linux-kernel - Re: [PATCH 1/2] dt-bindings: usb: Introduce GPIO-based SBU mux

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Date:   Fri, 19 Aug 2022 13:14:25 -0700
From:   Prashant Malani <pmalani@...omium.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        linux-usb@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Pin-yen Lin <treapking@...omium.org>
Subject: Re: [PATCH 1/2] dt-bindings: usb: Introduce GPIO-based SBU mux

> This would do that for us, but when all four lanes are connected from
> the qmp phy directly to the connector we could just as easily have done
> it with one endpoint.
>
>         qmp_phy {
>                 ports {
>                         port@0 {
>                                 reg = <0>;
>                                 endpoint@0 {
>                                         reg = <0>;
>                                         remote-endpoint = <&usb_c_ss>;
>                                         data-lanes = <1 2 3 0>
>                                 };
>                         };
>                 };
>         };
>
> So should we explicitly have two endpoints in the usb-c-connector for
> the two pairs all the time, or should we represent that via data-lanes
> and only split up the connector's endpoint if we need to connect the
> usb-c-connector to two different endpoints?

I like 2 endpoints to represent the usb-c-connector, but that doesn't seem
to be compatible (without introducing `data-lanes`, at least) with all
the various
combinations on the remote side, if that remote side is a DRM bridge with DP
output capability (like it6505 or anx7625).
That type of DRM bridge supports 1, 2 or 4 lane DP connections.

So, how about 4 endpoints (1 for each SS lane) in the usb-c-connector port@1?
That should support every conceivable configuration and bridge/PHY hardware.
and also allows a way to specify any lane remapping (similar to what
"data lanes" does)
if that is required.
Then we are consistent with what an endpoint represents, regardless of whether
the DRM bridge has a DP panel (1,2 or 4 lane) or Type-C connector  (2
or 4 lane) on its output side.