[RFC,05/10] dt-bindings: pwm: Add bindings for PWM function in Netronix EC

The Netronix embedded controller as found in Kobo Aura and Tolino Shine
supports one PWM channel, which is used to control the frontlight
brightness on these devices.

Known problems:
- `make dt_binding_check` shows the following warnings:
  Documentation/devicetree/bindings/mfd/netronix,ntxec.example.dts:49.17-42:
  Warning (pwms_property): /example-0/backlight:pwms: cell 2 is not a
  phandle reference
  Documentation/devicetree/bindings/mfd/netronix,ntxec.example.dts:49.17-42:
  Warning (pwms_property): /example-0/backlight:pwms: Could not get
  phandle node for (cell 2)

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
---
 .../bindings/mfd/netronix,ntxec.yaml          | 13 ++++++++
 .../bindings/pwm/netronix,ntxec-pwm.yaml      | 33 +++++++++++++++++++
 2 files changed, 46 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/pwm/netronix,ntxec-pwm.yaml

--
2.27.0

On Sun, 21 Jun 2020 00:42:16 +0200
Jonathan Neuschäfer <j.neuschaefer@gmx.net> wrote:

> The Netronix embedded controller as found in Kobo Aura and Tolino Shine
> supports one PWM channel, which is used to control the frontlight
> brightness on these devices.
> 
> Known problems:
> - `make dt_binding_check` shows the following warnings:
>   Documentation/devicetree/bindings/mfd/netronix,ntxec.example.dts:49.17-42:
>   Warning (pwms_property): /example-0/backlight:pwms: cell 2 is not a
>   phandle reference
>   Documentation/devicetree/bindings/mfd/netronix,ntxec.example.dts:49.17-42:
>   Warning (pwms_property): /example-0/backlight:pwms: Could not get
>   phandle node for (cell 2)
> 
In the tolino sources in ./drivers/misc/ntx-misc.c I find this line

        if(4==gptHWCFG->m_val.bFL_PWM) {

No idea what it does but I would expect to have a kind of translation to
a dt property?

> Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
> ---
>  .../bindings/mfd/netronix,ntxec.yaml          | 13 ++++++++
>  .../bindings/pwm/netronix,ntxec-pwm.yaml      | 33 +++++++++++++++++++
>  2 files changed, 46 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/pwm/netronix,ntxec-pwm.yaml
> 
> diff --git a/Documentation/devicetree/bindings/mfd/netronix,ntxec.yaml b/Documentation/devicetree/bindings/mfd/netronix,ntxec.yaml
> index 596df460f98eb..6562c41c5a9a9 100644
> --- a/Documentation/devicetree/bindings/mfd/netronix,ntxec.yaml
> +++ b/Documentation/devicetree/bindings/mfd/netronix,ntxec.yaml
> @@ -31,6 +31,9 @@ properties:
>      description:
>        The EC can signal interrupts via a GPIO line
> 
> +  pwm:
> +    $ref: ../pwm/netronix,ntxec-pwm.yaml
> +
>  required:
>    - compatible
>    - reg
> @@ -53,5 +56,15 @@ examples:
>                      interrupts = <11 IRQ_TYPE_EDGE_FALLING>;
>                      interrupt-controller;
>                      #interrupt-cells = <1>;
> +
> +                    ec_pwm: pwm {
> +                            compatible = "netronix,ntxec-pwm";
> +                            #pwm-cells = <1>;
shouldn't that be 2?
> +                    };
>              };
>      };
> +
> +    backlight {
> +            compatible = "pwm-backlight";
> +            pwms = <&ec_pwm 0 50000>;
since you have 2 values after the &ec_pwm 

> +    };
> diff --git a/Documentation/devicetree/bindings/pwm/netronix,ntxec-pwm.yaml b/Documentation/devicetree/bindings/pwm/netronix,ntxec-pwm.yaml
> new file mode 100644
> index 0000000000000..1dc1b1aba081c
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/pwm/netronix,ntxec-pwm.yaml
> @@ -0,0 +1,33 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/pwm/netronix,ntxec-pwm.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: PWM functionality in Netronix embedded controller
> +
> +maintainers:
> +  - Jonathan Neuschäfer <j.neuschaefer@gmx.net>
> +
> +description: |
> +  See also Documentation/devicetree/bindings/mfd/netronix,ntxec.yaml
> +
> +  The Netronix EC contains PWM functionality, which is usually used to drive
> +  the backlight LED.
> +
> +  The following PWM channels are supported:
> +    - 0: The PWM channel controlled by registers 0xa1-0xa7
> +
> +allOf:
> +  - $ref: pwm.yaml#
> +
> +properties:
> +  compatible:
> +    const: netronix,ntxec-pwm
> +
> +  "#pwm-cells":
> +    const: 1

shouln't that be 2?
> +
> +required:
> +  - compatible
> +  - "#pwm-cells"
> --
> 2.27.0
> 
> 

Regards,
Andreas

On Sun, Jun 21, 2020 at 08:41:23PM +0200, Andreas Kemnade wrote:
> On Sun, 21 Jun 2020 00:42:16 +0200
> Jonathan Neuschäfer <j.neuschaefer@gmx.net> wrote:
> 
> > The Netronix embedded controller as found in Kobo Aura and Tolino Shine
> > supports one PWM channel, which is used to control the frontlight
> > brightness on these devices.
> > 
> > Known problems:
> > - `make dt_binding_check` shows the following warnings:
> >   Documentation/devicetree/bindings/mfd/netronix,ntxec.example.dts:49.17-42:
> >   Warning (pwms_property): /example-0/backlight:pwms: cell 2 is not a
> >   phandle reference
> >   Documentation/devicetree/bindings/mfd/netronix,ntxec.example.dts:49.17-42:
> >   Warning (pwms_property): /example-0/backlight:pwms: Could not get
> >   phandle node for (cell 2)
> > 
> In the tolino sources in ./drivers/misc/ntx-misc.c I find this line
> 
>         if(4==gptHWCFG->m_val.bFL_PWM) {
> 
> No idea what it does but I would expect to have a kind of translation to
> a dt property?

As far as I understand it, FL_PWM=4 means that there is a second PWM
channel, in order to provide different backlight colors.

I think it should be possible to simply extend the binding to list
another available PWM channel, once we add support for such hardware.

> > +                    ec_pwm: pwm {
> > +                            compatible = "netronix,ntxec-pwm";
> > +                            #pwm-cells = <1>;
> shouldn't that be 2?
> > +                    };
> >              };
> >      };
> > +
> > +    backlight {
> > +            compatible = "pwm-backlight";
> > +            pwms = <&ec_pwm 0 50000>;
> since you have 2 values after the &ec_pwm 
[...]
> > +properties:
> > +  compatible:
> > +    const: netronix,ntxec-pwm
> > +
> > +  "#pwm-cells":
> > +    const: 1
> 
> shouln't that be 2?

Right, I'll fix that.


Thanks,
Jonathan