Re: [RFC PATCH 7/8] dt-bindings: Add bindings documentation for RISC-V idle states

[Rob Herring <robh@kernel.org>]

On Sun, Feb 21, 2021 at 03:07:57PM +0530, Anup Patel wrote:
> The RISC-V CPU idle states will be described in DT under the
> /cpus/riscv-idle-states DT node. This patch adds the bindings
> documentation for riscv-idle-states DT nodes and idle state DT
> nodes under it.
> 
> Signed-off-by: Anup Patel <anup.patel@wdc.com>
> ---
>  .../bindings/riscv/idle-states.yaml           | 250 ++++++++++++++++++
>  1 file changed, 250 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/riscv/idle-states.yaml
> 
> diff --git a/Documentation/devicetree/bindings/riscv/idle-states.yaml b/Documentation/devicetree/bindings/riscv/idle-states.yaml
> new file mode 100644
> index 000000000000..3eff763fed23
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/riscv/idle-states.yaml
> @@ -0,0 +1,250 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/riscv/idle-states.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: RISC-V idle states binding description
> +
> +maintainers:
> +  - Anup Patel <anup.patel@wdc.com>
> +
> +description: |+
> +  RISC-V systems can manage power consumption dynamically, where HARTs
> +  (or CPUs) [1] can be put in different platform specific suspend (or
> +  idle) states (ranging from simple WFI, power gating, etc). The RISC-V
> +  SBI [2] hart state management extension provides a standard mechanism
> +  for OSes to request HART state transitions.
> +
> +  The platform specific suspend (or idle) states of a hart can be either
> +  retentive or non-rententive in nature. A retentive suspend state will
> +  preserve hart register and CSR values for all privilege modes whereas
> +  a non-retentive suspend state will not preserve hart register and CSR
> +  values. The suspend (or idle) state entered by executing the WFI
> +  instruction is considered standard on all RISC-V systems and therefore
> +  must not be listed in device tree.
> +
> +  The device tree binding definition for RISC-V idle states described
> +  in this document is quite similar to the ARM idle states [3].
> +
> +  References
> +
> +  [1] RISC-V Linux Kernel documentation - CPUs bindings
> +      Documentation/devicetree/bindings/riscv/cpus.yaml
> +
> +  [2] RISC-V Supervisor Binary Interface (SBI)
> +      http://github.com/riscv/riscv-sbi-doc/riscv-sbi.adoc
> +
> +  [3] ARM idle states binding description - Idle states bindings
> +      Documentation/devicetree/bindings/arm/idle-states.yaml

I'd assume there's common parts we can share.

> +
> +properties:
> +  $nodename:
> +    const: riscv-idle-states

Just 'idle-states' like Arm.

> +
> +patternProperties:
> +  "^(cpu|cluster)-":
> +    type: object
> +    description: |
> +      Each state node represents an idle state description and must be
> +      defined as follows.
> +

       additionalProperties: false

> +    properties:
> +      compatible:
> +        const: riscv,idle-state
> +
> +      local-timer-stop:
> +        description:
> +          If present the CPU local timer control logic is lost on state
> +          entry, otherwise it is retained.
> +        type: boolean
> +
> +      entry-latency-us:
> +        description:
> +          Worst case latency in microseconds required to enter the idle state.
> +
> +      exit-latency-us:
> +        description:
> +          Worst case latency in microseconds required to exit the idle state.
> +          The exit-latency-us duration may be guaranteed only after
> +          entry-latency-us has passed.
> +
> +      min-residency-us:
> +        description:
> +          Minimum residency duration in microseconds, inclusive of preparation
> +          and entry, for this idle state to be considered worthwhile energy
> +          wise (refer to section 2 of this document for a complete description).
> +
> +      wakeup-latency-us:
> +        description: |
> +          Maximum delay between the signaling of a wake-up event and the CPU
> +          being able to execute normal code again. If omitted, this is assumed
> +          to be equal to:
> +
> +            entry-latency-us + exit-latency-us
> +
> +          It is important to supply this value on systems where the duration
> +          of PREP phase (see diagram 1, section 2) is non-neglibigle. In such
> +          systems entry-latency-us + exit-latency-us will exceed
> +          wakeup-latency-us by this duration.
> +
> +      idle-state-name:
> +        $ref: /schemas/types.yaml#/definitions/string
> +        description:
> +          A string used as a descriptive name for the idle state.
> +
> +    required:
> +      - compatible
> +      - entry-latency-us
> +      - exit-latency-us
> +      - min-residency-us
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +
> +    cpus {
> +        #size-cells = <0>;
> +        #address-cells = <1>;
> +
> +        cpu@0 {
> +            device_type = "cpu";
> +            compatible = "riscv";
> +            reg = <0x0>;
> +            riscv,isa = "rv64imafdc";
> +            mmu-type = "riscv,sv48";
> +            cpu-idle-states = <&CPU_RET_0_0 &CPU_NONRET_0_0
> +                            &CLUSTER_RET_0 &CLUSTER_NONRET_0>;

You should need to add this property to your cpu schema.

> +
> +            cpu_intc0: interrupt-controller {
> +                #interrupt-cells = <1>;
> +                compatible = "riscv,cpu-intc";
> +                interrupt-controller;
> +            };
> +        };
> +
> +        cpu@1 {
> +            device_type = "cpu";
> +            compatible = "riscv";
> +            reg = <0x1>;
> +            riscv,isa = "rv64imafdc";
> +            mmu-type = "riscv,sv48";
> +            cpu-idle-states = <&CPU_RET_0_0 &CPU_NONRET_0_0
> +                            &CLUSTER_RET_0 &CLUSTER_NONRET_0>;
> +
> +            cpu_intc1: interrupt-controller {
> +                #interrupt-cells = <1>;
> +                compatible = "riscv,cpu-intc";
> +                interrupt-controller;
> +            };
> +        };
> +
> +        cpu@10 {
> +            device_type = "cpu";
> +            compatible = "riscv";
> +            reg = <0x10>;
> +            riscv,isa = "rv64imafdc";
> +            mmu-type = "riscv,sv48";
> +            cpu-idle-states = <&CPU_RET_1_0 &CPU_NONRET_1_0
> +                            &CLUSTER_RET_1 &CLUSTER_NONRET_1>;
> +
> +            cpu_intc10: interrupt-controller {
> +                #interrupt-cells = <1>;
> +                compatible = "riscv,cpu-intc";
> +                interrupt-controller;
> +            };
> +        };
> +
> +        cpu@11 {
> +            device_type = "cpu";
> +            compatible = "riscv";
> +            reg = <0x11>;
> +            riscv,isa = "rv64imafdc";
> +            mmu-type = "riscv,sv48";
> +            cpu-idle-states = <&CPU_RET_1_0 &CPU_NONRET_1_0
> +                            &CLUSTER_RET_1 &CLUSTER_NONRET_1>;
> +
> +            cpu_intc11: interrupt-controller {
> +                #interrupt-cells = <1>;
> +                compatible = "riscv,cpu-intc";
> +                interrupt-controller;
> +            };
> +        };
> +
> +        riscv-idle-states {
> +            CPU_RET_0_0: cpu-retentive-0-0 {
> +                compatible = "riscv,idle-state";
> +                riscv,sbi-suspend-param = <0x10000000>;

Not documented.

> +                entry-latency-us = <20>;
> +                exit-latency-us = <40>;
> +                min-residency-us = <80>;
> +            };
> +
> +            CPU_NONRET_0_0: cpu-nonretentive-0-0 {
> +                compatible = "riscv,idle-state";
> +                riscv,sbi-suspend-param = <0x90000000>;
> +                entry-latency-us = <250>;
> +                exit-latency-us = <500>;
> +                min-residency-us = <950>;
> +            };
> +
> +            CLUSTER_RET_0: cluster-retentive-0 {
> +                compatible = "riscv,idle-state";
> +                riscv,sbi-suspend-param = <0x11000000>;
> +                local-timer-stop;
> +                entry-latency-us = <50>;
> +                exit-latency-us = <100>;
> +                min-residency-us = <250>;
> +                wakeup-latency-us = <130>;
> +            };
> +
> +            CLUSTER_NONRET_0: cluster-nonretentive-0 {
> +                compatible = "riscv,idle-state";
> +                riscv,sbi-suspend-param = <0x91000000>;
> +                local-timer-stop;
> +                entry-latency-us = <600>;
> +                exit-latency-us = <1100>;
> +                min-residency-us = <2700>;
> +                wakeup-latency-us = <1500>;
> +            };
> +
> +            CPU_RET_1_0: cpu-retentive-1-0 {
> +                compatible = "riscv,idle-state";
> +                riscv,sbi-suspend-param = <0x10000010>;
> +                entry-latency-us = <20>;
> +                exit-latency-us = <40>;
> +                min-residency-us = <80>;
> +            };
> +
> +            CPU_NONRET_1_0: cpu-nonretentive-1-0 {
> +                compatible = "riscv,idle-state";
> +                riscv,sbi-suspend-param = <0x90000010>;
> +                entry-latency-us = <250>;
> +                exit-latency-us = <500>;
> +                min-residency-us = <950>;
> +            };
> +
> +            CLUSTER_RET_1: cluster-retentive-1 {
> +                compatible = "riscv,idle-state";
> +                riscv,sbi-suspend-param = <0x11000010>;
> +                local-timer-stop;
> +                entry-latency-us = <50>;
> +                exit-latency-us = <100>;
> +                min-residency-us = <250>;
> +                wakeup-latency-us = <130>;
> +            };
> +
> +            CLUSTER_NONRET_1: cluster-nonretentive-1 {
> +                compatible = "riscv,idle-state";
> +                riscv,sbi-suspend-param = <0x91000010>;
> +                local-timer-stop;
> +                entry-latency-us = <600>;
> +                exit-latency-us = <1100>;
> +                min-residency-us = <2700>;
> +                wakeup-latency-us = <1500>;
> +            };
> +        };
> +    };
> +
> +...
> -- 
> 2.25.1
>