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SubjectRe: [PATCH 2/3] dt-bindings: iio: wrapper: add io-channel-unit-converter
On Sat, 24 Mar 2018 13:53:19 +0000
Jonathan Cameron <jic23@kernel.org> wrote:

> On Mon, 19 Mar 2018 18:02:45 +0100
> Peter Rosin <peda@axentia.se> wrote:
>
> > Allow linear scaling and modification of the type of an io-channel.
> >
> > When an ADC channel measures the midpoint of a voltage divider, the
> > interesting voltage is often the voltage over the full resistance
> > of the divider. Likewise, measuring the voltage over a resistor is
> > often a way to get to the current through it.
> >
> > This binding allows description of such hardware which is external
> > to the ADC.
> >
> > Signed-off-by: Peter Rosin <peda@axentia.se>
> > ---
> > .../iio/wrapper/io-channel-unit-converter.txt | 84 ++++++++++++++++++++++
> Hmm. I'm not convinced by the naming really though I can see where you care
> coming from as it can effectively use a voltage ADC to measure a current.
>
> Lets see if the devicetree people or anyone else has a suggestion on this.
>
> Could go with AFE as that is how a chip doing this would normally be described.
> It's just that here we are doing it in old fashioned resistors...
>
> There are a few unusual elements in here binding wise so definitely looking
> for input on the bindings!
>
> Thanks,
>
> Jonathan
>
> > MAINTAINERS | 6 ++
> > 2 files changed, 90 insertions(+)
> > create mode 100644 Documentation/devicetree/bindings/iio/wrapper/io-channel-unit-converter.txt
> >
> > diff --git a/Documentation/devicetree/bindings/iio/wrapper/io-channel-unit-converter.txt b/Documentation/devicetree/bindings/iio/wrapper/io-channel-unit-converter.txt
> > new file mode 100644
> > index 000000000000..23af661abe32
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/iio/wrapper/io-channel-unit-converter.txt
> > @@ -0,0 +1,84 @@
> > +I/O channel unit converter bindings
> > +
> > +Allow linear scaling and modification of the type of an io-channel.
> I can certainly conceive that we will have simple non linear cases in future
> though they get awfully hard to describe so we can tackle that when it
> happens.
> > +
> > +When an ADC channel measures the midpoint of a voltage divider, the
> > +interesting voltage is often the voltage over the full resistance
> > +of the divider. Likewise, measuring the voltage over a resistor is
> > +often a way to get to the current through it.
> > +
> > +Required properties:
> > +- compatible : "io-channel-unit-converter"
> > +- io-channels : Channel node of the parent channel.
> > +- io-channel-names : Should be "parent".
> > +
> > +Optional properties:
> > +- numerator : The parent channel scale is multiplied by this value (default 1).
> > +- denominator : The parent channel scale is divided by this value (default 1).
> > +- type : The type of the wrapped channel is modified to this type. The default
> > + is to use the same type as the parent channel. Recognized types are:
> > + "voltage"
> > + "current"
> > +
> > +Example 1:
> > +The system voltage is circa 12V, but divided down with a 22/200
> > +voltage divider to adjust it to the ADC range.
> > +
> > +SYSV ADC GND
> > + + + +
> > + | .-----. | .----. |
> > + '--| 200 |-+-| 22 |--'
> > + '-----' '----'
> > +
> > +sysv {
> > + compatible = "io-channel-unit-converter";
> > + io-channles = <&maxadc 1>;
> > + io-channel-names = "parent";
> > +
> > + /* multiply the ADC voltage by 222/22 to get the system voltage */
> > + numerator = <222>; /* 200 + 22 */
> > + denominator = <22>;
> > +}
> > +
> > +&spi {
> > + maxadc: adc@0 {
> > + compatible = "maxim,max1027";
> > + reg = <0>;
> > + #io-channel-cells = <1>;
> > + interrupt-parent = <&gpio5>;
> > + interrupts = <15 IRQ_TYPE_EDGE_RISING>;
> > + spi-max-frequency = <1000000>;
> > + };
> > +};
> > +
> > +Example 2:
> > +The system current is measured by measuring the voltage over a
> > +3.3 ohm resistor.
> > +
> > +sysi {
> > + compatible = "io-channel-unit-converter";
> > + io-channles = <&tiadc 0>;
io-channels and same above.

> > + io-channel-names = "parent";
> > +
> > + /* divide the ADC voltage by 33/10 (i.e. 3.3) to get current */
> > + numerator = <10>;
> > + denominator = <33>;
> > + type = "current";
> > +}
> > +
> > +&i2c {
> > + tiadc: adc@48 {
> > + compatible = "ti,ads1015";
> > + reg = <0x48>;
> > + #io-channel-cells = <1>;
> > +
> > + #address-cells = <1>;
> > + #size-cells = <0>;
> > +
> > + channel@0 { /* IN0,IN1 differential */
> > + reg = <0>;
> > + ti,gain = <1>;
> > + ti,datarate = <4>;
> > + };
> > + };
> > +};
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 96e5503bfb60..5dd555c7b1b0 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -6884,6 +6884,12 @@ F: drivers/staging/iio/
> > F: include/linux/iio/
> > F: tools/iio/
> >
> > +IIO UNIT CONVERTER
> > +M: Peter Rosin <peda@axentia.se>
> > +L: linux-iio@vger.kernel.org
> > +S: Maintained
> > +F: Documentation/devicetree/bindings/iio/wrapper/io-channel-unit-converter.txt
> > +
> > IKANOS/ADI EAGLE ADSL USB DRIVER
> > M: Matthieu Castet <castet.matthieu@free.fr>
> > M: Stanislaw Gruszka <stf_xl@wp.pl>
>
> --
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