linux-kernel - Re: [PATCH V5 18/30] dt-bindings: csky CPU Bindings

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Date:   Thu, 27 Sep 2018 11:43:17 -0500
From:   Rob Herring <robh@...nel.org>
To:     Guo Ren <ren_guo@...ky.com>
Cc:     akpm@...ux-foundation.org, arnd@...db.de,
        daniel.lezcano@...aro.org, davem@...emloft.net,
        gregkh@...uxfoundation.org, jason@...edaemon.net,
        marc.zyngier@....com, mark.rutland@....com,
        mchehab+samsung@...nel.org, peterz@...radead.org,
        tglx@...utronix.de, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, devicetree@...r.kernel.org,
        green.hu@...il.com, palmer@...ive.com
Subject: Re: [PATCH V5 18/30] dt-bindings: csky CPU Bindings

On Tue, Sep 25, 2018 at 07:39:21AM +0800, Guo Ren wrote:
> This patch adds the documentation to describe that how to add cpu nodes in
> dts for SMP.
> 
> Signed-off-by: Guo Ren <ren_guo@...ky.com>
> ---
>  Documentation/devicetree/bindings/csky/cpus.txt | 70 +++++++++++++++++++++++++
>  1 file changed, 70 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/csky/cpus.txt
> 
> diff --git a/Documentation/devicetree/bindings/csky/cpus.txt b/Documentation/devicetree/bindings/csky/cpus.txt
> new file mode 100644
> index 0000000..ee3901d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/csky/cpus.txt
> @@ -0,0 +1,70 @@
> +==================
> +C-SKY CPU Bindings
> +==================
> +
> +The device tree allows to describe the layout of CPUs in a system through
> +the "cpus" node, which in turn contains a number of subnodes (ie "cpu")
> +defining properties for every cpu.
> +
> +Only SMP system need to care about the cpus node and single processor
> +needn't define cpus node at all.

We've generally found this is not true. Even for single core, you can 
have power domains, clocks for DVFS, etc.

> +
> +=====================================
> +cpus and cpu node bindings definition
> +=====================================
> +
> +- cpus node
> +
> +        Description: Container of cpu nodes
> +
> +        The node name must be "cpus".
> +
> +        A cpus node must define the following properties:
> +
> +        - #address-cells
> +                Usage: required
> +                Value type: <u32>
> +                Definition: must be set to 1
> +        - #size-cells
> +                Usage: required
> +                Value type: <u32>
> +                Definition: must be set to 0
> +
> +- cpu node
> +
> +        Description: Describes one of SMP cores
> +
> +        PROPERTIES
> +

You need a compatible property for cpu nodes.

> +        - device_type
> +                Usage: required
> +                Value type: <string>
> +                Definition: must be "cpu"
> +        - reg
> +                Usage: required
> +                Value type: <u32>
> +                Definition: CPU index
> +        - status:

You don't need to document status here.

> +                Usage: required
> +                Value type: <string>
> +                Definition: "ok"       means enable  the cpu-core
> +                            "disabled" means disable the cpu-core
> +
> +Example:
> +--------
> +
> +	cpus {
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +		cpu@0 {
> +			device_type = "cpu";
> +			reg = <0>;
> +			status = "ok";
> +		};
> +
> +		cpu@1 {
> +			device_type = "cpu";
> +			reg = <1>;
> +			status = "ok";
> +		};
> +	};
> -- 
> 2.7.4
>