Re: [PATCH 3/3] dt-bindings: hwmon: max31790: Add pwmout-pin-as-tach-input property

[Chanh Nguyen]

On 18/03/2024 16:53, Chanh Nguyen wrote:
> On 12/03/2024 00:34, Rob Herring wrote:
> > On Mon, Mar 11, 2024 at 06:13:47PM +0700, Chanh Nguyen wrote:
> > > Add pwmout-pin-as-tach-input property.
> > >
> > > Signed-off-by: Chanh Nguyen <chanh@xxxxxxxxxxxxxxxxxxxxxx>
> > > ---
> > >   Documentation/devicetree/bindings/hwmon/max31790.yaml | 11 +++++++++++
> > >   1 file changed, 11 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/hwmon/max31790.yaml 
> > > b/Documentation/devicetree/bindings/hwmon/max31790.yaml
> > > index 5a93e6bdebda..447cac17053a 100644
> > > --- a/Documentation/devicetree/bindings/hwmon/max31790.yaml
> > > +++ b/Documentation/devicetree/bindings/hwmon/max31790.yaml
> > > @@ -25,6 +25,16 @@ properties:
> > >     reg:
> > >       maxItems: 1
> > > +  pwmout-pin-as-tach-input:
> > > +    description: |
> > > +      An array of six integers responds to six PWM channels for
> > > +      configuring the pwm to tach mode.
> > > +      When set to 0, the associated PWMOUT produces a PWM waveform for
> > > +      control of fan speed. When set to 1, PWMOUT becomes a TACH input
> > > +    $ref: /schemas/types.yaml#/definitions/uint8-array
> > > +    maxItems: 6
> > > +    minItems: 6
> >
> > Seems incomplete. For example, fan tachs have different number of
> > pulses per revolution, don't you need to know that too?
> >
> > There's a common fan binding now (or pending). You should use that and
> > this property won't be needed.
> >
> > Rob
>
> Thank Rob,
>
> I checked in the 
> Documentation/devicetree/bindings/hwmon/fan-common.yaml. I found the 
> tach-ch property, but it seems define the tach channel used for fan.
>
>    tach-ch:
>      description:
>        The tach channel used for the fan.
>      $ref: /schemas/types.yaml#/definitions/uint8-array
>
> I would like to define a new vendor property to configure the PWM-OUT 
> pin to become a TACH-IN pin. So I introduce the 
> "maxim,pwmout-pin-as-tach-input" property. Please help me share your 
> comments!

Hi Guenter and Rob,

I'm preparing for patch v2. I'm looking forward to hear your advice. 
Should I use the "tach-ch" property (a common fan property) or define 
new vendor property ("maxim,pwmout-pin-as-tach-input") for my purpose?

Thank you very much!
Chanh