linux-kernel - Re: [PATCH v4 3/5] dt-bindings: hwmon: Document adt7475 invert-pwm property

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Date:   Fri, 21 Feb 2020 16:04:45 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Chris Packham <chris.packham@...iedtelesis.co.nz>,
        Jean Delvare <jdelvare@...e.com>,
        Mark Rutland <mark.rutland@....com>,
        Linux HWMON List <linux-hwmon@...r.kernel.org>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Logan Shaw <logan.shaw@...iedtelesis.co.nz>
Subject: Re: [PATCH v4 3/5] dt-bindings: hwmon: Document adt7475 invert-pwm property

On Fri, Feb 21, 2020 at 9:53 AM Guenter Roeck <linux@...ck-us.net> wrote:
>
> On Fri, Feb 21, 2020 at 09:40:00AM -0600, Rob Herring wrote:
> > On Thu, Feb 20, 2020 at 10:16 PM Chris Packham
> > <chris.packham@...iedtelesis.co.nz> wrote:
> > >
> > > Add binding information for the invert-pwm property.
> > >
> > > Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
> > > ---
> > >
> > > Notes:
> > >     Changes in v4:
> > >     - use $ref uint32 and enum
> > >     - add adi vendor prefix
> > >
> > >     Cahnges in v3:
> > >     - new
> > >
> > >  Documentation/devicetree/bindings/hwmon/adt7475.yaml | 12 ++++++++++++
> > >  1 file changed, 12 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/hwmon/adt7475.yaml b/Documentation/devicetree/bindings/hwmon/adt7475.yaml
> > > index e40612ee075f..6a358b30586c 100644
> > > --- a/Documentation/devicetree/bindings/hwmon/adt7475.yaml
> > > +++ b/Documentation/devicetree/bindings/hwmon/adt7475.yaml
> > > @@ -50,6 +50,17 @@ patternProperties:
> > >       - $ref: /schemas/types.yaml#/definitions/uint32
> > >       - enum: [0, 1]
> > >
> > > +  "^adi,invert-pwm[1-3]$":
> > > +    description: |
> > > +      Configures the pwm output to use inverted logic. If set to 1
> > > +      the pwm uses a logic low output for 100% duty cycle. If set
> > > +      to 0 the pwm uses a logic high output for 100% duty cycle.
> > > +      If the property is absent the pwm retains it's configuration
> > > +      from the bios/bootloader.
> >
> > I believe we already have an inverted flag for consumers. That doesn't
> > work if you don't have a consumer described in DT, but then the
> > question is should you? Or is this something the user will want to
> > configure from userspace.
> >
>
> Normally that is a system property. It is difficult to imagine
> that it would ever have to be configured from userspace at runtime.
> Most of the time users won't have any idea, and the board datasheet
> (if avaible) won't list such information.

Yes, I agree and for those cases I'd expect the consumer is described
in DT too. I read and refreshed my memory on this binding after
sending this. I believe this is for a fan which I'd expect to be in DT
as fans need power and there's different types.

The userspace case I was thinking of was more the hobbyist boards with
PWM to a connector.

Rob