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

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Message-ID: <CAJMQK-iwF78=2PDMxp=cvS3sotNi7kjj1ZoVO9q_axejUPdLYA@mail.gmail.com>
Date:   Mon, 16 Dec 2019 15:16:23 +0800
From:   Hsin-Yi Wang <hsinyi@...omium.org>
To:     Rob Herring <robh+dt@...nel.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 List <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 Sat, Dec 14, 2019 at 5:29 AM Rob Herring <robh+dt@...nel.org> wrote:
>
> 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.
>
Then how about making it mt8173-oak-gpio-mux? Since this is currently
only used in this board.

> > +
> > +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.
Will add in next version, thanks
>
> > +
> > +    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.
>
It's muxed, but this is required because of [1], so it should be
removed in this example.

[1]https://elixir.bootlin.com/linux/v5.5-rc2/source/Documentation/devicetree/bindings/display/mediatek/mediatek,hdmi.txt#L24
> > +
> > +      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
> >