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GICv3: Document GICv3 save/restore helpers 

Give hints on how to use the GICv3 save/restore helpers in the
implementation of the PSCI handlers.

Change-Id: I86de1c27417b64c7ce290974964ef97ff678f676
Signed-off-by: Douglas Raillard <douglas.raillard@arm.com>
This commit is contained in:
Douglas Raillard 2017-08-02 16:57:32 +01:00 committed by Soby Mathew
parent b258278eec
commit c5229f8c0d
1 changed files with 28 additions and 5 deletions
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33
docs/porting-guide.rst
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@ -2107,13 +2107,32 @@ power domain levels. The handler needs to perform power management operation
corresponding to the local state at each power level. The generic code
expects the handler to succeed.
The difference between turning a power domain off versus suspending it
is that in the former case, the power domain is expected to re-initialize
its state when it is next powered on (see ``pwr_domain_on_finish()``). In the
latter case, the power domain is expected to save enough state so that it can
resume execution by restoring this state when its powered on (see
The difference between turning a power domain off versus suspending it is that
in the former case, the power domain is expected to re-initialize its state
when it is next powered on (see ``pwr_domain_on_finish()``). In the latter
case, the power domain is expected to save enough state so that it can resume
execution by restoring this state when its powered on (see
``pwr_domain_suspend_finish()``).
When suspending a core, the platform can also choose to power off the GICv3
Redistributor and ITS through an implementation-defined sequence. To achieve
this safely, the ITS context must be saved first. The architectural part is
implemented by the ``gicv3_its_save_disable()`` helper, but most of the needed
sequence is implementation defined and it is therefore the responsibility of
the platform code to implement the necessary sequence. Then the GIC
Redistributor context can be saved using the ``gicv3_rdistif_save()`` helper.
Powering off the Redistributor requires the implementation to support it and it
is the responsibility of the platform code to execute the right implementation
defined sequence.
When a system suspend is requested, the platform can also make use of the
``gicv3_distif_save()`` helper to save the context of the GIC Distributor after
it has saved the context of the Redistributors and ITS of all the cores in the
system. The context of the Distributor can be large and may require it to be
allocated in a special area if it cannot fit in the platform's global static
data, for example in DRAM. The Distributor can then be powered down using an
implementation-defined sequence.
plat\_psci\_ops.pwr\_domain\_pwr\_down\_wfi()
.............................................
@ -2159,6 +2178,10 @@ The ``target_state`` (first argument) has a similar meaning as described in
the ``pwr_domain_on_finish()`` operation. The generic code expects the platform
to succeed.
If the Distributor, Redistributors or ITS have been powered off as part of a
suspend, their context must be restored in this function in the reverse order
to how they were saved during suspend sequence.
plat\_psci\_ops.system\_off()
.............................