bindings: Add snapshot of dt bindings for arm-cache

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ARM processors cache binding description

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Device tree bindings for ARM processor caches adhere to the cache bindings

described in [3], in section 3.8 for multi-level and shared caches.

On ARM based systems most of the cache properties related to cache

geometry are probeable in HW, hence, unless otherwise stated, the properties

defined in ePAPR for multi-level and shared caches are to be considered

optional by default.

On ARM, caches are either architected (directly controlled by the processor

through coprocessor instructions and tightly coupled with the processor

implementation) or unarchitected (controlled through a memory mapped

interface, implemented as a stand-alone IP external to the processor

implementation).

This document provides the device tree bindings for ARM architected caches.

- ARM architected cache node

	Description: must be a direct child of the cpu node. A system

		     can contain multiple architected cache nodes per cpu node,

		     linked through the next-level-cache phandle. The

		     next-level-cache property in the cpu node points to

		     the first level of architected cache for the CPU.

		     The next-level-cache property in architected cache nodes

		     points to the respective next level of caching in the

		     hierarchy. An architected cache node with an empty or

		     missing next-level-cache property represents the last

		     architected cache level for the CPU.

		     On ARM v7 and v8 architectures, the order in which cache

		     nodes are linked through the next-level-cache phandle must

		     follow the ordering specified in the processors CLIDR (v7)

		     and CLIDR_EL1 (v8) registers, as described in [1][2],

		     implying that a cache node pointed at by a

		     next-level-cache phandle must correspond to a level

		     defined in CLIDR (v7) and CLIDR_EL1 (v8) greater than the

		     one the cache node containing the next-level-cache

		     phandle corresponds to.

	Since on ARM most of the cache properties are probeable in HW the

	properties described in [3] - section 3.8 multi-level and shared

	caches - shall be considered optional, with the following properties

	updates, specific for the ARM architected cache node.

	- compatible

		Usage: Required

		Value type: <string>

		Definition: value shall be "arm,arch-cache".

	- interrupts

		Usage: Optional

		Value type: See definition

		Definition: standard device tree property [3] that defines

			    the interrupt line associated with the cache.

			    The property can be accompanied by an

			    interrupt-names property, as described in [4].

	- power-domain

		Usage: Optional

		Value type: phandle

		Definition: A phandle and power domain specifier as defined by

			    bindings of power controller specified by the

			    phandle [5].

	- qcom,dump-size

		Usage: Optional

		Value type: <integer>

		Definition: The memory size needed to contain a copy of the

			    cache data and associated tag ram.

			    size = nways * nsets * (bytes per cache line +

			                            bytes tag ram per line)

Example(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>;

			next-level-cache = <&L1_0>;

			L1_0: l1-cache {

				compatible = "arm,arch-cache";

				next-level-cache = <&L2_0>;

			};

			L2_0: l2-cache {

				compatible = "arm,arch-cache";

			};

		};

		cpu@1 {

			device_type = "cpu";

			compatible = "arm,cortex-a15";

			reg = <0x1>;

			next-level-cache = <&L1_1>;

			L1_1: l1-cache {

				compatible = "arm,arch-cache";

				next-level-cache = <&L2_0>;

			};

		};

		cpu@2 {

			device_type = "cpu";

			compatible = "arm,cortex-a15";

			reg = <0x2>;

			next-level-cache = <&L1_2>;

			L1_2: l1-cache {

				compatible = "arm,arch-cache";

				next-level-cache = <&L2_0>;

			};

		};

		cpu@3 {

			device_type = "cpu";

			compatible = "arm,cortex-a15";

			reg = <0x3>;

			next-level-cache = <&L1_3>;

			L1_3: l1-cache {

				compatible = "arm,arch-cache";

				next-level-cache = <&L2_0>;

			};

		};

		cpu@100 {

			device_type = "cpu";

			compatible = "arm,cortex-a7";

			reg = <0x100>;

			next-level-cache = <&L1_4>;

			L1_4: l1-cache {

				compatible = "arm,arch-cache";

				next-level-cache = <&L2_1>;

			};

			L2_1: l2-cache {

				compatible = "arm,arch-cache";

			};

		};

		cpu@101 {

			device_type = "cpu";

			compatible = "arm,cortex-a7";

			reg = <0x101>;

			next-level-cache = <&L1_5>;

			L1_5: l1-cache {

				compatible = "arm,arch-cache";

				next-level-cache = <&L2_1>;

			};

		};

		cpu@102 {

			device_type = "cpu";

			compatible = "arm,cortex-a7";

			reg = <0x102>;

			next-level-cache = <&L1_6>;

			L1_6: l1-cache {

				compatible = "arm,arch-cache";

				next-level-cache = <&L2_1>;

			};

		};

		cpu@103 {

			device_type = "cpu";

			compatible = "arm,cortex-a7";

			reg = <0x103>;

			next-level-cache = <&L1_7>;

			L1_7: l1-cache {

				compatible = "arm,arch-cache";

				next-level-cache = <&L2_1>;

			};

		};

	};

[1] ARMv7-AR Reference Manual

    http://infocenter.arm.com/help/index.jsp

[2] ARMv8-A Reference Manual

    http://infocenter.arm.com/help/index.jsp

[3] ePAPR standard

    https://www.power.org/documentation/epapr-version-1-1/

[4] Kernel documentation - resource property bindings

    Documentation/devicetree/bindings/resource-names.txt

[5] Kernel documentation - power domain bindings

    Documentation/devicetree/bindings/power/power_domain.txt