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

[Guenter Roeck]

On 3/11/24 10:34, 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?

Per Documentation/ABI/testing/sysfs-class-hwmon:

What:           /sys/class/hwmon/hwmonX/fanY_pulses
Description:
                Number of tachometer pulses per fan revolution.

                Integer value, typically between 1 and 4.

                RW

                This value is a characteristic of the fan connected to the
                device's input, so it has to be set in accordance with the fan
                model.

                Should only be created if the chip has a register to configure
                the number of pulses. In the absence of such a register (and
                thus attribute) the value assumed by all devices is 2 pulses
                per fan revolution.

We only expect the property (and attribute) to exist if the controller
supports it.

Guenter