linux-kernel - Re: [v2 PATCH] dt-binding: usb: add usb-role-switch property

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Date:   Tue, 7 May 2019 17:13:05 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Chunfeng Yun <chunfeng.yun@...iatek.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mark Rutland <mark.rutland@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-usb@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Biju Das <biju.das@...renesas.com>,
        Yu Chen <chenyu56@...wei.com>, Min Guo <min.guo@...iatek.com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>
Subject: Re: [v2 PATCH] dt-binding: usb: add usb-role-switch property

On Tue, May 07, 2019 at 10:22:58AM +0800, Chunfeng Yun wrote:
> diff --git a/Documentation/devicetree/bindings/usb/generic.txt b/Documentation/devicetree/bindings/usb/generic.txt
> index 0a74ab8dfdc2..f5a6ad053ecc 100644
> --- a/Documentation/devicetree/bindings/usb/generic.txt
> +++ b/Documentation/devicetree/bindings/usb/generic.txt
> @@ -30,6 +30,11 @@ Optional properties:
>  			optional for OTG device.
>   - adp-disable: tells OTG controllers we want to disable OTG ADP, ADP is
>  			optional for OTG device.
> + - usb-role-switch: tells Dual-Role USB controllers we want to handle the role
> +			switch between host and device according to the state
> +			detected by the USB connector, typically for Type-C,
> +			Type-B(micro).
> +			see connector/usb-connector.txt.

That does not look correct to me. Firstly, USB role switches are not
always dual-role USB controllers. Secondly, stating what determines
the role irrelevant IMO.

Since this is a boolean property, the description for it should simply
explain what does it tell about the capabilities of the device that
has it. The description should not make any assumptions about the
users of the property, and since the property is a "generic" USB
property, I'm not sure it should make any assumptions about the type
of the device that has the property either. Also, I would really like
the description to show the type of the property.

Why not just say something like this:

"Boolean property informing that the device is capable of assigning
the USB data role (USB host or USB device) for a given USB connector."


thanks,

-- 
heikki