linux-kernel - Re: [PATCH RESEND 3/4] dt-bindings: drm/bridge: Add GPIO display mux binding

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Date:   Fri, 13 Dec 2019 07:53:59 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Hsin-Yi Wang <hsinyi@...omium.org>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Mark Rutland <mark.rutland@....com>,
        Nicolas Boichat <drinkcat@...omium.org>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Matthias Brugger <mbrugger@...e.com>,
        Russell King <rmk+kernel@....linux.org.uk>
Subject: Re: [PATCH RESEND 3/4] dt-bindings: drm/bridge: Add GPIO display mux binding

On Wed, Dec 11, 2019 at 12:19 AM Hsin-Yi Wang <hsinyi@...omium.org> wrote:
>
> From: Nicolas Boichat <drinkcat@...omium.org>
>
> Add bindings for Generic GPIO mux driver.
>
> Signed-off-by: Nicolas Boichat <drinkcat@...omium.org>
> Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>
> ---
> Change from RFC to v1:
> - txt to yaml
> ---
>  .../bindings/display/bridge/gpio-mux.yaml     | 89 +++++++++++++++++++
>  1 file changed, 89 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/display/bridge/gpio-mux.yaml
>
> diff --git a/Documentation/devicetree/bindings/display/bridge/gpio-mux.yaml b/Documentation/devicetree/bindings/display/bridge/gpio-mux.yaml
> new file mode 100644
> index 000000000000..cef098749066
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/bridge/gpio-mux.yaml
> @@ -0,0 +1,89 @@
> +# SPDX-License-Identifier: GPL-2.0
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/display/bridge/gpio-mux.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Generic display mux (1 input, 2 outputs)

What makes it generic? Doesn't the mux chip have power supply,
possibly a reset line or not, etc.? What about a mux where the GPIO
controls the mux?

Generally, we avoid 'generic' bindings because h/w is rarely generic.
You can have a generic driver which works on multiple devices.

> +
> +maintainers:
> +  - Nicolas Boichat <drinkcat@...omium.org>
> +
> +description: |
> +  This bindings describes a simple display (e.g. HDMI) mux, that has 1
> +  input, and 2 outputs. The mux status is controlled by hardware, and
> +  its status is read back using a GPIO.
> +
> +properties:
> +  compatible:
> +    const: gpio-display-mux
> +
> +  detect-gpios:
> +    maxItems: 1
> +    description: GPIO that indicates the active output
> +
> +  ports:
> +    type: object
> +
> +    properties:
> +      port@0:
> +        type: object
> +        description: |
> +          Video port for input.
> +
> +      port@1:
> +        type: object
> +        description: |
> +          2 video ports for output.
> +          The reg value in the endpoints matches the GPIO status: when
> +          GPIO is asserted, endpoint with reg value <1> is selected.

You should describe 'endpoint@0' and 'endpoint@1' here too.

> +
> +    required:
> +      - port@0
> +      - port@1
> +
> +required:
> +  - compatible
> +  - detect-gpios
> +  - ports
> +
> +examples:
> +  - |
> +    hdmi_mux: hdmi_mux {
> +      compatible = "gpio-display-mux";
> +      status = "okay";

Don't show status in examples.

> +      detect-gpios = <&pio 36 GPIO_ACTIVE_HIGH>;
> +      pinctrl-names = "default";
> +      pinctrl-0 = <&hdmi_mux_pins>;
> +      ddc-i2c-bus = <&hdmiddc0>;

Not documented. Is the i2c bus muxed too? If not, then this is in the
wrong place.

> +
> +      ports {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        port@0 { /* input */
> +          reg = <0>;
> +
> +          hdmi_mux_in: endpoint {
> +            remote-endpoint = <&hdmi0_out>;
> +          };
> +        };
> +
> +        port@1 { /* output */
> +          reg = <1>;
> +
> +          #address-cells = <1>;
> +          #size-cells = <0>;
> +
> +          hdmi_mux_out_anx: endpoint@0 {
> +            reg = <0>;
> +            remote-endpoint = <&anx7688_in>;
> +          };
> +
> +          hdmi_mux_out_hdmi: endpoint@1 {
> +            reg = <1>;
> +            remote-endpoint = <&hdmi_connector_in>;
> +          };
> +        };
> +      };
> +    };
> --
> 2.24.0.525.g8f36a354ae-goog
>