linux-kernel - Re: [PATCH v2 2/6] dt-bindings: usb: add binding for Type-B dual role switch by GPIO

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Message-ID: <1552636374.10179.121.camel@mhfsdcap03>
Date:   Fri, 15 Mar 2019 15:52:54 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     Rob Herring <robh+dt@...nel.org>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Mark Rutland <mark.rutland@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Adam Thomson <Adam.Thomson.Opensource@...semi.com>,
        Li Jun <jun.li@....com>,
        "Badhri Jagan Sridharan" <badhri@...gle.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Min Guo <min.guo@...iatek.com>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v2 2/6] dt-bindings: usb: add binding for Type-B dual
 role switch by GPIO

Hi Rob,

There are two ways that I think out to support type-B GPIO based dual
role switch.

The first one, as the series used:

&mtu3 {
    status = "okay";

    connector@0 {
        compatible = "usb-b-connector", "linux,typeb-switch-gpio";
        label = "micro-USB";
        type = "micro";
        id-gpio = <&pio 12 GPIO_ACTIVE_HIGH>;
        vbus-supply = <&usb_p0_vbus>;
    };
};

but there are some shortcomings:
1. It's not transparent, USB controller driver should be modified, and
call of_platform_populate() to create platform device for connector,
this is not friendly when the controller driver hasn't child node
before, and also not compatible with other cases, such as Type-C

2. It doesn't keep format consistent with the case using Type-C, or
using PMIC to detect ID pin.

3. vbus-supply will be got by USB controller driver if it aready
supports it


another way as following:

role_sw_iddig {
    compatible = "linux,typeb-switch-gpio";
    status = "okay";

    connector {
        compatible = "usb-b-connector";
        label = "micro-USB";
        type = "micro";
        id-gpios = <&pio 12 GPIO_ACTIVE_HIGH>;
        vbus-supply = <&usb_p0_vbus>;
    };

    port {
        bsw_ep: endpoint@0 {
            remote-endpoint = <&usb_role_sw>;
        };
    };
};

&mtu3 {
    status = "okay";

    port {
        usb_role_sw: endpoint@0 {
            remote-endpoint = <&bsw_ep>;
        };
    };
};

strength:
avoid the shortcomings of the first way
shortcoming:
it's a virtual device and seems not following graph.txt binding,

Do you have any suggestion?

Thanks


On Fri, 2019-03-15 at 15:38 +0800, Chunfeng Yun wrote:
> It's used to support dual role switch via GPIO when use Type-B
> receptacle
> 
> Signed-off-by: Chunfeng Yun <chunfeng.yun@...iatek.com>
> ---
> v2 changes:
>   1. new patch to make binding clear suggested by Hans
> ---
>  .../bindings/usb/typeb-switch-gpio.txt        | 26 +++++++++++++++++++
>  1 file changed, 26 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/usb/typeb-switch-gpio.txt
> 
> diff --git a/Documentation/devicetree/bindings/usb/typeb-switch-gpio.txt b/Documentation/devicetree/bindings/usb/typeb-switch-gpio.txt
> new file mode 100644
> index 000000000000..d46d83bc6500
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/usb/typeb-switch-gpio.txt
> @@ -0,0 +1,26 @@
> +USB Type-B dual role switch via a GPIO
> +
> +This is a virtual device used to switch dual role mode from the USB ID pin
> +connected to a GPIO pin.
> +
> +Required properties:
> +- compatible: Should be "linux,typeb-switch-gpio"
> +
> +Either one of id-gpios or vbus-gpios must be present, and both can be present
> +as well.
> +vbus-supply could be present if needed when support dual role mode.
> +	see connector/usb-connector.txt
> +
> +Example:
> +
> +&mtu3 {
> +	status = "okay";
> +
> +	connector@0 {
> +		compatible = "usb-b-connector", "linux,typeb-switch-gpio";
> +		label = "micro-USB";
> +		type = "micro";
> +		id-gpio = <&pio 12 GPIO_ACTIVE_HIGH>;
> +		vbus-supply = <&usb_p0_vbus>;
> +	};
> +};