drm/panel: Add generic DSI display controller YAML bindings

This adds a starting point for processing and defining generic
bindings used by DSI display controllers and panels attached to
the virtual DSI ports.

Cc: Stephan Gerhold <stephan@gerhold.net>
Cc: devicetree@vger.kernel.org
Suggested-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191128090726.51107-1-linus.walleij@linaro.orgReviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/display/dsi-controller.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/dsi-controller.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Common Properties for DSI Display Panels
+
+maintainers:
+  - Linus Walleij <linus.walleij@linaro.org>
+
+description: |
+  This document defines device tree properties common to DSI, Display
+  Serial Interface controllers and attached panels. It doesn't constitute
+  a device tree binding specification by itself but is meant to be referenced
+  by device tree bindings.
+
+  When referenced from panel device tree bindings the properties defined in
+  this document are defined as follows. The panel device tree bindings are
+  responsible for defining whether each property is required or optional.
+
+  Notice: this binding concerns DSI panels connected directly to a master
+  without any intermediate port graph to the panel. Each DSI master
+  can control one to four virtual channels to one panel. Each virtual
+  channel should have a node "panel" for their virtual channel with their
+  reg-property set to the virtual channel number, usually there is just
+  one virtual channel, number 0.
+
+properties:
+  $nodename:
+    pattern: "^dsi-controller(@.*)?$"
+
+  "#address-cells":
+    const: 1
+
+  "#size-cells":
+    const: 0
+
+patternProperties:
+  "^panel@[0-3]$":
+    description: Panels connected to the DSI link
+    type: object
+
+    properties:
+      reg:
+        minimum: 0
+        maximum: 3
+        description:
+          The virtual channel number of a DSI peripheral. Must be in the range
+          from 0 to 3, as DSI uses a 2-bit addressing scheme. Some DSI
+          peripherals respond to more than a single virtual channel. In that
+          case the reg property can take multiple entries, one for each virtual
+          channel that the peripheral responds to.
+
+      clock-master:
+        type: boolean
+        description:
+           Should be enabled if the host is being used in conjunction with
+           another DSI host to drive the same peripheral. Hardware supporting
+           such a configuration generally requires the data on both the busses
+           to be driven by the same clock. Only the DSI host instance
+           controlling this clock should contain this property.
+
+      enforce-video-mode:
+        type: boolean
+        description:
+          The best option is usually to run a panel in command mode, as this
+          gives better control over the panel hardware. However for different
+          reasons like broken hardware, missing features or testing, it may be
+          useful to be able to force a command mode-capable panel into video
+          mode.
+
+    required:
+      - reg
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    dsi-controller@a0351000 {
+        reg = <0xa0351000 0x1000>;
+        #address-cells = <1>;
+        #size-cells = <0>;
+        panel@0 {
+            compatible = "sony,acx424akp";
+            reg = <0>;
+            vddi-supply = <&ab8500_ldo_aux1_reg>;
+            reset-gpios = <&gpio2 1 GPIO_ACTIVE_LOW>;
+        };
+    };
+
+...