476 lines
10 KiB
Plaintext
476 lines
10 KiB
Plaintext
===========================================
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ARM topology binding description
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===========================================
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===========================================
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1 - Introduction
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===========================================
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In an ARM system, the hierarchy of CPUs is defined through three entities that
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are used to describe the layout of physical CPUs in the system:
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- cluster
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- core
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- thread
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The cpu nodes (bindings defined in [1]) represent the devices that
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correspond to physical CPUs and are to be mapped to the hierarchy levels.
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The bottom hierarchy level sits at core or thread level depending on whether
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symmetric multi-threading (SMT) is supported or not.
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For instance in a system where CPUs support SMT, "cpu" nodes represent all
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threads existing in the system and map to the hierarchy level "thread" above.
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In systems where SMT is not supported "cpu" nodes represent all cores present
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in the system and map to the hierarchy level "core" above.
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ARM topology bindings allow one to associate cpu nodes with hierarchical groups
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corresponding to the system hierarchy; syntactically they are defined as device
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tree nodes.
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The remainder of this document provides the topology bindings for ARM, based
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on the Devicetree Specification, available from:
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https://www.devicetree.org/specifications/
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If not stated otherwise, whenever a reference to a cpu node phandle is made its
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value must point to a cpu node compliant with the cpu node bindings as
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documented in [1].
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A topology description containing phandles to cpu nodes that are not compliant
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with bindings standardized in [1] is therefore considered invalid.
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===========================================
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2 - cpu-map node
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===========================================
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The ARM CPU topology is defined within the cpu-map node, which is a direct
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child of the cpus node and provides a container where the actual topology
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nodes are listed.
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- cpu-map node
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Usage: Optional - On ARM SMP systems provide CPUs topology to the OS.
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ARM uniprocessor systems do not require a topology
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description and therefore should not define a
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cpu-map node.
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Description: The cpu-map node is just a container node where its
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subnodes describe the CPU topology.
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Node name must be "cpu-map".
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The cpu-map node's parent node must be the cpus node.
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The cpu-map node's child nodes can be:
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- one or more cluster nodes
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Any other configuration is considered invalid.
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The cpu-map node can only contain three types of child nodes:
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- cluster node
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- core node
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- thread node
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whose bindings are described in paragraph 3.
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The nodes describing the CPU topology (cluster/core/thread) can only
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be defined within the cpu-map node and every core/thread in the system
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must be defined within the topology. Any other configuration is
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invalid and therefore must be ignored.
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===========================================
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2.1 - cpu-map child nodes naming convention
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===========================================
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cpu-map child nodes must follow a naming convention where the node name
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must be "clusterN", "coreN", "threadN" depending on the node type (ie
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cluster/core/thread) (where N = {0, 1, ...} is the node number; nodes which
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are siblings within a single common parent node must be given a unique and
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sequential N value, starting from 0).
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cpu-map child nodes which do not share a common parent node can have the same
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name (ie same number N as other cpu-map child nodes at different device tree
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levels) since name uniqueness will be guaranteed by the device tree hierarchy.
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===========================================
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3 - cluster/core/thread node bindings
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===========================================
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Bindings for cluster/cpu/thread nodes are defined as follows:
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- cluster node
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Description: must be declared within a cpu-map node, one node
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per cluster. A system can contain several layers of
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clustering and cluster nodes can be contained in parent
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cluster nodes.
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The cluster node name must be "clusterN" as described in 2.1 above.
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A cluster node can not be a leaf node.
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A cluster node's child nodes must be:
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- one or more cluster nodes; or
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- one or more core nodes
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Any other configuration is considered invalid.
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- core node
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Description: must be declared in a cluster node, one node per core in
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the cluster. If the system does not support SMT, core
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nodes are leaf nodes, otherwise they become containers of
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thread nodes.
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The core node name must be "coreN" as described in 2.1 above.
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A core node must be a leaf node if SMT is not supported.
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Properties for core nodes that are leaf nodes:
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- cpu
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Usage: required
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Value type: <phandle>
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Definition: a phandle to the cpu node that corresponds to the
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core node.
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If a core node is not a leaf node (CPUs supporting SMT) a core node's
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child nodes can be:
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- one or more thread nodes
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Any other configuration is considered invalid.
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- thread node
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Description: must be declared in a core node, one node per thread
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in the core if the system supports SMT. Thread nodes are
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always leaf nodes in the device tree.
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The thread node name must be "threadN" as described in 2.1 above.
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A thread node must be a leaf node.
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A thread node must contain the following property:
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- cpu
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Usage: required
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Value type: <phandle>
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Definition: a phandle to the cpu node that corresponds to
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the thread node.
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===========================================
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4 - Example dts
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===========================================
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Example 1 (ARM 64-bit, 16-cpu system, two clusters of clusters):
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cpus {
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#size-cells = <0>;
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#address-cells = <2>;
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cpu-map {
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cluster0 {
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cluster0 {
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core0 {
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thread0 {
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cpu = <&CPU0>;
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};
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thread1 {
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cpu = <&CPU1>;
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};
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};
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core1 {
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thread0 {
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cpu = <&CPU2>;
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};
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thread1 {
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cpu = <&CPU3>;
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};
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};
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};
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cluster1 {
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core0 {
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thread0 {
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cpu = <&CPU4>;
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};
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thread1 {
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cpu = <&CPU5>;
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};
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};
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core1 {
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thread0 {
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cpu = <&CPU6>;
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};
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thread1 {
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cpu = <&CPU7>;
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};
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};
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};
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};
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cluster1 {
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cluster0 {
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core0 {
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thread0 {
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cpu = <&CPU8>;
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};
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thread1 {
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cpu = <&CPU9>;
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};
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};
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core1 {
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thread0 {
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cpu = <&CPU10>;
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};
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thread1 {
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cpu = <&CPU11>;
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};
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};
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};
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cluster1 {
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core0 {
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thread0 {
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cpu = <&CPU12>;
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};
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thread1 {
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cpu = <&CPU13>;
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};
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};
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core1 {
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thread0 {
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cpu = <&CPU14>;
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};
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thread1 {
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cpu = <&CPU15>;
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};
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};
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};
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};
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};
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CPU0: cpu@0 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x0 0x0>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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CPU1: cpu@1 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x0 0x1>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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CPU2: cpu@100 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x0 0x100>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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CPU3: cpu@101 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x0 0x101>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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CPU4: cpu@10000 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x0 0x10000>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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CPU5: cpu@10001 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x0 0x10001>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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CPU6: cpu@10100 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x0 0x10100>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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CPU7: cpu@10101 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x0 0x10101>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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CPU8: cpu@100000000 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x1 0x0>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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CPU9: cpu@100000001 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x1 0x1>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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CPU10: cpu@100000100 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x1 0x100>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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CPU11: cpu@100000101 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x1 0x101>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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CPU12: cpu@100010000 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x1 0x10000>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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CPU13: cpu@100010001 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x1 0x10001>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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CPU14: cpu@100010100 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x1 0x10100>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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CPU15: cpu@100010101 {
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device_type = "cpu";
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compatible = "arm,cortex-a57";
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reg = <0x1 0x10101>;
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enable-method = "spin-table";
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cpu-release-addr = <0 0x20000000>;
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};
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};
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Example 2 (ARM 32-bit, dual-cluster, 8-cpu system, no SMT):
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cpus {
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#size-cells = <0>;
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#address-cells = <1>;
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cpu-map {
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cluster0 {
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core0 {
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cpu = <&CPU0>;
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};
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core1 {
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cpu = <&CPU1>;
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};
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core2 {
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cpu = <&CPU2>;
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};
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core3 {
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cpu = <&CPU3>;
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};
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};
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cluster1 {
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core0 {
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cpu = <&CPU4>;
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};
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core1 {
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cpu = <&CPU5>;
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};
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core2 {
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cpu = <&CPU6>;
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};
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core3 {
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cpu = <&CPU7>;
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};
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};
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};
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CPU0: cpu@0 {
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device_type = "cpu";
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compatible = "arm,cortex-a15";
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reg = <0x0>;
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};
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CPU1: cpu@1 {
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device_type = "cpu";
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compatible = "arm,cortex-a15";
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reg = <0x1>;
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};
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CPU2: cpu@2 {
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device_type = "cpu";
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compatible = "arm,cortex-a15";
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reg = <0x2>;
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};
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CPU3: cpu@3 {
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device_type = "cpu";
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compatible = "arm,cortex-a15";
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reg = <0x3>;
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};
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CPU4: cpu@100 {
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device_type = "cpu";
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compatible = "arm,cortex-a7";
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reg = <0x100>;
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};
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CPU5: cpu@101 {
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device_type = "cpu";
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compatible = "arm,cortex-a7";
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reg = <0x101>;
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};
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CPU6: cpu@102 {
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device_type = "cpu";
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compatible = "arm,cortex-a7";
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reg = <0x102>;
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};
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CPU7: cpu@103 {
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device_type = "cpu";
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compatible = "arm,cortex-a7";
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reg = <0x103>;
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};
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};
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===============================================================================
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[1] ARM Linux kernel documentation
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Documentation/devicetree/bindings/arm/cpus.txt
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