GitLab

fixes ARM-Software/tf-issues#346

Change-Id: I946c8eab650bba7407775462ce91f394d767e079
Signed-off-by: Douglas Raillard <douglas.raillard@arm.com>

This patch fixes the type of the return value of bl1_plat_mem_check()
in the porting guide. It also specifies the expected return value.

Change-Id: I7c437342b8bfb1e621d74b2edf0aaf97b913216a
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>

Do not double the phrase "called with the".
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Fix one of the two titles that ended up being the same, although both
describe different things.

Change-Id: I66ecf369643709898ee4c014659d8f85c0480643

This patch adds common changes to support AArch32 state in
BL1 and BL2. Following are the changes:

* Added functions for disabling MMU from Secure state.
* Added AArch32 specific SMC function.
* Added semihosting support.
* Added reporting of unhandled exceptions.
* Added uniprocessor stack support.
* Added `el3_entrypoint_common` macro that can be
  shared by BL1 and BL32 (SP_MIN) BL stages. The
  `el3_entrypoint_common` is similar to the AArch64
  counterpart with the main difference in the assembly
  instructions and the registers that are relevant to
  AArch32 execution state.
* Enabled `LOAD_IMAGE_V2` flag in Makefile for
  `ARCH=aarch32` and added check to make sure that
  platform has not overridden to disable it.

Change-Id: I33c6d8dfefb2e5d142fdfd06a0f4a7332962e1a3

This patch adds capability to load BL images based on image
descriptors instead of hard coded way of loading BL images.
This framework is designed such that it can be readily adapted
by any BL stage that needs to load images.

In order to provide the above capability the following new
platform functions are introduced:

  bl_load_info_t *plat_get_bl_image_load_info(void);
    This function returns pointer to the list of images that the
    platform has populated to load.

  bl_params_t *plat_get_next_bl_params(void);
    This function returns a pointer to the shared memory that the
    platform has kept aside to pass trusted firmware related
    information that next BL image needs.

  void plat_flush_next_bl_params(void);
    This function flushes to main memory all the params that
    are passed to next image.

  int bl2_plat_handle_post_image_load(unsigned int image_id)
    This function can be used by the platforms to update/use
    image information for given `image_id`.

`desc_image_load.c` contains utility functions which can be used
by the platforms to generate, load and executable, image list
based on the registered image descriptors.

This patch also adds new version of `load_image/load_auth_image`
functions in-order to achieve the above capability.

Following are the changes for the new version as compared to old:
  - Refactor the signature and only keep image_id and image_info_t
    arguments. Removed image_base argument as it is already passed
    through image_info_t. Given that the BL image base addresses and
    limit/size are already provided by the platforms, the meminfo_t
    and entry_point_info arguments are not needed to provide/reserve
    the extent of free memory for the given BL image.

  - Added check for the image size against the defined max size.
    This is needed because the image size could come from an
    unauthenticated source (e.g. the FIP header).
    To make this check, new member is added to the image_info_t
    struct for identifying the image maximum size.

New flag `LOAD_IMAGE_V2` is added in the Makefile.
Default value is 0.

NOTE: `TRUSTED_BOARD_BOOT` is currently not supported when
      `LOAD_IMAGE_V2` is enabled.

Change-Id: Ia7b643f4817a170d5a2fbf479b9bc12e63112e79

Partition driver requires the "PLAT_PARTITION_MAX_ENTRIES" definition.

By default, it's defined to 128 in partition driver. But it costs a lot
of memory, and only a few partition entries are really used in platform
partition table. If user wants use memory efficiently, user should
define the build flag in platform.mk instead.
Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>

This patch adds support for NODE_HW_STATE PSCI API by introducing a new
PSCI platform hook (get_node_hw_state). The implementation validates
supplied arguments, and then invokes this platform-defined hook and
returns its result to the caller. PSCI capabilities are updated
accordingly.

Also updates porting and firmware design guides.

Change-Id: I808e55bdf0c157002a7c104b875779fe50a68a30

This patch reworks type usage in generic code, drivers and ARM platform files
to make it more portable. The major changes done with respect to
type usage are as listed below:

* Use uintptr_t for storing address instead of uint64_t or unsigned long.
* Review usage of unsigned long as it can no longer be assumed to be 64 bit.
* Use u_register_t for register values whose width varies depending on
  whether AArch64 or AArch32.
* Use generic C types where-ever possible.

In addition to the above changes, this patch also modifies format specifiers
in print invocations so that they are AArch64/AArch32 agnostic. Only files
related to upcoming feature development have been reworked.

Change-Id: I9f8c78347c5a52ba7027ff389791f1dad63ee5f8

This patch adds following optional PSCI STAT functions:

- PSCI_STAT_RESIDENCY: This call returns the amount of time spent
  in power_state in microseconds, by the node represented by the
  `target_cpu` and the highest level of `power_state`.

- PSCI_STAT_COUNT: This call returns the number of times a
  `power_state` has been used by the node represented by the
  `target_cpu` and the highest power level of `power_state`.

These APIs provides residency statistics for power states that has
been used by the platform. They are implemented according to v1.0
of the PSCI specification.

By default this optional feature is disabled in the PSCI
implementation. To enable it, set the boolean flag
`ENABLE_PSCI_STAT` to 1. This also sets `ENABLE_PMF` to 1.

Change-Id: Ie62e9d37d6d416ccb1813acd7f616d1ddd3e8aff

A production ROM with TBB enabled must have the ability to boot test software
before a real ROTPK is deployed (e.g. manufacturing mode). Previously the
function plat_get_rotpk_info() must return a valid ROTPK for TBB to succeed.
This patch adds an additional bit `ROTPK_NOT_DEPLOYED` in the output `flags`
parameter from plat_get_rotpk_info(). If this bit is set, then the ROTPK
in certificate is used without verifying against the platform value.

Fixes ARM-software/tf-issues#381

Change-Id: Icbbffab6bff8ed76b72431ee21337f550d8fdbbb

* Move stdlib header files from include/stdlib to include/lib/stdlib for
  consistency with other library headers.
* Fix checkpatch paths to continue excluding stdlib files.
* Create stdlib.mk to define the stdlib source files and include directories.
* Include stdlib.mk from the top level Makefile.
* Update stdlib header path in the fip_create Makefile.
* Update porting-guide.md with the new paths.

Change-Id: Ia92c2dc572e9efb54a783e306b5ceb2ce24d27fa

This patch adds a new optional platform hook `pwr_domain_pwr_down_wfi()` in
the plat_psci_ops structure. This hook allows the platform to perform platform
specific actions including the wfi invocation to enter powerdown. This hook
is invoked by both psci_do_cpu_off() and psci_cpu_suspend_start() functions.
The porting-guide.md is also updated for the same.

This patch also modifies the `psci_power_down_wfi()` function to invoke
`plat_panic_handler` incase of panic instead of the busy while loop.

Fixes ARM-Software/tf-issues#375

Change-Id: Iba104469a1445ee8d59fb3a6fdd0a98e7f24dfa3

Added plat_get_syscnt_freq2, which is a 32 bit variant of the 64 bit
plat_get_syscnt_freq. The old one has been flagged as deprecated.
Common code has been updated to use this new version. Porting guide
has been updated.

Change-Id: I9e913544926c418970972bfe7d81ee88b4da837e

Add MAX_IO_BLOCK_DEVICES in porting guide. It's necessary to define
this macro to support io block device. With this macro, multiple
block devices could be opened at the same time. Each block device
stores its own state.
Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>

The translation table library code has moved from lib/aarch64/ to
lib/xlat_tables/ since commit 3ca9928d but the Porting Guide still
points to the old location. This patch fixes this issue.

Change-Id: I983a9a100d70eacf6bac71725ffbb4bb5f3732b0

It is up to the platform to implement the new plat_crash_print_regs macro to
report all relevant platform registers helpful for troubleshooting.

plat_crash_print_regs merges or calls previously defined plat_print_gic_regs
and plat_print_interconnect_regs macros for each existing platforms.

NOTE: THIS COMMIT REQUIRES ALL PLATFORMS THAT ENABLE THE `CRASH_REPORTING`
BUILD FLAG TO MIGRATE TO USE THE NEW `plat_crash_print_regs()` MACRO. BY
DEFAULT, `CRASH_REPORTING` IS ENABLED IN DEBUG BUILDS FOR ALL PLATFORMS.

Fixes: arm-software/tf-issues#373
Signed-off-by: Gerald Lejeune <gerald.lejeune@st.com>

To avoid confusion the build option BL33_BASE has been renamed to
PRELOADED_BL33_BASE, which is more descriptive of what it does and
doesn't get mistaken by similar names like BL32_BASE that work in a
completely different way.

NOTE: PLATFORMS USING BUILD OPTION `BL33_BASE` MUST CHANGE TO THE NEW
BUILD OPTION `PRELOADED_BL33_BASE`.

Change-Id: I658925ebe95406edf0325f15aa1752e1782aa45b

This patch modifies the return type of the platform API
`plat_get_ns_image_entrypoint()` from `unsigned long` to
`uintptr_t` in accordance with the coding guidelines.

Change-Id: Icb4510ca98b706aa4d535fe27e203394184fb4ca

lib/aarch64/xlat_helpers.c defines helper functions to build
translation descriptors, but no common code or upstream platform
port uses them. As the rest of the xlat_tables code evolves, there
may be conflicts with these helpers, therefore this code should be
removed.

Change-Id: I9f5be99720f929264818af33db8dada785368711

This patch adds support for non-volatile counter authentication to
the Authentication Module. This method consists of matching the
counter values provided in the certificates with the ones stored
in the platform. If the value from the certificate is lower than
the platform, the boot process is aborted. This mechanism protects
the system against rollback.

The TBBR CoT has been updated to include this method as part of the
authentication process. Two counters are used: one for the trusted
world images and another for the non trusted world images.

** NEW PLATFORM APIs (mandatory when TBB is enabled) **

int plat_get_nv_ctr(void *cookie, unsigned int *nv_ctr);

    This API returns the non-volatile counter value stored
    in the platform. The cookie in the first argument may be
    used to select the counter in case the platform provides
    more than one (i.e. TBSA compliant platforms must provide
    trusted and non-trusted counters). This cookie is specified
    in the CoT.

int plat_set_nv_ctr(void *cookie, unsigned int nv_ctr);

    This API sets a new counter value. The cookie may be
    used to select the counter to be updated.

An implementation of these new APIs for ARM platforms is also
provided. The values are obtained from the Trusted Non-Volatile
Counters peripheral. The cookie is used to pass the extension OID.
This OID may be interpreted by the platform to know which counter
must return. On Juno, The trusted and non-trusted counter values
have been tied to 31 and 223, respectively, and cannot be modified.

** IMPORTANT **

THIS PATCH BREAKS THE BUILD WHEN TRUSTED_BOARD_BOOT IS ENABLED. THE
NEW PLATFORM APIs INTRODUCED IN THIS PATCH MUST BE IMPLEMENTED IN
ORDER TO SUCCESSFULLY BUILD TF.

Change-Id: Ic943b76b25f2a37f490eaaab6d87b4a8b3cbc89a

The Firmware Design document is meant to provide a general overview
of the Trusted Firmware code. Although it is useful to provide some
guidance around the responsibilities of the platform layer, it should
not provide too much platform specific implementation details. Right
now, some sections are too tied to the implementation on ARM
platforms. This makes the Firmware Design document harder to digest.

This patch simplifies this aspect of the Firmware Design document.
The sections relating the platform initialisations performed by the
different BL stages have been simplified and the extra details about
the ARM platforms implementation have been moved to the Porting Guide
when appropriate.

This patch also provides various documentation fixes and additions
in the Firmware Design and Platform Porting Guide. In particular:

 - Update list of SMCs supported by BL1.

 - Remove MMU setup from architectural inits, as it is actually
   performed by platform code.

 - Similarly, move runtime services initialisation, BL2 image
   initialization and BL33 execution out of the platform
   initialisation paragraph.

 - List SError interrupt unmasking as part of BL1 architectural
   initialization.

 - Mention Trusted Watchdog enabling in BL1 on ARM platforms.

 - Fix order of steps in "BL2 image load and execution" section.

 - Refresh section about GICv3/GICv2 drivers initialisation on
   ARM platforms.

Change-Id: I32113c4ffdc26687042629cd8bbdbb34d91e3c14

Added a new platform porting function plat_panic_handler, to allow
platforms to handle unexpected error situations. It must be
implemented in assembly as it may be called before the C environment
is initialized. A default implementation is provided, which simply
spins.

Corrected all dead loops in generic code to call this function
instead. This includes the dead loop that occurs at the end of the
call to panic().

All unnecesary wfis from bl32/tsp/aarch64/tsp_exceptions.S have
been removed.

Change-Id: I67cb85f6112fa8e77bd62f5718efcef4173d8134

This patch clarifies a porting API in the Porting Guide that do not
follow the ARM Architecture Program Calling Standards (AAPCS). The
list of registers that are allowed to be clobbered by this API has
been updated in the Porting Guide.

Fixes ARM-software/tf-issues#259

Change-Id: Ibf2adda2e1fb3e9b8f53d8a918d5998356eb8fce

Enable alternative boot flow where BL2 does not load BL33 from
non-volatile storage, and BL31 hands execution over to a preloaded
BL33.

The flag used to enable this bootflow is BL33_BASE, which must hold
the entrypoint address of the BL33 image. The User Guide has been
updated with an example of how to use this option with a bootwrapped
kernel.

Change-Id: I48087421a7b0636ac40dca7d457d745129da474f

ARM PL061 GPIO driver requires the "PLAT_PL061_MAX_GPIOS" definition.
By default, it's defined to 32 in PL061 GPIO driver. If user wants
more PL061 controllers in platform, user should define the build
flag in platform.mk instead.
Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>

The memory translation library in Trusted Firmware supports
non-identity mappings for Physical to Virtual addresses since commit
f984ce84. However, the porting guide hasn't been updated
accordingly and still mandates the platform ports to use
identity-mapped page tables for all addresses.

This patch removes this out-dated information from the Porting Guide
and clarifies in which circumstances non-identity mapping may safely
be used.

Fixes ARM-software/tf-issues#258

Change-Id: I84dab9f3cabfc43794951b1828bfecb13049f706

The PL011 TRM (ARM DDI 0183G) specifies that the UART must be
disabled before any of the control registers are programmed. The
PL011 driver included in TF does not disable the UART, so the
initialization in BL2 and BL31 is violating this requirement
(and potentially in BL1 if the UART is enabled after reset).

This patch modifies the initialization function in the PL011
console driver to disable the UART before programming the
control registers.

Register clobber list and documentation updated.

Fixes ARM-software/tf-issues#300

Change-Id: I839b2d681d48b03f821ac53663a6a78e8b30a1a1

GIC v2 and v3 specification references in the porting guide
should refer to publically visible links, not ARM internal links.

Change-Id: Ib47c8adda6a03581f23bcaed72d71c08c7dd9fb1
Signed-off-by: Yuping Luo <yuping.luo@arm.com>

Migrate all direct usage of __attribute__ to usage of their
corresponding macros from cdefs.h.
e.g.:
 - __attribute__((unused)) -> __unused
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>

This patch adds a brief description of 'MAX_MMAP_REGIONS' and
'ADDR_SPACE_SIZE' to the Porting Guide. These fields must be defined
by the platform in order to use the translation table library.

Change-Id: Ida366458fe2bc01979091a014dc38da0fae5991e

Change-Id: I6f49bd779f2a4d577c6443dd160290656cdbc59b

This patch adds design documentation for the Firmware Update (FWU)
feature in `firmware-update.md`. It provides an overview of FWU,
describes the BL1 SMC interface, and includes diagrams showing
an example FWU boot flow and the FWU state machine.

This patch also updates the existing TF documents where needed:

*   `porting-guide.md`
*   `user-guide.md`
*   `firmware-design.md`
*   `rt-svc-writers-guide.md`
*   `trusted_board_boot.md`

Change-Id: Ie6de31544429b18f01327bd763175e218299a4ce
Co-Authored-By: Dan Handley <dan.handley@arm.com>

This patch updates the relevant documentation in ARM Trusted Firmware
for the new GIC drivers. The user-guide.md and porting-guide.md have been
updated as follows:

*  The build option to compile Trusted Firmware with different GIC drivers
   for FVP has been explained in the user-guide.md.

*  The implementation details of interrupt management framework porting
   APIs for GICv3 have been added in porting-guide.md.

*  The Linaro tracking kernel release does not work OOB in GICv3 mode.
   The instructions for changing UEFI configuration in order to run with
   the new GICv3 driver in ARM TF have been added to user-guide.md.

The interrupt-framework-design.md has been updated as follows:

*  Describes support for registering and handling interrupts targeted to EL3
   e.g. Group 0 interrupts in GICv3.

*  Describes the build option `TSP_NS_INTR_ASYNC_PREEMPT` in detail.

*  Describes preemption of TSP in S-EL1 by non secure interrupts and
   also possibly by higher priority EL3 interrupts.

*  Describes the normal world sequence for issuing `standard` SMC calls.

*  Modifies the document to correspond to the current state of interrupt
   handling in TSPD and TSP.

*  Modifies the various functions names in the document to reflect
   the current names used in code.

Change-Id: I78c9514b5be834f193405aad3c1752a4a9e27a6c

This patch removes the dash character from the image name, to
follow the image terminology in the Trusted Firmware Wiki page:

    https://github.com/ARM-software/arm-trusted-firmware/wiki

Changes apply to output messages, comments and documentation.

non-ARM platform files have been left unmodified.

Change-Id: Ic2a99be4ed929d52afbeb27ac765ceffce46ed76

This patch replaces all references to the SCP Firmware (BL0, BL30,
BL3-0, bl30) with the image terminology detailed in the TF wiki
(https://github.com/ARM-software/arm-trusted-firmware/wiki):

    BL0          -->  SCP_BL1
    BL30, BL3-0  -->  SCP_BL2
    bl30         -->  scp_bl2

This change affects code, documentation, build system, tools and
platform ports that load SCP firmware. ARM plaforms have been
updated to the new porting API.

IMPORTANT: build option to specify the SCP FW image has changed:

    BL30 --> SCP_BL2

IMPORTANT: This patch breaks compatibility for platforms that use BL2
to load SCP firmware. Affected platforms must be updated as follows:

    BL30_IMAGE_ID --> SCP_BL2_IMAGE_ID
    BL30_BASE --> SCP_BL2_BASE
    bl2_plat_get_bl30_meminfo() --> bl2_plat_get_scp_bl2_meminfo()
    bl2_plat_handle_bl30() --> bl2_plat_handle_scp_bl2()

Change-Id: I24c4c1a4f0e4b9f17c9e4929da815c4069549e58

This patch applies the TBBR naming convention to the certificates
and the corresponding extensions defined by the CoT:

    * Certificate UUID names
    * Certificate identifier names
    * OID names

Changes apply to:

    * Generic code (variables and defines)
    * The default certificate identifiers provided in the generic
      code
    * Build system
    * ARM platforms port
    * cert_create tool internal definitions
    * fip_create and cert_create tools command line options
    * Documentation

IMPORTANT: this change breaks the compatibility with platforms
that use TBBR. The platform will need to adapt the identifiers
and OIDs to the TBBR naming convention introduced by this patch:

Certificate UUIDs:

    UUID_TRUSTED_BOOT_FIRMWARE_BL2_CERT --> UUID_TRUSTED_BOOT_FW_CERT
    UUID_SCP_FIRMWARE_BL30_KEY_CERT --> UUID_SCP_FW_KEY_CERT
    UUID_SCP_FIRMWARE_BL30_CERT --> UUID_SCP_FW_CONTENT_CERT
    UUID_EL3_RUNTIME_FIRMWARE_BL31_KEY_CERT --> UUID_SOC_FW_KEY_CERT
    UUID_EL3_RUNTIME_FIRMWARE_BL31_CERT --> UUID_SOC_FW_CONTENT_CERT
    UUID_SECURE_PAYLOAD_BL32_KEY_CERT --> UUID_TRUSTED_OS_FW_KEY_CERT
    UUID_SECURE_PAYLOAD_BL32_CERT --> UUID_TRUSTED_OS_FW_CONTENT_CERT
    UUID_NON_TRUSTED_FIRMWARE_BL33_KEY_CERT --> UUID_NON_TRUSTED_FW_KEY_CERT
    UUID_NON_TRUSTED_FIRMWARE_BL33_CERT --> UUID_NON_TRUSTED_FW_CONTENT_CERT

Certificate identifiers:

    BL2_CERT_ID --> TRUSTED_BOOT_FW_CERT_ID
    BL30_KEY_CERT_ID --> SCP_FW_KEY_CERT_ID
    BL30_CERT_ID --> SCP_FW_CONTENT_CERT_ID
    BL31_KEY_CERT_ID --> SOC_FW_KEY_CERT_ID
    BL31_CERT_ID --> SOC_FW_CONTENT_CERT_ID
    BL32_KEY_CERT_ID --> TRUSTED_OS_FW_KEY_CERT_ID
    BL32_CERT_ID --> TRUSTED_OS_FW_CONTENT_CERT_ID
    BL33_KEY_CERT_ID --> NON_TRUSTED_FW_KEY_CERT_ID
    BL33_CERT_ID --> NON_TRUSTED_FW_CONTENT_CERT_ID

OIDs:

    TZ_FW_NVCOUNTER_OID --> TRUSTED_FW_NVCOUNTER_OID
    NTZ_FW_NVCOUNTER_OID --> NON_TRUSTED_FW_NVCOUNTER_OID
    BL2_HASH_OID --> TRUSTED_BOOT_FW_HASH_OID
    TZ_WORLD_PK_OID --> TRUSTED_WORLD_PK_OID
    NTZ_WORLD_PK_OID --> NON_TRUSTED_WORLD_PK_OID
    BL30_CONTENT_CERT_PK_OID --> SCP_FW_CONTENT_CERT_PK_OID
    BL30_HASH_OID --> SCP_FW_HASH_OID
    BL31_CONTENT_CERT_PK_OID --> SOC_FW_CONTENT_CERT_PK_OID
    BL31_HASH_OID --> SOC_AP_FW_HASH_OID
    BL32_CONTENT_CERT_PK_OID --> TRUSTED_OS_FW_CONTENT_CERT_PK_OID
    BL32_HASH_OID --> TRUSTED_OS_FW_HASH_OID
    BL33_CONTENT_CERT_PK_OID --> NON_TRUSTED_FW_CONTENT_CERT_PK_OID
    BL33_HASH_OID --> NON_TRUSTED_WORLD_BOOTLOADER_HASH_OID
    BL2U_HASH_OID --> AP_FWU_CFG_HASH_OID
    SCP_BL2U_HASH_OID --> SCP_FWU_CFG_HASH_OID
    NS_BL2U_HASH_OID --> FWU_HASH_OID

Change-Id: I1e047ae046299ca913911c39ac3a6e123bd41079

This patch overrides the default weak definition of
`bl31_plat_runtime_setup()` for ARM Standard platforms to
specify a BL31 runtime console. ARM Standard platforms are
now expected to define `PLAT_ARM_BL31_RUN_UART_BASE` and
`PLAT_ARM_BL31_RUN_UART_CLK_IN_HZ` macros which is required
by `arm_bl31_plat_runtime_setup()` to initialize the runtime
console.

The system suspend resume helper `arm_system_pwr_domain_resume()`
is fixed to initialize the runtime console rather than the boot
console on resumption from system suspend.

Fixes ARM-software/tf-issues#220

Change-Id: I80eafe5b6adcfc7f1fdf8b99659aca1c64d96975

It is not ideal for BL31 to continue to use boot console at
runtime which could be potentially uninitialized. This patch
introduces a new optional platform porting API
`bl31_plat_runtime_setup()` which allows the platform to perform
any BL31 runtime setup just prior to BL31 exit during cold boot.
The default weak implementation of this function will invoke
`console_uninit()` which will suppress any BL31 runtime logs.

On the ARM Standard platforms, there is an anomaly that
the boot console will be reinitialized on resumption from
system suspend in `arm_system_pwr_domain_resume()`. This
will be resolved in the following patch.

NOTE: The default weak definition of `bl31_plat_runtime_setup()`
disables the BL31 console. To print the BL31 runtime
messages, platforms must override this API and initialize a
runtime console.

Fixes ARM-software/tf-issues#328

Change-Id: Ibaf8346fcceb447fe1a5674094c9f8eb4c09ac4a

This patch introduces a new build option named COLD_BOOT_SINGLE_CPU,
which allows platforms that only release a single CPU out of reset to
slightly optimise their cold boot code, both in terms of code size
and performance.

COLD_BOOT_SINGLE_CPU defaults to 0, which assumes that the platform
may release several CPUs out of reset. In this case, the cold reset
code needs to coordinate all CPUs via the usual primary/secondary
CPU distinction.

If a platform guarantees that only a single CPU will ever be released
out of reset, there is no need to arbitrate execution ; the notion of
primary and secondary CPUs itself no longer exists. Such platforms
may set COLD_BOOT_SINGLE_CPU to 1 in order to compile out the
primary/secondary CPU identification in the cold reset code.

All ARM standard platforms can release several CPUs out of reset
so they use COLD_BOOT_SINGLE_CPU=0. However, on CSS platforms like
Juno, bringing up more than one CPU at reset should only be attempted
when booting an EL3 payload, as it is not fully supported in the
normal boot flow.

For platforms using COLD_BOOT_SINGLE_CPU=1, the following 2 platform
APIs become optional:
  - plat_secondary_cold_boot_setup();
  - plat_is_my_cpu_primary().
The Porting Guide has been updated to reflect that.

User Guide updated as well.

Change-Id: Ic5b474e61b7aec1377d1e0b6925d17dfc376c46b