linux-kernel - Re: [PATCH 01/18] dt-bindings: phy: tegra-xusb: Add usb-role-switch

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Date:   Fri, 6 Dec 2019 15:49:05 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Nagarjuna Kristam <nkristam@...dia.com>
Cc:     balbi@...nel.org, gregkh@...uxfoundation.org, jonathanh@...dia.com,
        mark.rutland@....com, robh+dt@...nel.org, kishon@...com,
        devicetree@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/18] dt-bindings: phy: tegra-xusb: Add usb-role-switch

On Fri, Dec 06, 2019 at 04:20:04PM +0530, Nagarjuna Kristam wrote:
> Add usb-role-switch property for Tegra210 and Tegra186 platforms. This
> entry is used by XUSB pad controller driver to register for role changes
> for OTG/Peripheral capable USB 2 ports.
> 
> Signed-off-by: Nagarjuna Kristam <nkristam@...dia.com>
> ---
>  Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt b/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt
> index 9fb682e..0f19ed6 100644
> --- a/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt
> +++ b/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt
> @@ -179,6 +179,10 @@ Optional properties:
>    is internal. In the absence of this property the port is considered to be
>    external.
>  - vbus-supply: phandle to a regulator supplying the VBUS voltage.
> +- usb-role-switch: boolean property to indicate use of USB Role Switch.

That first sentence here seems a bit useless and vague. It doesn't
really convey anything other than the name already does. Perhaps
something like:

	Boolean property to indicate that the port support OTG. If
	present, the port supports switching between USB host and
	peripheral roles.

> +  This property is MUST for OTG,Peripheral capable USB 2 ports. Connector

If this is mandatory, why not add it to the list of required properties?
I guess since it's only mandatory for ports that support OTG, perhaps we
could add a section "Required properties for OTG capable ports:" or
something like that? Then you can also omit the second sentence in the
description.

> +  should be added as subnode, see connector.txt. vbus-gpio in connector is

There's no file called "connector.txt". Are you referring to

	Documentation/devicetree/bindings/connector/usb-connector.txt

? Also, that file calls the property "vbus-gpios" and lists it as
optional. What would happen if we don't specify it? Doesn't that just
mean that we can't support role detection?

> +  Mandatory.

"mandatory"

Thierry

>  
>  ULPI ports:
>  -----------
> -- 
> 2.7.4
> 

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