diff --git a/docs/porting-guide.rst b/docs/porting-guide.rst
index 4d4cdcd..bf8dea7 100644
--- a/docs/porting-guide.rst
+++ b/docs/porting-guide.rst
@@ -2060,6 +2060,23 @@
 for the higher power domain levels depending on the result of state
 coordination. The generic code expects the handler to succeed.
 
+plat\_psci\_ops.pwr\_domain\_suspend\_pwrdown\_early() [optional]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This optional function may be used as a performance optimization to replace
+or complement pwr_domain_suspend() on some platforms. Its calling semantics
+are identical to pwr_domain_suspend(), except the PSCI implementation only
+calls this function when suspending to a power down state, and it guarantees
+that data caches are enabled.
+
+When HW_ASSISTED_COHERENCY = 0, the PSCI implementation disables data caches
+before calling pwr_domain_suspend(). If the target_state corresponds to a
+power down state and it is safe to perform some or all of the platform
+specific actions in that function with data caches enabled, it may be more
+efficient to move those actions to this function. When HW_ASSISTED_COHERENCY
+= 1, data caches remain enabled throughout, and so there is no advantage to
+moving platform specific actions to this function.
+
 plat\_psci\_ops.pwr\_domain\_suspend()
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~