamicEx type PCD, pair of "token space guid/token number" all need
// to be specificed for PcdSet/PcdGet accessing macro.
//
// Platform Token Number is started from 1, and inceased continuous. From whole
// platform scope, there are two zones: PEI Zone and DXE Zone
// |                      Platform Token Number
// ----------|----------------------------------------------------------------
// PEI Zone: |            1                 ~  PEI_LOCAL_TOKEN_NUMBER
// DXE Zone: | (PEI_LOCAL_TOKEN_NUMBER + 1) ~ (PEI_LOCAL_TOKEN_NUMBER + DXE_LOCAL_TOKEN_NUMBER)
//
// 3.2.3 Local Token Number
// To fast searching a PCD entry in PCD database, PCD driver translate
// platform token number to local token number via a mapping table.
// For binary DynamicEx type PCD, there is a another mapping table to translate
// "token space guid + token number" to local token number directly.
// Local token number is identifier for all internal interface in PCD PEI/DXE
// driver.
//
// A local token number is a 32-bit value in following meaning:
// 32 ------------- 28 ---------- 24 -------- 0
// | PCD type mask  | Datum Type  |  Offset  |
// +-----------------------------------------+
// where:
// PCd type mask: indicate Pcd type from following macro:
// PCD_TYPE_DATA
// PCD_TYPE_HII
// PCD_TYPE_VPD
// PCD_TYPE_STRING
// Datum Type   : indicate PCD vaue type from following macro:
// PCD_DATUM_TYPE_POINTER
// PCD_DATUM_TYPE_UINT8
// PCD_DATUM_TYPE_UINT16
// PCD_DATUM_TYPE_UINT32
// PCD_DATUM_TYPE_UINT64
// Offset      : indicate the related offset of PCD value in PCD database array.
// Based on local token number, PCD driver could fast determine PCD type, value
// type and get PCD entry from PCD database.
//
// 3.3 PCD Database binary file
// PCD Database binary file will be created at build time as the standalone binary image.
// To understand the binary image layout, PCD Database C structure is still generated
// as comments by build tools in PCD driver's autogen.h/
// autogen.c file. In generated C structure, following information is stored:
// - ExMapTable: This table is used translate a binary dynamicex type PCD's
// "tokenguid + token" to local token number.
// - LocalTokenNumberTable:
// This table stores all local token number in array, use "Internal
// token number" as array index to get PCD entry's offset fastly.
// - SizeTable:  This table stores the size information for all PCD entry.
// - GuidTable:  This table stores guid value for DynamicEx's token space,
// HII type PCD's variable GUID.
// - SkuIdTable: TBD
// - SystemSkuId: TBD
// - PCD value structure:
// Every PCD has a value record in PCD database. For different
// datum type PCD has different record structure which will be
// introduced in 3.3.1
//
// In a PCD database structure, there are two major area: Init and UnInit.
// Init area is use stored above PCD internal structure such as ExMapTable,
// LocalTokenNumberTable etc and the (default) value of PCD which has default
// value specified in platform DSC file.
// Unint area is used stored the value of PCD which has no default value in
// platform DSC file, the value of NULL, 0 specified in platform DSC file can
// be seemed as "no default value".
//
// 3.3.1 Simple Sample PCD Database C Structure
// A general sample of PCD database structue is as follows:
// typedef struct _PCD_DATABASE {
// typedef struct _PCD_DATABASE_INIT {
// //===== Following is PCD database internal maintain structures
// DYNAMICEX_MAPPING ExMapTable[PEI_EXMAPPING_TABLE_SIZE];
// UINT32            LocalTokenNumberTable[PEI_LOCAL_TOKEN_NUMBER_TABLE_SIZE];
// GUID              GuidTable[PEI_GUID_TABLE_SIZE];
// SIZE_INFO         SizeTable[PEI_SIZE_TABLE_SIZE];
// UINT8             SkuIdTable[PEI_SKUID_TABLE_SIZE];
// SKU_ID            SystemSkuId;
//
// //===== Following is value structure for PCD with default value
// ....
// ....
// ....
// } Init;
// typedef struct _PCD_DATABSE_UNINIT {
// //==== Following is value structure for PCD without default value
// ....
// ....
// } UnInit;
// }
//
// 3.3.2 PCD value structure in PCD database C structure
// The value's structure is generated by build tool in PCD database C structure.
// The PCDs in different datum type has different value structure.
//
// 3.3.2.1 UINT8/UINT16/UINT32/UINT64 datum type PCD
// The C structure for these datum type PCD is just a UINT8/UINT16/UINT32/UINT64
// data member in PCD database, For example:
// UINT16  PcdHardwareErrorRecordLevel_d3705011_bc19_4af7_be16_f68030378c15_VariableDefault_0;
// Above structure is generated by build tool, the member name is "PcdCName_Guidvalue"
// Member type is UINT16 according to PcdHardwareErrorRecordLevel declaration
// in DEC file.
//
// 3.3.2.2 VOID* datum type PCD
// The value of VOID* datum type PCD is a UINT8/UINT16 array in PCD database.
//
// 3.3.2.2.1 VOID* - string type
// If the default value for VOID* datum type PCD like L"xxx", the PCD is
// used for unicode string, and C structure of this datum type PCD is
// UINT16 string array in PCD database, for example:
// UINT16 StringTable[29];
// The number of 29 in above sample is max size of a unicode string.
//
// If the default value for VOID* datum type PCD like "xxx", the PCD is
// used for ascii string, and C structure of this datum type PCD is
// UINT8 string array in PCD database, for example:
// UINT8 StringTable[20];
// The number of 20 in above sample is max size of a ascii string.
//
// 3.3.2.2.2 VOID* - byte array
// If the default value of VOID* datum type PCD like {'0x29', '0x01', '0xf2'}
// the PCD is used for byte array. The generated structrue is same as
// above ascii string table,
// UINT8 StringTable[13];
// The number of 13 in above sample is max size of byte array.
//
// 3.3.3 Some utility structures in PCD Database
// 3.3.3.1 GuidTable
// GuidTable array is used to store all related GUID value in PCD database:
// - Variable GUID for HII type PCD
// - Token space GUID for dynamicex type PCD
//
// Copyright (c) 2006 - 2018, Intel Corporation. All rights reserved.<BR>
//
// SPDX-License-Identifier: BSD-2-Clause-Patent
//
// **/


#string STR_MODULE_ABSTRACT             #language en-US "PCD DXE driver manages the database that contains all dynamic PCD entries and produce the implementation of PCD protocol"

#string STR_MODULE_DESCRIPTION          #language en-US "PCD DXE driver manages the database that contains all dynamic PCD entries and produces the implementation of PCD protocol."