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

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Message-ID: <CACeCKac4eL9++QwbDBKrVTpUzhes=WczqZfh+cFiVgoO4py4MQ@mail.gmail.com>
Date:   Thu, 23 Jun 2022 12:08:21 -0700
From:   Prashant Malani <pmalani@...omium.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        bleung@...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>, 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>,
        Pin-Yen Lin <treapking@...omium.org>,
        Robert Foss <robert.foss@...aro.org>,
        Rob Herring <robh+dt@...nel.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 Thu, Jun 23, 2022 at 11:30 AM Stephen Boyd <swboyd@...omium.org> wrote:
>
> Quoting Prashant Malani (2022-06-22 10:34:30)
> > 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.
>
> Is there an update to the usb-c-connector binding to accept this port
> connection?

Not at this time. I don't think we should enforce that either.
(Type-C data-lines could theoretically be routed through intermediate
hardware like retimers/repeaters)

>
> > +
> > +    required:
> > +      - port@0
> > +
> > +required:
> > +  - compatible
> > +  - ports
> > +
> > +anyOf:
> > +  - required:
> > +      - mode-switch
> > +  - required:
> > +      - orientation-switch
> > +
> > +additionalProperties: true
> > +
> > +examples:
> > +  - |
> > +    drm-bridge {
> > +        usb-switch {
> > +            compatible = "typec-switch";
>
> I still don't understand the subnode design here. usb-switch as a
> container node indicates to me that this is a bus, but in earlier rounds
> of this series it was stated this isn't a bus.

I am not aware of this as a requirement. Can you please point me to the
documentation that states this needs to be the case?

> Why doesn't it work to
> merge everything inside usb-switch directly into the drm-bridge node?

I attempted to explain the rationale in the previous version [1], but
using a dedicated sub-node means the driver doesn't haven't to
inspect individual ports to determine which of them need switches
registered for them. If it sees a `typec-switch`, it registers a
mode-switch and/or orientation-switch. IMO it simplifies the hardware
device binding too.

It also maps with the internal block diagram for these hardware
components (for ex. the anx7625 crosspoint switch is a separate
sub-block within anx7625).

[1] https://lore.kernel.org/linux-usb/CACeCKaeH6qTTdG_huC4yw0xxG8TYEOtfPW3tiVNwYs=P4QVPXg@mail.gmail.com/

>
> > +            mode-switch;
> > +            orientation-switch;
> > +            ports {
> > +                #address-cells = <1>;
> > +                #size-cells = <0>;
> > +
> > +                port@0 {
> > +                    reg = <0>;
> > +                    anx_ep: endpoint {
> > +                        remote-endpoint = <&typec_controller>;
> > +                    };
> > +                };
> > +            };
> > +        };