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From:   Rob Herring <robh@kernel.org>
Date:   Thu, 20 May 2021 08:25:06 -0500
Message-ID: <CAL_JsqL9p1nOQs5V5xN167E860Gm+3dTRaOwpv2X+AP=cM1Q_g@mail.gmail.com>
Subject: Re: [PATCH v7 03/10] dt-bindings: drm/bridge: ti-sn65dsi86: Add
 aux-bus child
To:     Doug Anderson <dianders@chromium.org>
Cc:     Andrzej Hajda <a.hajda@samsung.com>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Sam Ravnborg <sam@ravnborg.org>,
        Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>,
        Lyude Paul <lyude@redhat.com>,
        Thierry Reding <treding@nvidia.com>,
        Stephen Boyd <swboyd@chromium.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Linus W <linus.walleij@linaro.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Rob Clark <robdclark@chromium.org>,
        Steev Klimaszewski <steev@kali.org>,
        Daniel Vetter <daniel@ffwll.ch>,
        David Airlie <airlied@linux.ie>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
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On Wed, May 19, 2021 at 4:06 PM Doug Anderson <dianders@chromium.org> wrote:
>
> Hi,
>
> On Wed, May 19, 2021 at 1:02 PM Rob Herring <robh@kernel.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@chromium.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#"

Right.

> > 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?

No. There's 2 ways to do that. The above does and adding $nodename in
dp-aux-bus.yaml will. The latter also means the schema will be applied
automatically to any node named 'aux-bus'. That means the schema will
be applied twice unless you have 'select: false'. The main advantage
of the latter case is it gets applied even without all the users
converted to schema.

> > Though perhaps
> > connectors are valid too?
>
> They might be. We could always add it later?

Sure.

Rob