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

Atish Patra
2018-12-12T18:23:29Z

On 12/11/18 6:31 PM, Rob Herring wrote:
> 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?
>
I will remove that. The examples are only for ARM/RISC-V specific.

>> +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.
>

ok sure.

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

My bad.

>> 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'.
>
Yeah it got mixed up. I will fix it in v2.

>> +
>> + ...
>> +
>> + cpu-map {
>> + cluster0 {
>> + core0 {
>> + cpu = <&L12>;
>> + };
>
> Mixed space and tabs.
>
>> + core1 {
>> + cpu = <&L15>;
>> + };
>> + core2 {
>> + cpu0 = <&L18>;
>> + };
>> + core3 {
>> + cpu0 = <&L21>;
>> + };
>> + };
>> + };
>
> Mixed space and tab.
>

Sorry. I will fix this.

Thanks for the review.

Regards,
Atish

>> +
>> + 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
>>
>