Re: [RFC PATCH v2 1/3] dt-bindings: gpio: Add gpio-delay binding document

[Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>]

On 14/12/2022 10:53, Alexander Stein wrote:
> This adds bindings for a GPIO enable/disable delay driver.
> 
> Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
> ---
>  .../devicetree/bindings/gpio/gpio-delay.yaml  | 75 +++++++++++++++++++
>  1 file changed, 75 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/gpio/gpio-delay.yaml
> 
> diff --git a/Documentation/devicetree/bindings/gpio/gpio-delay.yaml b/Documentation/devicetree/bindings/gpio/gpio-delay.yaml
> new file mode 100644
> index 000000000000..20871356e9b5
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/gpio/gpio-delay.yaml
> @@ -0,0 +1,75 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/gpio/gpio-delay.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: GPIO delay controller
> +
> +maintainers:
> +  - Alexander Stein <linux@ew.tq-group.com>
> +
> +description: |
> +  This binding describes an electrical setup where setting an GPIO output
> +  is delayed by some external setup, e.g. RC curcuit.
> +
> +  +----------+                    +-----------+
> +  |          |             VCC_B  |           |
> +  |          |              |     |           |
> +  |          | VCC_A        _     |           |
> +  |  GPIO    |             | | R  |  Consumer |
> +  |controller|        ___  |_|    |           |
> +  |          |       |   |  |     |           |
> +  |      [IOx|-------|   |--+-----|-----+     |
> +  |          |       |___|  |     |   input   |
> +  |          |              |     |           |
> +  +----------+             --- C  +-----------+
> +                           ---
> +                            |
> +                            -
> +                           GND
> +
> +  If the input on the consumer is controlled by an open-drain signal

If IOx is open-drain, what is the VCC_A on the diagram? I think it
wasn't present in original Laurent's diagram.

> +  attached to an RC curcuit the ramp-up delay is not under control
> +  of the GPIO controller.
> +
> +properties:
> +  compatible:
> +    const: gpio-delay
> +
> +  "#gpio-cells":
> +    description: |
> +      Specifies the pin, ramp-up and ramp-down delays. The
> +      delays are specified in microseconds.
> +    const: 3
> +
> +  input-gpios:
> +    description: Array of GPIOs which output signal change is delayed

maxItems: 32 or some other reasonable value

> +
> +  gpio-controller: true
> +
> +  gpio-line-names: true

and then the same maxItems.

> +
> +required:
> +  - compatible
> +  - "#gpio-cells"
> +  - gpio-controller
> +  - input-gpios
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/gpio/gpio.h>
> +
> +    enable_delay: enable-delay {
> +        compatible = "gpio-delay";

I am not sure whether the naming is the most accurate - it represents
desired behavior (so the delay in rising signal), not actual hardware
(RC filter), but maybe that's a bit more generic.

Anyway look fine for me.

> +        #gpio-cells = <3>;
> +        gpio-controller;
> +        input-gpios = <&gpio0 3 GPIO_ACTIVE_LOW>,
> +                      <&gpio3 1 GPIO_ACTIVE_HIGH>;
> +    };
> +
> +    consumer {
> +        enable-gpios = <&enable_delay 0 130000 30000>;
> +    };

Best regards,
Krzysztof