Re: [PATCH v5 1/3] dt-bindings: mfd: Add Gateworks System Controller bindings

[Tim Harvey <tharvey@gateworks.com>]

On Mon, Mar 2, 2020 at 12:49 PM Rob Herring <robh@kernel.org> wrote:
>

Rob,

Thanks for the review! Some questions below:

> On Mon, Feb 24, 2020 at 12:54:23PM -0800, Tim Harvey wrote:
> > This patch adds documentation of device-tree bindings for the
> > Gateworks System Controller (GSC).
> >
> > Signed-off-by: Tim Harvey <tharvey@gateworks.com>
> > ---
> > v5:
> >  - resolve dt_binding_check issues
> >
> > v4:
> >  - move to using pwm<n>_auto_point<m>_{pwm,temp} for FAN PWM
> >  - remove unncessary resolution/scaling properties for ADCs
> >  - update to yaml
> >  - remove watchdog
> >
> > v3:
> >  - replaced _ with -
> >  - remove input bindings
> >  - added full description of hwmon
> >  - fix unit address of hwmon child nodes
> > ---
> >  .../devicetree/bindings/mfd/gateworks-gsc.yaml     | 158 +++++++++++++++++++++
> >  1 file changed, 158 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/mfd/gateworks-gsc.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/mfd/gateworks-gsc.yaml b/Documentation/devicetree/bindings/mfd/gateworks-gsc.yaml
> > new file mode 100644
> > index 00000000..f7c1a05
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/mfd/gateworks-gsc.yaml
> > @@ -0,0 +1,158 @@
> > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/mfd/gateworks-gsc.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Gateworks System Controller multi-function device
> > +
> > +description: |
> > +  The GSC is a Multifunction I2C slave device with the following submodules:
> > +   - Watchdog Timer
> > +   - GPIO
> > +   - Pushbutton controller
> > +   - Hardware Monitore with ADC's for temperature and voltage rails and
>
> typo

will fix

>
> > +     fan controller
> > +
> > +maintainers:
> > +  - Tim Harvey <tharvey@gateworks.com>
> > +  - Robert Jones <rjones@gateworks.com>
> > +
> > +properties:
> > +  $nodename:
> > +    pattern: "gsc@[0-9a-f]{1,2}"
> > +  compatible:
> > +    const: gw,gsc
>
> That's not very specific.
>

Do you mean something like 'gw,system-controller' would be better
instead of the gsc abbreviation for 'Gateworks System Controller'?

> +
> > +  reg:
> > +    description: I2C device address
> > +    maxItems: 1
> > +
> > +  interrupts:
> > +    maxItems: 1
> > +
> > +  interrupt-controller: true
> > +
> > +  "#interrupt-cells":
> > +    const: 1
> > +    description: The IRQ number
>
> description is wrong. You can just drop it.
>

ok

> > +
> > +  hwmon:
>
> 'hwmon' is a Linux thing. I'm suspicious...
>

Yes, we've discussed this before and I understand that DT shouldn't
use terminology that is Linux specific (which is why I replaced
'hwmon' with 'adc' in the ADC nodes below) but I still see a long of
dt bindings in Documentation/devicetree/bindings with the word 'hwmon'
in them.

Perhaps this makes more sense?

adc {
  compatible = "gw,gsc-adc";
  #address-cells = <1>;
  #size-cells = <0>;

  channel@6 {
    type = "gw,hwmon-temperature";
    reg = <0x06>;
    label = "temp";
  };
  ...
};


> > +    type: object
> > +    description: Optional Hardware Monitoring module
> > +
> > +    properties:
> > +      compatible:
> > +        const: gw,gsc-hwmon
> > +
> > +      "#address-cells":
> > +        const: 1
> > +
> > +      "#size-cells":
> > +        const: 0
> > +
> > +      gw,fan-base:
> > +        $ref: /schemas/types.yaml#/definitions/uint32
> > +        description: The fan controller base address
>
> Shouldn't this be described as a node in the DT or be implied by the
> compatible?

It does look out of place there. Would adding another subnode outside
of the (perhaps misnamed) 'hwmon' node make more sense?:

fan:
 properties:
   compatible: gw,gsc-fancontroller
   reg:
     description: address of the fan controller base register
     maxItems: 1

>
> > +
> > +    patternProperties:
> > +      "^adc@[0-2]$":
>
> There's only one number space at any level. So if you ever need anything
> else at this level, it can't have an address. Just something to
> consider.
>

yes, one number space is ok if I understand what you mean but I meant
this to be "^adc@[0-9]+$" to support the number of ADC pins the part
supports.

> > +        type: object
> > +        description: |
> > +          Properties for a single ADC which can report cooked values
> > +          (ie temperature sensor based on thermister), raw values
> > +          (ie voltage rail with a pre-scaling resistor divider).
> > +
> > +        properties:
> > +          reg:
> > +            description: Register of the ADC
> > +            maxItems: 1
> > +
> > +          label:
> > +            description: Name of the ADC input
> > +
> > +          type:
>
> Very generic property name, but it's not generic. Needs a vendor prefix
> at least.

You mean the property name of 'type' is fine, but the values will need
to be vendor specific like 'gw,temperature', 'gw,voltage',
'gw,voltage-raw' or is it inappropriate to use 'type'?

>
> > +            description: |
> > +              temperature in C*10 (temperature),
> > +              pre-scaled voltage value (voltage),
> > +              or scaled based on an optional resistor divider and optional
> > +              offset (voltage-raw)
> > +            enum:
> > +              - temperature
> > +              - voltage
> > +              - voltage-raw
> > +
> > +          gw,voltage-divider:
> > +            allOf:
> > +              - $ref: /schemas/types.yaml#/definitions/uint32-array
> > +            description: values of resistors for divider on raw ADC input
> > +            items:
> > +              - description: R1
> > +              - description: R2
>
> Needs a standard unit suffix. With that, you can drop the type
> reference.

I understand the unit suffix but not sure what you mean by type
reference. Do you mean:

gw,voltage-divider-milli-ohms:
  description: values of resistors for divider on raw ADC input
    items:
      - description: R1
      - description: R2

>
> > +
> > +          gw,voltage-offset:
> > +            $ref: /schemas/types.yaml#/definitions/uint32
> > +            description: |
> > +              A positive uV voltage offset to apply to a raw ADC
> > +              (ie to compensate for a diode drop).
>
> Needs a unit suffix.

ok

Thanks!

Tim