Allow device tree to be modified by additonal device tree sections

This patch allows the following construct:

/ {
	property-a = "old";
	property-b = "does not change";
};

/ {
	property-a = "changed";
	property-c = "new";
	node-a {
	};
};

Where the later device tree overrides the properties found in the
earlier tree.  This is useful for laying down a template device tree
in an include file and modifying it for a specific board without having
to clone the entire tree.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

4 files changed, 126 insertions, 4 deletions

diff --git a/tests/multilabel.dts b/tests/multilabel.dts
index 87c175c..31116ce 100644
--- a/tests/multilabel.dts
+++ b/tests/multilabel.dts
@@ -3,26 +3,27 @@
 m1: mq: /memreserve/ 0 0x1000;
 
 / {
-	p1: px: prop = "foo";
+	p0: pw: prop = "foo";
 
 	/* Explicit phandles */
 	n1: nx: node1 {
 		linux,phandle = <0x2000>;
 		ref = <&{/node2}>; /* reference precedes target */
-		lref = <&ny>;
+		p1: px: lref = <&ny>;
 	};
 	ny: n2: node2 {
-		phandle = <0x1>;
+		p2: py: phandle = <0x1>;
 		ref = <&{/node1}>; /* reference after target */
 		lref = <&nx>;
 	};
 
 	/* Implicit phandles */
 	n3: node3 {
-		ref = <&{/node4}>;
+		p3: ref = <&{/node4}>;
 		lref = <&n4>;
 	};
 	n4: node4 {
+		p4: prop;
 	};
 
 	/* Explicit phandle with implicit value */
@@ -34,5 +35,8 @@ m1: mq: /memreserve/ 0 0x1000;
 	n5: nz: node5 {
 		linux,phandle = <&n5>;
 		phandle = <&nz>;
+		n1 = &n1;
+		n2 = &n2;
+		n3 = &n3;
 	};
 };
diff --git a/tests/multilabel_merge.dts b/tests/multilabel_merge.dts
new file mode 100644
index 0000000..1632300
--- /dev/null
+++ b/tests/multilabel_merge.dts
@@ -0,0 +1,66 @@
+/dts-v1/;
+
+m1: mq: /memreserve/ 0 0x1000;
+
+/ {
+	p0: pw: prop = "foo";
+
+	/* Explicit phandles */
+	n1: node1 {
+		linux,phandle = <0x2000>;
+		ref = <&{/node2}>; /* reference precedes target */
+		p1: lref;
+	};
+	node2 {
+		phandle = <0x1>;
+		ref = <&{/node1}>; /* reference after target */
+		lref = <&nx>;
+	};
+
+	/* Implicit phandles */
+	n3: node3 {
+		p3: ref = <&{/node4}>;
+		lref = <&n4>;
+	};
+	n4: node4 {
+		p4: prop = "foo";
+	};
+
+	/* Explicit phandle with implicit value */
+	/* This self-reference is the standard way to tag a node as requiring
+	 * a phandle (perhaps for reference by nodes that will be dynamically
+	 * added) without explicitly allocating it a phandle.
+	 * The self-reference requires some special internal handling, though
+	 * so check it actually works */
+	n5: nz: node5 {
+		linux,phandle = <&n5>;
+		phandle = <&nz>;
+		n1 = &n1;
+		n2 = &n2;
+		n3 = &n3;
+	};
+};
+
+/ {
+	/* Append labels (also changes property content) */
+	nx: node1 {
+		px: lref = <&ny>;
+	};
+
+	/* Add multiple labels */
+	ny: n2: node2 {
+		/* Add a label to a property */
+		p2: py: phandle = <0x1>;
+	};
+
+	/* Reassigning the same label should be a no-op */
+	n3: node3 {
+		p3: ref = <&{/node4}>;
+	};
+
+	/* Redefining a node/property should not remove labels */
+	node4 {
+		prop;
+	};
+
+};
diff --git a/tests/run_tests.sh b/tests/run_tests.sh
index 08535ad..43b9d44 100755
--- a/tests/run_tests.sh
+++ b/tests/run_tests.sh
@@ -297,6 +297,13 @@ dtc_tests () {
 	 done
     done
 
+    # Check merge/overlay functionality
+    run_dtc_test -I dts -O dtb -o dtc_tree1_merge.test.dtb test_tree1_merge.dts
+    tree1_tests dtc_tree1_merge.test.dtb test_tree1.dtb
+    run_dtc_test -I dts -O dtb -o multilabel_merge.test.dtb multilabel_merge.dts
+    run_test references multilabel.test.dtb
+    run_test dtbs_equal_ordered multilabel.test.dtb multilabel_merge.test.dtb
+
     # Check some checks
     check_tests dup-nodename.dts duplicate_node_names
     check_tests dup-propname.dts duplicate_property_names
diff --git a/tests/test_tree1_merge.dts b/tests/test_tree1_merge.dts
new file mode 100644
index 0000000..f580da8
--- /dev/null
+++ b/tests/test_tree1_merge.dts
@@ -0,0 +1,45 @@
+/dts-v1/;
+/memreserve/ 0xdeadbeef00000000 0x100000;
+/memreserve/ 123456789 010000;
+
+/ {
+	compatible = "test_tree1";
+	prop-int = "wrong!";
+	prop-str = "hello world";
+
+	subnode@1 {
+		compatible = "subnode1";
+
+		subsubnode {
+			compatible = "subsubnode1", "subsubnode";
+			prop-int = <0xdeadbeef>;
+		};
+
+		ss1 {
+		};
+	};
+
+	subnode@2 {
+		linux,phandle = <0x2000>;
+		prop-int = <123456789>;
+
+		ss2 {
+		};
+	};
+};
+
+/ {
+	prop-int = <0xdeadbeef>;
+	subnode@1 {
+		prop-int = [deadbeef];
+	};
+	subnode@2 {
+		subsubnode@0 {
+			phandle = <0x2001>;
+			compatible = "subsubnode2", "subsubnode";
+			prop-int = <0726746425>;
+		};
+	};
+};
+
+