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

[Douglas Anderson <dianders@chromium.org>]

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:
+    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 {
+            compatible = "boe,nv133fhm-n62";
+            power-supply = <&pp3300_dx_edp>;
+            backlight = <&backlight>;
+            hpd-gpios = <&sn65dsi86_bridge 2 GPIO_ACTIVE_HIGH>;
+
+            port {
+              panel_in_edp: endpoint {
+                remote-endpoint = <&sn65dsi86_out>;
+              };
+            };
+          };
+        };
       };
     };
   - |
-- 
2.31.1.751.gd2f1c929bd-goog