Hi Peter, On Fri Jun 11, 2021 at 3:37 AM EDT, Peter Rosin wrote: > Hi! > > Should "amplifier" really be part of the name for this binding when it's > now > just a generic voltage-to-temperature rescale binding? Or, perhaps a > better > description is THE generic voltage-to-temperature rescale binding? I went with temperature-sense-amplifier because it resembled what you had for the current sense binding, and because of the generic scaling factor in v2. > > But that's not a strong opinion, I know next to nothing about these > things > and it might be that an amplifier is involved in the vast majority of > cases? > Maybe it's enough to be more explicit in the describing text that the > binding > is intended for analog front ends lacking an amplifier as well? I just > find > it a bit confusing since there are actual HW that calls itself > "temperature > sence amplifiers" that I think this binding targets but then isn't > exemplified anywhere. > > Also, it disturbs my sense of symmetry if volt->temp gets a generic > binding like this, when volt->current and volt->volt have bindings for > specific front ends. Again, it's not a strong opinion, I'm just pointing > it > out. For the record, I started out with a generic volt->current binding > similar to this volt->temp binding, but got push-back so that we now > have > two specific volt->current bindings. Again, I'm just pointing this out, > and > I'm perfectly aware that "rules" and opinions change over time. I agree with you that it can be confusing given that some temperature sensors call themselves "temperature sense amplifiers". In v1, temperature-sense-amplifier was used for that kind of device. I liked having one binding per front end type like we had in v1 because the devicetree ends up listing hardware parameters which I find is more explicit. I went with a generic one for v2 because I thought it would make it applicable to other use-cases and simplify implementation. I don't have strong feelings about keeping v2 over v1 bindings, and given what we talked about v1 might be better here. Do you have a preference? > > On 2021-06-07 16:47, Liam Beguin wrote: > > From: Liam Beguin <lvb@xxxxxxxxxx> > > > > An ADC is often used to measure other quantities indirectly. This > > binding describe such a use case, the measurement of a temperature > > through an analog front end connected to a voltage channel. > > > > Signed-off-by: Liam Beguin <lvb@xxxxxxxxxx> > > --- > > .../iio/afe/temperature-sense-amplifier.yaml | 57 +++++++++++++++++++ > > MAINTAINERS | 1 + > > 2 files changed, 58 insertions(+) > > create mode 100644 Documentation/devicetree/bindings/iio/afe/temperature-sense-amplifier.yaml > > > > diff --git a/Documentation/devicetree/bindings/iio/afe/temperature-sense-amplifier.yaml b/Documentation/devicetree/bindings/iio/afe/temperature-sense-amplifier.yaml > > new file mode 100644 > > index 000000000000..08f97f052a91 > > --- /dev/null > > +++ b/Documentation/devicetree/bindings/iio/afe/temperature-sense-amplifier.yaml > > @@ -0,0 +1,57 @@ > > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) > > +%YAML 1.2 > > +--- > > +$id: http://devicetree.org/schemas/iio/afe/temperature-sense-amplifier.yaml# > > +$schema: http://devicetree.org/meta-schemas/core.yaml# > > + > > +title: Temperature Sense Amplifier > > + > > +maintainers: > > + - Liam Beguin <lvb@xxxxxxxxxx> > > Here, you claim maintainership... > > > + > > +description: | > > + When an io-channel measures the output voltage of a temperature analog front > > + end such as an RTD (resistance thermometer) or a temperature to current > > + sensor, the interesting measurement is almost always the corresponding > > + temperature, not the voltage output. This binding describes such a circuit. > > Why would you convert from a voltage if you have a "temperature to > current > sensor"? Such a sensor should give you a current. Yeah yeah, I get it, > you > bake some resistance into the "gain" and you are done. But I think these > things should be explicitly mentioned with examples. I think it would be > a > lot less terse if you spell out a couple of common ways to connect one > of > these linear temperature sensors and how that then maps to the gain that > the > consumer of the binding needs to use. > > It would also be a good thing to mention sensors by name, so that > someone > grepping for them finds this binding. It's a djungle out there. > You're right adding sensors names here would be very useful. I'll rework the description with your suggestions and add specific examples with maybe schematic drawings like in voltage-divider.yaml. > > + > > +properties: > > + compatible: > > + const: temperature-sense-amplifier > > + > > + io-channels: > > + maxItems: 1 > > + description: | > > + Channel node of a voltage io-channel. > > + > > + '#io-channel-cells': > > + const: 1 > > + > > + sense-gain-mult: > > + $ref: /schemas/types.yaml#/definitions/uint32 > > + description: Amplifier gain multiplier. The default is <1>. > > + > > + sense-gain-div: > > + $ref: /schemas/types.yaml#/definitions/uint32 > > + description: Amplifier gain divider. The default is <1>. > > + > > + sense-offset-millicelsius: > > + description: Amplifier offset. The default is <0>. > > + > > +additionalProperties: false > > +required: > > + - compatible > > + - io-channels > > + > > +examples: > > + - | > > + pt1000_1: temperature-sensor { > > + compatible = "temperature-sense-amplifier"; > > + #io-channel-cells = <1>; > > + io-channels = <&temp_adc 3>; > > + > > + sense-gain-mult = <1000000>; > > + sense-gain-div = <3908>; > > + sense-offset-millicelsius = <(-255885)>; > > + }; > > +... > > diff --git a/MAINTAINERS b/MAINTAINERS > > index e679d422b472..4f7b4ee9f19b 100644 > > --- a/MAINTAINERS > > +++ b/MAINTAINERS > > @@ -8887,6 +8887,7 @@ L: linux-iio@xxxxxxxxxxxxxxx > > S: Maintained > > F: Documentation/devicetree/bindings/iio/afe/current-sense-amplifier.yaml > > F: Documentation/devicetree/bindings/iio/afe/current-sense-shunt.yaml > > +F: Documentation/devicetree/bindings/iio/afe/temperature-sense-amplifier.yaml > > ...and here, you give maintenance to me. I didn't want all afe bindings > so I > didn't put an asterisk there for a reason :-) Sorry about that :-) I don't really know what the convention is here. I put myself as a maintainer on the yaml file since I created it. For the MAINTAINERS patch, would something like this be better? IIO UNIT CONVERTER (TEMPERATURE) M: Liam Beguin <liambeguin@xxxxxxxxx> R: Peter Rosin <peda@xxxxxxxxxx> F: Documentation/devicetree/bindings/iio/afe/temperature-sense-amplifier.yaml Should I also add myself as a reviewer to the iio-rescaler driver for the temperature related changes? Also, I noticed an issue with the offset. When we're not using a processed channel, the upstream channel scale has to be applied to the offset which I forgot to do. I'm working on this for v3. Thanks for your time, Liam > This binding is backed by the iio-rescale driver, so it's not totally > alien > for me to maintain it, but I'd be more happy if you listed yourself as I > think > you intended to? > > Cheers, > Peter > > > F: Documentation/devicetree/bindings/iio/afe/voltage-divider.yaml > > F: drivers/iio/afe/iio-rescale.c > > > >
