linux-kernel - Re: [PATCH v17 1/4] dt-bindings: msm: disp: add yaml schemas for DPU bindings

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Date:   Fri, 21 May 2021 13:51:30 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Krishna Manikandan <mkrishn@...eaurora.org>
Cc:     dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, kalyan_t@...eaurora.org,
        tanmay@...eaurora.org, abhinavk@...eaurora.org,
        robdclark@...il.com, vinod.koul@...aro.org, dianders@...omium.org,
        khsieh@...eaurora.org, robh+dt@...nel.org, sean@...rly.run,
        robh@...nel.org
Subject: Re: [PATCH v17 1/4] dt-bindings: msm: disp: add yaml schemas for DPU bindings

Quoting Bjorn Andersson (2021-05-21 09:00:29)
> On Fri 21 May 05:27 CDT 2021, Krishna Manikandan wrote:
> > diff --git a/Documentation/devicetree/bindings/display/msm/dpu-sc7180.yaml b/Documentation/devicetree/bindings/display/msm/dpu-sc7180.yaml
> [..]
> > +      ports:
> > +        $ref: /schemas/graph.yaml#/properties/ports
> > +        description: |
> > +          Contains the list of output ports from DPU device. These ports
> > +          connect to interfaces that are external to the DPU hardware,
> > +          such as DSI, DP etc. Each output port contains an endpoint that
> > +          describes how it is connected to an external interface.
> > +
> > +        properties:
> > +          port@0:
> > +            $ref: /schemas/graph.yaml#/properties/port
> > +            description: DPU_INTF1 (DSI1)
> > +
> > +          port@2:
> > +            $ref: /schemas/graph.yaml#/properties/port
> > +            description: DPU_INTF0 (DP)
>
> Why is port@0 INTF1 and why is port@2 INTF0? In the binding you're
> translating the two ports that are described are 0 and 1, representing
> INTF1 and INTF2, or DSI1 and DSI2, respectively.
>
> Further more, I have a need for somehow describing the pairing of 4 DP
> INTFs (INTF 0, 3, 4 and 5) and how they are connected to the 3+1 DP+eDP
> controllers.
>
> Downstream this seems to be handled by adding cell-index to the DP
> controllers and then matching that against the numbering in the driver's
> INTF array. But rather than adding cell-index to map this, can't we
> define that the port index is the INTF-number here?
>
>
> This would obviously break compatibility with existing DTBs, but we
> could start by doing it selectively for the new compatibles, fix up the
> existing dts files and then drop the selective application after 1 or 2
> LTS releases.

I requested that the existing DT not change a while ago when the DP
interface was being added to this binding. Is it possible to figure out
what interface it is that the port is for from the binding? It feels
like the problem is that the driver wants to look through the graph and
make connectors for each one, but it doesn't know what type of connector
to make.