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

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Date: Fri, 7 Jun 2024 23:46:52 +0700
From: Chanh Nguyen <chanh@...eremail.onmicrosoft.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
 Guenter Roeck <linux@...ck-us.net>, Conor Dooley <conor@...nel.org>
Cc: Chanh Nguyen <chanh@...amperecomputing.com>,
 Jean Delvare <jdelvare@...e.com>, Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Justin Ledford
 <justinledford@...gle.com>, devicetree@...r.kernel.org,
 linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
 OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
 Open Source Submission <patches@...erecomputing.com>,
 Phong Vo <phong@...amperecomputing.com>,
 Thang Nguyen <thang@...amperecomputing.com>,
 Quan Nguyen <quan@...amperecomputing.com>
Subject: Re: [PATCH v2 3/3] dt-bindings: hwmon: max31790: Add
 maxim,pwmout-pin-as-tach-input property



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@os.amperecomputing.com/)
>>
>> 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
>