Re: [RFT PATCH v1 2/4] dt-binding: cpu-topology: Move cpu-map to a common binding.

Rob Herring
2018-12-12T02:31:27Z

On Thu, Nov 29, 2018 at 03:28:18PM -0800, Atish Patra wrote:
> cpu-map binding can be used to described cpu topology for both
> RISC-V & ARM. It makes more sense to move the binding to document
> to a common place.
>
> The relevant discussion can be found here.
> https://lkml.org/lkml/2018/11/6/19
>
> Signed-off-by: Atish Patra <atish.patra@wdc.com>
> ---
> .../{arm/topology.txt => cpu/cpu-topology.txt} | 81 ++++++++++++++++++----
> 1 file changed, 67 insertions(+), 14 deletions(-)
> rename Documentation/devicetree/bindings/{arm/topology.txt => cpu/cpu-topology.txt} (86%)
>
> diff --git a/Documentation/devicetree/bindings/arm/topology.txt b/Documentation/devicetree/bindings/cpu/cpu-topology.txt
> similarity index 86%
> rename from Documentation/devicetree/bindings/arm/topology.txt
> rename to Documentation/devicetree/bindings/cpu/cpu-topology.txt
> index 66848355..1de6fbce 100644
> --- a/Documentation/devicetree/bindings/arm/topology.txt
> +++ b/Documentation/devicetree/bindings/cpu/cpu-topology.txt
> @@ -1,12 +1,12 @@
> ===========================================
> -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
> @@ -14,9 +14,6 @@ are used to describe the layout of physical CPUs in the system:
> - 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.
>
> @@ -25,33 +22,37 @@ 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
> +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 remainder of this document provides the topology bindings for ARM/RISC-V, based

You already said who are current users, why restrict it to ARM and
RISC-V here?

> +on the Devicetree Specification, available at [4].
> +
> +The cpu nodes (bindings defined in [1] for ARM or [2] for RISC-V) represent the devices that
> +correspond to physical CPUs and are to be mapped to the hierarchy levels.

The cpu topology isn't dependent on anything beyond what the DT spec
says for cpu nodes so I think this can be simplified to just refer to
the spec.

Plus, shouldn't [2] (numa) be [3] here.

> 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].
> +documented in [1] or [3] for respective ISA.
> 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 [1] or [3] 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.
>
> @@ -494,8 +495,60 @@ cpus {
> };
> };
>
> +Example 3: HiFive Unleashed (RISC-V 64 bit, 4 core system)
> +
> +cpus {
> + #address-cells = <2>;
> + #size-cells = <2>;
> + compatible = "sifive,fu540g", "sifive,fu500";
> + model = "sifive,hifive-unleashed-a00";

This is wrong. Looks like the root node, but called 'cpus'.

> +
> + ...
> +
> + cpu-map {
> + cluster0 {
> + core0 {
> + cpu = <&L12>;
> + };

Mixed space and tabs.

> + core1 {
> + cpu = <&L15>;
> + };
> + core2 {
> + cpu0 = <&L18>;
> + };
> + core3 {
> + cpu0 = <&L21>;
> + };
> + };
> + };

Mixed space and tab.

> +
> + L12: cpu@1 {
> + device_type = "cpu";
> + compatible = "sifive,rocket0", "riscv";
> + reg = <0x1>;
> + }
> +
> + L15: cpu@2 {
> + device_type = "cpu";
> + compatible = "sifive,rocket0", "riscv";
> + reg = <0x2>;
> + }
> + L18: cpu@3 {
> + device_type = "cpu";
> + compatible = "sifive,rocket0", "riscv";
> + reg = <0x3>;
> + }
> + L21: cpu@4 {
> + device_type = "cpu";
> + compatible = "sifive,rocket0", "riscv";
> + reg = <0x4>;
> + }
> +};
> ===============================================================================
> [1] ARM Linux kernel documentation
> Documentation/devicetree/bindings/arm/cpus.txt
> [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/
> --
> 2.7.4
>