[PATCH v2 4/8] MdePkg: Add NULL instance of TRNG Library

["Sami Mujawar" <sami.mujawar@arm.com>]

Bugzilla: 3668 (https://bugzilla.tianocore.org/show_bug.cgi?id=3668)

The True Random Number Generator (TRNG) library defines an
interface to access the entropy source on a platform. On
platforms that do not have access to an entropy source, a
NULL instance of the TRNG library may be useful to satisfy
the build dependency.

Therefore, add a NULL instance of the TRNG library.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
---

Notes:
    v2:
     - MdePkg\Include\Library\TrngLib.h is base type     [LIMING]
       library. It can use RETURN_STATUS instead of
       EFI_STATUS.
     - Replaced EFI_STATUS with RETURN_STATUS.           [SAMI]
     - MdePkg\Include\Library\TrngLib.h API parameter    [LIMING]
       doesn't require CONST. CONST means the value
       specified by the input pointer will not be
       changed in API implementation.
     - Removed the use of constant pointers in the       [SAMI]
       TRNG API.

 MdePkg/Library/BaseTrngLibNull/BaseTrngLibNull.c   | 111 ++++++++++++++++++++
 MdePkg/Library/BaseTrngLibNull/BaseTrngLibNull.inf |  30 ++++++
 MdePkg/Library/BaseTrngLibNull/BaseTrngLibNull.uni |  12 +++
 MdePkg/MdePkg.dsc                                  |   1 +
 4 files changed, 154 insertions(+)

diff --git a/MdePkg/Library/BaseTrngLibNull/BaseTrngLibNull.c b/MdePkg/Library/BaseTrngLibNull/BaseTrngLibNull.c
new file mode 100644
index 0000000000000000000000000000000000000000..406a1e8587ccfb0cd903bf7a3794f16627eb0a84
--- /dev/null
+++ b/MdePkg/Library/BaseTrngLibNull/BaseTrngLibNull.c
@@ -0,0 +1,111 @@
+/** @file
+  Null version of TRNG (True Random Number Generator) services.
+
+  Copyright (c) 2021, Arm Limited. All rights reserved.<BR>
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+  @par Glossary:
+    - TRNG - True Random Number Generator
+**/
+
+#include <Library/DebugLib.h>
+#include <Library/TrngLib.h>
+
+/** Get the TRNG version.
+
+  A TRNG may be implemented by the system firmware, in which case this
+  function shall return the version information for the TRNG implementation.
+  Returning version information is optional and if not implemented,
+  RETURN_UNSUPPORTED shall be returned.
+
+  @param [out]  MajorRevision     Major revision.
+  @param [out]  MinorRevision     Minor revision.
+
+  @retval  RETURN_SUCCESS            The function completed successfully.
+  @retval  RETURN_INVALID_PARAMETER  Invalid parameter.
+  @retval  RETURN_UNSUPPORTED        Function not implemented.
+**/
+RETURN_STATUS
+EFIAPI
+GetTrngVersion (
+  OUT UINT16  *MajorRevision,
+  OUT UINT16  *MinorRevision
+  )
+{
+  ASSERT (FALSE);
+  return RETURN_UNSUPPORTED;
+}
+
+/** Get the UUID of the TRNG backend.
+
+  A TRNG may be implemented by the system firmware, in which case this
+  function shall return the UUID for the TRNG implementation.
+  Returning the TRNG UUID is optional and if not implemented, RETURN_UNSUPPORTED
+  shall be returned.
+
+  @param [out]  Guid              UUID of the TRNG backend.
+
+  @retval  RETURN_SUCCESS            The function completed successfully.
+  @retval  RETURN_INVALID_PARAMETER  Invalid parameter.
+  @retval  RETURN_UNSUPPORTED        Function not implemented.
+**/
+RETURN_STATUS
+EFIAPI
+GetTrngUuid (
+  OUT GUID  *Guid
+  )
+{
+  ASSERT (FALSE);
+  return RETURN_UNSUPPORTED;
+}
+
+/** Returns maximum number of entropy bits that can be returned in a single
+    call.
+
+  @return Returns the maximum number of Entropy bits that can be returned
+          in a single call to GetEntropy().
+**/
+UINTN
+EFIAPI
+GetTrngMaxSupportedEntropyBits (
+  VOID
+  )
+{
+  ASSERT (FALSE);
+  return 0;
+}
+
+/** Returns N bits of conditioned entropy.
+
+  See [3] Section 2.3.1 GetEntropy: An Interface to the Entropy Source
+    GetEntropy
+      Input:
+        bits_of_entropy: the requested amount of entropy
+      Output:
+        entropy_bitstring: The string that provides the requested entropy.
+      status: A Boolean value that is TRUE if the request has been satisfied,
+              and is FALSE otherwise.
+    Note: In this implementation this function returns a status code instead
+          of a boolean value.
+
+  @param  [in]   EntropyBits  Number of entropy bits requested.
+  @param  [out]  Buffer       Buffer to return the entropy bits.
+  @param  [in]   BufferSize   Size of the Buffer in bytes.
+
+  @retval  RETURN_SUCCESS            The function completed successfully.
+  @retval  RETURN_INVALID_PARAMETER  Invalid parameter.
+  @retval  RETURN_UNSUPPORTED        Function not implemented.
+  @retval  RETURN_BAD_BUFFER_SIZE    Buffer size is too small.
+  @retval  RETURN_NOT_READY          No Entropy available.
+**/
+RETURN_STATUS
+EFIAPI
+GetEntropy (
+  IN  CONST UINTN   EntropyBits,
+  OUT       UINT8   *Buffer,
+  IN  CONST UINTN   BufferSize
+  )
+{
+  ASSERT (FALSE);
+  return RETURN_UNSUPPORTED;
+}
diff --git a/MdePkg/Library/BaseTrngLibNull/BaseTrngLibNull.inf b/MdePkg/Library/BaseTrngLibNull/BaseTrngLibNull.inf
new file mode 100644
index 0000000000000000000000000000000000000000..a700cf66f457f8898d5c51a7b9c0b3d7643ff7f9
--- /dev/null
+++ b/MdePkg/Library/BaseTrngLibNull/BaseTrngLibNull.inf
@@ -0,0 +1,30 @@
+## @file
+#  Null instance of TRNG (True Random Number Generator) Library.
+#
+#  Copyright (c) 2021, Arm Limited. All rights reserved.<BR>
+#
+#  SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+[Defines]
+  INF_VERSION                    = 0x0001001B
+  BASE_NAME                      = BaseTrngLibNull
+  MODULE_UNI_FILE                = BaseTrngLibNull.uni
+  FILE_GUID                      = ABDE1C87-4F50-4B82-9133-7A79E13F69AB
+  MODULE_TYPE                    = BASE
+  VERSION_STRING                 = 1.0
+  LIBRARY_CLASS                  = TrngLib
+
+#
+#  VALID_ARCHITECTURES           = IA32 X64 ARM AARCH64
+#
+
+[Sources]
+  BaseTrngLibNull.c
+
+[Packages]
+  MdePkg/MdePkg.dec
+
+[LibraryClasses]
+  DebugLib
diff --git a/MdePkg/Library/BaseTrngLibNull/BaseTrngLibNull.uni b/MdePkg/Library/BaseTrngLibNull/BaseTrngLibNull.uni
new file mode 100644
index 0000000000000000000000000000000000000000..1ec7def522e5975e9621eb280776251b1e5502ca
--- /dev/null
+++ b/MdePkg/Library/BaseTrngLibNull/BaseTrngLibNull.uni
@@ -0,0 +1,12 @@
+// /** @file
+// Null Instance of TRNG (True Random Number Generator) Library.
+//
+//  Copyright (c) 2021, Arm Limited. All rights reserved.<BR>
+//
+// SPDX-License-Identifier: BSD-2-Clause-Patent
+//
+// **/
+
+#string STR_MODULE_ABSTRACT             #language en-US "Null instance of TRNG Library"
+
+#string STR_MODULE_DESCRIPTION          #language en-US "This library instance should be used with modules that inherit an (indirect) dependency on the TrngLib class, but never actually call TrngLib APIs for consuming Entropy."
diff --git a/MdePkg/MdePkg.dsc b/MdePkg/MdePkg.dsc
index a94959169b2fd9d4b5bf7ad903bf5ce06566c60e..f83753e132e9b9eb4152927fc182701fb1e70ca4 100644
--- a/MdePkg/MdePkg.dsc
+++ b/MdePkg/MdePkg.dsc
@@ -67,6 +67,7 @@ [Components]
   MdePkg/Library/DxeRngLib/DxeRngLib.inf
   MdePkg/Library/BaseRngLibNull/BaseRngLibNull.inf
   MdePkg/Library/BaseRngLibTimerLib/BaseRngLibTimerLib.inf
+  MdePkg/Library/BaseTrngLibNull/BaseTrngLibNull.inf
 
   MdePkg/Library/BaseSerialPortLibNull/BaseSerialPortLibNull.inf
   MdePkg/Library/BaseSynchronizationLib/BaseSynchronizationLib.inf
-- 
'Guid(CE165669-3EF3-493F-B85D-6190EE5B9759)'