linux-kernel - Re: [PATCH v2 2/2] dt-bindings: hwmon: add MAX31790

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Date:   Fri, 22 Sep 2023 07:42:42 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Conor Dooley <conor@...nel.org>,
        Delphine_CC_Chiu/WYHQ/Wiwynn <Delphine_CC_Chiu@...ynn.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        "patrick@...cx.xyz" <patrick@...cx.xyz>,
        Jean Delvare <jdelvare@...e.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] dt-bindings: hwmon: add MAX31790

On 9/22/23 02:53, Conor Dooley wrote:
> On Fri, Sep 22, 2023 at 02:33:06AM +0000, Delphine_CC_Chiu/WYHQ/Wiwynn wrote:
>>>> On Fri, Sep 15, 2023 at 02:29:24PM +0800, Delphine CC Chiu wrote:
> 
>>>>> +  pwm-as-tach:
>>>>
>>>> I don't see any other users of this in-tree, so you'd need a vendor
>>>> prefix. That said, I'm once bitten, twice shy about fan related
>>>> properties in hwmon, so I would definitely like Rob to comment on this
>>>> whole binding.
>>>
>>> Please see this[1] and comment on it to ensure it meets your needs.
>>> Otherwise, omit any fan related properties for now.
>>>
>> This property could only be used in max31790 driver. Would it be ok if we add
>> vendor prefix like "maxim, pwm-as-tach"?
> 
> I think the answer to this is a pretty straightforward no. The goal is
> to create a set of common fan properties that works for multiple
> usecases, not create one specifically for each user...
> 

Another chip with configurable channel configuration is nct7802, where
individual channels can be configured as temperature or voltage sensor.
We are using sensor-type to select the mode in that driver. Maybe something
similar would make sense / be acceptable here.

>>>> +examples:
>>>> +  - |
>>>> +    i2c {
>>>> +      #address-cells = <1>;
>>>> +      #size-cells = <0>;
>>>> +
>>>> +      pwm@20 {
>>>> +        compatible = "maxim,max31790";
>>>> +        reg = <0x20>;
>>>> +        pwm-as-tach = <2 5>;
>>>
>>> This would be <2>, <5>; no?
>>>
>> I refer to the other binding documents in hwmon and most of them were using
>> the format like <2 5> as an array.
> 
> Which also makes this moot, since it'll be going away.
> 
>>>> diff --git a/MAINTAINERS b/MAINTAINERS index
>>>> c8fdd0d03907..97e13b6bf51d 100644
>>>> --- a/MAINTAINERS
>>>> +++ b/MAINTAINERS
>>>> @@ -1371,6 +1371,12 @@ F:
>>>        Documentation/devicetree/bindings/hwmon/adi,max31760.yaml
>>>>   F: Documentation/hwmon/max31760.rst
>>>>   F: drivers/hwmon/max31760.c
>>>>
>>>> +ANALOG DEVICES INC MAX31790 DRIVER
>>>> +M: Delphine CC Chiu  <Delphine_CC_Chiu@...ynn.com>
>>>> +S: Odd Fixes
>>>
>>> This is a pretty odd status for something you're newly adding.
>>> How come it's not going to be maintained?
>>>
>> We are not the authors of this driver but we want to add a feature to
>> config PWM as TACH that was descripted in the datasheet of MAX31790.
>> Should we set the status to maintained?
> 
> It's really up to you. I just found it curious & wanted to ask why it
> was that way.
> 

It is misleading because it downgrades the driver from "supported"
(like all other hwmon drivers) to "odd fixes".

Guenter