Re: [PATCH v3 1/5] dt-bindings: Powerzone new bindings

Ulf Hansson
2021-12-02T14:42:52Z

On Wed, 1 Dec 2021 at 17:41, Daniel Lezcano <daniel.lezcano@linaro.org> wrote:
>
> The proposed bindings are describing a set of powerzones.
>
> A power zone is the logical name for a component which is capable of
> power capping and where we can measure the power consumption.
>
> A power zone can aggregate several power zones in terms of power
> measurement and power limitations. That allows to apply power
> constraint to a group of components and let the system balance the
> allocated power in order to comply with the constraint.
>
> The ARM System Control and Management Interface (SCMI) can provide a
> power zone description.
>
> The powerzone semantic is also found on the Intel platform with the
> RAPL register.
>
> The Linux kernel powercap framework deals with the powerzones:
>
> https://www.kernel.org/doc/html/latest/power/powercap/powercap.html
>
> The powerzone can also represent a group of children powerzones, hence
> the description can result on a hierarchy. Such hierarchy already
> exists with the hardware or can be represented and computed from the
> kernel.
>
> The hierarchical description was initially proposed but not desired
> given there are other descriptions like the power domain proposing
> almost the same description.
>
> https://lore.kernel.org/all/CAL_JsqLuLcHj7525tTUmh7pLqe7T2j6UcznyhV7joS8ipyb_VQ@mail.gmail.com/
>
> The description gives the power constraint dependencies to apply on a
> specific group of logically or physically aggregated devices. They do
> not represent the physical location or the power domains of the SoC
> even if the description could be similar.
>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Ulf Hansson <ulf.hansson@linaro.org>
> Cc: Rob Herring <robh+dt@kernel.org>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

This looks good to me, feel free to add:

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>

Kind regards
Uffe

> ---
> V3:
> - Removed required property 'compatible'
> - Removed powerzone-cells from the topmost node
> - Removed powerzone-cells from cpus 'consumers' in example
> - Set additionnal property to false
> V2:
> - Added pattern properties and stick to powerzone-*
> - Added required property compatible and powerzone-cells
> - Added additionnal property
> - Added compatible
> - Renamed to 'powerzones'
> - Added missing powerzone-cells to the topmost node
> - Fixed errors reported by 'make DT_CHECKER_FLAGS=-m dt_binding_check'
> V1: Initial post
> ---
> .../devicetree/bindings/power/powerzones.yaml | 97 +++++++++++++++++++
> 1 file changed, 97 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/power/powerzones.yaml
>
> diff --git a/Documentation/devicetree/bindings/power/powerzones.yaml b/Documentation/devicetree/bindings/power/powerzones.yaml
> new file mode 100644
> index 000000000000..ddb790acfea6
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/power/powerzones.yaml
> @@ -0,0 +1,97 @@
> +# SPDX-License-Identifier: GPL-2.0
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/power/powerzones.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Power zones description
> +
> +maintainers:
> + - Daniel Lezcano <daniel.lezcano@linaro.org>
> +
> +description: |+
> +
> + A System on Chip contains a multitude of active components and each
> + of them is a source of heat. Even if a temperature sensor is not
> + present, a source of heat can be controlled by acting on the
> + consumed power via different techniques.
> +
> + A powerzone describes a component or a group of components where we
> + can control the maximum power consumption. For instance, a group of
> + CPUs via the performance domain, a LCD screen via the brightness,
> + etc ...
> +
> + Different components when they are used together can significantly
> + increase the overall temperature, so the description needs to
> + reflect this dependency in order to assign a power budget for a
> + group of powerzones.
> +
> + This description is done via a hierarchy and the DT reflects it. It
> + does not represent the physical location or a topology, eg. on a
> + big.Little system, the little CPUs may not be represented as they do
> + not contribute significantly to the heat, however the GPU can be
> + tied with the big CPUs as they usually have a connection for
> + multimedia or game workloads.
> +
> +properties:
> + $nodename:
> + const: powerzones
> +
> +patternProperties:
> + "^(powerzone)([@-].*)?$":
> + type: object
> + description:
> + A node representing a powerzone acting as an aggregator for all
> + its children powerzones.
> +
> + properties:
> + "#powerzone-cells":
> + description:
> + Number of cells in powerzone specifier. Typically 0 for nodes
> + representing but it can be any number in the future to
> + describe parameters of the powerzone.
> +
> + powerzones:
> + description:
> + A phandle to a parent powerzone. If no powerzone attribute is
> + set, the described powerzone is the topmost in the hierarchy.
> +
> + required:
> + - "#powerzone-cells"
> +
> +additionalProperties: false
> +
> +examples:
> + - |
> + powerzones {
> +
> + SOC_PZ: powerzone-soc {
> + #powerzone-cells = <0>;
> + };
> +
> + PKG_PZ: powerzone-pkg {
> + #powerzone-cells = <0>;
> + powerzones = <&SOC_PZ>;
> + };
> +
> + GPU_PZ: powerzone-gpu {
> + #powerzone-cells = <0>;
> + powerzones = <&PKG_PZ>;
> + };
> + };
> +
> + - |
> + A57_0: big@0 {
> + compatible = "arm,cortex-a57";
> + reg = <0x0 0x0>;
> + device_type = "cpu";
> + powerzones = <&PKG_PZ>;
> + };
> +
> + A57_1: big@1 {
> + compatible = "arm,cortex-a57";
> + reg = <0x0 0x0>;
> + device_type = "cpu";
> + powerzones = <&PKG_PZ>;
> + };
> +...
> --
> 2.25.1
>