Re: [PATCH v2 3/3] dt-bindings: hwmon: max31790: Add maxim,pwmout-pin-as-tach-input property

[Chanh Nguyen]

On 16/04/2024 11:52, Chanh Nguyen wrote:
> On 14/04/2024 13:07, Krzysztof Kozlowski wrote:
> > On 14/04/2024 06:22, Chanh Nguyen wrote:
> > > The max31790 supports six pins, which are dedicated PWM outputs. Any 
> > > of the
> > > six PWM outputs can also be configured to serve as tachometer inputs,
> > > allowing for up to 12 tachometer fans to be monitored.
> > >
> > > Add a new vendor-specific property, 'maxim,pwmout-pin-as-tach-input',
> > > to allow PWMOUT to become a TACH input.
> > >
> > > 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.
> > >
> > > Signed-off-by: Chanh Nguyen <chanh@xxxxxxxxxxxxxxxxxxxxxx>
> > > ---
> > > Changes in v2:
> > >   - Update the vendor property name to 
> > > "maxim,pwmout-pin-as-tach-input"   [Rob]
> > >   - Update commit 
> > > message                                                 [Krzysztof]
> >
> > Please put binding before its user.
>
> Hi Krzysztof, I'll drop this [Path 3/3] in the patch series v3.
>
> My patch series will only be two patches. They are "dt-bindings: hwmon: 
> Add maxim max31790" and "hwmon: (max31790): Support config PWM output 
> becomes TACH"
>
> > > ---
> > >   .../devicetree/bindings/hwmon/maxim,max31790.yaml     | 11 +++++++++++
> > >   1 file changed, 11 insertions(+)
> > >
> > > diff --git 
> > > a/Documentation/devicetree/bindings/hwmon/maxim,max31790.yaml 
> > > b/Documentation/devicetree/bindings/hwmon/maxim,max31790.yaml
> > > index a561e5a3e9e4..2d4f50bc7c41 100644
> > > --- a/Documentation/devicetree/bindings/hwmon/maxim,max31790.yaml
> > > +++ b/Documentation/devicetree/bindings/hwmon/maxim,max31790.yaml
> > > @@ -30,6 +30,16 @@ properties:
> > >     resets:
> > >       maxItems: 1
> > > +  maxim,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
> >
> > tach-ch solves your case. You define which inputs should be used for 
> > tach.
>
> Agree Krzysztof. I'll use the tach-ch property from the fan-common.yaml 
> to solve my case. So I will not need to define a new vendor property as 
> "maxim,pwmout-pin-as-tach-input". I'll drop this [Path 3/3] in the patch 
> series v3.
>
>
> > Best regards,
> > Krzysztof


Hi Krzysztof,

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


In my purpose, I would like to configure the pwm output pins to become 
tachometer input pins by setting bit[0] in the Configuration Register.


I think a vendor property is suitable for this purpose. It is only 
available on specific MAX31790 fan controllers and not on other fan 
controller devices. So I think we can't use the "tach-ch" in 
fan-common.yaml.

I discussed it in the thread
https://lore.kernel.org/lkml/ce8b2b49-b194-42f7-8f83-fcbf7b460970@xxxxxxxxxxxxxxxxxxxxxxxxxx/ 
, but I have not yet received Rob's response.

Please share your comment with me. I hope that will help us make a final 
decision.

Thank Krzysztof very much!