Re: [PATCH 2/3] dt-bindings: iio: wrapper: add io-channel-unit-converter
From: Jonathan Cameron <jic23@kernel.org>
Date: 2018-03-24 13:53:19
Also in:
linux-iio, lkml
On Mon, 19 Mar 2018 18:02:45 +0100 Peter Rosin [off-list ref] 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 <redacted> --- .../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
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MAINTAINERS | 6 ++ 2 files changed, 90 insertions(+) create mode 100644 Documentation/devicetree/bindings/iio/wrapper/io-channel-unit-converter.txtdiff --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.
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+ +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-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>