linux-kernel - Re: [PATCH v7 03/10] dt-bindings: drm/bridge: ti-sn65dsi86: Add aux-bus child

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Date:   Wed, 19 May 2021 14:06:04 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Sam Ravnborg <sam@...nborg.org>,
        Stanislav Lisovskiy <stanislav.lisovskiy@...el.com>,
        Lyude Paul <lyude@...hat.com>,
        Thierry Reding <treding@...dia.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Linus W <linus.walleij@...aro.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Rob Clark <robdclark@...omium.org>,
        Steev Klimaszewski <steev@...i.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 03/10] dt-bindings: drm/bridge: ti-sn65dsi86: Add
 aux-bus child

Hi,

On Wed, May 19, 2021 at 1:02 PM Rob Herring <robh@...nel.org> wrote:
>
> On Mon, May 17, 2021 at 01:09:00PM -0700, Douglas Anderson wrote:
> > We want to be able to list an eDP panel as a child of a ti-sn65dsi86
> > node to represent the fact that the panel is connected to the bridge's
> > DP AUX bus. Though the panel and the bridge chip are connected in
> > several ways, the DP AUX bus is the primary control interface between
> > the two and thus makes the most sense to model in device tree
> > hierarchy.
> >
> > Listing a panel in this way makes it possible for the panel driver to
> > easily get access to the DP AUX bus that it resides on, which can be
> > useful to help in auto-detecting the panel and for turning on various
> > bits.
> >
> > NOTE: it's still possible to continue using the bridge chip and point
> > to a panel that _isn't_ listed as a child of the bridge chip (since
> > it's worked that way previously), but that should be deprecated since
> > there is no downside to listing the panel under the bridge chip.
> >
> > The idea for this bus's design was hashed out over IRC [1].
> >
> > [1] https://people.freedesktop.org/~cbrill/dri-log/?channel=dri-devel&date=2021-05-11
> >
> > Signed-off-by: Douglas Anderson <dianders@...omium.org>
> > ---
> > Possibly we might want something fancier that could be included by
> > other eDP controller bindings. If we want to do this, I'd love to be
> > pointed at a good example to follow.
> >
> > Changes in v7:
> > - ti-sn65dsi86: Add aux-bus child patch new for v7.
> >
> >  .../bindings/display/bridge/ti,sn65dsi86.yaml | 22 ++++++++++++++++++-
> >  1 file changed, 21 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml
> > index 26932d2e86ab..51f5a29e216c 100644
> > --- a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml
> > +++ b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml
> > @@ -70,6 +70,11 @@ properties:
> >      const: 1
> >      description: See ../../pwm/pwm.yaml for description of the cell formats.
> >
> > +  aux-bus:
>
> As this is a node:
>
> type: object
>
> > +    description:
> > +      It is recommended that you place your panel under the aux-bus node
> > +      here to represent the control hierarchy.
> > +
> >    ports:
> >      $ref: /schemas/graph.yaml#/properties/ports
> >
> > @@ -201,11 +206,26 @@ examples:
> >
> >            port@1 {
> >              reg = <1>;
> > -            endpoint {
> > +            sn65dsi86_out: endpoint {
> >                remote-endpoint = <&panel_in_edp>;
> >              };
> >            };
> >          };
> > +
> > +        aux-bus {
> > +          panel {
>
> We should perhaps have a separate aux-bus schema.

Yeah. Before spending lots of time digging into how to do this I
wanted to see if anyone was going to give me a big-old NAK on the
whole approach. ;-)

I guess I'd make a file called "dp-aux-bus.yaml" (maybe right under
bindings/display?) and then I'd include it like this:

aux-bus:
  $ref: "../dp-aux-bus.yaml#"


> Something should
> define the child node is 'panel' and nothing else.

At the moment the code also requires that the node name is 'aux-bus'.
Any objections to that?


> Though perhaps
> connectors are valid too?

They might be. We could always add it later?