From: Rob Herring <robh@kernel.org>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Jean Delvare <jdelvare@suse.com>,
Guenter Roeck <linux@roeck-us.net>,
linux-hwmon@vger.kernel.org,
Javier Martinez Canillas <javier@dowhile0.org>,
Johannes Pointner <johannes.pointner@gmail.com>,
Peter Rosin <peda@axentia.se>,
Jonathan Cameron <Jonathan.Cameron@huawei.com>,
devicetree@vger.kernel.org
Subject: Re: [PATCH v2] dt-bindings: hwmon: Convert NTC thermistor to YAML
Date: Mon, 12 Jul 2021 08:57:49 -0600 [thread overview]
Message-ID: <20210712145749.GA1911897@robh.at.kernel.org> (raw)
In-Reply-To: <20210703173456.4002549-1-linus.walleij@linaro.org>
On Sat, Jul 03, 2021 at 07:34:56PM +0200, Linus Walleij wrote:
> This converts the NTC thermistor DT bindings to YAML. Some care had to
> be taken since I had to add some illustrations to make the connection
> layouts graspable.
>
> Cc: Javier Martinez Canillas <javier@dowhile0.org>
> Cc: Johannes Pointner <johannes.pointner@gmail.com>
> Cc: Peter Rosin <peda@axentia.se>
> Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Cc: devicetree@vger.kernel.org
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
> ChangeLog v1->v2:
> - Realize I need to CC devicetree@vger.kernel.org on this.
> - Fix Javier's mail address.
> - Drop Naveen's mail (bouncing)
> ---
> .../bindings/hwmon/ntc-thermistor.yaml | 142 ++++++++++++++++++
> .../bindings/hwmon/ntc_thermistor.txt | 44 ------
> 2 files changed, 142 insertions(+), 44 deletions(-)
> create mode 100644 Documentation/devicetree/bindings/hwmon/ntc-thermistor.yaml
> delete mode 100644 Documentation/devicetree/bindings/hwmon/ntc_thermistor.txt
>
> diff --git a/Documentation/devicetree/bindings/hwmon/ntc-thermistor.yaml b/Documentation/devicetree/bindings/hwmon/ntc-thermistor.yaml
> new file mode 100644
> index 000000000000..87589da631c9
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/hwmon/ntc-thermistor.yaml
> @@ -0,0 +1,142 @@
> +# 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
All these can be 1 enum.
> + # 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
And these too.
> +
> + # See /schemas/thermal/thermal-sensor.yaml for details
Drop. (I hope to generate documentation from the schema and
automagically create references/links.)
> + "#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>;
> + };
next prev parent reply other threads:[~2021-07-12 14:57 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-03 17:34 [PATCH v2] dt-bindings: hwmon: Convert NTC thermistor to YAML Linus Walleij
2021-07-12 14:57 ` Rob Herring [this message]
2021-07-14 15:49 ` Linus Walleij
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