netdev - Re: [PATCH 1/2] dt-bindings: net: Add rfkill-gpio binding

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Date:   Wed, 21 Dec 2022 16:36:05 +0100
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Rob Herring <robh@...nel.org>
Cc:     Johannes Berg <johannes@...solutions.net>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-wireless@...r.kernel.org, kernel@...gutronix.de
Subject: Re: [PATCH 1/2] dt-bindings: net: Add rfkill-gpio binding

On Mi, 2022-12-21 at 08:45 -0600, Rob Herring wrote:
> On Wed, Dec 21, 2022 at 11:48:02AM +0100, Philipp Zabel wrote:
> > Add a device tree binding document for GPIO controlled rfkill switches.
> > The name, type, shutdown-gpios and reset-gpios properties are the same
> > as defined for ACPI.
> > 
> > Signed-off-by: Philipp Zabel <p.zabel@...gutronix.de>
> > ---
> >  .../devicetree/bindings/net/rfkill-gpio.yaml  | 60 +++++++++++++++++++
> >  1 file changed, 60 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/net/rfkill-gpio.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/net/rfkill-gpio.yaml b/Documentation/devicetree/bindings/net/rfkill-gpio.yaml
> > new file mode 100644
> > index 000000000000..6e62e6c96456
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/net/rfkill-gpio.yaml
> > @@ -0,0 +1,60 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: "http://devicetree.org/schemas/net/rfkill-gpio.yaml#"
> > +$schema: "http://devicetree.org/meta-schemas/core.yaml#"
> > +
> > +title: GPIO controlled rfkill switch
> > +
> > +maintainers:
> > +  - Johannes Berg <johannes@...solutions.net>
> > +  - Philipp Zabel <p.zabel@...gutronix.de>
> > +
> > +properties:
> > +  compatible:
> > +    const: rfkill-gpio
> > +
> > +  name:
> 
> Did you test this? Something should complain, but maybe not. The problem 
> is 'name' is already a property in the unflattened DT (and old FDT 
> formats).

Thank you. Maybe this was hidden by the fact that I set the name
property to the same string as the node's name.

> 'label' would be appropriate perhaps, but why do we care what the name 
> is?

This is meant to be the identifier of the rfkill API object. It is the
content of /sys/class/rfkill/rfkill0/name, and the 'ID' in the rfkill
command line tool, that can be used to select a switch, in case a
device has multiple radios of the same type.

> > +    $ref: /schemas/types.yaml#/definitions/string
> > +    description: rfkill switch name, defaults to node name
> > +
> > +  type:
> 
> Too generic. Property names should ideally have 1 type globally. I think 
> 'type' is already in use. 'radio-type' instead?

These values correspond to the 'enum rfkill_type' in Linux UAPI, but I
think in this context 'radio-type' would be better than 'rfkill-type'.

> > +    description: rfkill radio type
> > +    enum:
> > +      - wlan
> > +      - bluetooth
> > +      - ultrawideband
> > +      - wimax
> > +      - wwan
> > +      - gps
> > +      - fm
> > +      - nfc
> > +
> > +  shutdown-gpios:
> > +    maxItems: 1
> > +
> > +  reset-gpios:
> > +    maxItems: 1
> 
> I'm lost as to why there are 2 GPIOs.

I don't know either.  My assumption is that this is for devices that
are radio silenced by just asserting their reset pin (for example GPS
chips). The driver handles them the same.

I could remove reset-gpios and make shutdown-gpios required.

> > +
> > +required:
> > +  - compatible
> > +  - type
> > +
> > +oneOf:
> > +  - required:
> > +      - shutdown-gpios
> > +  - required:
> > +      - reset-gpios
> 
> But only 1 can be present? So just define 1 GPIO name.

The intent was that only one of them would be required.

> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    #include <dt-bindings/gpio/gpio.h>
> > +
> > +    rfkill-pcie-wlan {
> 
> Node names should be generic.

What could be a generic name for this - is "rfkill" acceptable even
though it is a Linux subsystem name? Or would "rf-kill-switch" be
better?

How should they be called if there are multiple of them?

> > +        compatible = "rfkill-gpio";
> > +        name = "rfkill-pcie-wlan";
> > +        type = "wlan";
> > +        shutdown-gpios = <&gpio2 25 GPIO_ACTIVE_HIGH>;
> > +    };
> > -- 
> > 2.30.2

regards
Philipp