Enable PSCI_STAT_COUNT/RESIDENCY for ARM standard platforms

This patch enables optional PSCI functions `PSCI_STAT_COUNT` and
`PSCI_STAT_RESIDENCY` for ARM standard platforms. The optional platform
API 'translate_power_state_by_mpidr()' is implemented for the Juno
platform. 'validate_power_state()' on Juno downgrades PSCI CPU_SUSPEND
requests for the system power level to the cluster power level.
Hence, it is not suitable for validating the 'power_state' parameter
passed in a PSCI_STAT_COUNT/RESIDENCY call.

Change-Id: I9548322676fa468d22912392f2325c2a9f96e4d2

plat/arm/board/juno/juno_pm.c

@@ -59,6 +59,19 @@ static int juno_validate_power_state(unsigned int power_state,
 	return rc;
 }
 
+/*
+ * Custom `translate_power_state_by_mpidr` handler for Juno. Unlike in the
+ * `juno_validate_power_state`, we do not down-grade the system power
+ * domain level request in `power_state` as it will be used to query the
+ * PSCI_STAT_COUNT/RESIDENCY at the system power domain level.
+ */
+static int juno_translate_power_state_by_mpidr(u_register_t mpidr,
+		unsigned int power_state,
+		psci_power_state_t *output_state)
+{
+	return arm_validate_power_state(power_state, output_state);
+}
+
 /*******************************************************************************
  * Export the platform handlers via plat_arm_psci_pm_ops. The ARM Standard
  * platform will take care of registering the handlers with PSCI.
@@ -74,5 +87,6 @@ const plat_psci_ops_t plat_arm_psci_pm_ops = {
 	.system_reset			= css_system_reset,
 	.validate_power_state		= juno_validate_power_state,
 	.validate_ns_entrypoint		= arm_validate_ns_entrypoint,
-	.get_sys_suspend_power_state	= css_get_sys_suspend_power_state
+	.get_sys_suspend_power_state	= css_get_sys_suspend_power_state,
+	.translate_power_state_by_mpidr = juno_translate_power_state_by_mpidr
 };

plat/arm/common/arm_common.mk

@@ -82,6 +82,9 @@ ARM_BL31_IN_DRAM		:=	0
 $(eval $(call assert_boolean,ARM_BL31_IN_DRAM))
 $(eval $(call add_define,ARM_BL31_IN_DRAM))
 
+# Enable PSCI_STAT_COUNT/RESIDENCY APIs on ARM platforms
+ENABLE_PSCI_STAT = 1
+
 PLAT_INCLUDES		+=	-Iinclude/common/tbbr				\
 				-Iinclude/plat/arm/common			\
 				-Iinclude/plat/arm/common/aarch64