Re: [PATCH v5 1/4] hwmon: ltc2978: device tree bindings documentation

[Guenter Roeck]

On 10/03/2014 05:27 AM, Mark Rutland wrote:
> On Thu, Oct 02, 2014 at 07:37:48PM +0100, atull@xxxxxxxxxxxxxxxxxxxxx wrote:
> > From: Alan Tull <atull@xxxxxxxxxxxxxxxxxxxxx>
> >
> > Add device tree bindings documentation for ltc2978.
> >
> > Signed-off-by: Alan Tull <atull@xxxxxxxxxxxxxxxxxxxxx>
> > ---
> > v2: clean whitespace
> > ---
> >   .../devicetree/bindings/hwmon/ltc2978.txt          |   41 ++++++++++++++++++++
> >   1 file changed, 41 insertions(+)
> >   create mode 100644 Documentation/devicetree/bindings/hwmon/ltc2978.txt
> >
> > diff --git a/Documentation/devicetree/bindings/hwmon/ltc2978.txt b/Documentation/devicetree/bindings/hwmon/ltc2978.txt
> > new file mode 100644
> > index 0000000..b2d9c4d
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/hwmon/ltc2978.txt
> > @@ -0,0 +1,41 @@
> > +ltc2978
> > +
> > +Required properties:
> > + - compatible: one of: ltc2974, ltc2977, ltc2978, ltc3880, ltc3883, ltm4676
>
> Could we please format this like:
>
> - compatible: should contain one of:
>    * "ltc2974"
>    * "ltc2977"
>    * "ltc2978"
>    * "ltc3880"
>    * "ltc3883"
>    * "ltm4676"
>
> Given the file name, are these all variants of ltc2978?
>
> > + - reg: I2C address
> > +
> > +Optional properties:
> > + Name of the optional regulator subnode must be "regulators".
> > +  - #address-cells must be 1.
>
> What's the single address cell used for?
I think this is required by the regulator bindings.
Other regulators use the same, though they don't typically
mention it in the properties list but only in the examples.

> > +  - #size-cells must be 0.
> > +
> > + For each regulator:
> > +  - reg: regulator number
>
> Which can be...?
>
> What does this correspond to in the HW?
Channel number or index. Pretty much the 0..7 from the name below.

> > +  - regulator-compatible: must be vout_en<regulator number> such as vout_en3
> > +    valid range is:
> > +      ltc2977, ltc2978 : vout_en0 - vout_en7
> > +      ltc2974          : vout_en0 - vout_en3
> > +      ltc3880, ltm4676 : vout_en0 - vout_en1
> > +      ltc3883          : vout_en0 only
>
> In other bindings I believe I've seen the node name used for this.
Seems like per-device names are chosen for other regulators.
PMBus commonly uses the term "VOUT" for output voltages,
so vout[0-7] should be ok.

Which reminds me: We had earlier asked to drop the "_en" from the strings
as unnecessary.

> Mark, what's the preferred scheme for identifying regulators in a
> container node?
>
> > +  - regulator-name: arbitrary name for regulator
>
> Drop the 'aribtarary'. Either this should be the name of the regulator
> on the board, or it shouldn't be necessary.
Not sure if it even needs to be documented here. It is already documented
in Documentation/devicetree/bindings/regulator/regulator.txt.

> Mark.
>
> > +
> > +Example:
> > +ltc2978@5e {
> > +	compatible = "ltc2978";
> > +	reg = <0x5e>;
> > +	regulators {
> > +		#address-cells = <1>;
> > +		#size-cells = <0>;
> > +
> > +		vdacp0_reg: regulator@0 {
> > +			reg = <0>;
> > +			regulator-compatible = "vout_en0";
> > +			regulator-name = "FPGA-2.5V";
> > +		};
> > +		vdacp2_reg: regulator@2 {
> > +			reg = <2>;
> > +			regulator-compatible = "vout_en2";
> > +			regulator-name = "FPGA-1.5V";
> > +		};
> > +	};
> > +};
> > --
> > 1.7.9.5

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