dt-bindings: example-schema: Add some additional examples and commentary

Add examples for properties with standard units, child nodes,
dependencies, and if/then schema. Also, make some minor updates based on
common questions and review issues.
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/example-schema.yaml

-# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
 # Copyright 2018 Linaro Ltd.
 %YAML 1.2
 ---
@@ -71,7 +71,7 @@ properties:
     # minItems/maxItems equal to 2 is implied
 
   reg-names:
-    # The core schema enforces this is a string array
+    # The core schema enforces this (*-names) is a string array
     items:
       - const: core
       - const: aux
@@ -79,7 +79,8 @@ properties:
   clocks:
     # Cases that have only a single entry just need to express that with maxItems
     maxItems: 1
-    description: bus clock
+    description: bus clock. A description is only needed for a single item if
+      there's something unique to add.
 
   clock-names:
     items:
@@ -127,6 +128,14 @@ properties:
     maxItems: 1
     description: A connection of the 'foo' gpio line.
 
+  # *-supply is always a single phandle, so nothing more to define.
+  foo-supply: true
+
+  # Vendor specific properties
+  #
+  # Vendor specific properties have slightly different schema requirements than
+  # common properties. They must have at least a type definition and
+  # 'description'.
   vendor,int-property:
     description: Vendor specific properties must have a description
     # 'allOf' is the json-schema way of subclassing a schema. Here the base
@@ -137,9 +146,9 @@ properties:
       - enum: [2, 4, 6, 8, 10]
 
   vendor,bool-property:
-    description: Vendor specific properties must have a description
-    # boolean properties is one case where the json-schema 'type' keyword
-    # can be used directly
+    description: Vendor specific properties must have a description. Boolean
+      properties are one case where the json-schema 'type' keyword can be used
+      directly.
     type: boolean
 
   vendor,string-array-property:
@@ -151,14 +160,72 @@ properties:
           - enum: [ foo, bar ]
           - enum: [ baz, boo ]
 
+  vendor,property-in-standard-units-microvolts:
+    description: Vendor specific properties having a standard unit suffix
+      don't need a type.
+    enum: [ 100, 200, 300 ]
+
+  child-node:
+    description: Child nodes are just another property from a json-schema
+      perspective.
+    type: object  # DT nodes are json objects
+    properties:
+      vendor,a-child-node-property:
+        description: Child node properties have all the same schema
+          requirements.
+        type: boolean
+
+    required:
+      - vendor,a-child-node-property
+
+# Describe the relationship between different properties
+dependencies:
+  # 'vendor,bool-property' is only allowed when 'vendor,string-array-property'
+  # is present
+  vendor,bool-property: [ vendor,string-array-property ]
+  # Expressing 2 properties in both orders means all of the set of properties
+  # must be present or none of them.
+  vendor,string-array-property: [ vendor,bool-property ]
+
 required:
   - compatible
   - reg
   - interrupts
   - interrupt-controller
 
+# if/then schema can be used to handle conditions on a property affecting
+# another property. A typical case is a specific 'compatible' value changes the
+# constraints on other properties.
+#
+# For multiple 'if' schema, group them under an 'allOf'.
+#
+# If the conditionals become too unweldy, then it may be better to just split
+# the binding into separate schema documents.
+if:
+  properties:
+    compatible:
+      contains:
+        const: vendor,soc2-ip
+then:
+  required:
+    - foo-supply
+
+# Ideally, the schema should have this line otherwise any other properties
+# present are allowed. There's a few common properties such as 'status' and
+# 'pinctrl-*' which are added automatically by the tooling.
+#
+# This can't be used in cases where another schema is referenced
+# (i.e. allOf: [{$ref: ...}]).
+additionalProperties: false
+
 examples:
-  # Examples are now compiled with dtc
+  # Examples are now compiled with dtc and validated against the schemas
+  #
+  # Examples have a default #address-cells and #size-cells value of 1. This can
+  # be overridden or an appropriate parent bus node should be shown (such as on
+  # i2c buses).
+  #
+  # Any includes used have to be explicitly included.
   - |
     node@1000 {
           compatible = "vendor,soc4-ip", "vendor,soc1-ip";