Re: [PATCH v3 2/3] dt-bindings: thermal: Add yaml bindings for thermal cooling-devices

[Amit Kucheria <amit.kucheria@linaro.org>]

On Wed, Mar 25, 2020 at 3:51 PM Lukasz Luba <lukasz.luba@arm.com> wrote:
>
> 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.

Thanks for the review.

Will fix.