powercap: arm_scmi: Add SCMI Powercap based driver

Add a powercap driver that, using the ARM SCMI Protocol to query the SCMI
platform firmware for the list of existing Powercap domains, registers all
of such discovered domains under the new 'arm-scmi' powercap control type.

A new simple powercap zone and constraint is registered for all the SCMI
powercap zones that are found.

Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

MAINTAINERS

@@ -19977,6 +19977,7 @@ F:	drivers/clk/clk-sc[mp]i.c
 F:	drivers/cpufreq/sc[mp]i-cpufreq.c
 F:	drivers/firmware/arm_scmi/
 F:	drivers/firmware/arm_scpi.c
+F:	drivers/powercap/arm_scmi_powercap.c
 F:	drivers/regulator/scmi-regulator.c
 F:	drivers/reset/reset-scmi.c
 F:	include/linux/sc[mp]i_protocol.h

drivers/powercap/Kconfig

@@ -44,6 +44,19 @@ config IDLE_INJECT
 	  synchronously on a set of specified CPUs or alternatively
 	  on a per CPU basis.
 
+config ARM_SCMI_POWERCAP
+	tristate "ARM SCMI Powercap driver"
+	depends on ARM_SCMI_PROTOCOL
+	help
+	  This enables support for the ARM Powercap based on ARM SCMI
+	  Powercap protocol.
+
+	  ARM SCMI Powercap protocol allows power limits to be enforced
+	  and monitored against the SCMI Powercap domains advertised as
+	  available by the SCMI platform firmware.
+
+	  When compiled as module it will be called arm_scmi_powercap.ko.
+
 config DTPM
 	bool "Power capping for Dynamic Thermal Power Management (EXPERIMENTAL)"
 	depends on OF

drivers/powercap/Makefile

@@ -6,3 +6,4 @@ obj-$(CONFIG_POWERCAP)	+= powercap_sys.o
 obj-$(CONFIG_INTEL_RAPL_CORE) += intel_rapl_common.o
 obj-$(CONFIG_INTEL_RAPL) += intel_rapl_msr.o
 obj-$(CONFIG_IDLE_INJECT) += idle_inject.o
+obj-$(CONFIG_ARM_SCMI_POWERCAP) += arm_scmi_powercap.o