[PATCH v2] MdePkg/Library: Install dummy variable arch protocol

[Jagadeesh Ujja <jagadeesh.ujja@arm.com>]

In a system implementing the variable store in MM, there are no variable
arch protocol and variable write arch protocol installed into the
DXE_SMM protocol database. On such systems, it is not required to
locate these protocols by the DXE runtime variable drivers because
it can be assumed that these protocols are already installed in the MM
context. But then such an implementation will deviate from the existing
traditional MM based variable driver implementation.

So in order to maintain consistency with the traditional MM variable
driver implementation, allow platforms to install dummy versions of
these protocols into the DXE protocol database but these protocol will
not be consumed by non-secure variable service runtime driver.

The Platform which uses StandaloneMM based secure variable storage
have to include this library as below.

  ArmPkg/Drivers/MmCommunicationDxe/MmCommunication.inf {
    <LibraryClasses>
      NULL|MdePkg/Library/VariableMmDependency/VariableMmDependency.inf
  }

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jagadeesh Ujja <jagadeesh.ujja@arm.com>
---
Changes since v1:
- This is a next version of patch 
   “MdeModulePkg/VariableSmmRuntimeDxe: Refactor locating Variable Arch Protocol”.
   [https://lists.01.org/pipermail/edk2-devel/2019-February/036885.html]
- Addressed the comments from Ard Biesheuvel and Zeng Star
- Can this library be placed in MdePkg rather then the StandaloneMmPkg?

 MdePkg/Library/VariableMmDependency/VariableMmDependency.c   | 85 ++++++++++++++++++++
 MdePkg/Library/VariableMmDependency/VariableMmDependency.inf | 48 +++++++++++
 2 files changed, 133 insertions(+)

diff --git a/MdePkg/Library/VariableMmDependency/VariableMmDependency.c b/MdePkg/Library/VariableMmDependency/VariableMmDependency.c
new file mode 100644
index 0000000..6e5117e
--- /dev/null
+++ b/MdePkg/Library/VariableMmDependency/VariableMmDependency.c
@@ -0,0 +1,85 @@
+/** @file
+  Runtime DXE part corresponding to StanaloneMM variable module.
+
+This module installs dummy variable arch protocol and dummy variable write arch protocol
+to StandaloneMM runtime variable service.
+
+Copyright (c) 2019, ARM Ltd. All rights reserved.
+
+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.
+
+**/
+
+#include <Library/DebugLib.h>
+#include <Library/UefiBootServicesTableLib.h>
+
+/**
+  Notify the system that the SMM variable driver is ready.
+**/
+VOID
+VariableNotifySmmReady (
+  VOID
+  )
+{
+  EFI_STATUS            Status;
+  EFI_HANDLE            Handle;
+
+  Handle = NULL;
+  Status = gBS->InstallProtocolInterface (
+                  &Handle,
+                  &gEfiSmmVariableProtocolGuid,
+                  EFI_NATIVE_INTERFACE,
+                  NULL
+                  );
+  ASSERT_EFI_ERROR (Status);
+}
+
+/**
+  Notify the system that the SMM variable write driver is ready.
+**/
+VOID
+VariableNotifySmmWriteReady (
+  VOID
+  )
+{
+  EFI_STATUS            Status;
+  EFI_HANDLE            Handle;
+
+  Handle = NULL;
+  Status = gBS->InstallProtocolInterface (
+                  &Handle,
+                  &gSmmVariableWriteGuid,
+                  EFI_NATIVE_INTERFACE,
+                  NULL
+                  );
+  ASSERT_EFI_ERROR (Status);
+}
+
+/**
+  The constructor function calls and installs dummy variable arch protocol and
+  dummy variable write arch protocol to StandaloneMM runtime variable service
+
+  @param  ImageHandle   The firmware allocated handle for the EFI image.
+  @param  SystemTable   A pointer to the Management mode System Table.
+
+  @retval EFI_SUCCESS   The constructor always returns EFI_SUCCESS.
+
+**/
+EFI_STATUS
+EFIAPI
+VariableMmDependencyLibConstructor (
+  IN EFI_HANDLE                           ImageHandle,
+  IN EFI_SYSTEM_TABLE                     *SystemTable
+  )
+{
+  VariableNotifySmmReady();
+  VariableNotifySmmWriteReady();
+  return EFI_SUCCESS;
+}
+
diff --git a/MdePkg/Library/VariableMmDependency/VariableMmDependency.inf b/MdePkg/Library/VariableMmDependency/VariableMmDependency.inf
new file mode 100644
index 0000000..09fd200
--- /dev/null
+++ b/MdePkg/Library/VariableMmDependency/VariableMmDependency.inf
@@ -0,0 +1,48 @@
+## @file
+#  Runtime DXE part corresponding to StanaloneMM variable module.
+#
+#  This module installs dummy variable arch protocol and dummy variable write arch protocol
+#  to StandaloneMM runtime variable service.
+#
+# Copyright (c) 2019, ARM Ltd. All rights reserved.
+# 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.
+#
+##
+
+[Defines]
+  INF_VERSION                    = 0x0001001A
+  BASE_NAME                      = VariableMmDependency
+  FILE_GUID                      = 64BC4129-778E-4867-BA07-13999A4DEC3F
+  MODULE_TYPE                    = DXE_RUNTIME_DRIVER
+  VERSION_STRING                 = 1.0
+  PI_SPECIFICATION_VERSION       = 0x00010032
+  LIBRARY_CLASS                  = NULL
+  CONSTRUCTOR                    = VariableMmDependencyLibConstructor
+
+#
+# The following information is for reference only and not required by the build tools.
+#
+#  VALID_ARCHITECTURES           = AARCH64
+#
+#
+
+[Sources]
+  VariableMmDependency.c
+
+[Packages]
+  MdePkg/MdePkg.dec
+  MdeModulePkg/MdeModulePkg.dec
+
+[Protocols]
+  gEfiSmmVariableProtocolGuid
+
+[Guids]
+  gSmmVariableWriteGuid
+
+[Depex]
+  TRUE
-- 
2.7.4