Correct overlay syntactic sugar for generating target-path fragments

We've recently added "syntactic sugar" support to generate runtime dtb
overlays using similar syntax to the compile time overlays we've had for
a while.  This worked with the &label { ... } syntax, adjusting an existing
labelled node, but would fail with the &{/path} { ... } syntax attempting
to adjust an existing node referenced by its path.

The previous code would always try to use the "target" property in the
output overlay, which needs to be fixed up, and __fixups__ can only encode
symbols, not paths, so the result could never work properly.

This adds support for the &{/path} syntax for overlays, translating it into
the "target-path" encoding in the output.  It also changes existing
behaviour a little because we now unconditionally one fragment for each
overlay section in the source.  Previously we would only create a fragment
if we couldn't locally resolve the node referenced.  We need this for
path references, because the path is supposed to be referencing something
in the (not yet known) base tree, rather than the overlay tree we are
working with now.  In particular one useful case for path based overlays
is using &{/} - but the constructed overlay tree will always have a root
node, meaning that without the change that would attempt to resolve the
fragment locally, which is not what we want.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

dtc-parser.y

@@ -190,18 +190,18 @@ devicetree:
 		}
 	| devicetree DT_REF nodedef
 		{
-			struct node *target = get_node_by_ref($1, $2);
-
-			if (target) {
-				merge_nodes(target, $3);
+			/*
+			 * We rely on the rule being always:
+			 *   versioninfo plugindecl memreserves devicetree
+			 * so $-1 is what we want (plugindecl)
+			 */
+			if ($<flags>-1 & DTSF_PLUGIN) {
+				add_orphan_node($1, $3, $2);
 			} else {
-				/*
-				 * We rely on the rule being always:
-				 *   versioninfo plugindecl memreserves devicetree
-				 * so $-1 is what we want (plugindecl)
-				 */
-				if ($<flags>-1 & DTSF_PLUGIN)
-					add_orphan_node($1, $3, $2);
+				struct node *target = get_node_by_ref($1, $2);
+
+				if (target)
+					merge_nodes(target, $3);
 				else
 					ERROR(&@2, "Label or path %s not found", $2);
 			}

livetree.c

@@ -224,10 +224,16 @@ struct node * add_orphan_node(struct node *dt, struct node *new_node, char *ref)
 	struct data d = empty_data;
 	char *name;
 
-	d = data_add_marker(d, REF_PHANDLE, ref);
-	d = data_append_integer(d, 0xffffffff, 32);
+	if (ref[0] == '/') {
+		d = data_append_data(d, ref, strlen(ref) + 1);
 
-	p = build_property("target", d);
+		p = build_property("target-path", d);
+	} else {
+		d = data_add_marker(d, REF_PHANDLE, ref);
+		d = data_append_integer(d, 0xffffffff, 32);
+
+		p = build_property("target", d);
+	}
 
 	xasprintf(&name, "fragment@%u",
 			next_orphan_fragment++);

tests/overlay_overlay_bypath.dts

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2016 NextThing Co
+ * Copyright (c) 2016 Free Electrons
+ * Copyright (c) 2016 Konsulko Inc.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+/dts-v1/;
+/plugin/;
+
+/* Test that we can change an int by another */
+&{/test-node} {
+	test-int-property = <43>;
+};
+
+/* Test that we can replace a string by a longer one */
+&{/test-node} {
+	test-str-property = "foobar";
+};
+
+/* Test that we add a new property */
+&{/test-node} {
+	test-str-property-2 = "foobar2";
+};
+
+/* Test that we add a new node (by phandle) */
+&{/test-node} {
+	new-node {
+		new-property;
+	};
+};
+
+&{/} {
+	local: new-local-node {
+		new-property;
+	};
+};
+
+&{/} {
+	test-several-phandle = <&local>, <&local>;
+};
+
+&{/test-node} {
+	sub-test-node {
+		new-sub-test-property;
+	};
+};

tests/run_tests.sh

@@ -251,13 +251,25 @@ dtc_overlay_tests () {
     run_test check_path overlay_overlay_nosugar.test.dtb exists "/__fixups__"
     run_test check_path overlay_overlay_nosugar.test.dtb exists "/__local_fixups__"
 
+    # Using target-path
+    run_dtc_test -I dts -O dtb -o overlay_overlay_bypath.test.dtb overlay_overlay_bypath.dts
+    run_test check_path overlay_overlay_bypath.test.dtb not-exists "/__symbols__"
+    run_test check_path overlay_overlay_bypath.test.dtb not-exists "/__fixups__"
+    run_test check_path overlay_overlay_bypath.test.dtb exists "/__local_fixups__"
+
     # Check building works the same as manual constructions
     run_test dtbs_equal_ordered overlay_overlay.test.dtb overlay_overlay_nosugar.test.dtb
 
     run_dtc_test -I dts -O dtb -o overlay_overlay_manual_fixups.test.dtb overlay_overlay_manual_fixups.dts
     run_test dtbs_equal_ordered overlay_overlay.test.dtb overlay_overlay_manual_fixups.test.dtb
 
+    run_dtc_test -I dts -O dtb -o overlay_overlay_no_fixups.test.dtb overlay_overlay_no_fixups.dts
+    run_test dtbs_equal_ordered overlay_overlay_bypath.test.dtb overlay_overlay_no_fixups.test.dtb
+
+    # Check we can actually apply the result
+    run_dtc_test -I dts -O dtb -o overlay_base_no_symbols.test.dtb overlay_base.dts
     run_test overlay overlay_base.test.dtb overlay_overlay.test.dtb
+    run_test overlay overlay_base_no_symbols.test.dtb overlay_overlay_bypath.test.dtb
 
     # test plugin source to dtb and back
     run_dtc_test -I dtb -O dts -o overlay_overlay_decompile.test.dts overlay_overlay.test.dtb