Re: [PATCH 3/3] staging: iio: docs: add ad7192 doc to detail dt usage

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On Sun, 2018-01-14 at 12:56 +0000, Jonathan Cameron wrote:
> On Wed, 10 Jan 2018 13:29:56 +0200
> <alexandru.ardelean@xxxxxxxxxx> wrote:
> 
> > From: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
> > 
> > Document the device-tree bindings of the "ad7192" driver.
> > Added datasheet references for supported devices,
> > explanation for each property supported by the driver,
> > and an example.
> > 
> > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
> > ---
> >  .../staging/iio/Documentation/adc/adi,ad7192.txt   | 71
> > ++++++++++++++++++++++
> >  1 file changed, 71 insertions(+)
> >  create mode 100644
> > drivers/staging/iio/Documentation/adc/adi,ad7192.txt
> > 
> > diff --git a/drivers/staging/iio/Documentation/adc/adi,ad7192.txt
> > b/drivers/staging/iio/Documentation/adc/adi,ad7192.txt
> > new file mode 100644
> > index 000000000000..1f8f769a003f
> > --- /dev/null
> > +++ b/drivers/staging/iio/Documentation/adc/adi,ad7192.txt
> > @@ -0,0 +1,71 @@
> > +Analog Devices AD719x ADC Driver
> > +
> > +Reference:
> > +[1] http://www.analog.com/en/products/analog-to-digital-converters
> > /ad7190.html
> > +[2] http://www.analog.com/en/products/analog-to-digital-converters
> > /ad7192.html
> > +[3] http://www.analog.com/en/products/analog-to-digital-converters
> > /ad7193.html
> > +[4] http://www.analog.com/en/products/analog-to-digital-converters
> > /ad7195.html
> > +
> > +Required properties:
> > +  - compatible: Should be "adi,ad7190", "adi,ad7192", "adi,ad7193"
> > +  or "adi,ad7195"
> > +  - reg: SPI chip select number for the device
> > +  - spi-cpol, spi-cpha: Controller support only mode 3, so both
> > spi-cpol
> > +  and spi-cpha should be present
> > +  - spi-max-frequency: Definition as per
> > +  see: Documentation/devicetree/bindings/spi/spi-bus.txt
> > +  - interrupt-parent: phandle to the parent interrupt controller
> > +  see: Documentation/devicetree/bindings/interrupt-
> > controller/interrupts.txt
> > +  - interrupts: IRQ line for the ADC
> > +  see: Documentation/devicetree/bindings/interrupt-
> > controller/interrupts.txt
> > +
> > +Recommended properties:
> > +  - adi,clock-source-select: sets the clock source to be used;
> > values are
> > +   * 0 - external crystal, connected from pin MCLK1 to MCLK2
> > +   * 1 - external clock, applied to MCLK2 pin
> > +   * 2 - internal 4.92 Mhz clock; pin MCLK2 is tristated (default)
> > +   * 3 - internal 4.92 Mhz clock; internal clock is available on
> > MCLK2
> 
> For the external clock there are standard bindings
> Documentation/devicetree/bindings/clock/clock-bindings.txt
> If one is specified assume it should be used.
> 
> For the crystal a quick grep suggests that clocknames are used in
> somecases
> at least to distinguish between osc and xtal.

ack
will use clock bindings

> 
> Final pair probably need a specific devicetree binding like
> adi,clockout or something...  (not thought much on that name!)
> 
> 
> > +  - adi,external-clock-Hz: if "adi,clock-source-select" is value
> > '1',
> > +  this value should be specified to the ADC
> > +  - avdd-supply: Analog Supply Voltage, 4.75V to 5.25V. AVDD is
> > +  independent of DVDD
> > +  - dvdd-supply: Digital Supply Voltage, 2.7V to 5.25V. DVDD
> > +  is independent of AVDD
> 
> Regulators not values + add a cross reference to the regulator docs.
> I would make this required rather than optional.  Easy to supply
> fixed regs in devicetree if it makes sense and will simplify
> things in the long run if we know they are awlays there.
> 
> 

ack

> > +
> > +Optional properties:
> > +  - adi,refin2-pins-enable: select external reference to be
> > applied
> > +  to P1,REFIN2(+) & P0,REFIN2(-) pins instead of REFIN1(+) &
> > REFIN1(-);
> > +  not available for "ad7195"
> > +  - adi,rejection-60-Hz-enable: enables simultaneous 50/60 Hz
> > rejection
> > +  - adi,chop-enable: enable chop to minimize ADC offset and offset
> > drift
> > +  - adi,buffer-enable: enables the buffer on the analog inputs
> > +  - adi,burnout-currents-enable: when selected, the 500 nA current
> > sources
> > +  in the signal path are enabled; can be enabled only when buffer
> > is active
> > +  and chop is disabled
> 
> These are an oddity.  I'm unclear on whether you would ever have them
> on
> all the time.  Sounds like detection hardware that you'd run in an
> initial
> self test to check your transducer isn't blown.
> 

they're chip-settings done at init time
the names may need some work, maybe even the types ;
it could be that these may even work at runtime, in which case, a sysfs
binding may be more interesting
i'd have to investigate more in-depth

> 
> > +  - adi,sinc3-filter-enable: enables the SINC3 filter; if unset
> > +  the SINC4 digital filter is used after the modulator
> 
> so this is a selection between two filters.  Good if the naming
> implies this..
> 
> > +  - adi,unipolar-enable: when this is set voltage ranges must be
> > unipolar
> > +  (e.g 0 to 5V) versus bipolar voltage ranges (e.g. -5V to 5V)
> 
> That isn't close to what I'm reading from the datasheet.
> 
> "A bipolar input range does not
> imply that the part can tolerate negative voltages with respect to
> system AGND. "
> 
> This is about using a second input as the differential negative vs
> using
> the common reference input...

will re-visit
i'll admit this stuff is not yet my forte, but I'll make an effort to
learn

> 
> > +
> > +Example:
> > +ad7190@0 {
> > +	compatible = "adi,ad7190";
> > +	reg = <0>;
> > +	spi-max-frequency = <1000000>;
> > +	spi-cpol;
> > +	spi-cpha;
> > +
> > +	#interrupt-cells = <2>;
> > +	interrupts = <25 0x2>;
> > +	interrupt-parent = <&gpio>;
> > +	avdd-supply = <&adc_avdd>;
> > +
> > +	adi,clock-source-select = /bits/ 8 <0>;
> > +
> > +	adi,refin2-pins-enable;
> > +	adi,rejection-60-Hz-enable;
> > +	adi,buffer-enable;
> > +	adi,burnout-currents-enable;
> > +	adi,sinc3-filter-enable;
> > +	adi,unipolar-enable;
> > +};
> 
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