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

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Message-ID: <CACeCKadt3aoz8MZvy+tGHCxiHOPty4cLcG7AGS+oMEVnREt4sw@mail.gmail.com>
Date:   Fri, 19 Aug 2022 15:55:07 -0700
From:   Prashant Malani <pmalani@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Stephen Boyd <swboyd@...omium.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

On Fri, Aug 19, 2022 at 3:01 PM Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
>
>
> You can't physically connect 1, 2 or 4 lanes of DP from a DP chip to
> your usb-c-connector at the same time as you physically connect 0, 2 or
> 4 lanes of USB from a USB PHY.

I apologize in case I'm misunderstanding, but why is that not possible?
anx7625 allows that configuration (2 lane DP + 2 lane USB going to
a single USB-C-connector)

Since the discussion is to support various conceivable hardware configurations
That same anx7625 can support 1 1-lane DP (or 2 1-lane DPs), and 1
2-lane Type-C output.
The cross-point switch allows for that level of configuration.

> > 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.
>
> Wouldn't that prevent you from handling orientation switching, given
> that the graph is static?

It depends. If the end-points from the usb-c-connector
go to the same switch, then it should allow orientation switching
(anx7625 allows
this). The port driver would just tell the orientation switch(es) attached to
it that we are in NORMAL or REVERSE orientation.

The graph is static, since the hardware line routing between components
doesn't change (e.g SSTX1 from the Type-C port is always routed to Pin
X1,X2 on the switch hardware), but that is what the switch is for.
Note that in this case, the expectation is that
the switch driver only registers 1 switch (it can figure out that all
4 endpoints
go to the same Type-C port).

The limitation to orientation switching would depend on how the
hardware is routed.