On Sun Jul 4, 2021 at 1:02 PM EDT, Jonathan Cameron wrote: > On Wed, 30 Jun 2021 21:00:33 -0400 > Liam Beguin <liambeguin@xxxxxxxxx> wrote: > > > From: Liam Beguin <lvb@xxxxxxxxxx> > > > > An ADC is often used to measure other quantities indirectly. This > > binding describe one case, the measurement of a temperature through the > > voltage across an RTD resistor such as a PT1000. > > > > Signed-off-by: Liam Beguin <lvb@xxxxxxxxxx> > > --- > > .../iio/afe/temperature-sense-rtd.yaml | 101 ++++++++++++++++++ > > MAINTAINERS | 7 ++ > > 2 files changed, 108 insertions(+) > > create mode 100644 Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml > > > > diff --git a/Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml b/Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml > > new file mode 100644 > > index 000000000000..e23e74e63ec5 > > --- /dev/null > > +++ b/Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml > > @@ -0,0 +1,101 @@ > > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) > > +%YAML 1.2 > > +--- > > +$id: http://devicetree.org/schemas/iio/afe/temperature-sense-rtd.yaml# > > +$schema: http://devicetree.org/meta-schemas/core.yaml# > > + > > +title: Temperature Sense RTD > > + > > +maintainers: > > + - Liam Beguin <lvb@xxxxxxxxxx> > > + > > +description: | > > + RTDs (Resistance Temperature Detectors) are a kind of temperature sensors > > + used to get a linear voltage to temperature reading within a give range > > + (usually 0 to 100 degrees Celsius). > > + > > + When an io-channel measures the output voltage across an RTD such as a > > + PT1000, the interesting measurement is almost always the corresponding > > + temperature, not the voltage output. This binding describes such a circuit. > > + > > + The general transfer function here is (using SI units) > > + > > + V = R(T) * iexc > > + R(T) = r0 * (1 + alpha * T) > > + T = 1 / (alpha * r0 * iexc) * (V - r0 * iexc) > > + > > + The following circuit matches what's in the examples section. > > + > > + 5V0 > > + ----- > > + | > > + +---+----+ > > + | R 5k | > > + +---+----+ > > + | > > + V 1mA > > + | > > + +---- Vout > > + | > > + +---+----+ > > + | PT1000 | > > + +---+----+ > > + | > > + ----- > > + GND > > + > > +properties: > > + compatible: > > + const: temperature-sense-rtd > > + > > + io-channels: > > + maxItems: 1 > > + description: | > > + Channel node of a voltage io-channel. > > + > > + '#io-channel-cells': > > + const: 1 > > Only 1 channel, so this should be 0. For consumers of this driver > they only need to identify the device, not the device + channel. > > https://github.com/devicetree-org/dt-schema/blob/master/schemas/iio/iio.yaml > Thanks for pointing that out. will fix. > > + > > + excitation-current-microamp: > > + description: The current fed through the RTD sensor. > > + > > + alpha-ppm-per-celsius: > > + description: | > > + alpha can also be expressed in micro-ohms per ohm Celsius. It's a linear > > + approximation of the resistance versus temperature relationship > > + between 0 and 100 degrees Celsius. > > + > > + alpha = (R_100 - R_0) / (100 * R_0) > > + > > + Where, R_100 is the resistance of the sensor at 100 degrees Celsius, and > > + R_0 (or r-naught-ohms) is the resistance of the sensor at 0 degrees > > + Celsius. > > + > > + Pure platinum has an alpha of 3925. Industry standards such as IEC60751 > > + and ASTM E-1137 specify an alpha of 3850. > > + > > + r-naught-ohms: > > + description: | > > + Resistance of the sensor at 0 degrees Celsius. > > + Common values are 100 for PT100, 500 for PT500, and 1000 for PT1000 > > + > > +additionalProperties: false > > +required: > > + - compatible > > + - io-channels > > + - excitation-current-microamp > > + - alpha-ppm-per-celsius > > + - r-naught-ohms > > + > > +examples: > > + - | > > + pt1000_1: temperature-sensor0 { > > + compatible = "temperature-sense-rtd"; > > + #io-channel-cells = <1>; > > + io-channels = <&temp_adc1 0>; > > + > > + excitation-current-microamp = <1000>; /* i = U/R = 5 / 5000 */ > > + alpha-ppm-per-celsius = <3908>; > > + r-naught-ohms = <1000>; > > + }; > > +... > > diff --git a/MAINTAINERS b/MAINTAINERS > > index 9bf553e53f0f..ed80e671a16a 100644 > > --- a/MAINTAINERS > > +++ b/MAINTAINERS > > @@ -8897,6 +8897,13 @@ F: Documentation/devicetree/bindings/iio/afe/current-sense-shunt.yaml > > F: Documentation/devicetree/bindings/iio/afe/voltage-divider.yaml > > F: drivers/iio/afe/iio-rescale.c > > > > +IIO UNIT CONVERTER (TEMPERATURE) > > +M: Liam Beguin <liambeguin@xxxxxxxxx> > > +R: Peter Rosin <peda@xxxxxxxxxx> > > +L: linux-iio@xxxxxxxxxxxxxxx > > +S: Maintained > > +F: Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml > > I'm not sure we'd normally bother with a MAINTAINERS entry when it is > just the binding doc > (as rest is in the driver). The binding doc itself has it's own local > maintainers entry > which is the more useful one. > You're right, it makes sense to drop the changes to MAINTAINERS as the information is already contained it the bindings. I added this after briefly talking about it with Peter. Thanks again for reviewing these changes, Liam > > + > > IKANOS/ADI EAGLE ADSL USB DRIVER > > M: Matthieu Castet <castet.matthieu@xxxxxxx> > > M: Stanislaw Gruszka <stf_xl@xxxxx>
