linux-kernel - Re: [PATCH v7 1/4] dt-bindings: hwmon: fan: Add fan binding to schema

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Message-ID: <25b37a72-4415-2ed5-0415-040af174a70a@roeck-us.net>
Date:   Tue, 22 Nov 2022 11:25:29 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Naresh Solanki <naresh.solanki@...ements.com>,
        devicetree@...r.kernel.org, Jean Delvare <jdelvare@...e.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-hwmon@...r.kernel.org,
        Patrick Rudolph <patrick.rudolph@...ements.com>
Subject: Re: [PATCH v7 1/4] dt-bindings: hwmon: fan: Add fan binding to schema

On 11/21/22 04:29, Naresh Solanki 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
>        $ref: fan-common.yaml#
> 
> Signed-off-by: Naresh Solanki <Naresh.Solanki@...ements.com>
> ---
>   .../devicetree/bindings/hwmon/fan-common.yaml | 47 +++++++++++++++++++
>   1 file changed, 47 insertions(+)
>   create mode 100644 Documentation/devicetree/bindings/hwmon/fan-common.yaml
> 
> diff --git a/Documentation/devicetree/bindings/hwmon/fan-common.yaml b/Documentation/devicetree/bindings/hwmon/fan-common.yaml
> new file mode 100644
> index 000000000000..0535d37624cc
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/hwmon/fan-common.yaml
> @@ -0,0 +1,47 @@
> +# SPDX-License-Identifier: GPL-2.0-or-later OR BSD-2-Clause
> +%YAML 1.2
> +---
> +$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
> +
> +  min-rpm:
> +    description:
> +      Min RPM supported by fan.
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +
> +  pulses-per-revolution:
> +    description:
> +      The number of pulse from fan sensor per revolution.
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +
> +  target-rpm:
> +    description:
> +      Target RPM the fan should be configured during driver probe.
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +
> +  pwms:
> +    description:
> +      PWM provider.
> +
> +  label:
> +    description:
> +      Optional fan label
> +
> +  fan-supply:
> +    description:
> +      Power supply for fan.
> +
> +additionalProperties: true
> +
> +...

Still, from my second reply to v6:

 > Another property which is definitely missing and needed
 > will be DC vs. PWM control. That is currently pwm[1-*]_mode
 > in sysfs attributes, but it is really a fan attribute.
 >
 > Many fans are DC controlled, so this property is absolutely
 > necessary.

Plus, with DC control there is no pwm. It would be absolutely wrong
to declare that a fan controller MUST be pwm based.

Ultimately, there are three types of fan controllers:

- PWM control, such as MAX6639
- DC control, such as MAX6620 or MAX6650/6651
- Configurable, such as MAX1669 or pretty much all fan controllers
   included in SuperIO chips

Generic fan control bindings simply _have_ to take this into account.

Guenter