Re: [PATCH 2/3] dt-bindings: hwmon: Add bindings for Google Chromium EC HWMON

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

On Thu, Apr 13, 2017 at 03:01:40PM -0500, Rob Herring wrote:
> On Fri, Apr 07, 2017 at 03:00:09PM -0700, Moritz Fischer wrote:
> > From: Moritz Fischer <mdf@kernel.org>
> > 
> > Add bindings for the Chromium EC HWMON. The Chromium EC HWMON
> > allows monitoring of temperature sensors and fans attached to the
> > EC.
> > 
> > Signed-off-by: Moritz Fischer <mdf@kernel.org>
> > ---
> >  .../devicetree/bindings/hwmon/cros-ec-hwmon.txt    | 25 ++++++++++++++++++++++
> >  1 file changed, 25 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/hwmon/cros-ec-hwmon.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/hwmon/cros-ec-hwmon.txt b/Documentation/devicetree/bindings/hwmon/cros-ec-hwmon.txt
> > new file mode 100644
> > index 0000000..4c94869
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/hwmon/cros-ec-hwmon.txt
> > @@ -0,0 +1,25 @@
> > +Chromium Embedded Controller EC temperature and fan control
> > +-----------------------------------------------------------
> > +
> > +Google's Chromium EC HWMON is a hwmon implemented byimplemented by the Chromium EC
> > +firmware attached to the Embedded Controller (EC) and controlled via a host-command
> > +interface.
> > +
> > +An EC HWMON node should be only found as a sub-node of the EC node (see
> > +Documentation/devicetree/bindings/mfd/cros-ec.txt).
> > +
> > +Required properties:
> > +- compatible: Must contain "google,cros-ec-hwmon"
> > +
> > +Example:
> > +	embedded-controller@1e {
> > +		reg = <0x1e>;
> > +		compatible = "google,cros-ec-i2c";
> > +		interrupts = <0 IRQ_TYPE_LEVEL_LOW>;
> > +		interrupt-parent = <&gpio0>;
> > +
> > +		hwmon {
> > +			compatible = "google,cros-ec-hwmon";
> 
> This is sufficient for all devices? I don't see that DT provides 
> anything here other than instantiating a device, but the parent device 
> can just as easily do that.
> 
The parent driver (drivers/mfd/cros_ec_i2c.c) calls cros_ec_register(),
which uses uses of_platform_populate() to populate all sub-devices.
There are various examples in the dts files (look for "google,cros-ec").
Does it really make sense to start a second method for instantiating
sub-devices ?

Thanks,
Guenter