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

[Chanh Nguyen]

On 09/05/2024 15:29, Krzysztof Kozlowski wrote:
> On 08/05/2024 05:44, Chanh Nguyen wrote:
> > > > > >
> > > > >
> > > > > I am not even sure how to define tach-ch to mean "use the pwm output pin
> > > > > associated with this tachometer input channel not as pwm output
> > > > > but as tachometer input". That would be a boolean, not a number.
> > > >
> > > > Thank Guenter,
> > > >
> > > > I reviewed again the "tach-ch" property, which is used in the
> > > > https://elixir.bootlin.com/linux/v6.9-rc6/source/Documentation/devicetree/bindings/hwmon/aspeed,g6-pwm-tach.yaml#L68 and https://elixir.bootlin.com/linux/v6.9-rc6/source/drivers/hwmon/aspeed-g6-pwm-tach.c#L434
> > > >
> > > > That is something completely different from my purpose.
> > >
> > > Based on its definition, tach-ch is associated with fans, and it looks
> > > like the .yaml file groups multiple sets of fans into a single
> > > fan node.
> > >
> > > In the simple case that would be
> > >       tach-ch = <1>
> > > ...
> > >       tach-ch = <12>
> > >
> > > or, if all fans are controlled by a single pwm
> > >       tach-ch = <1 2 3 4 5 6 8 9 10 11 12>
> > >
> > > The existence of tachometer channel 7..12 implies that pwm channel
> > > (tachometer
> > > channel - 6) is used as tachometer channel. That should be sufficient to
> > > program
> > > the chip for that channel. All you'd have to do is to ensure that pwm
> > > channel
> > > "X" is not listed as tachometer channel "X + 6", and program pwm channel
> > > "X - 6"
> > > for tachometer channels 7..12 as tachometer channels.
> >
> > Hi Guenter,
> >
> > I applied the patch [2/3] in my patch series
> > (https://lore.kernel.org/lkml/20240414042246.8681-3-chanh@xxxxxxxxxxxxxxxxxxxxxx/)
> >
> > My device tree is configured as below, I would like to configure PWMOUT
> > pins 5 and 6 to become the tachometer input pins.
>
> And what is wrong in described common tach-ch property? I think we
> explained it three times and you did not provide any arguments, what's
> missing. Instead you say "I want something like this in DTS" which is
> not an argument and does not help discussion.

Hi Krzysztof,

Apologies for any inconvenience caused by the delayed response.

I'll to support the child nodes by having different tach-ch values. I 
suggest the child nodes and the "tach-ch" is optional, it will not be 
added to "required:". Do you have any comments? Please help me share!

This is a brief binding
...
properties:
  compatible:
    const: maxim,max31790

  reg:
    maxItems: 1

  clocks:
    maxItems: 1

  resets:
    maxItems: 1

patternProperties:
  "^fan-[0-9]+$":
    $ref: fan-common.yaml#
    unevaluatedProperties: false

required:
  - compatible
  - reg

additionalProperties: false

examples:
  - |
    i2c {
      #address-cells = <1>;
      #size-cells = <0>;

      pwm_provider: fan-controller@20 {
        compatible = "maxim,max31790";
        reg = <0x20>;
        clocks = <&sys_clk>;
        resets = <&reset 0>;

        fan-0 {
          pwms = <&pwm_provider 1>;
          tach-ch = <1 2>;
        };

        fan-1 {
          pwms = <&pwm_provider 2>;
          tach-ch = <7 8>;
        };
      };
    };


If it's OK, I'm going to push the patch series v3 soon.

Thanks,
Chanh Ng

> Best regards,
> Krzysztof