diff --git a/docs/components/granule-protection-tables-design.rst b/docs/components/granule-protection-tables-design.rst
new file mode 100644
index 0000000..07637dd
--- /dev/null
+++ b/docs/components/granule-protection-tables-design.rst
@@ -0,0 +1,235 @@
+Granule Protection Tables Library
+=================================
+
+This document describes the design of the granule protection tables (GPT)
+library used by Trusted Firmware-A (TF-A). This library provides the APIs needed
+to initialize the GPTs based on a data structure containing information about
+the systems memory layout, configure the system registers to enable granule
+protection checks based on these tables, and transition granules between
+different PAS (physical address spaces) at runtime.
+
+Arm CCA adds two new security states for a total of four: root, realm, secure, and
+non-secure. In addition to new security states, corresponding physical address
+spaces have been added to control memory access for each state. The PAS access
+allowed to each security state can be seen in the table below.
+
+.. list-table:: Security states and PAS access rights
+   :widths: 25 25 25 25 25
+   :header-rows: 1
+
+   * -
+     - Root state
+     - Realm state
+     - Secure state
+     - Non-secure state
+   * - Root PAS
+     - yes
+     - no
+     - no
+     - no
+   * - Realm PAS
+     - yes
+     - yes
+     - no
+     - no
+   * - Secure PAS
+     - yes
+     - no
+     - yes
+     - no
+   * - Non-secure PAS
+     - yes
+     - yes
+     - yes
+     - yes
+
+The GPT can function as either a 1 level or 2 level lookup depending on how a
+PAS region is configured. The first step is the level 0 table, each entry in the
+level 0 table controls access to a relatively large region in memory (block
+descriptor), and the entire region can belong to a single PAS when a one step
+mapping is used, or a level 0 entry can link to a level 1 table where relatively
+small regions (granules) of memory can be assigned to different PAS with a 2
+step mapping. The type of mapping used for each PAS is determined by the user
+when setting up the configuration structure.
+
+Design Concepts and Interfaces
+------------------------------
+
+This section covers some important concepts and data structures used in the GPT
+library.
+
+There are three main parameters that determine how the tables are organized and
+function: the PPS (protected physical space) which is the total amount of
+protected physical address space in the system, PGS (physical granule size)
+which is how large each level 1 granule is, and L0GPTSZ (level 0 GPT size) which
+determines how much physical memory is governed by each level 0 entry. A granule
+is the smallest unit of memory that can be independently assigned to a PAS.
+
+L0GPTSZ is determined by the hardware and is read from the GPCCR_EL3 register.
+PPS and PGS are passed into the APIs at runtime and can be determined in
+whatever way is best for a given platform, either through some algorithm or hard
+coded in the firmware.
+
+GPT setup is split into two parts: table creation and runtime initialization. In
+the table creation step, a data structure containing information about the
+desired PAS regions is passed into the library which validates the mappings,
+creates the tables in memory, and enables granule protection checks. In the
+runtime initialization step, the runtime firmware locates the existing tables in
+memory using the GPT register configuration and saves important data to a
+structure used by the granule transition service which will be covered more
+below.
+
+In the reference implementation for FVP models, you can find an example of PAS
+region definitions in the file ``include/plat/arm/common/arm_pas_def.h``. Table
+creation API calls can be found in ``plat/arm/common/arm_bl2_setup.c`` and
+runtime initialization API calls can be seen in
+``plat/arm/common/arm_bl31_setup.c``.
+
+Defining PAS regions
+~~~~~~~~~~~~~~~~~~~~
+
+A ``pas_region_t`` structure is a way to represent a physical address space and
+its attributes that can be used by the GPT library to initialize the tables.
+
+This structure is composed of the following:
+
+#. The base physical address
+#. The region size
+#. The desired attributes of this memory region (mapping type, PAS type)
+
+See the ``pas_region_t`` type in ``include/lib/gpt_rme/gpt_rme.h``.
+
+The programmer should provide the API with an array containing ``pas_region_t``
+structures, then the library will check the desired memory access layout for
+validity and create tables to implement it.
+
+``pas_region_t`` is a public type, however it is recommended that the macros
+``GPT_MAP_REGION_BLOCK`` and ``GPT_MAP_REGION_GRANULE`` be used to populate
+these structures instead of doing it manually to reduce the risk of future
+compatibility issues. These macros take the base physical address, region size,
+and PAS type as arguments to generate the pas_region_t structure. As the names
+imply, ``GPT_MAP_REGION_BLOCK`` creates a region using only L0 mapping while
+``GPT_MAP_REGION_GRANULE`` creates a region using L0 and L1 mappings.
+
+Level 0 and Level 1 Tables
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The GPT initialization APIs require memory to be passed in for the tables to be
+constructed, ``gpt_init_l0_tables`` takes a memory address and size for building
+the level 0 tables and ``gpt_init_pas_l1_tables`` takes an address and size for
+building the level 1 tables which are linked from level 0 descriptors. The
+tables should have PAS type ``GPT_GPI_ROOT`` and a typical system might place
+its level 0 table in SRAM and its level 1 table(s) in DRAM.
+
+Granule Transition Service
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The Granule Transition Service allows memory mapped with GPT_MAP_REGION_GRANULE
+ownership to be changed using SMC calls. Non-secure granules can be transitioned
+to either realm or secure space, and realm and secure granules can be
+transitioned back to non-secure. This library only allows memory mapped as
+granules to be transitioned, memory mapped as blocks have their GPIs fixed after
+table creation.
+
+Library APIs
+------------
+
+The public APIs and types can be found in ``include/lib/gpt_rme/gpt_rme.h`` and this
+section is intended to provide additional details and clarifications.
+
+To create the GPTs and enable granule protection checks the APIs need to be
+called in the correct order and at the correct time during the system boot
+process.
+
+#. Firmware must enable the MMU.
+#. Firmware must call ``gpt_init_l0_tables`` to initialize the level 0 tables to
+   a default state, that is, initializing all of the L0 descriptors to allow all
+   accesses to all memory. The PPS is provided to this function as an argument.
+#. DDR discovery and initialization by the system, the discovered DDR region(s)
+   are then added to the L1 PAS regions to be initialized in the next step and
+   used by the GTSI at runtime.
+#. Firmware must call ``gpt_init_pas_l1_tables`` with a pointer to an array of
+   ``pas_region_t`` structures containing the desired memory access layout. The
+   PGS is provided to this function as an argument.
+#. Firmware must call ``gpt_enable`` to enable granule protection checks by
+   setting the correct register values.
+#. In systems that make use of the granule transition service, runtime
+   firmware must call ``gpt_runtime_init`` to set up the data structures needed
+   by the GTSI to find the tables and transition granules between PAS types.
+
+API Constraints
+~~~~~~~~~~~~~~~
+
+The values allowed by the API for PPS and PGS are enumerated types
+defined in the file ``include/lib/gpt_rme/gpt_rme.h``.
+
+Allowable values for PPS along with their corresponding size.
+
+* ``GPCCR_PPS_4GB`` (4GB protected space, 0x100000000 bytes)
+* ``GPCCR_PPS_64GB`` (64GB protected space, 0x1000000000 bytes)
+* ``GPCCR_PPS_1TB`` (1TB protected space, 0x10000000000 bytes)
+* ``GPCCR_PPS_4TB`` (4TB protected space, 0x40000000000 bytes)
+* ``GPCCR_PPS_16TB`` (16TB protected space, 0x100000000000 bytes)
+* ``GPCCR_PPS_256TB`` (256TB protected space, 0x1000000000000 bytes)
+* ``GPCCR_PPS_4PB`` (4PB protected space, 0x10000000000000 bytes)
+
+Allowable values for PGS along with their corresponding size.
+
+* ``GPCCR_PGS_4K`` (4KB granules, 0x1000 bytes)
+* ``GPCCR_PGS_16K`` (16KB granules, 0x4000 bytes)
+* ``GPCCR_PGS_64K`` (64KB granules, 0x10000 bytes)
+
+Allowable values for L0GPTSZ along with the corresponding size.
+
+* ``GPCCR_L0GPTSZ_30BITS`` (1GB regions, 0x40000000 bytes)
+* ``GPCCR_L0GPTSZ_34BITS`` (16GB regions, 0x400000000 bytes)
+* ``GPCCR_L0GPTSZ_36BITS`` (64GB regions, 0x1000000000 bytes)
+* ``GPCCR_L0GPTSZ_39BITS`` (512GB regions, 0x8000000000 bytes)
+
+Note that the value of the PPS, PGS, and L0GPTSZ definitions is an encoded value
+corresponding to the size, not the size itself. The decoded hex representations
+of the sizes have been provided for convenience.
+
+The L0 table memory has some constraints that must be taken into account.
+
+* The L0 table must be aligned to either the table size or 4096 bytes, whichever
+  is greater. L0 table size is the total protected space (PPS) divided by the
+  size of each L0 region (L0GPTSZ) multiplied by the size of each L0 descriptor
+  (8 bytes). ((PPS / L0GPTSZ) * 8)
+* The L0 memory size must be greater than or equal to the table size.
+* The L0 memory must fall within a PAS of type GPT_GPI_ROOT.
+
+The L1 memory also has some constraints.
+
+* The L1 tables must be aligned to their size. The size of each L1 table is the
+  size of each L0 region (L0GPTSZ) divided by the granule size (PGS) divided by
+  the granules controlled in each byte (2). ((L0GPTSZ / PGS) / 2)
+* There must be enough L1 memory supplied to build all requested L1 tables.
+* The L1 memory must fall within a PAS of type GPT_GPI_ROOT.
+
+If an invalid combination of parameters is supplied, the APIs will print an
+error message and return a negative value. The return values of APIs should be
+checked to ensure successful configuration.
+
+Sample Calculation for L0 memory size and alignment
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Let PPS=GPCCR_PPS_4GB and L0GPTSZ=GPCCR_L0GPTSZ_30BITS
+
+We can find the total L0 table size with ((PPS / L0GPTSZ) * 8)
+
+Substitute values to get this: ((0x100000000 / 0x40000000) * 8)
+
+And solve to get 32 bytes. In this case, 4096 is greater than 32, so the L0
+tables must be aligned to 4096 bytes.
+
+Sample calculation for L1 table size and alignment
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Let PGS=GPCCR_PGS_4K and L0GPTSZ=GPCCR_L0GPTSZ_30BITS
+
+We can find the size of each L1 table with ((L0GPTSZ / PGS) / 2).
+
+Substitute values: ((0x40000000 / 0x1000) / 2)
+
+And solve to get 0x20000 bytes per L1 table.