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Sender: Guenter Roeck <groeck7@gmail.com>
To:     Oskar Senft <osk@google.com>, linux-hwmon@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     Jean Delvare <jdelvare@suse.com>, Rob Herring <robh+dt@kernel.org>
References: <20210910130337.2025426-1-osk@google.com>
From:   Guenter Roeck <linux@roeck-us.net>
Subject: Re: [PATCH] dt-bindings: hwmon: Add nct7802 bindings
Message-ID: <71c17c47-ca9e-e9d2-7b89-cc25b512c06a@roeck-us.net>
Date:   Fri, 10 Sep 2021 09:10:07 -0700
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On 9/10/21 6:03 AM, Oskar Senft wrote:
> Document bindings for the Nuvoton NCT7802Y driver.
> 
> Signed-off-by: Oskar Senft <osk@google.com>
> ---
>   .../bindings/hwmon/nuvoton,nct7802.yaml       | 66 +++++++++++++++++++
>   1 file changed, 66 insertions(+)
>   create mode 100644 Documentation/devicetree/bindings/hwmon/nuvoton,nct7802.yaml
> 
> diff --git a/Documentation/devicetree/bindings/hwmon/nuvoton,nct7802.yaml b/Documentation/devicetree/bindings/hwmon/nuvoton,nct7802.yaml
> new file mode 100644
> index 000000000000..bc4b69aeb116
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/hwmon/nuvoton,nct7802.yaml
> @@ -0,0 +1,66 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +
> +$id: http://devicetree.org/schemas/hwmon/nuvoton,nct7802.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Nuvoton NCT7802Y Hardware Monitoring IC
> +
> +maintainers:
> +  - Guenter Roeck <linux@roeck-us.net>
> +
> +description: |
> +  The NCT7802Y is a hardware monitor IC which supports one on-die and up to
> +  5 remote temperature sensors with SMBus interface.
> +
> +  Datasheets:
> +    https://www.nuvoton.com/export/resource-files/Nuvoton_NCT7802Y_Datasheet_V12.pdf
> +
> +properties:
> +  compatible:
> +    enum:
> +      - nuvoton,nct7802
> +
> +  reg:
> +    maxItems: 1
> +
> +  nuvoton,rtd-modes:
> +    description: |
> +      Select modes for the three RTDs.
> +
At the very least, "RTD" should be defined. The datasheet doesn't say explicitly,
but I suspect it means "Remote Temperature Diode".

> +      The order is RTD1, RTD2, RTD3.
> +
> +      Valid values for RTD1 and RTD2 are:
> +        "closed",
> +        "current",
> +        "thermistor",
> +        "voltage"
> +
> +      Valid values for RTD3 are:
> +        "closed",
> +        "thermistor",
> +        "voltage"
> +    type: stringlist

I am not sure what "closed" means (the datasheet doesn't say), but I suspect it means
that the sensor is disabled (?). For the other modes, the translation to the standard
ABI is:

current -> 3 (thermal diode)
thermistor -> 4 (thermistor)
voltage -> 2 (3904 transistor)

That makes me wonder if it would be better to define generic thermal sensor
properties (possibly aligned with the ABI) instead of chip specific ones.
That would probably require sub-nodes to be able to express if a specific
sensor is enabled/disabled. Rob, any thoughts ?

Thanks,
Guenter

> +
> +required:
> +  - compatible
> +  - reg
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    i2c {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        nct7802@28 {
> +            compatible = "nuvoton,nct7802";
> +            reg = <0x28>;
> +            nuvoton,sensor-modes =
> +              /* RTD1 */ "thermistor",
> +              /* RTD2 */ "voltage",
> +              /* RTD3 */ "closed";
> +        };
> +    };
>