Re: [PATCH 1/2] dt-bindings: hwmon: add binding documentation for adt7475

[Guenter Roeck]

On 11/6/18 8:27 PM, Chris Packham wrote:
> On 7/11/18 5:24 PM, Guenter Roeck wrote:
> > On 11/6/18 8:00 PM, Chris Packham wrote:
> > > With the addition of the invert-pwm property the adt7475 needs its own
> > > binding documentation rather being captured under trivial-devices.txt.
> > >
> > > Signed-off-by: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>
> > > ---
> > >     .../devicetree/bindings/hwmon/adt7475.txt     | 22 +++++++++++++++++++
> > >     .../devicetree/bindings/trivial-devices.txt   |  4 ----
> > >     2 files changed, 22 insertions(+), 4 deletions(-)
> > >     create mode 100644 Documentation/devicetree/bindings/hwmon/adt7475.txt
> > >
> > > diff --git a/Documentation/devicetree/bindings/hwmon/adt7475.txt b/Documentation/devicetree/bindings/hwmon/adt7475.txt
> > > new file mode 100644
> > > index 000000000000..79255439e157
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/hwmon/adt7475.txt
> > > @@ -0,0 +1,22 @@
> > > +*ADT7475 hwmon sensor.
> > > +
> > > +Required properties:
> > > +- compatible: One of
> > > +	"adi,adt7473"
> > > +	"adi,adt7475"
> > > +	"adi,adt7476"
> > > +	"adi,adt7490"
> > > +
> > > +- reg: I2C address
> > > +
> > > +optional properties:
> > > +
> > > +- invert-pwm: This configures the PWM to use logic low for 100% duty cycle.
> > > +
> > > +Example:
> > > +
> > > +hwmon@2e {
> > > +	compatible = ;
> > > +	reg = <0x2e>;
> > > +	invert-pwm;
> >
> > If I understand correctly, the flag is set per pwm channel. A single global
> > property seems inappropriate.
>
> Yes it is per-channel. But I was having a hard time imagining a hardware
> design that would use both inverted and non-inverted at the same time.

People can be inventive. Sometimes too much so.

> Do you have a preference for how the properties should look?
>
>     invert-pwm[123]?
>
>     invert-pwm = <0x7>;?
Ultimately we'll have to find a generic way of defining devicetree properties for
hardware monitoring devices, not just for pwm but for all sensor types. A sub-node
per channel seems to be the most likely answer, but I think that is a long way off
(and will require lengthy discussions about acceptable properties).

I was looking into pwm DT properties, but they define a set of flags
(PWM_POLARITY_INVERTED, PWM_POLARITY_NORMAL).

The g762 driver uses "pwm_polarity". Underscore - hmm. Other drivers use module
parameters, sysfs attributes (pwmX_invert in asc7621 driver), or platform data
(g762, max6639).

Maybe pwm-polarity = <PWM_POLARITY_NORMAL | PWM_POLARITY_INVERTED> ?
No idea if that makes sense. Or just a boolean pwm-polarity-inverted.

Thinking about it per channel vs. per chip ... other drivers also seem to
use a single property / attribute for the entire chip, so that is fine here
as well. We can always extend it if needed.

Anyway, I am fine with whatever Rob accepts.

Guenter

> > Guenter
> >
> > > +};
> > > diff --git a/Documentation/devicetree/bindings/trivial-devices.txt b/Documentation/devicetree/bindings/trivial-devices.txt
> > > index 69c934aec13b..4f29100d6bbf 100644
> > > --- a/Documentation/devicetree/bindings/trivial-devices.txt
> > > +++ b/Documentation/devicetree/bindings/trivial-devices.txt
> > > @@ -14,10 +14,6 @@ ad,ad7414		SMBus/I2C Digital Temperature Sensor in 6-Pin SOT with SMBus Alert an
> > >     ad,adm9240		ADM9240:  Complete System Hardware Monitor for uProcessor-Based Systems
> > >     adi,adt7461		+/-1C TDM Extended Temp Range I.C
> > >     adt7461			+/-1C TDM Extended Temp Range I.C
> > > -adi,adt7473		+/-1C TDM Extended Temp Range I.C
> > > -adi,adt7475		+/-1C TDM Extended Temp Range I.C
> > > -adi,adt7476		+/-1C TDM Extended Temp Range I.C
> > > -adi,adt7490		+/-1C TDM Extended Temp Range I.C
> > >     adi,adxl345		Three-Axis Digital Accelerometer
> > >     adi,adxl346		Three-Axis Digital Accelerometer (backward-compatibility value "adi,adxl345" must be listed too)
> > >     ams,iaq-core		AMS iAQ-Core VOC Sensor