Re: [PATCH 2/3] dt-bindings: iio: temperature: ltc2983: support more parts

Nuno Sá
2022-10-17T09:37:50Z

Hi Krzysztof,

As I wrote the original bindings, let me reply to some of your
points...

On Sun, 2022-10-16 at 21:59 -0400, Krzysztof Kozlowski wrote:
> On 14/10/2022 08:37, Cosmin Tanislav wrote:
> > From: Cosmin Tanislav <cosmin.tanislav@analog.com>
> >
> > Add support for the following parts:
> >  * LTC2984
> >  * LTC2986
> >  * LTM2985
> >
> > The LTC2984 is a variant of the LTC2983 with EEPROM.
> > The LTC2986 is a variant of the LTC2983 with only 10 channels,
> > EEPROM and support for active analog temperature sensors.
> > The LTM2985 is software-compatible with the LTC2986.
> >
> > Signed-off-by: Cosmin Tanislav <cosmin.tanislav@analog.com>
> > ---
> >  .../bindings/iio/temperature/adi,ltc2983.yaml | 63
> > +++++++++++++++++--
> >  1 file changed, 59 insertions(+), 4 deletions(-)
> >
> > diff --git
> > a/Documentation/devicetree/bindings/iio/temperature/adi,ltc2983.yam
> > l
> > b/Documentation/devicetree/bindings/iio/temperature/adi,ltc2983.yam
> > l
> > index 722781aa4697..c33ab524fb64 100644
> > ---
> > a/Documentation/devicetree/bindings/iio/temperature/adi,ltc2983.yam
> > l
> > +++
> > b/Documentation/devicetree/bindings/iio/temperature/adi,ltc2983.yam
> > l
> > @@ -4,19 +4,27 @@
> >  $id:
> > http://devicetree.org/schemas/iio/temperature/adi,ltc2983.yaml#
> >  $schema: http://devicetree.org/meta-schemas/core.yaml#
> >
> > -title: Analog Devices LTC2983 Multi-sensor Temperature system
> > +title: Analog Devices LTC2983, LTC2986, LTM2985 Multi-sensor
> > Temperature system
> >
> >  maintainers:
> >    - Nuno Sá <nuno.sa@analog.com>
> >
> >  description: |
> > -  Analog Devices LTC2983 Multi-Sensor Digital Temperature
> > Measurement System
> > +  Analog Devices LTC2983, LTC2984, LTC2986, LTM2985 Multi-Sensor
> > Digital
> > +  Temperature Measurement Systems
> > +
> >
> > https://www.analog.com/media/en/technical-documentation/data-sheets/2983fc.pdf
> > +
> > https://www.analog.com/media/en/technical-documentation/data-sheets/2984fb.pdf
> > +
> > https://www.analog.com/media/en/technical-documentation/data-sheets/29861fa.pdf
> > +
> > https://www.analog.com/media/en/technical-documentation/data-sheets/ltm2985.pdf
> >
> >  properties:
> >    compatible:
> >      enum:
> >        - adi,ltc2983
> > +      - adi,ltc2984
> > +      - adi,ltc2986
> > +      - adi,ltm2985
> >
> >    reg:
> >      maxItems: 1
> > @@ -26,7 +34,7 @@ properties:
> >
> >    adi,mux-delay-config-us:
> >      description:
> > -      The LTC2983 performs 2 or 3 internal conversion cycles per
> > temperature
> > +      The device performs 2 or 3 internal conversion cycles per
> > temperature
> >        result. Each conversion cycle is performed with different
> > excitation and
> >        input multiplexer configurations. Prior to each conversion,
> > these
> >        excitation circuits and input switch configurations are
> > changed and an
> > @@ -145,7 +153,7 @@ patternProperties:
> >        adi,three-conversion-cycles:
> >          description:
> >            Boolean property which set's three conversion cycles
> > removing
> > -          parasitic resistance effects between the LTC2983 and the
> > diode.
> > +          parasitic resistance effects between the device and the
> > diode.
> >          type: boolean
> >
> >        adi,average-on:
> > @@ -353,6 +361,41 @@ patternProperties:
> >          description: Boolean property which set's the adc as
> > single-ended.
> >          type: boolean
> >
> > +  "^temp@":
>
> There is already a property for thermocouple. Isn't a thermocouple a
> temperature sensor? IOW, why new property is needed?
>

Well, most of the patternProps in this bindings are temperature
sensors... It's just that the device(s) support different types of
them. 'adi,sensor-type' is used to identify each sensor (as this
translates in different configurations being written in the device
channels).

> > +    type: object
> > +    description:
> > +      Represents a channel which is being used as an active analog
> > temperature
> > +      sensor.
> > +
> > +    properties:
> > +      adi,sensor-type:
> > +        description:
> > +          Identifies the sensor as an active analog temperature
> > sensor.
> > +        $ref: /schemas/types.yaml#/definitions/uint32
> > +        const: 31
> > +
> > +      adi,single-ended:
> > +        description: Boolean property which sets the sensor as
> > single-ended.
>
> Drop "Boolean property which sets" - it's obvious from the type.
>
>
>
> > +        type: boolean
> > +
> > +      adi,custom-temp:
> > +        description:
> > +          This is a table, where each entry should be a pair of
>
> "This is a table" - obvious from the type.
>
> > +          voltage(mv)-temperature(K). The entries must be given in
> > nv and uK
>
> mv-K or nv-uK? Confusing...

Yeah, a bit. In Cosmin defense, I think he's just keeping the same
"style" as the rest of the properties...

>
> > +          so that, the original values must be multiplied by
> > 1000000. For
> > +          more details look at table 71 and 72.
>
> There is no table 71 in the bindings... It seems you pasted it from
> somewhere.

I'm fairly sure this refers to the datasheet. I see now that this can
be confusing (again this kind of references are being (ab)used in the
rest of the file).

>
> > +          Note should be signed, but dtc doesn't currently
> > maintain the
> > +          sign.
>
> What do you mean? "Maintain" as allow or keep when building FDT?
> What's
> the problem of using negative numbers here and why it should be part
> of
> bindings?
>
> > +        $ref: /schemas/types.yaml#/definitions/uint64-matrix
> > +        minItems: 3
> > +        maxItems: 64
> > +        items:
> > +          minItems: 2
> > +          maxItems: 2
>
> Instead describe the items with "description" (and maybe constraints)
> like here:
>
> https://elixir.bootlin.com/linux/v5.19/source/Documentation/devicetree/bindings/iio/adc/st,stm32-adc.yaml#L278
>

Neat... My only comment (which probably applies to my previous ones) is
that the rest of the properties are already in this "style". So maybe,
follow up patches with small clean-ups would be more appropriate?
>

- Nuno Sá