linux-kernel - Re: [PATCH v4 1/3] dt-bindings: hwmon: fan: Add fan binding to schema

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Message-ID: <CAL_JsqKT52ULEZjKo9emEAt74nH2OpMO8ymLLKM_T-NzAwqGog@mail.gmail.com>
Date:   Wed, 26 Oct 2022 08:37:29 -0500
From:   Rob Herring <robh@...nel.org>
To:     Naresh Solanki <naresh.solanki@...ements.com>
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 v4 1/3] dt-bindings: hwmon: fan: Add fan binding to schema

On Tue, Oct 25, 2022 at 4:16 AM Naresh Solanki
<naresh.solanki@...ements.com> wrote:
>
>
>
> On 24-10-2022 09:48 pm, Rob Herring wrote:
> > So if we unload and reload the driver module, it should go back to the
> > default?
> This is RPM to be set during probe if desired.
> >
> > I think it is really, 'target RPM if not already configured' which could
> > be keep the setting from a register (e.g. what the bootloader set) or
> > perhaps you already have temperature information to use...
> Yes. missed it. It should be target-rpm will correct this. in next version.
> >
> >> +    $ref: /schemas/types.yaml#/definitions/uint32
> >> +  pwm-frequency:
> >> +    description:
> >> +      PWM frequency for fan in Hertz(Hz).
> >> +    $ref: /schemas/types.yaml#/definitions/uint32
> >> +
> >> +  pwm-polarity-inverse:
> >> +    description:
> >> +      Inverse PWM polarity for fan.
> >> +    type: boolean
> > As I said before, the PWM binding handles these 2 settings. Use it. Yes,
> > it's a bit of an overkill when the child is the consumer of the parent.
> > Until some 'clever' h/w engineer decides to use one of the PWMs for
> > something else like a backlight.
> I would like you to consider this as something recommended by fan
> datasheet for the given fan instance.
> This info can be used by fan controller driver to configure PWM
> source/provider accordingly.
>
> If you still feel that may not make sense then I'll remove this property.

You evidently don't understand my comments. My suggestion is to do this:

fanc: fan-controller {
  #pwm-cells = <3>;
  ...

  fan {
    pwms = <&fanc 0 500000  PWM_POLARITY_INVERTED>;
    ...
  };
};

0 is PWM number and 500000 is the PWM frequency. The 3rd cell are per
consumer flags. See pwm.txt for more details.

Rob