linux-kernel - Re: [PATCH v2 1/3] dt-bindings: hwmon: fan: Add fan binding to schema

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Date:   Wed, 12 Oct 2022 01:17:06 +0530
From:   Naresh Solanki <naresh.solanki@...ements.com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     devicetree@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>,
        Jean Delvare <jdelvare@...e.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-kernel@...r.kernel.org, linux-hwmon@...r.kernel.org,
        Patrick Rudolph <patrick.rudolph@...ements.com>
Subject: Re: [PATCH v2 1/3] dt-bindings: hwmon: fan: Add fan binding to schema

Hi Rob, Guenter, Krzysztof,

I want to align with the implementation for the fan dt schema.

Current implementation is intending to use fan-common.yaml only for the purpose
of defining fan property as I felt this is the best way. This is how
other drivers have approached(eg: leds)

With this fan-controller driver will configure the chip  based on fan
characteristics accordingly.
target-rpm/default-rpm is included in it to enable driver configure
fan controllers during driver
probe.

Fan datasheets do specify the pwm frequency used to evaluate its
characteristic. That is the reason I've
included pwm-frequency here which fan-controller drivers can use &
initialize pwm frequency accordingly.

I'm ok with other approaches so do provide your perspective.

Regards,
Naresh Solanki

On Wed, 12 Oct 2022 at 00:35, Rob Herring <robh+dt@...nel.org> wrote:
>
> On Tue, Oct 11, 2022 at 5:47 AM Naresh Solanki
> <naresh.solanki@...ements.com> wrote:
> >
> > Add common fan properties bindings to a schema.
> >
> > Bindings for fan controllers can reference the common schema for the
> > fan
> >
> > child nodes:
> >
> >   patternProperties:
> >     "^fan@[0-2]":
> >       type: object
> >       allOf:
>
> Don't allOf here.
>
> >         - $ref: fan-common.yaml#
> >
> > Signed-off-by: Naresh Solanki <Naresh.Solanki@...ements.com>
> > ---
> >  .../devicetree/bindings/hwmon/fan-common.yaml | 80 +++++++++++++++++++
> >  1 file changed, 80 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/hwmon/fan-common.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/hwmon/fan-common.yaml b/Documentation/devicetree/bindings/hwmon/fan-common.yaml
> > new file mode 100644
> > index 000000000000..abc8375da646
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/hwmon/fan-common.yaml
> > @@ -0,0 +1,80 @@
> > +# SPDX-License-Identifier: GPL-2.0-only
>
> Dual license with BSD-2-Clause.
>
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/hwmon/fan-common.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Common fan properties
> > +
> > +maintainers:
> > +  - Naresh Solanki <naresh.solanki@...ements.com>
> > +
> > +properties:
> > +  max-rpm:
> > +    description:
> > +      Max RPM supported by fan
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +
> > +  pulse-per-revolution:
>
> The already in use property is 'pulses-per-revolution'.
>
> > +    description:
> > +      The number of pulse from fan sensor per revolution.
> > +    $ref: /schemas/types.yaml#/definitions/uint32
>
> I assume there's a known set of values various fans have?
>
> > +
> > +  target-rpm:
> > +    description:
> > +      Target RPM the fan should be configured during driver probe.
>
> Which driver? I think 'default-rpm' would be a better name.
>
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +
> > +  pwm-frequency:
> > +    description:
> > +      PWM frequency for fan.
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +
> > +  pwm-polarity-inverse:
> > +    description:
> > +      PWM polarity for fan.
> > +    type: boolean
>
> Both of these properties are handled by the PWM binding already. I
> think this should use it even though the PWMs are just connected to
> the child nodes. There's always the possibility that someone hooks up
> a fan controller PWM to something else besides a fan.
>
> > +
> > +  label:
> > +    description:
> > +      Optional fan label
> > +    $ref: /schemas/types.yaml#/definitions/string
>
> Doesn't a fan need power? 'fan-supply' is already in use, so that could be used.
>
> > +
> > +additionalProperties: true
> > +
> > +examples:
> > +  - |
>
> Drop the example here as you have it in the max6639 schema.
>
> > +
> > +
> > +    i2c {
> > +        #address-cells = <1>;
> > +        #size-cells = <0>;
> > +
> > +        fan-controller@30 {
> > +            compatible = "maxim,max6639";
> > +            reg = <0x30>;
> > +            #address-cells = <1>;
> > +            #size-cells = <0>;
> > +
> > +            fan@0 {
> > +                reg = <0>;
> > +                label = "CPU0_Fan";
> > +                max-rpm = <32000>;
> > +                pulse-per-revolution = <2>;
> > +                target-rpm = <2000>;
> > +                pwm-frequency = <25000>;
> > +            };
> > +
> > +            fan@1 {
> > +                reg = <1>;
> > +                label = "PCIe0_Fan";
> > +                max-rpm = <32000>;
> > +                pulse-per-revolution = <2>;
> > +                target-rpm = <2000>;
> > +                pwm-frequency = <25000>;
> > +            };
> > +
> > +        };
> > +    };
> > +
> > +...
> >
> > base-commit: 0cf46a653bdae56683fece68dc50340f7520e6c4
> > --
> > 2.37.3
> >