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SubjectRe: [PATCH v3 2/3] dt-bindings: thermal: Add yaml bindings for thermal cooling-devices
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Hi Amit,

On 3/25/20 6:34 AM, Amit Kucheria wrote:
> As part of moving the thermal bindings to YAML, split it up into 3
> bindings: thermal sensors, cooling devices and thermal zones.
>
> The property #cooling-cells is required in each device that acts as a
> cooling device - whether active or passive. So any device that can
> throttle its performance to passively reduce heat dissipation (e.g.
> cpus, gpus) and any device that can actively dissipate heat at different
> levels (e.g. fans) will contain this property.
>
> Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
> ---
> .../thermal/thermal-cooling-devices.yaml | 116 ++++++++++++++++++
> 1 file changed, 116 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/thermal/thermal-cooling-devices.yaml
>
> diff --git a/Documentation/devicetree/bindings/thermal/thermal-cooling-devices.yaml b/Documentation/devicetree/bindings/thermal/thermal-cooling-devices.yaml
> new file mode 100644
> index 000000000000..b5599f7859f8
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/thermal/thermal-cooling-devices.yaml
> @@ -0,0 +1,116 @@
> +# SPDX-License-Identifier: (GPL-2.0)
> +# Copyright 2020 Linaro Ltd.
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/thermal/thermal-cooling-devices.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Thermal cooling device binding
> +
> +maintainers:
> + - Amit Kucheria <amitk@kernel.org>
> +
> +description: |
> + Thermal management is achieved in devicetree by describing the sensor hardware
> + and the software abstraction of cooling devices and thermal zones required to
> + take appropriate action to mitigate thermal overload.
> +
> + The following node types are used to completely describe a thermal management
> + system in devicetree:
> + - thermal-sensor: device that measures temperature, has SoC-specific bindings
> + - cooling-device: device used to dissipate heat either passively or artively
> + - thermal-zones: a container of the following node types used to describe all
> + thermal data for the platform
> +
> + This binding describes the cooling devices.
> +
> + There are essentially two ways to provide control on power dissipation:
> + - Passive cooling: by means of regulating device performance. A typical
> + passive cooling mechanism is a CPU that has dynamic voltage and frequency
> + scaling (DVFS), and uses lower frequencies as cooling states.
> + - Active cooling: by means of activating devices in order to remove the
> + dissipated heat, e.g. regulating fan speeds.
> +
> + Any cooling device has a range of cooling states (i.e. different levels of
> + heat dissipation). They also have a way to determine the state of cooling in
> + which the device is. For example, a fan's cooling states correspond to the
> + different fan speeds possible. Cooling states are referred to by single
> + unsigned integers, where larger numbers mean greater heat dissipation. The
> + precise set of cooling states associated with a device should be defined in
> + a particular device's binding.

[snip]

> +
> + thermal-zones {
> + cpu0-thermal {
> + polling-delay-passive = <250>;
> + polling-delay = <1000>;
> +
> + thermal-sensors = <&tsens0 1>;
> +
> + trips {
> + cpu0_alert0: trip-point0 {
> + temperature = <90000>;
> + hysteresis = <2000>;
> + type = "passive";
> + };
> + };
> +
> + cooling-maps {
> + map0 {
> + trip = <&cpu0_alert0>;
> + cooling-device = <&CPU0 THERMAL_NO_LIMIT
> + THERMAL_NO_LIMIT>;

Maybe add something like this, to better reflect the description:

trip = <&cpu0_alert0>;
/* Corresponds to 1000MHz in OPP table */
cooling-device = <&CPU0 5 5>;

This is less confusing than THERMAL_NO_LIMIT.

Regards,
Lukasz

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