Date:   Tue, 28 Jun 2022 12:23:36 -0600
From:   Rob Herring <robh@...nel.org>
To:     Prashant Malani <pmalani@...omium.org>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        bleung@...omium.org, swboyd@...omium.org,
        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>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "open list:DRM DRIVERS" <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>,
        Pin-Yen Lin <treapking@...omium.org>,
        Robert Foss <robert.foss@...aro.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Xin Ji <xji@...logixsemi.com>
Subject: Re: [PATCH v5 1/9] dt-bindings: usb: Add Type-C switch binding

On Mon, Jun 27, 2022 at 02:43:39PM -0700, Prashant Malani wrote:
> Hello Rob,
> 
> On Mon, Jun 27, 2022 at 2:04 PM Rob Herring <robh@...nel.org> wrote:
> >
> > On Wed, Jun 22, 2022 at 05:34:30PM +0000, Prashant Malani wrote:
> > > Introduce a binding which represents a component that can control the
> > > routing of USB Type-C data lines as well as address data line
> > > orientation (based on CC lines' orientation).
> > >
> > > Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> > > Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> > > Reviewed-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>
> > > Tested-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>
> > > Signed-off-by: Prashant Malani <pmalani@...omium.org>
> > > ---
> > >
> > > Changes since v4:
> > > - Added Reviewed-by tags.
> > > - Patch moved to 1/9 position (since Patch v4 1/7 and 2/7 were
> > >   applied to usb-next)
> > >
> > > Changes since v3:
> > > - No changes.
> > >
> > > Changes since v2:
> > > - Added Reviewed-by and Tested-by tags.
> > >
> > > Changes since v1:
> > > - Removed "items" from compatible.
> > > - Fixed indentation in example.
> > >
> > >  .../devicetree/bindings/usb/typec-switch.yaml | 74 +++++++++++++++++++
> > >  1 file changed, 74 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/usb/typec-switch.yaml
> > >
> > > diff --git a/Documentation/devicetree/bindings/usb/typec-switch.yaml b/Documentation/devicetree/bindings/usb/typec-switch.yaml
> > > new file mode 100644
> > > index 000000000000..78b0190c8543
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/usb/typec-switch.yaml
> > > @@ -0,0 +1,74 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/usb/typec-switch.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: USB Type-C Switch
> > > +
> > > +maintainers:
> > > +  - Prashant Malani <pmalani@...omium.org>
> > > +
> > > +description:
> > > +  A USB Type-C switch represents a component which routes USB Type-C data
> > > +  lines to various protocol host controllers (e.g USB, VESA DisplayPort,
> > > +  Thunderbolt etc.) depending on which mode the Type-C port, port partner
> > > +  and cable are operating in. It can also modify lane routing based on
> > > +  the orientation of a connected Type-C peripheral.
> > > +
> > > +properties:
> > > +  compatible:
> > > +    const: typec-switch
> > > +
> > > +  mode-switch:
> > > +    type: boolean
> > > +    description: Specify that this switch can handle alternate mode switching.
> > > +
> > > +  orientation-switch:
> > > +    type: boolean
> > > +    description: Specify that this switch can handle orientation switching.
> > > +
> > > +  ports:
> > > +    $ref: /schemas/graph.yaml#/properties/ports
> > > +    description: OF graph binding modelling data lines to the Type-C switch.
> > > +
> > > +    properties:
> > > +      port@0:
> > > +        $ref: /schemas/graph.yaml#/properties/port
> > > +        description: Link between the switch and a Type-C connector.
> > > +
> > > +    required:
> > > +      - port@0
> > > +
> > > +required:
> > > +  - compatible
> > > +  - ports
> > > +
> > > +anyOf:
> > > +  - required:
> > > +      - mode-switch
> > > +  - required:
> > > +      - orientation-switch
> > > +
> > > +additionalProperties: true
> > > +
> > > +examples:
> > > +  - |
> > > +    drm-bridge {
> > > +        usb-switch {
> > > +            compatible = "typec-switch";
> >
> > Unless this child is supposed to represent what the parent output is
> > connected to, this is just wrong as, at least for the it6505 chip, it
> > doesn't know anything about Type-C functionality. The bridge is
> > just a protocol converter AFAICT.
> 
> I'll let Pin-Yen comment on the specifics of the it6505 chip.

We're all waiting...

> > If the child node represents what the output is connected to (like a
> > bus), then yes that is a pattern we have used.
> 
> For the anx7625 case, the child node does represent what the output is connected
> to (the usb-c-connector via the switch). Does that not qualify? Or do you mean
> the child node should be a usb-c-connector itself?
> 
> > For example, a panel
> > represented as child node of a display controller. However, that only
> > works for simple cases, and is a pattern we have gotten away from in
> > favor of using the graph binding.
> 
> The child node will still use a OF graph binding to connect to the
> usb-c-connector.
> Is that insufficient to consider a child node usage here?
> By "using the graph binding", do you mean "only use the top-level ports" ?
> I'm trying to clarify this, so that it will inform future versions and patches.

What I want to see is block diagrams of possible h/w with different 
scenarios and then what the binding looks like in those cases. The 
switching/muxing could be in the SoC, a bridge chip, a Type C 
controller, a standalone mux chip, or ????. If you want a somewhat 
genericish binding, then you need to consider all of these.

I don't really have the b/w to work thru all this (and switch/mux is 
just one part of dealing with Type-C). This is just one of about a 
hundred patches I get to review a week.

Rob

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