Re: [PATCH v2 2/2] hwmon: Add driver for Texas Instruments TMP512/513 sensor chips

[Guenter Roeck <linux@roeck-us.net>]

On Tue, Oct 01, 2019 at 09:36:30PM +0000, Tremblay, Eric wrote:
> > On Tue, Oct 01, 2019 at 05:50:32PM +0000, Tremblay, Eric wrote:
> > > hwmon: Add DT bindings for TMP513 driver
> > >
> > > Signed-off-by: Eric Tremblay <etremblay@distech-controls.com>
> > > ---
> > >  .../devicetree/bindings/hwmon/tmp513.txt      | 33 +++++++++++++++++++
> > >  1 file changed, 33 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/hwmon/tmp513.txt
> > >
> > > diff --git a/Documentation/devicetree/bindings/hwmon/tmp513.txt
> > > b/Documentation/devicetree/bindings/hwmon/tmp513.txt
> > > new file mode 100644
> > > index 000000000000..0f61793cbf2f
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/hwmon/tmp513.txt
> > > @@ -0,0 +1,33 @@
> > > +TMP513 system monitor sensor
> > > +-------------------------
> > > +
> > > +Require node properties:
> > > +- compatible: one of
> > > +		"ti,tmp512"
> > > +		"ti,tmp513"
> > > +- reg : the I2C address of the device. This is 0x5c, 0x5d, 0x5e, or 0x5f.
> > > +- shunt-resistor-uohm : The shunt resistor value in uOhm.
> > > +
> > > +Optional properties:
> > > +- bus-voltage-range: 32V or 16V, default to 32V.
> > > +- max-expected-current-ma: Maximum expected current value. Default to max possible value.
> > > +- pga-gain: The gain value for the PGA function. This is 8, 4, 2 or 1. Default to 8.
> > > +- temp_2_nfactor: nFactor for remote channel 1. Value according to Table 11 in datasheet.
> > > +- temp_3_nfactor: nFactor for remote channel 2. Value according to Table 11 in datasheet.
> > > +- temp_4_nfactor: nFactor for remote channel 3. Value according to Table 11 in datasheet,
> > > +				  TMP513 only.
> > > +- temp_hysteresis: Hystereris for temperature limits.
> > 
> > There is a standard sysfs attribute for hysteresis values, and I assume this is one parameter that users might want to change at
> > runtime. Why not use it ?
> 
> In those sensors, the hysteresis setting is global to all channels. Is it still a standard sysfs attribute in that case ? If yes, should I name it
> temp_crit_hyst to show that is a global parameter ?

That is the case for many chips. The most common solution is to support
the attribute for all channels and make only the first channel writeable.
When doing that, add a note to the documentation indicating that writing
one attribute affects all attributes.

temp_crit_hyst doesn't help because it is non-standard and the "sensors"
command won't see it.

Guenter

> > 
> > > +
> > > +Example:
> > > +	tmp513@5c {
> > > +		  compatible = "ti,tmp513";
> > > +		  reg = <0x5C>;
> > > +		  shunt-resistor-uohm = <330>;
> > > +		  bus-voltage-range = <32>;
> > > +		  pga-gain = <8>;
> > > +		  max-expected-current-ma = <100>;
> > > +		  temp_2_nfactor = <0x01>;
> > > +		  temp_3_nfactor = <0x02>;
> > > +		  temp_4_nfactor = <0x03>;
> > > +		  temp_hysteresis = <5>;
> > > +	};
> > > --
> > > 2.17.1
> > >