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diff --git a/Documentation/devicetree/bindings/arm/topology.txt b/Documentation/devicetree/bindings/arm/topology.txt new file mode 100644 index 000000000..de9eb0486 --- /dev/null +++ b/Documentation/devicetree/bindings/arm/topology.txt @@ -0,0 +1,475 @@ +=========================================== +ARM topology binding description +=========================================== + +=========================================== +1 - Introduction +=========================================== + +In an ARM system, the hierarchy of CPUs is defined through three entities that +are used to describe the layout of physical CPUs in the system: + +- cluster +- core +- thread + +The cpu nodes (bindings defined in [1]) represent the devices that +correspond to physical CPUs and are to be mapped to the hierarchy levels. + +The bottom hierarchy level sits at core or thread level depending on whether +symmetric multi-threading (SMT) is supported or not. + +For instance in a system where CPUs support SMT, "cpu" nodes represent all +threads existing in the system and map to the hierarchy level "thread" above. +In systems where SMT is not supported "cpu" nodes represent all cores present +in the system and map to the hierarchy level "core" above. + +ARM topology bindings allow one to associate cpu nodes with hierarchical groups +corresponding to the system hierarchy; syntactically they are defined as device +tree nodes. + +The remainder of this document provides the topology bindings for ARM, based +on the Devicetree Specification, available from: + +https://www.devicetree.org/specifications/ + +If not stated otherwise, whenever a reference to a cpu node phandle is made its +value must point to a cpu node compliant with the cpu node bindings as +documented in [1]. +A topology description containing phandles to cpu nodes that are not compliant +with bindings standardized in [1] is therefore considered invalid. + +=========================================== +2 - cpu-map node +=========================================== + +The ARM CPU topology is defined within the cpu-map node, which is a direct +child of the cpus node and provides a container where the actual topology +nodes are listed. + +- cpu-map node + + Usage: Optional - On ARM SMP systems provide CPUs topology to the OS. + ARM uniprocessor systems do not require a topology + description and therefore should not define a + cpu-map node. + + Description: The cpu-map node is just a container node where its + subnodes describe the CPU topology. + + Node name must be "cpu-map". + + The cpu-map node's parent node must be the cpus node. + + The cpu-map node's child nodes can be: + + - one or more cluster nodes + + Any other configuration is considered invalid. + +The cpu-map node can only contain three types of child nodes: + +- cluster node +- core node +- thread node + +whose bindings are described in paragraph 3. + +The nodes describing the CPU topology (cluster/core/thread) can only +be defined within the cpu-map node and every core/thread in the system +must be defined within the topology. Any other configuration is +invalid and therefore must be ignored. + +=========================================== +2.1 - cpu-map child nodes naming convention +=========================================== + +cpu-map child nodes must follow a naming convention where the node name +must be "clusterN", "coreN", "threadN" depending on the node type (ie +cluster/core/thread) (where N = {0, 1, ...} is the node number; nodes which +are siblings within a single common parent node must be given a unique and +sequential N value, starting from 0). +cpu-map child nodes which do not share a common parent node can have the same +name (ie same number N as other cpu-map child nodes at different device tree +levels) since name uniqueness will be guaranteed by the device tree hierarchy. + +=========================================== +3 - cluster/core/thread node bindings +=========================================== + +Bindings for cluster/cpu/thread nodes are defined as follows: + +- cluster node + + Description: must be declared within a cpu-map node, one node + per cluster. A system can contain several layers of + clustering and cluster nodes can be contained in parent + cluster nodes. + + The cluster node name must be "clusterN" as described in 2.1 above. + A cluster node can not be a leaf node. + + A cluster node's child nodes must be: + + - one or more cluster nodes; or + - one or more core nodes + + Any other configuration is considered invalid. + +- core node + + Description: must be declared in a cluster node, one node per core in + the cluster. If the system does not support SMT, core + nodes are leaf nodes, otherwise they become containers of + thread nodes. + + The core node name must be "coreN" as described in 2.1 above. + + A core node must be a leaf node if SMT is not supported. + + Properties for core nodes that are leaf nodes: + + - cpu + Usage: required + Value type: <phandle> + Definition: a phandle to the cpu node that corresponds to the + core node. + + If a core node is not a leaf node (CPUs supporting SMT) a core node's + child nodes can be: + + - one or more thread nodes + + Any other configuration is considered invalid. + +- thread node + + Description: must be declared in a core node, one node per thread + in the core if the system supports SMT. Thread nodes are + always leaf nodes in the device tree. + + The thread node name must be "threadN" as described in 2.1 above. + + A thread node must be a leaf node. + + A thread node must contain the following property: + + - cpu + Usage: required + Value type: <phandle> + Definition: a phandle to the cpu node that corresponds to + the thread node. + +=========================================== +4 - Example dts +=========================================== + +Example 1 (ARM 64-bit, 16-cpu system, two clusters of clusters): + +cpus { + #size-cells = <0>; + #address-cells = <2>; + + cpu-map { + cluster0 { + cluster0 { + core0 { + thread0 { + cpu = <&CPU0>; + }; + thread1 { + cpu = <&CPU1>; + }; + }; + + core1 { + thread0 { + cpu = <&CPU2>; + }; + thread1 { + cpu = <&CPU3>; + }; + }; + }; + + cluster1 { + core0 { + thread0 { + cpu = <&CPU4>; + }; + thread1 { + cpu = <&CPU5>; + }; + }; + + core1 { + thread0 { + cpu = <&CPU6>; + }; + thread1 { + cpu = <&CPU7>; + }; + }; + }; + }; + + cluster1 { + cluster0 { + core0 { + thread0 { + cpu = <&CPU8>; + }; + thread1 { + cpu = <&CPU9>; + }; + }; + core1 { + thread0 { + cpu = <&CPU10>; + }; + thread1 { + cpu = <&CPU11>; + }; + }; + }; + + cluster1 { + core0 { + thread0 { + cpu = <&CPU12>; + }; + thread1 { + cpu = <&CPU13>; + }; + }; + core1 { + thread0 { + cpu = <&CPU14>; + }; + thread1 { + cpu = <&CPU15>; + }; + }; + }; + }; + }; + + CPU0: cpu@0 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x0 0x0>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; + + CPU1: cpu@1 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x0 0x1>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; + + CPU2: cpu@100 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x0 0x100>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; + + CPU3: cpu@101 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x0 0x101>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; + + CPU4: cpu@10000 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x0 0x10000>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; + + CPU5: cpu@10001 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x0 0x10001>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; + + CPU6: cpu@10100 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x0 0x10100>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; + + CPU7: cpu@10101 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x0 0x10101>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; + + CPU8: cpu@100000000 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x1 0x0>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; + + CPU9: cpu@100000001 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x1 0x1>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; + + CPU10: cpu@100000100 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x1 0x100>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; + + CPU11: cpu@100000101 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x1 0x101>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; + + CPU12: cpu@100010000 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x1 0x10000>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; + + CPU13: cpu@100010001 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x1 0x10001>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; + + CPU14: cpu@100010100 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x1 0x10100>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; + + CPU15: cpu@100010101 { + device_type = "cpu"; + compatible = "arm,cortex-a57"; + reg = <0x1 0x10101>; + enable-method = "spin-table"; + cpu-release-addr = <0 0x20000000>; + }; +}; + +Example 2 (ARM 32-bit, dual-cluster, 8-cpu system, no SMT): + +cpus { + #size-cells = <0>; + #address-cells = <1>; + + cpu-map { + cluster0 { + core0 { + cpu = <&CPU0>; + }; + core1 { + cpu = <&CPU1>; + }; + core2 { + cpu = <&CPU2>; + }; + core3 { + cpu = <&CPU3>; + }; + }; + + cluster1 { + core0 { + cpu = <&CPU4>; + }; + core1 { + cpu = <&CPU5>; + }; + core2 { + cpu = <&CPU6>; + }; + core3 { + cpu = <&CPU7>; + }; + }; + }; + + CPU0: cpu@0 { + device_type = "cpu"; + compatible = "arm,cortex-a15"; + reg = <0x0>; + }; + + CPU1: cpu@1 { + device_type = "cpu"; + compatible = "arm,cortex-a15"; + reg = <0x1>; + }; + + CPU2: cpu@2 { + device_type = "cpu"; + compatible = "arm,cortex-a15"; + reg = <0x2>; + }; + + CPU3: cpu@3 { + device_type = "cpu"; + compatible = "arm,cortex-a15"; + reg = <0x3>; + }; + + CPU4: cpu@100 { + device_type = "cpu"; + compatible = "arm,cortex-a7"; + reg = <0x100>; + }; + + CPU5: cpu@101 { + device_type = "cpu"; + compatible = "arm,cortex-a7"; + reg = <0x101>; + }; + + CPU6: cpu@102 { + device_type = "cpu"; + compatible = "arm,cortex-a7"; + reg = <0x102>; + }; + + CPU7: cpu@103 { + device_type = "cpu"; + compatible = "arm,cortex-a7"; + reg = <0x103>; + }; +}; + +=============================================================================== +[1] ARM Linux kernel documentation + Documentation/devicetree/bindings/arm/cpus.txt |