diff --git a/docs/getting_started/porting-guide.rst b/docs/getting_started/porting-guide.rst
index d063ec7..be3f0bb 100644
--- a/docs/getting_started/porting-guide.rst
+++ b/docs/getting_started/porting-guide.rst
@@ -2009,6 +2009,53 @@
 
 The default implementation only prints out a warning message.
 
+.. _porting_guide_trng_requirements:
+
+TRNG porting requirements
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The |TRNG| backend requires the platform to provide the following values
+and mandatory functions.
+
+Values
+......
+
+value: uuid_t plat_trng_uuid [mandatory]
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This value must be defined to the UUID of the TRNG backend that is specific to
+the hardware after ``plat_trng_setup`` function is called. This value must
+conform to the SMCCC calling convention; The most significant 32 bits of the
+UUID must not equal ``0xffffffff`` or the signed integer ``-1`` as this value in
+w0 indicates failure to get a TRNG source.
+
+Functions
+.........
+
+Function: void plat_entropy_setup(void) [mandatory]
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+::
+
+  Argument: none
+  Return: none
+
+This function is expected to do platform-specific initialization of any TRNG
+hardware. This may include generating a UUID from a hardware-specific seed.
+
+Function: bool plat_get_entropy(uint64_t \*out) [mandatory]
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+::
+
+  Argument: uint64_t *
+  Return: bool
+  Out : when the return value is true, the entropy has been written into the
+  storage pointed to
+
+This function writes entropy into storage provided by the caller. If no entropy
+is available, it must return false and the storage must not be written.
+
 Power State Coordination Interface (in BL31)
 --------------------------------------------
 
@@ -2941,7 +2988,7 @@
 
 --------------
 
-*Copyright (c) 2013-2020, Arm Limited and Contributors. All rights reserved.*
+*Copyright (c) 2013-2021, Arm Limited and Contributors. All rights reserved.*
 
 .. _PSCI: http://infocenter.arm.com/help/topic/com.arm.doc.den0022c/DEN0022C_Power_State_Coordination_Interface.pdf
 .. _Arm Generic Interrupt Controller version 2.0 (GICv2): http://infocenter.arm.com/help/topic/com.arm.doc.ihi0048b/index.html