Re: [PATCH v4 3/3] dt-bindings: leds: Convert pwm to yaml

[Rob Herring <robh@kernel.org>]

On Fri, Sep 18, 2020 at 9:12 AM Alexander Dahl <ada@thorsis.com> wrote:
>
> Hello Rob,
>
> thanks for your feedback. I have some questions/remarks on this new yaml
> binding stuff before sending v5 (which will also replace patch 1/3 with a
> different approach btw).
>
> Am Dienstag, 15. September 2020, 22:37:35 CEST schrieb Rob Herring:
> > On Fri, Sep 11, 2020 at 05:40:04PM +0200, Alexander Dahl wrote:
> > > The example was adapted slightly to make use of the 'function' and
> > > 'color' properties.  License discussed with the original author.
> > >
> > > Suggested-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
> > > Signed-off-by: Alexander Dahl <post@lespocky.de>
> > > Acked-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
> > > Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>
> > > ---
> > >
> > > Notes:
> > >     v3 -> v4:
> > >       * added Cc to original author of the binding
> > >
> > >     v2 -> v3:
> > >       * changed license identifier to recommended one
> > >       * added Acked-by
> > >
> > >     v2:
> > >       * added this patch to series (Suggested-by: Jacek Anaszewski)
> > >
> > >  .../devicetree/bindings/leds/leds-pwm.txt     | 50 -----------
> > >  .../devicetree/bindings/leds/leds-pwm.yaml    | 85 +++++++++++++++++++
> > >  2 files changed, 85 insertions(+), 50 deletions(-)
> > >  delete mode 100644 Documentation/devicetree/bindings/leds/leds-pwm.txt
> > >  create mode 100644 Documentation/devicetree/bindings/leds/leds-pwm.yaml
> > >
> > > diff --git a/Documentation/devicetree/bindings/leds/leds-pwm.txt
> > > b/Documentation/devicetree/bindings/leds/leds-pwm.txt deleted file mode
> > > 100644
> > > index 6c6583c35f2f..000000000000
> > > --- a/Documentation/devicetree/bindings/leds/leds-pwm.txt
> > > +++ /dev/null
> > > @@ -1,50 +0,0 @@
> > > -LED connected to PWM
> > > -
> > > -Required properties:
> > > -- compatible : should be "pwm-leds".
> > > -
> > > -Each LED is represented as a sub-node of the pwm-leds device.  Each
> > > -node's name represents the name of the corresponding LED.
> > > -
> > > -LED sub-node properties:
> > > -- pwms : PWM property to point to the PWM device (phandle)/port (id) and
> > > to -  specify the period time to be used: <&phandle id period_ns>;
> > > -- pwm-names : (optional) Name to be used by the PWM subsystem for the PWM
> > > device -  For the pwms and pwm-names property please refer to:
> > > -  Documentation/devicetree/bindings/pwm/pwm.txt
> > > -- max-brightness : Maximum brightness possible for the LED
> > > -- active-low : (optional) For PWMs where the LED is wired to supply
> > > -  rather than ground.
> > > -- label :  (optional)
> > > -  see Documentation/devicetree/bindings/leds/common.txt
> > > -- linux,default-trigger :  (optional)
> > > -  see Documentation/devicetree/bindings/leds/common.txt
> > > -
> > > -Example:
> > > -
> > > -twl_pwm: pwm {
> > > -   /* provides two PWMs (id 0, 1 for PWM1 and PWM2) */
> > > -   compatible = "ti,twl6030-pwm";
> > > -   #pwm-cells = <2>;
> > > -};
> > > -
> > > -twl_pwmled: pwmled {
> > > -   /* provides one PWM (id 0 for Charing indicator LED) */
> > > -   compatible = "ti,twl6030-pwmled";
> > > -   #pwm-cells = <2>;
> > > -};
> > > -
> > > -pwmleds {
> > > -   compatible = "pwm-leds";
> > > -   kpad {
> > > -           label = "omap4::keypad";
> > > -           pwms = <&twl_pwm 0 7812500>;
> > > -           max-brightness = <127>;
> > > -   };
> > > -
> > > -   charging {
> > > -           label = "omap4:green:chrg";
> > > -           pwms = <&twl_pwmled 0 7812500>;
> > > -           max-brightness = <255>;
> > > -   };
> > > -};
> > > diff --git a/Documentation/devicetree/bindings/leds/leds-pwm.yaml
> > > b/Documentation/devicetree/bindings/leds/leds-pwm.yaml new file mode
> > > 100644
> > > index 000000000000..c74867492424
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/leds/leds-pwm.yaml
> > > @@ -0,0 +1,85 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/leds/leds-pwm.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: LEDs connected to PWM
> > > +
> > > +maintainers:
> > > +  - Pavel Machek <pavel@ucw.cz>
> > > +
> > > +description:
> > > +  Each LED is represented as a sub-node of the pwm-leds device.  Each
> > > +  node's name represents the name of the corresponding LED.
> > > +
> > > +properties:
> > > +  compatible:
> > > +    const: pwm-leds
> > > +
> > > +patternProperties:
> >
> > > +  "^pwm-led-([0-9a-f])$":
> > '^led-([0-9a-f])' would be my preference. A bit more on that below.
>
> Fine for me.
>
> > What about a single child case?
>
> One child or multiple childs.  I found .dts files with one to four sub-nodes
> of the pwm-leds device in current master.

For the single child case, you need to allow for just 'led' then. So
this I think: '^led(-[0-9a-f]+)?$'

> > > +    type: object
> > > +
> > > +    $ref: common.yaml#
> > > +
> > > +    properties:
> > > +      pwms:
> > > +        description:
> > > +          "PWM property to point to the PWM device (phandle)/port (id)
> > > +          and to specify the period time to be used:
> > > +          <&phandle id period_ns>;"
> >
> > No need to redefine a common property.
>
> Should this look like in 'Documentation/devicetree/bindings/leds/backlight/
> pwm-backlight.yaml' then?

Yes.

>
> > What is needed is how many pwms? I'd assume 1 only: 'maxItems: 1'
>
> Yes, one pwm channel per LED.
>
> > > +
> > > +      pwm-names:
> > > +        description:
> > > +          "Name to be used by the PWM subsystem for the PWM device For
> > > +          the pwms and pwm-names property please refer to:
> > > +          Documentation/devicetree/bindings/pwm/pwm.txt"
> >
> > Same here.
> >
> > > +
> > > +      max-brightness:
> > > +        description:
> > > +          Maximum brightness possible for the LED
> >
> > Needs a type $ref.
>
> fwnode_property_read_u32() is used to read this.

$ref: /schemas/types.yaml#/definitions/uint32

>
> >
> > > +
> > > +      active-low:
> > > +        description:
> > > +          For PWMs where the LED is wired to supply rather than ground.
> >
> > type: boolean
> >
> > > +
> > > +    required:
> > > +      - pwms
> > > +      - max-brightness
> >
> > additionalProperties: false
> >
> > That will cause errors if child node names were not consistent (no one
> > checked, so they won't be). We could just allow anything, but I prefer
> > to move things to be consistent yet try to capture any existing pattern.
>
> Child node names follow no scheme at all currently as far as I could see,
> examples from real current .dts files:
>
>   panel, led-red, blueled, kpad, front, green, pwm_blue, ds1, network_red,
> alarm-brightness, pmu_stat, overo, heartbeat, power, …

So you can do this to allow any child node name:

additonalProperties:
  type: object
  $ref: common.yaml#

  ... everything you have under pwm-led-*

Or how gpio-keys.yaml was done also works.

Rob