Re: [PATCHv5 1/4] dt-bindings: wiegand: add Wiegand controller common properties

["Martin Zaťovič" <m.zatovic1@gmail.com>]

On Thu, Aug 24, 2023 at 08:37:01AM -0500, Rob Herring wrote:
> On Thu, Aug 24, 2023 at 01:10:12PM +0200, Martin Zaťovič wrote:
> > Wiegand bus is defined by a Wiegand controller node. This node
> > can contain one or more device nodes for devices attached to
> > the controller(it is advised to only connect one device as Wiegand
> > is a point-to-point bus).
> 
> How would multiple devices work? Seems like you'd need some sort of mux 
> which would be another node. If there's not really any need, then I'd 
> just say it's only a single device. Either way the binding needs to 
> define this.
> 
> > 
> > Wiegand controller needs to specify several attributes such as
> > the pulse length in order to function properly. These attributes
> > are documented here.
> > 
> > Acked-by: Linus Walleij <linus.walleij@linaro.org>
> > Reviewed-by: Rob Herring <robh@kernel.org>
> > Signed-off-by: Martin Zaťovič <m.zatovic1@gmail.com>
> > ---
> >  .../bindings/wiegand/wiegand-controller.yaml  | 39 +++++++++++++++++++
> >  MAINTAINERS                                   |  5 +++
> >  2 files changed, 44 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/wiegand/wiegand-controller.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/wiegand/wiegand-controller.yaml b/Documentation/devicetree/bindings/wiegand/wiegand-controller.yaml
> > new file mode 100644
> > index 000000000000..8f36287e4fed
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/wiegand/wiegand-controller.yaml
> > @@ -0,0 +1,39 @@
> > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/wiegand/wiegand-controller.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Wiegand Generic Controller Common Properties
> > +
> > +maintainers:
> > +  - Martin Zaťovič <m.zatovic1@gmail.com>
> > +
> > +description:
> > +  Wiegand busses can be described with a node for the Wiegand controller device
> > +  and a set of child nodes for each SPI slave on the bus.
> 
> Some more detail on what Wiegand is would be useful. Link to spec? What 
> it is used for?

There is no official Wiegand datasheet out there. I can include the summary of
some proprietary documents about Wiegand, like the commit message of the second
commit in the series.

> 
> > +
> > +properties:
> > +  $nodename:
> > +    pattern: "^wiegand(@.*|-[0-9a-f])?$"
> 
> The '-[0-9a-f]' suffix should be decimal rather than hex.
> 
> > +
> > +  pulse-len-us:
> > +    description:
> > +      Length of the low pulse in microseconds.
> > +
> > +  interval-len-us:
> > +    description:
> > +      Length of a whole bit (both the pulse and the high phase) in microseconds.
> > +
> > +  frame-gap-us:
> > +    description:
> > +      Length of the last bit of a frame (both the pulse and the high phase) in
> > +      microseconds.
> 
> If you have multiple devices, you need to define the child node format. 
> Specifically, you need addresses for multiple devices. So you need to 
> define the unit-address format, #address-cells and #size-cells values, 
> and any constraints on 'reg' such as max address and/or number of entries.

I see.. the bus should really only allow one device to be connected.
That means, there is no need to define anything else in this file, right?
I will explicitely mention it in the Description and I will add the

unevaluatedPropertied:
  type: object

to the wiegand-gpio.yaml file so that adding a child node is allowed.

> 
> Rob

With regards,
Martin Zaťovič