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

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Date: Tue, 26 Mar 2024 17:33:17 +0700
From: Chanh Nguyen <chanh@...eremail.onmicrosoft.com>
To: Rob Herring <robh@...nel.org>, Guenter Roeck <linux@...ck-us.net>,
 Chanh Nguyen <chanh@...amperecomputing.com>
Cc: Jean Delvare <jdelvare@...e.com>,
 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 3/3] dt-bindings: hwmon: max31790: Add
 pwmout-pin-as-tach-input property



On 18/03/2024 16:53, Chanh Nguyen wrote:
> 
> 
> On 12/03/2024 00:34, 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@...amperecomputing.com>
>>> ---
>>>   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?
>>
>> There's a common fan binding now (or pending). You should use that and
>> this property won't be needed.
>>
>> Rob
> 
> Thank Rob,
> 
> 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
> 
> I would like to define a new vendor property to configure the PWM-OUT 
> pin to become a TACH-IN pin. So I introduce the 
> "maxim,pwmout-pin-as-tach-input" property. Please help me share your 
> comments!

Hi Guenter and Rob,

I'm preparing for patch v2. I'm looking forward to hear your advice. 
Should I use the "tach-ch" property (a common fan property) or define 
new vendor property ("maxim,pwmout-pin-as-tach-input") for my purpose?

Thank you very much!
Chanh