dt-bindings: hwmon: Convert NTC thermistor to YAML

# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)

---

$id: http://devicetree.org/schemas/hwmon/ntc-thermistor.yaml#

$schema: http://devicetree.org/meta-schemas/core.yaml#

title: NTC thermistor temperature sensors

maintainers:

  - Naveen Krishna Chatradhi <ch.naveen@samsung.com>

  - Linus Walleij <linus.walleij@linaro.org>

description: |

  Thermistors with negative temperature coefficient (NTC) are resistors that

  vary in resistance in an often non-linear way in relation to temperature.

  The negative temperature coefficient means that the resistance decreases

  as the temperature rises. Since the relationship between resistance and

  temperature is non-linear, software drivers most often need to use a look

  up table and interpolation to get from resistance to temperature.

  When used in practice, a thermistor is often connected between ground, a

  pull-up resistor or/and a pull-down resistor and a fixed voltage like this:

      + e.g. 5V = pull-up voltage (puv)

      |

     +-+

     | |

     | | Pull-up resistor

     | | (puo)

     +-+

      |-------------------------o

     +-+ |                      ^

     | |/                       |

     | /                        |

     |/| Thermistor             | Measured voltage (mv)

     / |                        | "connected ground"

    /| |                        |

     +-+                        |

      |-------------------------o

     +-+                        ^

     | |                        |

     | | Pull-down resistor     | Measured voltage (mv)

     | | (pdo)                  | "connected positive"

     +-+                        |

      |                         |

      |                         v

      + GND                     GND

  The arrangements of where we measure the voltage over the thermistor are

  called "connected ground" and "connected positive" and shall be understood as

  the cases when either pull-up or pull-down resistance is zero.

  If the pull-up resistance is 0 one end of the thermistor is connected to the

  positive voltage and we get the thermistor on top of a pull-down resistor

  and we take the measure between the thermistor and the pull-down resistor.

  Conversely if the pull-down resistance is zero, one end of the thermistor is

  connected to ground and we get the thermistor under the pull-up resistor

  and we take the measure between the pull-up resistor and the thermistor.

  We can use both pull-up and pull-down resistors at the same time, and then

  the figure illustrates where the voltage will be measured for the "connected

  ground" and "connected positive" cases.

properties:

  $nodename:

    pattern: "^thermistor(.*)?$"

  compatible:

    oneOf:

      - const: epcos,b57330v2103

      - const: epcos,b57891s0103

      - const: murata,ncp15wb473

      - const: murata,ncp18wb473

      - const: murata,ncp21wb473

      - const: murata,ncp03wb473

      - const: murata,ncp15wl333

      - const: murata,ncp03wf104

      - const: murata,ncp15xh103

      # Deprecated "ntp," compatible strings

      - const: ntc,ncp15wb473

        deprecated: true

      - const: ntc,ncp18wb473

        deprecated: true

      - const: ntc,ncp21wb473

        deprecated: true

      - const: ntc,ncp03wb473

        deprecated: true

      - const: ntc,ncp15wl333

        deprecated: true

  "#thermal-sensor-cells":

    description: Thermal sensor cells if used for thermal sensoring.

    const: 0

  pullup-uv:

    $ref: /schemas/types.yaml#/definitions/uint32

    description: Pull-up voltage in micro volts. Must always be specified.

  pullup-ohm:

    $ref: /schemas/types.yaml#/definitions/uint32

    description: Pull-up resistance in ohms. Must always be specified, even

      if zero.

  pulldown-ohm:

    $ref: /schemas/types.yaml#/definitions/uint32

    description: Pull-down resistance in ohms. Must always be specified, even

      if zero.

  connected-positive:

    $ref: /schemas/types.yaml#/definitions/flag

    description: Indicates how the thermistor is connected in series with

      a pull-up and/or a pull-down resistor. See the description above for

      an illustration. If this flag is NOT specified, the thermistor is assumed

      to be connected-ground, which usually means a pull-down resistance of

      zero but complex arrangements are possible.

  # See /schemas/iio/adc/adc.yaml

  io-channels:

    maxItems: 1

    description: IIO ADC channel to read the voltage over the resistor. Must

      always be specified.

required:

  - compatible

  - pullup-uv

  - pullup-ohm

  - pulldown-ohm

  - io-channels

additionalProperties: false

examples:

  - |

    thermistor0 {

      compatible = "murata,ncp18wb473";

      io-channels = <&gpadc 0x06>;

      pullup-uv = <1800000>;

      pullup-ohm = <220000>;

      pulldown-ohm = <0>;

      #thermal-sensor-cells = <0>;

    };

NTC Thermistor hwmon sensors

-------------------------------

Requires node properties:

- "compatible" value : one of

	"epcos,b57330v2103"

	"epcos,b57891s0103"

	"murata,ncp15wb473"

	"murata,ncp18wb473"

	"murata,ncp21wb473"

	"murata,ncp03wb473"

	"murata,ncp15wl333"

	"murata,ncp03wf104"

	"murata,ncp15xh103"

/* Usage of vendor name "ntc" is deprecated */

<DEPRECATED>	"ntc,ncp15wb473"

<DEPRECATED>	"ntc,ncp18wb473"

<DEPRECATED>	"ntc,ncp21wb473"

<DEPRECATED>	"ntc,ncp03wb473"

<DEPRECATED>	"ntc,ncp15wl333"

- "pullup-uv"	Pull up voltage in micro volts

- "pullup-ohm"	Pull up resistor value in ohms

- "pulldown-ohm" Pull down resistor value in ohms

- "connected-positive" Always ON, If not specified.

		Status change is possible.

- "io-channels"	Channel node of ADC to be used for

		conversion.

Optional node properties:

- "#thermal-sensor-cells" Used to expose itself to thermal fw.

Read more about iio bindings at

	https://github.com/devicetree-org/dt-schema/blob/master/schemas/iio/

Example:

	ncp15wb473@0 {

		compatible = "murata,ncp15wb473";

		pullup-uv = <1800000>;

		pullup-ohm = <47000>;

		pulldown-ohm = <0>;

		io-channels = <&adc 3>;

	};