PSCI: Add pwr_domain_pwr_down_wfi() hook in plat_psci_ops
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
diff --git a/docs/porting-guide.md b/docs/porting-guide.md
index 0cd3613..8947def 100644
--- a/docs/porting-guide.md
+++ b/docs/porting-guide.md
@@ -1715,6 +1715,22 @@
resume execution by restoring this state when its powered on (see
`pwr_domain_suspend_finish()`).
+#### plat_psci_ops.pwr_domain_pwr_down_wfi()
+
+This is an optional function and, if implemented, is expected to perform
+platform specific actions including the `wfi` invocation which allows the
+CPU to powerdown. Since this function is invoked outside the PSCI locks,
+the actions performed in this hook must be local to the CPU or the platform
+must ensure that races between multiple CPUs cannot occur.
+
+The `target_state` has a similar meaning as described in the `pwr_domain_off()`
+operation and it encodes the platform coordinated target local power states for
+the CPU power domain and its parent power domain levels. This function must
+not return back to the caller.
+
+If this function is not implemented by the platform, PSCI generic
+implementation invokes `psci_power_down_wfi()` for power down.
+
#### plat_psci_ops.pwr_domain_on_finish()
This function is called by the PSCI implementation after the calling CPU is