linux-kernel - Re: [PATCH v5 1/9] dt-bindings: usb: Add Type-C switch binding

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Date:   Wed, 13 Jul 2022 14:58:05 -0700
From:   Prashant Malani <pmalani@...omium.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Stephen Boyd <swboyd@...omium.org>,
        Pin-yen Lin <treapking@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        Benson Leung <bleung@...omium.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Nícolas F . R . A . Prado 
        <nfraprado@...labora.com>, Allen Chen <allen.chen@....com.tw>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>, devicetree@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>,
        José Expósito <jose.exposito89@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Maxime Ripard <maxime@...no.tech>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Xin Ji <xji@...logixsemi.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [PATCH v5 1/9] dt-bindings: usb: Add Type-C switch binding

On Tue, Jul 12, 2022 at 10:45 AM Rob Herring <robh@...nel.org> wrote:
>
> > I agree with you; I'm saying my interpretation of the comments of this
> > thread are that it's not the intended usage of the it6505 part, so the driver
> > shouldn't be updated to support that.
>
> That's not the right interpretation. There should not be some Type-C
> specific child mux/switch node because the device has no such h/w within
> it. Assuming all the possibilities Stephen outlined are valid, it's
> clear this lane selection has nothing to do with Type-C. It does have an
> output port for its DP output already and using that to describe the
> connection to DP connector(s) and/or Type-C connector(s) should be
> handled.

Got it. Thanks for the clarification.

>
> Whether the driver is type-C aware is a separate question from the
> binding. I would think the driver just needs to be told (or it can ask)
> which endpoint should be active and it just enables output on the
> corresponding lanes for that endpoint.

Is it acceptable to tag the end-points with a "mode-switch" /
"orientation-switch"
property? Something like the following:

```
        dp-bridge@5c {
            compatible = "ite,it6505";
            ...
            port {
                #adderss-cells = <1>;
                #size-cells = <0>;

                ite_typec0: endpoint@0 {
                    reg = <0>;
                    mode-switch;
                    remote-endpoint = <&typec_connector0>;
                };
                ite_typec1: endpoint@1 {
                    reg = <1>;
                    mode-switch;
                    remote-endpoint = <&typec_connector1>;
                };
            };
        };
```
Or should the DRM bridge device binding not have those properties in
the end-points either?
The reasons those are required are:
- The Type-C matching code looks for the "mode-switch" identifier in
the fwnode while performing the switch matching [1]
- While we can look up whether the remote-endpoint is a
"usb-c-connector" in the bridge driver the
"mode-switch"/"orientation-switch" property tells the bridge driver
whether to register just a mode-switch, an orientation switch or both.

Best regards,

- Prashant

[1] https://elixir.bootlin.com/linux/v5.19-rc6/source/drivers/usb/typec/mux.c#L347