===========================================
-ARM topology binding description
+CPU topology binding description
===========================================
===========================================
1 - Introduction
===========================================
-In an ARM system, the hierarchy of CPUs is defined through three entities that
+In a SMP system, the hierarchy of CPUs is defined through three entities that
are used to describe the layout of physical CPUs in the system:
- socket
- 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.
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
+CPU 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:
+Currently, only ARM/RISC-V intend to use this cpu topology binding but it may be
+used for any other architecture as well.
-https://www.devicetree.org/specifications/
+The cpu nodes, as per bindings defined in [4], represent the devices that
+correspond to physical CPUs and are to be mapped to the hierarchy levels.
-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.
+with bindings standardized in [4] is therefore considered invalid.
===========================================
2 - cpu-map node
===========================================
-The ARM CPU topology is defined within the cpu-map node, which is a direct
+The ARM/RISC-V 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
+ Usage: Optional - On SMP systems provide CPUs topology to the OS.
+ Uniprocessor systems do not require a topology
description and therefore should not define a
cpu-map node.
};
};
+Example 3: HiFive Unleashed (RISC-V 64 bit, 4 core system)
+
+{
+ #address-cells = <2>;
+ #size-cells = <2>;
+ compatible = "sifive,fu540g", "sifive,fu500";
+ model = "sifive,hifive-unleashed-a00";
+
+ ...
+ cpus {
+ #address-cells = <1>;
+ #size-cells = <0>;
+ cpu-map {
+ socket0 {
+ cluster0 {
+ core0 {
+ cpu = <&CPU1>;
+ };
+ core1 {
+ cpu = <&CPU2>;
+ };
+ core2 {
+ cpu0 = <&CPU2>;
+ };
+ core3 {
+ cpu0 = <&CPU3>;
+ };
+ };
+ };
+ };
+
+ CPU1: cpu@1 {
+ device_type = "cpu";
+ compatible = "sifive,rocket0", "riscv";
+ reg = <0x1>;
+ }
+
+ CPU2: cpu@2 {
+ device_type = "cpu";
+ compatible = "sifive,rocket0", "riscv";
+ reg = <0x2>;
+ }
+ CPU3: cpu@3 {
+ device_type = "cpu";
+ compatible = "sifive,rocket0", "riscv";
+ reg = <0x3>;
+ }
+ CPU4: cpu@4 {
+ device_type = "cpu";
+ compatible = "sifive,rocket0", "riscv";
+ reg = <0x4>;
+ }
+ }
+};
===============================================================================
[1] ARM Linux kernel documentation
Documentation/devicetree/bindings/arm/cpus.yaml
[2] Devicetree NUMA binding description
Documentation/devicetree/bindings/numa.txt
+[3] RISC-V Linux kernel documentation
+ Documentation/devicetree/bindings/riscv/cpus.txt
+[4] https://www.devicetree.org/specifications/