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

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Message-ID: <20240423-gallantly-slurp-24adbfbd6f09@spud>
Date: Tue, 23 Apr 2024 18:02:36 +0100
From: Conor Dooley <conor@...nel.org>
To: Chanh Nguyen <chanh@...eremail.onmicrosoft.com>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
	Chanh Nguyen <chanh@...amperecomputing.com>,
	Jean Delvare <jdelvare@...e.com>,
	Guenter Roeck <linux@...ck-us.net>,
	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 Tue, Apr 23, 2024 at 03:45:12PM +0700, Chanh Nguyen wrote:
> 
> 
> 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@...amperecomputing.com>
> > > > ---
> > > > 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.

Can you explain why you think that only MAX31790 fan controllers are
capable of an arbitrary mapping of PWM outputs to TACH inputs?

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