GitLab

There used to be 2 warm reset entry points:

 - the "on finisher", for when the core has been turned on using a
   PSCI CPU_ON call;

 - the "suspend finisher", entered upon resumption from a previous
   PSCI CPU_SUSPEND call.

The appropriate warm reset entry point used to be programmed into the
mailboxes by the power management hooks.

However, it is not required to provide this information to the PSCI
entry point code, as it can figure it out by itself. By querying affinity
info state, a core is able to determine on which execution path it is.
If the state is ON_PENDING then it means it's been turned on else
it is resuming from suspend.

This patch unifies the 2 warm reset entry points into a single one:
psci_entrypoint(). The patch also implements the necessary logic
to distinguish between the 2 types of warm resets in the power up
finisher.

The plat_setup_psci_ops() API now takes the
secure entry point as an additional parameter to enable the platforms
to configure their mailbox. The platform hooks `pwr_domain_on`
and `pwr_domain_suspend` no longer take secure entry point as
a parameter.

Change-Id: I7d1c93787b54213aefdbc046b8cd66a555dfbfd9

The state-id field in the power-state parameter of a CPU_SUSPEND call can be
used to describe composite power states specific to a platform. The current PSCI
implementation does not interpret the state-id field. It relies on the target
power level and the state type fields in the power-state parameter to perform
state coordination and power management operations. The framework introduced
in this patch allows the PSCI implementation to intepret generic global states
like RUN, RETENTION or OFF from the State-ID to make global state coordination
decisions and reduce the complexity of platform ports. It adds support to
involve the platform in state coordination which facilitates the use of
composite power states and improves the support for entering standby states
at multiple power domains.

The patch also includes support for extended state-id format for the power
state parameter as specified by PSCIv1.0.

The PSCI implementation now defines a generic representation of the power-state
parameter. It depends on the platform port to convert the power-state parameter
(possibly encoding a composite power state) passed in a CPU_SUSPEND call to this
representation via the `validate_power_state()` plat_psci_ops handler. It is an
array where each index corresponds to a power level. Each entry contains the
local power state the power domain at that power level could enter.

The meaning of the local power state values is platform defined, and may vary
between levels in a single platform. The PSCI implementation constrains the
values only so that it can classify the state as RUN, RETENTION or OFF as
required by the specification:
   * zero means RUN
   * all OFF state values at all levels must be higher than all RETENTION
     state values at all levels
   * the platform provides PLAT_MAX_RET_STATE and PLAT_MAX_OFF_STATE values
     to the framework

The platform also must define the macros PLAT_MAX_RET_STATE and
PLAT_MAX_OFF_STATE which lets the PSCI implementation find out which power
domains have been requested to enter a retention or power down state. The PSCI
implementation does not interpret the local power states defined by the
platform. The only constraint is that the PLAT_MAX_RET_STATE <
PLAT_MAX_OFF_STATE.

For a power domain tree, the generic implementation maintains an array of local
power states. These are the states requested for each power domain by all the
cores contained within the domain. During a request to place multiple power
domains in a low power state, the platform is passed an array of requested
power-states for each power domain through the plat_get_target_pwr_state()
API. It coordinates amongst these states to determine a target local power
state for the power domain. A default weak implementation of this API is
provided in the platform layer which returns the minimum of the requested
power-states back to the PSCI state coordination.

Finally, the plat_psci_ops power management handlers are passed the target
local power states for each affected power domain using the generic
representation described above. The platform executes operations specific to
these target states.

The platform power management handler for placing a power domain in a standby
state (plat_pm_ops_t.pwr_domain_standby()) is now only used as a fast path for
placing a core power domain into a standby or retention state should now be
used to only place the core power domain in a standby or retention state.

The extended state-id power state format can be enabled by setting the
build flag PSCI_EXTENDED_STATE_ID=1 and it is disabled by default.

Change-Id: I9d4123d97e179529802c1f589baaa4101759d80c

This patch removes the assumption in the current PSCI implementation that MPIDR
based affinity levels map directly to levels in a power domain tree. This
enables PSCI generic code to support complex power domain topologies as
envisaged by PSCIv1.0 specification. The platform interface for querying
the power domain topology has been changed such that:

1. The generic PSCI code does not generate MPIDRs and use them to query the
   platform about the number of power domains at a particular power level. The
   platform now provides a description of the power domain tree on the SoC
   through a data structure. The existing platform APIs to provide the same
   information have been removed.

2. The linear indices returned by plat_core_pos_by_mpidr() and
   plat_my_core_pos() are used to retrieve core power domain nodes from the
   power domain tree. Power domains above the core level are accessed using a
   'parent' field in the tree node descriptors.

The platform describes the power domain tree in an array of 'unsigned
char's. The first entry in the array specifies the number of power domains at
the highest power level implemented in the system. Each susbsequent entry
corresponds to a power domain and contains the number of power domains that are
its direct children. This array is exported to the generic PSCI implementation
via the new `plat_get_power_domain_tree_desc()` platform API.

The PSCI generic code uses this array to populate its internal power domain tree
using the Breadth First Search like algorithm. The tree is split into two
arrays:

1. An array that contains all the core power domain nodes

2. An array that contains all the other power domain nodes

A separate array for core nodes allows certain core specific optimisations to
be implemented e.g. remove the bakery lock, re-use per-cpu data framework for
storing some information.

Entries in the core power domain array are allocated such that the
array index of the domain is equal to the linear index returned by
plat_core_pos_by_mpidr() and plat_my_core_pos() for the MPIDR
corresponding to that domain. This relationship is key to be able to use
an MPIDR to find the corresponding core power domain node, traverse to higher
power domain nodes and index into arrays that contain core specific
information.

An introductory document has been added to briefly describe the new interface.

Change-Id: I4b444719e8e927ba391cae48a23558308447da13

This patch introduces new platform APIs and context management helper APIs
to support the new topology framework based on linear core position. This
framework will be introduced in the follwoing patch and it removes the
assumption that the MPIDR based affinity levels map directly to levels
in a power domain tree. The new platforms APIs and context management
helpers based on core position are as described below:

* plat_my_core_pos() and plat_core_pos_by_mpidr()

These 2 new mandatory platform APIs are meant to replace the existing
'platform_get_core_pos()' API. The 'plat_my_core_pos()' API returns the
linear index of the calling core and 'plat_core_pos_by_mpidr()' returns
the linear index of a core specified by its MPIDR. The latter API will also
validate the MPIDR passed as an argument and will return an error code (-1)
if an invalid MPIDR is passed as the argument. This enables the caller to
safely convert an MPIDR of another core to its linear index without querying
the PSCI topology tree e.g. during a call to PSCI CPU_ON.

Since the 'plat_core_pos_by_mpidr()' API verifies an MPIDR, which is always
platform specific, it is no longer possible to maintain a default implementation
of this API. Also it might not be possible for a platform port to verify an
MPIDR before the C runtime has been setup or the topology has been initialized.
This would prevent 'plat_core_pos_by_mpidr()' from being callable prior to
topology setup. As a result, the generic Trusted Firmware code does not call
this API before the topology setup has been done.

The 'plat_my_core_pos' API should be able to run without a C runtime.
Since this API needs to return a core position which is equal to the one
returned by 'plat_core_pos_by_mpidr()' API for the corresponding MPIDR,
this too cannot have default implementation and is a mandatory API for
platform ports. These APIs will be implemented by the ARM reference platform
ports later in the patch stack.

* plat_get_my_stack() and plat_set_my_stack()

These APIs are the stack management APIs which set/return stack addresses
appropriate for the calling core. These replace the 'platform_get_stack()' and
'platform_set_stack()' APIs. A default weak MP version and a global UP version
of these APIs are provided for the platforms.

* Context management helpers based on linear core position

A set of new context management(CM) helpers viz cm_get_context_by_index(),
cm_set_context_by_index(), cm_init_my_context() and cm_init_context_by_index()
are defined which are meant to replace the old helpers which took MPIDR
as argument. The old CM helpers are implemented based on the new helpers to
allow for code consolidation and will be deprecated once the switch to the new
framework is done.

Change-Id: I89758632b370c2812973a4b2efdd9b81a41f9b69

As per Section 4.2.2. in the PSCI specification, the term "affinity"
is used in the context of describing the hierarchical arrangement
of cores. This often, but not always, maps directly to the processor
power domain topology of the system. The current PSCI implementation
assumes that this is always the case i.e. MPIDR based levels of
affinity always map to levels in a power domain topology tree.

This patch is the first in a series of patches which remove this
assumption. It removes all occurences of the terms "affinity
instances and levels" when used to describe the power domain
topology. Only the terminology is changed in this patch. Subsequent
patches will implement functional changes to remove the above
mentioned assumption.

Change-Id: Iee162f051b228828310610c5a320ff9d31009b4e

This patch optimizes the invocation of the platform power management hooks for
ON, OFF and SUSPEND such that they are called only for the highest affinity
level which will be powered off/on. Earlier, the hooks were being invoked for
all the intermediate levels as well.

This patch requires that the platforms migrate to the new semantics of the PM
hooks.  It also removes the `state` parameter from the pm hooks as the `afflvl`
parameter now indicates the highest affinity level for which power management
operations are required.

Change-Id: I57c87931d8a2723aeade14acc710e5b78ac41732

This patch creates a copy of the existing PSCI files and related psci.h and
platform.h header files in a new `PSCI1.0` directory. The changes for the
new PSCI power domain topology and extended state-ID frameworks will be
added incrementally to these files. This incremental approach will
aid in review and in understanding the changes better. Once all the
changes have been introduced, these files will replace the existing PSCI
files.

Change-Id: Ibb8a52e265daa4204e34829ed050bddd7e3316ff

This patch adds support for SYSTEM_SUSPEND API as mentioned in the PSCI 1.0
specification. This API, on being invoked on the last running core on a
supported platform, will put the system into a low power mode with memory
retention.

The psci_afflvl_suspend() internal API has been reused as most of the actions
to suspend a system are the same as invoking the PSCI CPU_SUSPEND API with the
target affinity level as 'system'. This API needs the 'power state' parameter
for the target low power state. This parameter is not passed by the caller of
the SYSTEM_SUSPEND API. Hence, the platform needs to implement the
get_sys_suspend_power_state() platform function to provide this information.
Also, the platform also needs to add support for suspending the system to the
existing 'plat_pm_ops' functions: affinst_suspend() and
affinst_suspend_finish().

Change-Id: Ib6bf10809cb4e9b92f463755608889aedd83cef5

This patch removes the plat_get_max_afflvl() platform API
and instead replaces it with a platform macro PLATFORM_MAX_AFFLVL.
This is done because the maximum affinity level for a platform
is a static value and it is more efficient for it to be defined
as a platform macro.

NOTE: PLATFORM PORTS NEED TO BE UPDATED ON MERGE OF THIS COMMIT

Fixes ARM-Software/tf-issues#265

Change-Id: I31d89b30c2ccda30d28271154d869060d50df7bf

This patch implements the PSCI_FEATURES function which is a mandatory
API in the PSCI 1.0 specification. A capability variable is
constructed during initialization by examining the plat_pm_ops and
spd_pm_ops exported by the platform and the Secure Payload Dispatcher.
This is used by the PSCI FEATURES function to determine which
PSCI APIs are supported by the platform.

Change-Id: I147ffc1bd5d90b469bd3cc4bbe0a20e95c247df7

This patch extends the build option `USE_COHERENT_MEMORY` to
conditionally remove coherent memory from the memory maps of
all boot loader stages. The patch also adds necessary
documentation for coherent memory removal in firmware-design,
porting and user guides.

Fixes ARM-Software/tf-issues#106

Change-Id: I260e8768c6a5c2efc402f5804a80657d8ce38773

This patch moves the bakery locks out of coherent memory to normal memory.
This implies that the lock information needs to be placed on a separate cache
line for each cpu. Hence the bakery_lock_info_t structure is allocated in the
per-cpu data so as to minimize memory wastage. A similar platform per-cpu
data is introduced for the platform locks.

As a result of the above changes, the bakery lock api is completely changed.
Earlier, a reference to the lock structure was passed to the lock implementation.
Now a unique-id (essentially an index into the per-cpu data array) and an offset
into the per-cpu data for bakery_info_t needs to be passed to the lock
implementation.

Change-Id: I1e76216277448713c6c98b4c2de4fb54198b39e0

This patch fixes a crash due to corruption of cpu_ops
data structure. During the secondary CPU boot, after the
cpu_ops has been initialized in the per cpu-data, the
dcache lines need to invalidated so that the update in
memory can be seen later on when the dcaches are turned ON.
Also, after initializing the psci per cpu data, the dcache
lines are flushed so that they are written back to memory
and dirty dcache lines are avoided.

Fixes ARM-Software/tf-issues#271

Change-Id: Ia90f55e9882690ead61226eea5a5a9146d35f313

This patch fixes the assertion failure when CPU_SUSPEND is invoked with
an affinity level higher than supported by the platform by adding suitable
checks for affinity level within `psci_cpu_suspend`. Also added suitable
bound checks within `psci_aff_map_get_idx` to prevent indexing beyond array
limits.

Fixes ARM-software/tf-issues#260

Change-Id: I04b75c49729e6c6d1983add590f60146c8fc3630

This patch implements the following cleanups in PSCI generic code:

1. It reworks the affinity level specific handlers in the PSCI implementation
   such that.

   a. Usage of the 'rc' local variable is restricted to only where it is
      absolutely needed

   b. 'plat_state' local variable is defined only when a direct invocation of
      plat_get_phys_state() does not suffice.

   c. If a platform handler is not registered then the level specific handler
      returns early.

2. It limits the use of the mpidr_aff_map_nodes_t typedef to declaration of
   arrays of the type instead of using it in function prototypes as well.

3. It removes dangling declarations of __psci_cpu_off() and
   __psci_cpu_suspend(). The definitions of these functions were removed in
   earlier patches.

Change-Id: I51e851967c148be9c2eeda3a3c41878f7b4d6978

This patch adds APIs to find, save and retrieve the highest affinity level which
will enter or exit from the physical OFF state during a PSCI power management
operation. The level is stored in per-cpu data.

It then reworks the PSCI implementation to perform cache maintenance only
when the handler for the highest affinity level to enter/exit the OFF state is
called.

For example. during a CPU_SUSPEND operation, state management is done prior to
calling the affinity level specific handlers. The highest affinity level which
will be turned off is determined using the psci_find_max_phys_off_afflvl()
API. This level is saved using the psci_set_max_phys_off_afflvl() API. In the
code that does generic handling for each level, prior to performing cache
maintenance it is first determined if the current affinity level matches the
value returned by psci_get_max_phys_off_afflvl(). Cache maintenance is done if
the values match.

This change allows the last CPU in a cluster to perform cache maintenance
independently. Earlier, cache maintenance was started in the level 0 handler and
finished in the level 1 handler. This change in approach will facilitate
implementation of tf-issues#98.

Change-Id: I57233f0a27b3ddd6ddca6deb6a88b234525b0ae6

This patch adds a structure defined by the PSCI service to the per-CPU data
array. The structure is used to save the 'power_state' parameter specified
during a 'cpu_suspend' call on the current CPU. This parameter was being saved
in the cpu node in the PSCI topology tree earlier.

The existing API to return the state id specified during a PSCI CPU_SUSPEND call
i.e. psci_get_suspend_stateid(mpidr) has been renamed to
psci_get_suspend_stateid_by_mpidr(mpidr). The new psci_get_suspend_stateid() API
returns the state id of the current cpu.

The psci_get_suspend_afflvl() API has been changed to return the target affinity
level of the current CPU. This was specified using the 'mpidr' parameter in the
old implementation.

The behaviour of the get_power_on_target_afflvl() has been tweaked such that
traversal of the PSCI topology tree to locate the affinity instance node for the
current CPU is done only in the debug build as it is an expensive operation.

Change-Id: Iaad49db75abda471f6a82d697ee6e0df554c4caf

psci_suspend_context is an array of cache-line aligned structures
containing the single power_state integer per cpu. This array is
the only structure indexed by the aff_map_node.data integer.

This patch saves 2KB of BL3-1 memory by placing the CPU
power_state value directly in the aff_map_node structure. As a
result, this value is now never cached and the cache clean when
writing the value is no longer required.

Fixes ARM-software/tf-issues#195

Change-Id: Ib4c70c8f79eed295ea541e7827977a588a19ef9b

Consolidate all BL3-1 CPU context initialization for cold boot, PSCI
and SPDs into two functions:
*  The first uses entry_point_info to initialize the relevant
   cpu_context for first entry into a lower exception level on a CPU
*  The second populates the EL1 and EL2 system registers as needed
   from the cpu_context to ensure correct entry into the lower EL

This patch alters the way that BL3-1 determines which exception level
is used when first entering EL1 or EL2 during cold boot - this is now
fully determined by the SPSR value in the entry_point_info for BL3-3,
as set up by the platform code in BL2 (or otherwise provided to BL3-1).

In the situation that EL1 (or svc mode) is selected for a processor
that supports EL2, the context management code will now configure all
essential EL2 register state to ensure correct execution of EL1. This
allows the platform code to run non-secure EL1 payloads directly
without requiring a small EL2 stub or OS loader.

Change-Id: If9fbb2417e82d2226e47568203d5a369f39d3b0f

All callers of cm_get_context() pass the calling CPU MPIDR to the
function. Providing a specialised version for the current
CPU results in a reduction in code size and better readability.

The current function has been renamed to cm_get_context_by_mpidr()
and the existing name is now used for the current-CPU version.

The same treatment has been done to cm_set_context(), although
only both forms are used at present in the PSCI and TSPD code.

Change-Id: I91cb0c2f7bfcb950a045dbd9ff7595751c0c0ffb

Some data variables were declared but not used. These have been
removed.

Change-Id: I038632af3c32d88984cd25b886c43ff763269bf9

This patch implements the register reporting when unhandled exceptions are
taken in BL3-1. Unhandled exceptions will result in a dump of registers
to the console, before halting execution by that CPU. The Crash Stack,
previously called the Exception Stack, is used for this activity.
This stack is used to preserve the CPU context and runtime stack
contents for debugging and analysis.

This also introduces the per_cpu_ptr_cache, referenced by tpidr_el3,
to provide easy access to some of BL3-1 per-cpu data structures.
Initially, this is used to provide a pointer to the Crash stack.

panic() now prints the the error file and line number in Debug mode
and prints the PC value in release mode.

The Exception Stack is renamed to Crash Stack with this patch.
The original intention of exception stack is no longer valid
since we intend to support several valid exceptions like IRQ
and FIQ in the trusted firmware context. This stack is now
utilized for dumping and reporting the system state when a
crash happens and hence the rename.

Fixes ARM-software/tf-issues#79 Improve reporting of unhandled exception

Change-Id: I260791dc05536b78547412d147193cdccae7811a

Reduce the number of header files included from other header
files as much as possible without splitting the files. Use forward
declarations where possible. This allows removal of some unnecessary
"#ifndef __ASSEMBLY__" statements.

Also, review the .c and .S files for which header files really need
including and reorder the #include statements alphabetically.

Fixes ARM-software/tf-issues#31

Change-Id: Iec92fb976334c77453e010b60bcf56f3be72bd3e

Add tag names to all unnamed structs in header files. This
allows forward declaration of structs, which is necessary to
reduce header file nesting (to be implemented in a subsequent
commit).

Also change the typedef names across the codebase to use the _t
suffix to be more conformant with the Linux coding style. The
coding style actually prefers us not to use typedefs at all but
this is considered a step too far for Trusted Firmware.

Also change the IO framework structs defintions to use typedef'd
structs to be consistent with the rest of the codebase.

Change-Id: I722b2c86fc0d92e4da3b15e5cab20373dd26786f

Make codebase consistent in its use of #include "" syntax for
user includes and #include <> syntax for system includes.

Fixes ARM-software/tf-issues#65

Change-Id: If2f7c4885173b1fd05ac2cde5f1c8a07000c7a33

This patch saves the 'power_state' parameter prior to suspending
a cpu and invalidates it upon its resumption. The 'affinity level'
and 'state id' fields of this parameter can be read using a set of
public and private apis. Validation of power state parameter is
introduced which checks for SBZ bits are zero.
This change also takes care of flushing the parameter from the cache
to main memory. This ensures that it is available after cpu reset
when the caches and mmu are turned off. The earlier support for
saving only the 'affinity level' field of the 'power_state' parameter
has also been reworked.

Fixes ARM-Software/tf-issues#26
Fixes ARM-Software/tf-issues#130

Change-Id: Ic007ccb5e39bf01e0b67390565d3b4be33f5960a

This patch implements ARM Standard Service as a runtime service and adds
support for call count, UID and revision information SMCs. The existing
PSCI implementation is subsumed by the Standard Service calls and all
PSCI calls are therefore dispatched by the Standard Service to the PSCI
handler.

At present, PSCI is the only specification under Standard Service. Thus
call count returns the number of PSCI calls implemented. As this is the
initial implementation, a revision number of 0.1 is returned for call
revision.

Fixes ARM-software/tf-issues#62

Change-Id: I6d4273f72ad6502636efa0f872e288b191a64bc1

This patch creates a 'services' directory and moves the PSCI under
it. Other runtime services e.g. the Secure Payload Dispatcher service
will be placed under the same directory in the future.

Also fixes issue ARM-software/tf-issues#12

Change-Id: I187f83dcb660b728f82155d91882e961d2255068

This patch uses the reworked exception handling support to handle
runtime service requests through SMCs following the SMC calling
convention. This is a giant commit since all the changes are
inter-related. It does the following:

1. Replace the old exception handling mechanism with the new one
2. Enforce that SP_EL0 is used C runtime stacks.
3. Ensures that the cold and warm boot paths use the 'cpu_context'
   structure to program an ERET into the next lower EL.
4. Ensures that SP_EL3 always points to the next 'cpu_context'
   structure prior to an ERET into the next lower EL
5. Introduces a PSCI SMC handler which completes the use of PSCI as a
   runtime service

Change-Id: I661797f834c0803d2c674d20f504df1b04c2b852
Co-authored-by: Achin Gupta <achin.gupta@arm.com>

This patch introduces the framework to enable registration and
initialisation of runtime services. PSCI is registered and initialised
as a runtime service. Handling of runtime service requests will be
implemented in subsequent patches.

Change-Id: Id21e7ddc5a33d42b7d6e455b41155fc5441a9547

This patch uses the context library to save and restore EL3 state on
the 'cpu_context' data structures allocated by PSCI for managing
non-secure state context on each cpu.

Change-Id: I19c1f26578204a7cd9e0a6c582ced0d97ee4cf80

Also fix warnings generated in release builds when assert code
is absent.

Change-Id: I45b9173d3888f9e93e98eb5b4fdc06727ba5cbf4

The psci implementation does not track target affinity level requests
specified during cpu_suspend calls correctly as per the following
example.

1. cpu0.cluster0 calls cpu_suspend with the target affinity level as 0
2. Only the cpu0.cluster0 is powered down while cluster0 remains
   powered up
3. cpu1.cluster0 calls cpu_off to power itself down to highest
   possible affinity level
4. cluster0 will be powered off even though cpu0.cluster0 does not
   allow cluster shutdown

This patch introduces reference counts at affinity levels > 0 to track
the number of cpus which want an affinity instance at level X to
remain powered up. This instance can be turned off only if its
reference count is 0. Cpus still undergo the normal state transitions
(ON, OFF, ON_PENDING, SUSPEND) but the higher levels can only be
either ON or OFF depending upon their reference count.

The above issue is thus fixed as follows:

1. cluster0's reference count is incremented by two when cpu0 and cpu1
   are initially powered on.

2. cpu0.cluster0 calls cpu_suspend with the target affinity level as
   0. This does not affect the cluster0 reference count.

3. Only the cpu0.cluster0 is powered down while cluster0 remains
   powered up as it has a non-zero reference count.

4. cpu1.cluster0 call cpu_off to power itself down to highest possible
   affinity level. This decrements the cluster0 reference count.

5. cluster0 is still not powered off since its reference count will at
   least be 1 due to the restriction placed by cpu0.

Change-Id: I433dfe82b946f5f6985b1602c2de87800504f7a9

Change-Id: Ic7fb61aabae1d515b9e6baf3dd003807ff42da60

This patch performs a major rework of the psci generic implementation
to achieve the following:

1. replace recursion with iteration where possible to aid code
   readability e.g. affinity instance states are changed iteratively
   instead of recursively.

2. acquire pointers to affinity instance nodes at the beginning of a
   psci operation. All subsequent actions use these pointers instead
   of calling psci_get_aff_map_node() repeatedly e.g. management of
   locks has been abstracted under functions which use these pointers
   to ensure correct ordering. Helper functions have been added to
   create these abstractions.

3. assertions have been added to cpu level handlers to ensure correct
   state transition

4. the affinity level extents specified to various functions have the
   same meaning i.e. start level is always less than the end level.

Change-Id: If0508c3a7b20ea3ddda2a66128429382afc3dfc8

- Add instructions for contributing to ARM Trusted Firmware.

- Update copyright text in all files to acknowledge contributors.

Change-Id: I9311aac81b00c6c167d2f8c889aea403b84450e5