RE: [PATCH v2 1/2] dt-bindings: hwmon: ltc2991: add bindings

["Miclaus, Antoniu" <Antoniu.Miclaus@xxxxxxxxxx>]

--
Antoniu Miclăuş

> -----Original Message-----
> From: Conor Dooley <conor@xxxxxxxxxx>
> Sent: Monday, October 2, 2023 4:01 PM
> To: Miclaus, Antoniu <Antoniu.Miclaus@xxxxxxxxxx>
> Cc: Jean Delvare <jdelvare@xxxxxxxx>; Guenter Roeck <linux@roeck-
> us.net>; Rob Herring <robh+dt@xxxxxxxxxx>; Krzysztof Kozlowski
> <krzysztof.kozlowski+dt@xxxxxxxxxx>; Conor Dooley
> <conor+dt@xxxxxxxxxx>; Jonathan Corbet <corbet@xxxxxxx>; linux-
> hwmon@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; linux-doc@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v2 1/2] dt-bindings: hwmon: ltc2991: add bindings
> 
> [External]
> 
> Hey,
> 
> On Mon, Oct 02, 2023 at 01:18:14PM +0300, Antoniu Miclaus wrote:
> > Add dt-bindings for ltc2991 octal i2c voltage, current and temperature
> > monitor.
> >
> > Signed-off-by: Antoniu Miclaus <antoniu.miclaus@xxxxxxxxxx>
> > ---
> > changes in v2:
> >  - make compatible const type
> >  - remove `|` where not necessary
> >  - switch to micro-ohms for the shunt resistor property
> >  - add vendor prefix for temperature-enable
> 
> Thanks for the updates...
> 
> >  .../bindings/hwmon/adi,ltc2991.yaml           | 114 ++++++++++++++++++
> >  1 file changed, 114 insertions(+)
> >  create mode 100644
> Documentation/devicetree/bindings/hwmon/adi,ltc2991.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/hwmon/adi,ltc2991.yaml
> b/Documentation/devicetree/bindings/hwmon/adi,ltc2991.yaml
> > new file mode 100644
> > index 000000000000..3811ea07a04f
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/hwmon/adi,ltc2991.yaml
> > @@ -0,0 +1,114 @@
> > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +
> > +$id: http://devicetree.org/schemas/hwmon/adi,ltc2991.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Analog Devices LTC2991 Octal I2C Voltage, Current and Temperature
> Monitor
> > +
> > +maintainers:
> > +  - Antoniu Miclaus <antoniu.miclaus@xxxxxxxxxx>
> > +
> > +description: |
> > +  The LTC2991 is used to monitor system temperatures, voltages and
> currents.
> > +  Through the I2C serial interface, the eight monitors can individually
> measure
> > +  supply voltages and can be paired for differential measurements of
> current
> > +  sense resistors or temperature sensing transistors.
> > +
> > +  Datasheet:
> > +    https://www.analog.com/en/products/ltc2991.html
> > +
> > +properties:
> > +  compatible:
> > +    const: adi,ltc2991
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  '#address-cells':
> > +    const: 1
> > +
> > +  '#size-cells':
> > +    const: 0
> > +
> > +  vcc-supply: true
> > +
> > +patternProperties:
> > +  "^channel@[0-3]$":
> > +    type: object
> > +    description:
> > +      Represents the differential/temperature channels.
> > +
> > +    properties:
> > +      reg:
> > +        description:
> > +          The channel number. LTC2991 can monitor 4 currents/temperatures.
> > +        items:
> > +          minimum: 0
> > +          maximum: 3
> > +
> > +      shunt-resistor-micro-ohms:
> > +        description:
> > +          The value of curent sense resistor in miliohms. Enables differential
> > +          input pair.
> > +
> > +      adi,temperature-enable:
> > +        description:
> > +          Enables temperature readings for a input pair.
> > +        type: boolean
> 
> ...but I did not see an answer to my question on v1:
> 	TBH, this seems like it is used just to control software behaviour.
> 	Why would you want to actually disable this in DT?
> In other words, is there something in that hardware that precludes
> measuring temperature for channels that do not contain this property?
> 
> Thanks,
> Conor.
> 
Sorry for missing that. I took in consideration this approach based on the pin functions
described in the datasheet (page 8 of 32). For example the V1 pin of the part can support
3 different configurations: "V1 (Pin 1): First Monitor Input. This pin can be configured
as a single-ended input (0V to 4.9V) or the positive inputfor a differential or remote diode
temperature measurement (in combination with V2)."
Moreover, looking at the multiple typical applications examples at the end of the datasheet
there is a specific adjacent hardware circuit connected to this part for the temperature
measurements configurations.

Thank you,
Antoniu
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - vcc-supply
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    i2c {
> > +        #address-cells = <1>;
> > +        #size-cells = <0>;
> > +
> > +        hwmon@48 {
> > +            compatible = "adi,ltc2991";
> > +            reg = <0x48>;
> > +            vcc-supply = <&vcc>;
> > +        };
> > +    };
> > +  - |
> > +    i2c {
> > +        #address-cells = <1>;
> > +        #size-cells = <0>;
> > +
> > +        hwmon@48 {
> > +            #address-cells = <1>;
> > +            #size-cells = <0>;
> > +
> > +            compatible = "adi,ltc2991";
> > +            reg = <0x48>;
> > +            vcc-supply = <&vcc>;
> > +
> > +            channel@0 {
> > +                    reg = <0x0>;
> > +                    shunt-resistor-micro-ohms = <100000>;
> > +            };
> > +
> > +            channel@1 {
> > +                    reg = <0x1>;
> > +                    shunt-resistor-micro-ohms = <100000>;
> > +            };
> > +
> > +            channel@2 {
> > +                    reg = <0x2>;
> > +                    temperature-enable;
> > +            };
> > +
> > +            channel@3 {
> > +                    reg = <0x3>;
> > +                    temperature-enable;
> > +            };
> > +        };
> > +    };
> > +...
> > --
> > 2.42.0
> >