Re: [PATCH v11 7/9] dt-bindings: display: bridge: it6505: Add mode-switch support

[Pin-yen Lin <treapking@chromium.org>]

On Thu, Feb 9, 2023 at 9:58 PM Rob Herring <robh@kernel.org> wrote:
>
> On Wed, Feb 8, 2023 at 10:00 PM Pin-yen Lin <treapking@chromium.org> wrote:
> >
> > Hi Rob,
> >
> > Thanks for the review.
> >
> > On Wed, Feb 8, 2023 at 4:52 AM Rob Herring <robh@kernel.org> wrote:
> > >
> > > On Sat, Feb 04, 2023 at 09:30:38PM +0800, Pin-yen Lin wrote:
> > > > ITE IT6505 can be used in systems to switch the DP traffic between
> > > > two downstreams, which can be USB Type-C DisplayPort alternate mode
> > > > lane or regular DisplayPort output ports.
> > > >
> > > > Update the binding to accommodate this usage by introducing a
> > > > data-lanes and a mode-switch property on endpoints.
> > > >
> > > > Signed-off-by: Pin-yen Lin <treapking@chromium.org>
> > > >
> > > > ---
> > > >
> > > > Changes in v11:
> > > > - Updated the description of the endpoints in the bindings
> > > > - Referenced video-interfaces.yaml instead for the endpoints binding
> > > > - Removed duplicated definitions from inherited schema
> > > >
> > > > Changes in v9:
> > > > - Fixed subject prefix again
> > > > - Changed the naming of the example node for it6505
> > > >
> > > > Changes in v8:
> > > > - Updated bindings for data-lanes property
> > > > - Fixed subject prefix
> > > >
> > > > Changes in v7:
> > > > - Fixed issues reported by dt_binding_check.
> > > > - Updated the schema and the example dts for data-lanes.
> > > > - Changed to generic naming for the example dts node.
> > > >
> > > > Changes in v6:
> > > > - Remove switches node and use endpoints and data-lanes property to
> > > >   describe the connections.
> > > >
> > > >  .../bindings/display/bridge/ite,it6505.yaml   | 101 +++++++++++++++---
> > > >  1 file changed, 88 insertions(+), 13 deletions(-)
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/display/bridge/ite,it6505.yaml b/Documentation/devicetree/bindings/display/bridge/ite,it6505.yaml
> > > > index b16a9d9127dd..8ae9c5cba22c 100644
> > > > --- a/Documentation/devicetree/bindings/display/bridge/ite,it6505.yaml
> > > > +++ b/Documentation/devicetree/bindings/display/bridge/ite,it6505.yaml
> > > > @@ -75,22 +75,49 @@ properties:
> > > >        port@1:
> > > >          $ref: /schemas/graph.yaml#/$defs/port-base
> > > >          unevaluatedProperties: false
> > > > -        description: Video port for DP output
> > > > +        description:
> > > > +          Video port for DP output. Each endpoint connects to a video output
> > > > +          downstream, and the "data-lanes" property is used to describe the pin
> > > > +          connections. 0, 1, 2, 3 in "data-lanes" maps to TX0, TX1, TX2, TX3,
> > > > +          respectively.
> > > >
> > > > -        properties:
> > > > -          endpoint:
> > > > -            $ref: /schemas/graph.yaml#/$defs/endpoint-base
> > > > +
> > > > +        patternProperties:
> > > > +          "^endpoint@[01]$":
> > > > +            $ref: /schemas/media/video-interfaces.yaml#
> > > >              unevaluatedProperties: false
> > > >
> > > >              properties:
> > > > +              reg: true
> > > > +
> > > > +              remote-endpoint: true
> > > > +
> > > >                data-lanes:
> > > > -                minItems: 1
> > > > -                uniqueItems: true
> > > > -                items:
> > > > -                  - enum: [ 0, 1 ]
> > > > -                  - const: 1
> > > > -                  - const: 2
> > > > -                  - const: 3
> > > > +                oneOf:
> > > > +                  - items:
> > > > +                      - enum: [0, 1, 2, 3]
> > > > +
> > > > +                  - items:
> > > > +                      - const: 0
> > > > +                      - const: 1
> > > > +
> > > > +                  - items:
> > > > +                      - const: 2
> > > > +                      - const: 3
> > > > +
> > > > +                  - items:
> > > > +                      - const: 0
> > > > +                      - const: 1
> > > > +                      - const: 2
> > > > +                      - const: 3
> > > > +
> > > > +              mode-switch:
> > > > +                type: boolean
> > > > +                description: Register this node as a Type-C mode switch or not.
> > >
> > > Existing users put this property in the device's node, not the endpoint.
> > > That seems more like a property of the device, than the DP link.
> >
> > In our use case, we want to register two mode switches for the same
> > device. That's why we put the "mode-switch" property in the endpoints
> > instead of the device node.
>
> Then do that. Register a mode switch for each endpoint connected to a
> USB-C connector. You can walk the graph to see what type of connector.
>
> The only way I could see this as an issue is you have 2 USB-C
> connectors and one is a mode switch and one is not. Not sure if such a
> scenario is likely or possible. If it is, please educate me.

We can know which endpoints should be registered as a MUX by walking
through the graph, but the typec_mux_match[1] checks if the node
explicitly specifies a "mode-switch" property. So we still have to put
the property in the endpoints.

[1]: https://elixir.bootlin.com/linux/latest/source/drivers/usb/typec/mux.c#L265
>
> > > You are using fwnode_typec_mux_get(), right?
> >
> > Yes. This is called by cros_ec_typec.c[1] in our use case.
>
> That code looks for 'mode-switch' in the device's node, not the
> endpoint. So how does it work for you?

We modified the function in patch 1/9 of this series to make it also
look for endpoints.
>
> Rob

Regards,
Pin-yen