linux-kernel - Re: [PATCH v1 1/2] dt-bindings: iio: adc: Add binding for Nuvoton NCT720x ADCs

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Message-ID: <20241109142943.3d960742@jic23-huawei>
Date: Sat, 9 Nov 2024 14:29:43 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Yu-Hsian Yang <j2anfernee@...il.com>
Cc: Chanh Nguyen <chanh@...eremail.onmicrosoft.com>, avifishman70@...il.com,
 tmaimon77@...il.com, tali.perry1@...il.com, venture@...gle.com,
 yuenn@...gle.com, benjaminfair@...gle.com, lars@...afoo.de,
 robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
 nuno.sa@...log.com, dlechner@...libre.com, javier.carrasco.cruz@...il.com,
 andy@...nel.org, marcelo.schmitt@...log.com, olivier.moysan@...s.st.com,
 mitrutzceclan@...il.com, matteomartelli3@...il.com, alisadariana@...il.com,
 joao.goncalves@...adex.com, marius.cristea@...rochip.com,
 mike.looijmans@...ic.nl, chanh@...amperecomputing.com, KWLIU@...oton.com,
 yhyang2@...oton.com, openbmc@...ts.ozlabs.org, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/2] dt-bindings: iio: adc: Add binding for Nuvoton
 NCT720x ADCs

On Sat, 9 Nov 2024 13:42:28 +0000
Jonathan Cameron <jic23@...nel.org> wrote:

> On Wed, 6 Nov 2024 17:22:35 +0800
> Yu-Hsian Yang <j2anfernee@...il.com> wrote:
> 
> > Dear Chanh Nguyen,
> > 
> > Thank you for your response.
> > 
> > Chanh Nguyen <chanh@...eremail.onmicrosoft.com> 於 2024年11月6日 週三 下午12:58寫道：  
> > >
> > >
> > >
> > > On 06/11/2024 09:39, Eason Yang wrote:    
> > > > This adds a binding specification for the Nuvoton NCT7201/NCT7202
> > > > family of ADCs.
> > > >
> > > > Signed-off-by: Eason Yang <j2anfernee@...il.com>
> > > > ---
> > > >   .../bindings/iio/adc/nuvoton,nct720x.yaml     | 47 +++++++++++++++++++
> > > >   MAINTAINERS                                   |  1 +
> > > >   2 files changed, 48 insertions(+)
> > > >   create mode 100644 Documentation/devicetree/bindings/iio/adc/nuvoton,nct720x.yaml
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/iio/adc/nuvoton,nct720x.yaml b/Documentation/devicetree/bindings/iio/adc/nuvoton,nct720x.yaml
> > > > new file mode 100644
> > > > index 000000000000..3052039af10e
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/iio/adc/nuvoton,nct720x.yaml
> > > > @@ -0,0 +1,47 @@
> > > > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > > > +%YAML 1.2
> > > > +---
> > > > +$id: http://devicetree.org/schemas/iio/adc/nuvoton,nct720x.yaml#
> > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > +
> > > > +title: Nuvoton nct7202 and similar ADCs
> > > > +
> > > > +maintainers:
> > > > +  - Eason Yang <yhyang2@...oton.com>
> > > > +
> > > > +description: |
> > > > +   Family of ADCs with i2c interface.
> > > > +
> > > > +properties:
> > > > +  compatible:
> > > > +    enum:
> > > > +      - nuvoton,nct7201
> > > > +      - nuvoton,nct7202
> > > > +
> > > > +  reg:
> > > > +    maxItems: 1
> > > > +
> > > > +  read-vin-data-size:    
> > >
> > > Is it generic property or vendor property? I tried to find in the
> > > https://github.com/torvalds/linux/tree/master/Documentation/devicetree/bindings
> > > , but it seems this property hasn't been used on other devices.
> > >
> > > If it is vendor property, then I think it should include a vendor
> > > prefix. For examples:
> > >
> > > https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/iio/adc/adi%2Cad7780.yaml#L50
> > > https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/iio/adc/fsl%2Cvf610-adc.yaml#L42
> > > https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/iio/adc/st%2Cstmpe-adc.yaml#L22
> > >
> > >    
> > 
> > I would add a vendor prefix for it.  
> 
> Why do we want this at all?  Is this device sufficiently high
> performance that Linux will ever want to trade of resolution against
> sampling speed?
> 
> If so that seems like a policy control that belongs in userspace. Note
> that to support that in IIO I would want a strong justification for why we dno't
> just set it to 16 always. We just go for maximum resolution in the vast majority
> of drivers that support control of this.
I'd misunderstood what this is. It's a control no what the i2c word size is.
Do we actually care about supporting rubbish i2c controllers?  How many
can't do a word access?

If you do it should be detected from the controller rather than in DT.

> 
> 
> >   
> > > > +    description: number of data bits per read vin
> > > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > > +    enum: [8, 16]
> > > > +
> > > > +required:
> > > > +  - compatible
> > > > +  - reg
> > > > +  - read-vin-data-size
> > > > +
> > > > +additionalProperties: false
> > > > +
> > > > +examples:
> > > > +  - |
> > > > +    i2c {
> > > > +        #address-cells = <1>;
> > > > +        #size-cells = <0>;
> > > > +
> > > > +        nct7202@1d {    
> > >
> > > I think the Node name should follow
> > > https://devicetree-specification.readthedocs.io/en/latest/chapter2-devicetree-basics.html#generic-names-recommendation
> > >
> > >
> > > For some examples that were merged before
> > >
> > > https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/iio/adc/adi%2Cad7091r5.yaml#L102
> > > https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/iio/adc/maxim%2Cmax1238.yaml#L73
> > > https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/iio/adc/ti%2Cadc081c.yaml#L49
> > >    
> > 
> > I would change it for the node naming.
> >   
> > > > +            compatible = "nuvoton,nct7202";
> > > > +            reg = <0x1d>;
> > > > +            read-vin-data-size = <8>;
> > > > +        };
> > > > +    };
> > > > diff --git a/MAINTAINERS b/MAINTAINERS
> > > > index 91d0609db61b..68570c58e7aa 100644
> > > > --- a/MAINTAINERS
> > > > +++ b/MAINTAINERS
> > > > @@ -2746,6 +2746,7 @@ L:      openbmc@...ts.ozlabs.org (moderated for non-subscribers)
> > > >   S:  Supported
> > > >   F:  Documentation/devicetree/bindings/*/*/*npcm*
> > > >   F:  Documentation/devicetree/bindings/*/*npcm*
> > > > +F:   Documentation/devicetree/bindings/iio/adc/nuvoton,nct720x.yaml
> > > >   F:  Documentation/devicetree/bindings/rtc/nuvoton,nct3018y.yaml
> > > >   F:  arch/arm/boot/dts/nuvoton/nuvoton-npcm*
> > > >   F:  arch/arm/mach-npcm/    
> > >    
> 
>