=================
ARM CPUs bindings
=================

The device tree allows to describe the layout of CPUs in a system through
the "cpus" node, which in turn contains a number of subnodes (ie "cpu")
defining properties for every cpu.

Bindings for CPU nodes follow the Devicetree Specification, available from:

https://www.devicetree.org/specifications/

with updates for 32-bit and 64-bit ARM systems provided in this document.

================================
Convention used in this document
================================

This document follows the conventions described in the Devicetree
Specification, with the addition:

- square brackets define bitfields, eg reg[7:0] value of the bitfield in
  the reg property contained in bits 7 down to 0

=====================================
cpus and cpu node bindings definition
=====================================

The ARM architecture, in accordance with the Devicetree Specification,
requires the cpus and cpu nodes to be present and contain the properties
described below.

- cpus node

	Description: Container of cpu nodes

	The node name must be "cpus".

	A cpus node must define the following properties:

	- #address-cells
		Usage: required
		Value type: <u32>

		Definition depends on ARM architecture version and
		configuration:

			# On uniprocessor ARM architectures previous to v7
			  value must be 1, to enable a simple enumeration
			  scheme for processors that do not have a HW CPU
			  identification register.
			# On 32-bit ARM 11 MPcore, ARM v7 or later systems
			  value must be 1, that corresponds to CPUID/MPIDR
			  registers sizes.
			# On ARM v8 64-bit systems value should be set to 2,
			  that corresponds to the MPIDR_EL1 register size.
			  If MPIDR_EL1[63:32] value is equal to 0 on all CPUs
			  in the system, #address-cells can be set to 1, since
			  MPIDR_EL1[63:32] bits are not used for CPUs
			  identification.
	- #size-cells
		Usage: required
		Value type: <u32>
		Definition: must be set to 0

- cpu node

	Description: Describes a CPU in an ARM based system

	PROPERTIES

	- device_type
		Usage: required
		Value type: <string>
		Definition: must be "cpu"
	- reg
		Usage and definition depend on ARM architecture version and
		configuration:

			# On uniprocessor ARM architectures previous to v7
			  this property is required and must be set to 0.

			# On ARM 11 MPcore based systems this property is
			  required and matches the CPUID[11:0] register bits.

			  Bits [11:0] in the reg cell must be set to
			  bits [11:0] in CPU ID register.

			  All other bits in the reg cell must be set to 0.

			# On 32-bit ARM v7 or later systems this property is
			  required and matches the CPU MPIDR[23:0] register
			  bits.

			  Bits [23:0] in the reg cell must be set to
			  bits [23:0] in MPIDR.

			  All other bits in the reg cell must be set to 0.

			# On ARM v8 64-bit systems this property is required
			  and matches the MPIDR_EL1 register affinity bits.

			  * If cpus node's #address-cells property is set to 2

			    The first reg cell bits [7:0] must be set to
			    bits [39:32] of MPIDR_EL1.

			    The second reg cell bits [23:0] must be set to
			    bits [23:0] of MPIDR_EL1.

			  * If cpus node's #address-cells property is set to 1

			    The reg cell bits [23:0] must be set to bits [23:0]
			    of MPIDR_EL1.

			  All other bits in the reg cells must be set to 0.

	- compatible:
		Usage: required
		Value type: <string>
		Definition: should be one of:
			    "arm,arm710t"
			    "arm,arm720t"
			    "arm,arm740t"
			    "arm,arm7ej-s"
			    "arm,arm7tdmi"
			    "arm,arm7tdmi-s"
			    "arm,arm9es"
			    "arm,arm9ej-s"
			    "arm,arm920t"
			    "arm,arm922t"
			    "arm,arm925"
			    "arm,arm926e-s"
			    "arm,arm926ej-s"
			    "arm,arm940t"
			    "arm,arm946e-s"
			    "arm,arm966e-s"
			    "arm,arm968e-s"
			    "arm,arm9tdmi"
			    "arm,arm1020e"
			    "arm,arm1020t"
			    "arm,arm1022e"
			    "arm,arm1026ej-s"
			    "arm,arm1136j-s"
			    "arm,arm1136jf-s"
			    "arm,arm1156t2-s"
			    "arm,arm1156t2f-s"
			    "arm,arm1176jzf"
			    "arm,arm1176jz-s"
			    "arm,arm1176jzf-s"
			    "arm,arm11mpcore"
			    "arm,cortex-a5"
			    "arm,cortex-a7"
			    "arm,cortex-a8"
			    "arm,cortex-a9"
			    "arm,cortex-a12"
			    "arm,cortex-a15"
			    "arm,cortex-a17"
			    "arm,cortex-a53"
			    "arm,cortex-a57"
			    "arm,cortex-a72"
			    "arm,cortex-a73"
			    "arm,cortex-m0"
			    "arm,cortex-m0+"
			    "arm,cortex-m1"
			    "arm,cortex-m3"
			    "arm,cortex-m4"
			    "arm,cortex-r4"
			    "arm,cortex-r5"
			    "arm,cortex-r7"
			    "brcm,brahma-b15"
			    "brcm,vulcan"
			    "cavium,thunder"
			    "cavium,thunder2"
			    "faraday,fa526"
			    "intel,sa110"
			    "intel,sa1100"
			    "marvell,feroceon"
			    "marvell,mohawk"
			    "marvell,pj4a"
			    "marvell,pj4b"
			    "marvell,sheeva-v5"
			    "nvidia,tegra132-denver"
			    "nvidia,tegra186-denver"
			    "qcom,krait"
			    "qcom,kryo"
			    "qcom,scorpion"
	- enable-method
		Value type: <stringlist>
		Usage and definition depend on ARM architecture version.
			# On ARM v8 64-bit this property is required and must
			  be one of:
			     "psci"
			     "spin-table"
			# On ARM 32-bit systems this property is optional and
			  can be one of:
			    "actions,s500-smp"
			    "allwinner,sun6i-a31"
			    "allwinner,sun8i-a23"
			    "arm,realview-smp"
			    "brcm,bcm11351-cpu-method"
			    "brcm,bcm23550"
			    "brcm,bcm2836-smp"
			    "brcm,bcm-nsp-smp"
			    "brcm,brahma-b15"
			    "marvell,armada-375-smp"
			    "marvell,armada-380-smp"
			    "marvell,armada-390-smp"
			    "marvell,armada-xp-smp"
			    "marvell,98dx3236-smp"
			    "mediatek,mt6589-smp"
			    "mediatek,mt81xx-tz-smp"
			    "qcom,gcc-msm8660"
			    "qcom,kpss-acc-v1"
			    "qcom,kpss-acc-v2"
			    "renesas,apmu"
			    "rockchip,rk3036-smp"
			    "rockchip,rk3066-smp"
			    "ste,dbx500-smp"

	- cpu-release-addr
		Usage: required for systems that have an "enable-method"
		       property value of "spin-table".
		Value type: <prop-encoded-array>
		Definition:
			# On ARM v8 64-bit systems must be a two cell
			  property identifying a 64-bit zero-initialised
			  memory location.

	- qcom,saw
		Usage: required for systems that have an "enable-method"
		       property value of "qcom,kpss-acc-v1" or
		       "qcom,kpss-acc-v2"
		Value type: <phandle>
		Definition: Specifies the SAW[1] node associated with this CPU.

	- qcom,acc
		Usage: required for systems that have an "enable-method"
		       property value of "qcom,kpss-acc-v1" or
		       "qcom,kpss-acc-v2"
		Value type: <phandle>
		Definition: Specifies the ACC[2] node associated with this CPU.

	- cpu-idle-states
		Usage: Optional
		Value type: <prop-encoded-array>
		Definition:
			# List of phandles to idle state nodes supported
			  by this cpu [3].

	- capacity-dmips-mhz
		Usage: Optional
		Value type: <u32>
		Definition:
			# u32 value representing CPU capacity [4] in
			  DMIPS/MHz, relative to highest capacity-dmips-mhz
			  in the system.

	- rockchip,pmu
		Usage: optional for systems that have an "enable-method"
		       property value of "rockchip,rk3066-smp"
		       While optional, it is the preferred way to get access to
		       the cpu-core power-domains.
		Value type: <phandle>
		Definition: Specifies the syscon node controlling the cpu core
			    power domains.

	- dynamic-power-coefficient
		Usage: optional
		Value type: <prop-encoded-array>
		Definition: A u32 value that represents the running time dynamic
			    power coefficient in units of mW/MHz/uV^2. The
			    coefficient can either be calculated from power
			    measurements or derived by analysis.

			    The dynamic power consumption of the CPU  is
			    proportional to the square of the Voltage (V) and
			    the clock frequency (f). The coefficient is used to
			    calculate the dynamic power as below -

			    Pdyn = dynamic-power-coefficient * V^2 * f

			    where voltage is in uV, frequency is in MHz.

Example 1 (dual-cluster big.LITTLE system 32-bit):

	cpus {
		#size-cells = <0>;
		#address-cells = <1>;

		cpu@0 {
			device_type = "cpu";
			compatible = "arm,cortex-a15";
			reg = <0x0>;
		};

		cpu@1 {
			device_type = "cpu";
			compatible = "arm,cortex-a15";
			reg = <0x1>;
		};

		cpu@100 {
			device_type = "cpu";
			compatible = "arm,cortex-a7";
			reg = <0x100>;
		};

		cpu@101 {
			device_type = "cpu";
			compatible = "arm,cortex-a7";
			reg = <0x101>;
		};
	};

Example 2 (Cortex-A8 uniprocessor 32-bit system):

	cpus {
		#size-cells = <0>;
		#address-cells = <1>;

		cpu@0 {
			device_type = "cpu";
			compatible = "arm,cortex-a8";
			reg = <0x0>;
		};
	};

Example 3 (ARM 926EJ-S uniprocessor 32-bit system):

	cpus {
		#size-cells = <0>;
		#address-cells = <1>;

		cpu@0 {
			device_type = "cpu";
			compatible = "arm,arm926ej-s";
			reg = <0x0>;
		};
	};

Example 4 (ARM Cortex-A57 64-bit system):

cpus {
	#size-cells = <0>;
	#address-cells = <2>;

	cpu@0 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x0>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};

	cpu@1 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x1>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};

	cpu@100 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x100>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};

	cpu@101 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x101>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};

	cpu@10000 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x10000>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};

	cpu@10001 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x10001>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};

	cpu@10100 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x10100>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};

	cpu@10101 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x0 0x10101>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};

	cpu@100000000 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x1 0x0>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};

	cpu@100000001 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x1 0x1>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};

	cpu@100000100 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x1 0x100>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};

	cpu@100000101 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x1 0x101>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};

	cpu@100010000 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x1 0x10000>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};

	cpu@100010001 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x1 0x10001>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};

	cpu@100010100 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x1 0x10100>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};

	cpu@100010101 {
		device_type = "cpu";
		compatible = "arm,cortex-a57";
		reg = <0x1 0x10101>;
		enable-method = "spin-table";
		cpu-release-addr = <0 0x20000000>;
	};
};

--
[1] arm/msm/qcom,saw2.txt
[2] arm/msm/qcom,kpss-acc.txt
[3] ARM Linux kernel documentation - idle states bindings
    Documentation/devicetree/bindings/arm/idle-states.txt
[4] ARM Linux kernel documentation - cpu capacity bindings
    Documentation/devicetree/bindings/arm/cpu-capacity.txt