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

[Rob Herring <robh@kernel.org>]

On Wed, Jun 29, 2022 at 9:01 AM Pin-yen Lin <treapking@chromium.org> wrote:
>
> On Wed, Jun 29, 2022 at 10:33 PM Pin-yen Lin <treapking@chromium.org> wrote:
> >
> > On Wed, Jun 29, 2022 at 2:23 AM Rob Herring <robh@kernel.org> wrote:
> > >
> > > 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@kernel.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@linaro.org>
> > > > > > Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> > > > > > Reviewed-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
> > > > > > Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
> > > > > > Signed-off-by: Prashant Malani <pmalani@chromium.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@chromium.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...
> >
> > Yes it6505 is just a protocol converter. But in our use case, the output DP
> > lines are connected to the Type-C ports and the chip has to know which
> > port has DP Alt mode enabled. Does this justify a child node here?
> >
> > Does it make more sense if we we eliminate the usb-switch node here
> > and list the ports in the top level?

In the it6505 node? No, the it6505 h/w knows nothing about Type-C
switching so neither should its binding.

What device controls the switching in this case? Again, block diagrams
please if you want advice on what the binding should look like.

> > > > > 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.
>
> Then, is it suitable to put the switch binding into the drivers own bindings
> (i.e., the bindings for it6505 and anx7625), and introduce some helper
> functions to eliminate the duplication in the code?

Only for h/w devices that have switch h/w.

> Though we will have two similar bindings in two drivers with this approach.

While the anx7625 driver having Type-C awareness makes sense given it
has a switch and a type-C controller, that doesn't make sense for
it6505 (and every other bridge driver that's just providing DP
output).

Rob