***
PI v1.5 Specification Volume 4 defines Management Mode Core Interface
and defines EFI_MM_COMMUNICATION_PROTOCOL. This protocol provides a
means of communicating between drivers outside of MM and MMI
handlers inside of MM.

EFI_MM_COMMUNICATION_PROTOCOL
Summary
  This protocol provides a means of communicating between drivers outside of MM and MMI
  handlers inside of MM.

GUID
  #define EFI_MM_COMMUNICATION_PROTOCOL_GUID \
  { 0xc68ed8e2, 0x9dc6, 0x4cbd, 0x9d, 0x94, 0xdb, 0x65, 0xac, 0xc5, 0xc3, 0x32 }

Prototype
  typedef struct _EFI_MM_COMMUNICATION_PROTOCOL {
  EFI_MM_COMMUNICATE Communicate;
  } EFI_MM_COMMUNICATION_PROTOCOL;

Members
Communicate
  Sends/receives a message for a registered handler. See the Communicate()
  function description.

Description
  This protocol provides runtime services for communicating between DXE drivers and a registered
  MMI handler.

EFI_MM_COMMUNICATION_PROTOCOL.Communicate()
Summary
  Communicates with a registered handler.

Prototype
  typedef
  EFI_STATUS
  (EFIAPI *EFI_MM_COMMUNICATE) (
  IN CONST EFI_MM_COMMUNICATION_PROTOCOL *This,
  IN OUT VOID *CommBuffer,
  IN OUT UINTN *CommSize OPTIONAL
  );

Parameters
  This - The EFI_MM_COMMUNICATION_PROTOCOL instance.
  CommBuffer - Pointer to the buffer to convey into MMRAM.
  CommSize - The size of the data buffer being passed in. On exit, the size of data being returned.
                     Zero if the handler does not wish to reply with any data. This parameter is optional
                     and may be NULL.

Description
  This function provides a service to send and receive messages from a registered UEFI service. The EFI_MM_COMMUNICATION_PROTOCOL driver is responsible for doing any of the
  copies such that the data lives in boot-service-accessible RAM.
  A given implementation of the EFI_MM_COMMUNICATION_PROTOCOL may choose to use the EFI_MM_CONTROL_PROTOCOL for effecting the mode transition, or it may use some other method.
  The agent invoking the communication interface at runtime may be virtually mapped. The MM infrastructure code and handlers, on the other hand, execute in physical mode. As a result, the non-MM agent,
  which may be executing in the virtual-mode OS context (as a result of an OS invocation of the UEFI SetVirtualAddressMap() service), should use a contiguous memory buffer with a physical address before
  invoking this service. If the virtual address of the buffer is used, the MM Driver may not know how to do the appropriate virtual-to-physical conversion.
  To avoid confusion in interpreting frames, the CommunicateBuffer parameter should always begin with EFI_MM_COMMUNICATE_HEADER, which is defined in Related Definitions below.
  The header data is mandatory for messages sent into the MM agent.
  If the CommSize parameter is omitted the MessageLength field in the EFI_MM_COMMUNICATE_HEADER,
  in conjunction with the size of the header itself, can be used to ascertain the total size of the communication payload.
  If the MessageLength is zero, or too large for the MM implementation to manage, the MM implementation must update the MessageLength to reflect the size of the Data buffer that it can tolerate.
  If the CommSize parameter is passed into the call, but the integer it points to, has a value of 0, then this must be updated to reflect the maximum size of the CommBuffer that the implementation can tolerate.
  Once inside of MM, the MM infrastructure will call all registered handlers with the same HandlerType as the GUID specified by HeaderGuid and the CommBuffer pointing to Data.
  This function is not reentrant.
  The standard header is used at the beginning of the EFI_MM_INITIALIATION_HEADER structure during MM initialization. See "Related Definitions" below for more information.

Related Definitions
  typedef struct {
  EFI_GUID HeaderGuid;
  UINTN MessageLength;
  UINT8 Data[ANYSIZE_ARRAY];
  } EFI_MM_COMMUNICATE_HEADER;

  HeaderGuid - Allows for disambiguation of the message format. Type EFI_GUID is defined in
                       InstallProtocolInterface() in the UEFI Specification.
  MessageLength - Describes the size of Data (in bytes) and does not include the size of the header.
  Data - Designates an array of bytes that is MessageLength in size.

Status Codes Returned
  EFI_SUCCESS - The message was successfully posted.
  EFI_INVALID_PARAMETER - The buffer was NULL.
  EFI_BAD_BUFFER_SIZE - The buffer is too large for the MM implementation. If this error is
                                           returned, the MessageLength field in the CommBuffer
                                           header or the integer pointed by CommSize, are updated to reflect
                                           the maximum payload size the implementation can accommodate.
                                           See the function description above for more details.
  EFI_ACCESS_DENIED - The CommunicateBuffer parameter or CommSize
                                        parameter, if not omitted, are in address range that cannot be
                                        accessed by the MM environment.

This patchset implements it on AARCH64 Platform.
The PI concept of a Standalone MM environment is intialized during the
SEC phase in AARCH64 Platform i.e., On AARCH64, this environment is initialized
and locked down in the secure world.
This driver enables communication with the MM environment during boot and
runtime.
***
Changes Since v3:
(*) Review Comments from Meenakshi.
***
Changes Since v2:
(*) Review Comments from Ard, Udit.
(*) Added Cleanup code.
(*) Combined .inf and .c files in a single patch.
***
Changes Since v1:
(*) Update Review Comments from Ard, Jan, Achin.
(*) Reword Commit subject for the patches in the set to convey more meaningful summary. 
***
Supreeth Venkatesh (2):
  ArmPkg: Add PCDs needed for MM communication driver.
  ArmPkg/Drivers: Add EFI_MM_COMMUNICATION_PROTOCOL DXE driver.

 ArmPkg/ArmPkg.dec                                  |   3 +
 .../Drivers/MmCommunicationDxe/MmCommunication.c   | 340 +++++++++++++++++++++
 .../Drivers/MmCommunicationDxe/MmCommunication.inf |  50 +++
 3 files changed, 393 insertions(+)
 create mode 100644 ArmPkg/Drivers/MmCommunicationDxe/MmCommunication.c
 create mode 100644 ArmPkg/Drivers/MmCommunicationDxe/MmCommunication.inf

-- 
2.14.1

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