linux-kernel - Re: [PATCH 2/2] dt-bindings: add devicetree bindings for st-pwm regulator

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Date:	Wed, 17 Sep 2014 20:46:12 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Chris Zhong <zyw@...k-chips.com>,
	Heiko Stübner <heiko@...ech.de>,
	Tao Huang <huangtao@...k-chips.com>,
	Eddie Cai <cf@...k-chips.com>,
	zhangqing <zhangqing@...k-chips.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <Pawel.Moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"broonie@...nel.org" <broonie@...nel.org>,
	Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH 2/2] dt-bindings: add devicetree bindings for st-pwm
 regulator

On Wed, Sep 17, 2014 at 07:16:23PM +0100, Doug Anderson wrote:
> Chris,
> 
> On Wed, Sep 17, 2014 at 6:08 AM, Chris Zhong <zyw@...k-chips.com> wrote:
> > Document the st-pwm regulator
> >
> > Signed-off-by: Chris Zhong <zyw@...k-chips.com>
> >
> > ---
> >
> >  .../devicetree/bindings/regulator/st-pwm.txt       |   35 ++++++++++++++++++++
> >  1 file changed, 35 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/regulator/st-pwm.txt
> >
> > diff --git a/Documentation/devicetree/bindings/regulator/st-pwm.txt b/Documentation/devicetree/bindings/regulator/st-pwm.txt
> > new file mode 100644
> > index 0000000..38fec1d
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/regulator/st-pwm.txt
> > @@ -0,0 +1,35 @@
> > +st pwm regulator bindings
> > +
> > +Required properties:
> > +  - compatible: "pwm-regulator"
> 
> This compatible string doesn't include "st,b2105-pwm-regulator".
> 
> Should be something like:
> 
>   - compatible: Should be "pwm-regulator" to get voltage table / regulator
>     period from the device tree.  Deprecated: if "st,b2105-pwm-regulator" then
>     voltage table and regulator will be handled by the driver.

Do a list, with a bullet point for each string, like:

- compatible: should contain:
  * "pwm-regulator" when using voltage-table
  * "st,b2105-pwm-regulator" for .... (DEPRECATED)

That's easier to extend and it's clearer as to which strings the
comments above apply to.

> 
> Assuming that everyone is OK calling "st,b2105-pwm-regulator" the
> deprecated way of doing things.
> 
> 
> > +  - pwms: OF device-tree PWM specification (see PWM binding pwm.txt)
> > +  - voltage-table: voltage and duty table, include 2 merbers in each set of
> > +    brackets, first one is voltage(unit: uv), the next is duty(unit: percent)
> > +  - pwm-reg-period: duration (in nanoseconds) of one cycle

Perhaps just 'period-ns'? We know it applies to the PWM we're using as a
regulator.

That said, is this even needed? The pwm bindings describe that the
period would typically be described in the pwm-specifier, so duplicating
that feels wrong.

> 
> The voltage-table and pwm-reg-period should not be required if we're
> using "st,b2105-pwm-regulator".  If someone lists both
> "st,b2105-pwm-regulator" and "pwm-regulator" then I'd assume that
> you'd allow them to override via the device tree but fallback to the
> old hardcoded values.
> 
> 
> > +
> > +Any property defined as part of the core regulator binding defined in
> > +regulator.txt can also be used.
> > +
> > +Example:
> > +       pwm_regulator {
> > +                compatible = "st,b2105-pwm-regulator;
> > +                pwms = <&pwm1 0 1000000 0>;
> > +
> > +               voltage-table = <1114000 0>,
> > +                               <1095000 10>,
> > +                               <1076000 20>,
> > +                               <1056000 30>,
> > +                               <1036000 40>,
> > +                               <1016000 50>;
> > +
> > +               pwm-reg-period = <8448>;
> > +               regulators {
> > +                       vdd_logic: pwm-regulator {
> > +                               regulator-always-on;
> > +                               regulator-boot-on;
> > +                               regulator-min-microvolt = <1016000>;
> > +                               regulator-max-microvolt = <1114000>;
> > +                               regulator-name = "vdd_logic";
> > +                       };
> > +               };
> 
> I _think_ that the "regulators" subnode and the "pwm-regulator"
> subnode are not needed at all and should be removed.  Other instances
> of devices that are "just" regulators don't have it (like
> fixed-regulator, gpio-regulator, etc).

Yes. The pwm_regulator node _is_ the regulator, so the subnode is
bizarre.

Mark.
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