scripts: edtlib: do not inherit parent compatibles

Commit 0d4dca10b2 ("scripts: edtlib:
child binding compatibles match parents") was a hack meant to keep the
edtlib.Binding class in place without modifying some twister behavior
that needed further changes to work properly with first-class binding
objects.

This is a hack and is no longer necessary, so back out of this change.

Child Binding objects now have None compatible properties unless the
binding YAML explicitly sets a compatible.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>

scripts/dts/edtlib.py

@@ -1454,10 +1454,11 @@ class Binding:
       The free-form description of the binding.
 
     compatible:
-      The compatible string the binding matches. This is None if the Binding is
-      inferred from node properties. If the Binding is a child binding, then
-      this will be inherited from the parent binding unless the child binding
-      explicitly sets its own compatible.
+      The compatible string the binding matches.
+
+      This may be None. For example, it's None when the Binding is inferred
+      from node properties. It can also be None for Binding objects created
+      using 'child-binding:' with no compatible.
 
     prop2specs:
       A collections.OrderedDict mapping property names to PropertySpec objects
@@ -1564,14 +1565,6 @@ class Binding:
             if key.endswith("-cells"):
                 self.specifier2cells[key[:-len("-cells")]] = val
 
-        # Make child binding compatibles match ours if they are missing.
-        if self.compatible is not None:
-            child = self.child_binding
-            while child is not None:
-                if child.compatible is None:
-                    child.compatible = self.compatible
-                child = child.child_binding
-
     def __repr__(self):
         if self.compatible:
             compat = f" for compatible '{self.compatible}'"
@@ -1587,15 +1580,8 @@ class Binding:
     @property
     def compatible(self):
         "See the class docstring"
-        if hasattr(self, '_compatible'):
-            return self._compatible
         return self.raw.get('compatible')
 
-    @compatible.setter
-    def compatible(self, compatible):
-        "See the class docstring"
-        self._compatible = compatible
-
     @property
     def bus(self):
         "See the class docstring"

scripts/dts/test-bindings/child-binding-with-compat.yaml

@@ -2,7 +2,7 @@
 
 description: child-binding with separate compatible than the parent
 
-compatible: "child-binding-with-compat"
+compatible: "top-binding-with-compat"
 
 child-binding:
     compatible: child-compat

scripts/dts/test-bindings/child-binding.yaml

@@ -2,7 +2,7 @@
 
 description: child-binding test
 
-compatible: "child-binding"
+compatible: "top-binding"
 
 child-binding:
     description: child node

scripts/dts/test.dts

@@ -359,7 +359,7 @@
 	//
 
 	child-binding {
-		compatible = "child-binding";
+		compatible = "top-binding";
 		child-1 {
 			child-prop = <1>;
 			grandchild {

scripts/dts/testedtlib.py

@@ -181,15 +181,15 @@ def test_child_binding():
     child = top.child_binding
     assert Path(top.path) == binding_file
     assert Path(child.path) == binding_file
-    assert top.compatible == 'child-binding'
-    assert child.compatible == 'child-binding'
+    assert top.compatible == 'top-binding'
+    assert child.compatible is None
 
     binding_file = Path("test-bindings/child-binding-with-compat.yaml").resolve()
     top = edtlib.Binding(binding_file, {})
     child = top.child_binding
     assert Path(top.path) == binding_file
     assert Path(child.path) == binding_file
-    assert top.compatible == 'child-binding-with-compat'
+    assert top.compatible == 'top-binding-with-compat'
     assert child.compatible == 'child-compat'
 
 def test_props():