linux-kernel - Re: [RFCv2 PATCH 3/4] dt-bindings: gpio: add Wiegand GPIO driver dt documentation

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Message-ID: <959a45b0-b4bb-98df-20be-707aa0d26700@linaro.org>
Date:   Thu, 6 Oct 2022 10:23:49 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Martin Zaťovič <m.zatovic1@...il.com>,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        linus.walleij@...aro.org, brgl@...ev.pl,
        gregkh@...uxfoundation.org, jeffrey.l.hugo@...il.com,
        andersson@...nel.org, Michael.Srba@...nam.cz, saravanak@...gle.com,
        mani@...nel.org, hemantk@...eaurora.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-gpio@...r.kernel.org
Subject: Re: [RFCv2 PATCH 3/4] dt-bindings: gpio: add Wiegand GPIO driver dt
 documentation

On 05/10/2022 16:57, Martin Zaťovič wrote:
> The Wiegand GPIO driver uses two GPIO lines to transmit data -
> data-hi and data-lo. These lines need to be defined in the
> devicetree, otherwise the driver will not probe successfully.
> 
> Signed-off-by: Martin Zaťovič <m.zatovic1@...il.com>
> ---
>  .../bindings/gpio/gpio-wiegand.yaml           | 53 +++++++++++++++++++
>  1 file changed, 53 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/gpio/gpio-wiegand.yaml
> 
> diff --git a/Documentation/devicetree/bindings/gpio/gpio-wiegand.yaml b/Documentation/devicetree/bindings/gpio/gpio-wiegand.yaml
> new file mode 100644
> index 000000000000..3b235667ae17
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/gpio/gpio-wiegand.yaml
> @@ -0,0 +1,53 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/gpio/gpio-wiegand.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Wiegand GPIO controller
> +
> +description: |
> +  Wiegand GPIO controller running under Wiegand bus.

GPIO controllers need "gpio-controller" property, so this seems to be
something else.

> +
> +maintainers:
> +  - Martin Zaťovič <m.zatovic1@...il.com>
> +
> +properties:
> +  $nodename:
> +    pattern: "^wiegand-gpio@[0-9a-f]+$"

No need to enforce node name, unless this is for a class of devices. But
then why "gpio" not just "wiegand"?

> +
> +  compatible:
> +    const: wiegand,wiegand-gpio
> +
> +  data-hi-gpios:
> +    description: GPIO spec for data-hi line to use
> +    maxItems: 1
> +
> +  data-lo-gpios:
> +    description: GPIO spec for data-lo line to use
> +    maxItems: 1
> +
> +required:
> +  - compatible
> +  - data-hi-gpios
> +  - data-lo-gpios
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/gpio/gpio.h>
> +
> +    wiegand {
> +        compatible = "wiegand";
> +
> +        wiegand-gpio {

I have troubles understanding this. The "wiegand" node is the bus,
right? Then what is "wiegand-gpio"? GPIO controller? Then why it is not
marked as GPIO controller? What GPIOs does it control?

> +            compatible = "wiegand,wiegand-gpio";
> +            pinctrl-names = "default";
> +            pinctrl-0 = <&pinctrl_uart2_wiegand>;
> +            data-hi-gpios = <&gpio2 7 (GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN)>;
> +            data-lo-gpios = <&gpio2 6 (GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN)>;

Aren't these properties of the bus, not the device?

> +        };
> +    };
> +
> +...

Best regards,
Krzysztof