linux-kernel - Re: [RCF 2/3] hwmon: Document bindings for ads1118 adc driver

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Date:	Mon, 18 Jul 2016 05:51:41 -0700
From:	Joshua Clayton <stillcompiling@...il.com>
To:	Rob Herring <robh@...nel.org>
Cc:	Mark Rutland <mark.rutland@....com>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <kernel@...gutronix.de>,
	Fabio Estevam <fabio.estevam@....com>,
	Russell King <linux@...linux.org.uk>,
	Jean Delvare <jdelvare@...e.com>,
	Guenter Roeck <linux@...ck-us.net>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-hwmon@...r.kernel.org
Subject: Re: [RCF 2/3] hwmon: Document bindings for ads1118 adc driver

On Sunday, July 17, 2016 03:34:25 PM Rob Herring wrote:
> On Fri, Jul 15, 2016 at 05:18:22PM -0700, Joshua Clayton wrote:
> > ads1118 is a 4 input 16 bit adc with a buit-in temperature gauge
> > 
> > Signed-off-by: Joshua Clayton <stillcompiling@...il.com>
> > ---
> >  .../devicetree/bindings/hwmon/ads1118.txt          | 81 ++++++++++++++++++++++
> >  1 file changed, 81 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/hwmon/ads1118.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/hwmon/ads1118.txt b/Documentation/devicetree/bindings/hwmon/ads1118.txt
> > new file mode 100644
> > index 0000000..41c66dc
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/hwmon/ads1118.txt
> > @@ -0,0 +1,81 @@
> > +ADS1118 (SPI)
> > +
> > +The ADS1118 is 16-bit analog to digital converter with 4 inputs and a
> > +temperature sensor.
> > +The ADS1018 is a 12-bit version of the chip.
> > +
> > +The inputs can be single ended or differential pair combinations.
> > +
> > +Each channel, 0 - 4 may be configured as a single ended adc input.
> > +Channel 0 may be configured differentially with channel 1.
> > +Channels 0, 1, or 2 may be configured differentially with channel 3.
> > +
> > +To set up a differential pair, the lower channel should be have
> > +the ti,differential-endpoint property set to the higher channel in the pair.
> > +
> > +Each channel can be configured individually:
> > + - fullscale voltage range values are +/- microvolts
> > +    6144000, 4096000, 2048000, 1024000, 512000, or 256000
> > +
> > + - data_rate in samples per second
> > +    - for the ads1018:
> > +      128, 250, 490, 920, 1600, 2400, or 3300
> > +    - for the ads1118:
> > +      8, 16, 32, 64, 128, 250, or 860
> 
> Would be better if these are documented with the property itself.
> 
> > +
> > +The sensor contains an internal pullup register to keep the data output
> > +high when not in use. This may be disabled, but is enabled by default.
> > +
> > +1) The /ads1118 node
> > +
> > +  Required properties:
> > +
> > +   - compatible : must be "ti,ads1018" or "ti,ads1118"
> > +   - spi-cpha : spi phase set to 1 (spi polarity is 0)
> > +   - reg : the spi chipselect address
> > +   - #address-cells : must be <1>
> > +   - #size-cells : must be <0>
> > +
> > +  Optional properties:
> > +
> > +   - ti,tempsensor: enable the temperature sensor
> > +   - ti,pullup-disable: disable the internal pullup resistor
> 
> Explicitly state these are boolean.
> 
> > +
> > +  The node contains child nodes for each channel that the platform uses.
> > +
> > +2) channel nodes
> > +
> > +  Required properties:
> > +
> > +   - reg : the channel number (0, 1, 2, or 3)
> > +
> > +  Optional properties:
> > +
> > +   - ti,differential-endpoint: differential second endpoint.
> 
> Type?
Hmm. the type is numeric input "channel number". 1, 3 or "none" are
the only valid choices
> 
> > +   - ti,fullscale: fullscale range in +/- microvolts
> 
> Add standard unit suffix.
Will do
> 
> > +   - ti,datarate : the converter data rate in samples / second
> 
> Perhaps "-hz" here?
OK
> 
> > +
> > +  Example ADS1118 node:
> > +
> > +	ads1118@0 {
> > +		compatible = "ti,ads1118";
> > +		spi-max-frequency = <2450000>;
> > +		reg = <0>;
> > +		#address-cells = <1>;
> > +		#size-cells = <0>;
> > +		ti,tempsensor;
> > +		voltage0@0 {
> 
> Perhaps channel@0. Either way, drop the first 0.
Ah, thanks. I'll go with channel@0
> 
> > +			reg = <0>;
> > +			ti,fullscale = <6144000>;
> > +			ti,datarate = <860>;
> > +			ti,differential-endpoint = <1>;
> > +		};
> > +		voltage1@3 {
> > +			reg = <3>;
> > +			ti,fullscale = <6144000>;
> > +			ti,datarate = <475>;
> > +		};
> > +	};
> > +
> > +For the above example, The temperature sensor is enabled as well as
> > +channels 0 and 1 in differential mode, and channel 3 single ended.
>