libfdt: Add fdt_next_subnode() to permit easy subnode iteration

Iterating through subnodes with libfdt is a little painful to write as we
need something like this:

for (depth = 0, count = 0,
	offset = fdt_next_node(fdt, parent_offset, &depth);
     (offset >= 0) && (depth > 0);
     offset = fdt_next_node(fdt, offset, &depth)) {
	if (depth == 1) {
		/* code body */
	}
}

Using fdt_next_subnode() we can instead write this, which is shorter and
easier to get right:

for (offset = fdt_first_subnode(fdt, parent_offset);
     offset >= 0;
     offset = fdt_next_subnode(fdt, offset)) {
	/* code body */
}

Also, it doesn't require two levels of indentation for the loop body.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: David Gibson <david@gibson.dropbear.id.au>

libfdt/fdt.c

@@ -198,6 +198,34 @@ int fdt_next_node(const void *fdt, int offset, int *depth)
 	return offset;
 }
 
+int fdt_first_subnode(const void *fdt, int offset)
+{
+	int depth = 0;
+
+	offset = fdt_next_node(fdt, offset, &depth);
+	if (offset < 0 || depth != 1)
+		return -FDT_ERR_NOTFOUND;
+
+	return offset;
+}
+
+int fdt_next_subnode(const void *fdt, int offset)
+{
+	int depth = 1;
+
+	/*
+	 * With respect to the parent, the depth of the next subnode will be
+	 * the same as the last.
+	 */
+	do {
+		offset = fdt_next_node(fdt, offset, &depth);
+		if (offset < 0 || depth < 1)
+			return -FDT_ERR_NOTFOUND;
+	} while (depth > 1);
+
+	return offset;
+}
+
 const char *_fdt_find_string(const char *strtab, int tabsize, const char *s)
 {
 	int len = strlen(s) + 1;

libfdt/libfdt.h

@@ -136,6 +136,28 @@ uint32_t fdt_next_tag(const void *fdt, int offset, int *nextoffset);
 
 int fdt_next_node(const void *fdt, int offset, int *depth);
 
+/**
+ * fdt_first_subnode() - get offset of first direct subnode
+ *
+ * @fdt:	FDT blob
+ * @offset:	Offset of node to check
+ * @return offset of first subnode, or -FDT_ERR_NOTFOUND if there is none
+ */
+int fdt_first_subnode(const void *fdt, int offset);
+
+/**
+ * fdt_next_subnode() - get offset of next direct subnode
+ *
+ * After first calling fdt_first_subnode(), call this function repeatedly to
+ * get direct subnodes of a parent node.
+ *
+ * @fdt:	FDT blob
+ * @offset:	Offset of previous subnode
+ * @return offset of next subnode, or -FDT_ERR_NOTFOUND if there are no more
+ * subnodes
+ */
+int fdt_next_subnode(const void *fdt, int offset);
+
 /**********************************************************************/
 /* General functions                                                  */
 /**********************************************************************/

tests/Makefile.tests

@@ -20,7 +20,8 @@ LIB_TESTS_L = get_mem_rsv \
 	dtb_reverse dtbs_equal_unordered \
 	add_subnode_with_nops path_offset_aliases \
 	utilfdt_test \
-	integer-expressions
+	integer-expressions \
+	subnode_iterate
 LIB_TESTS = $(LIB_TESTS_L:%=$(TESTS_PREFIX)%)
 
 LIBTREE_TESTS_L = truncated_property

tests/run_tests.sh

@@ -241,6 +241,9 @@ libfdt_tests () {
 	tree1_tests_rw noppy.$basetree
     done
 
+    run_dtc_test -I dts -O dtb -o subnode_iterate.dtb subnode_iterate.dts
+    run_test subnode_iterate subnode_iterate.dtb
+
     # Tests for behaviour on various sorts of corrupted trees
     run_test truncated_property
 

tests/subnode_iterate.c

@@ -0,0 +1,94 @@
+/*
+ * libfdt - Flat Device Tree manipulation
+ *	Tests that fdt_next_subnode() works as expected
+ *
+ * Copyright (C) 2013 Google, Inc
+ *
+ * Copyright (C) 2007 David Gibson, IBM Corporation.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License
+ * as published by the Free Software Foundation; either version 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdint.h>
+
+#include <libfdt.h>
+
+#include "tests.h"
+#include "testdata.h"
+
+static void test_node(void *fdt, int parent_offset)
+{
+	fdt32_t subnodes;
+	const fdt32_t *prop;
+	int offset;
+	int count;
+	int len;
+
+	/* This property indicates the number of subnodes to expect */
+	prop = fdt_getprop(fdt, parent_offset, "subnodes", &len);
+	if (!prop || len != sizeof(fdt32_t)) {
+		FAIL("Missing/invalid subnodes property at '%s'",
+		     fdt_get_name(fdt, parent_offset, NULL));
+	}
+	subnodes = cpu_to_fdt32(*prop);
+
+	count = 0;
+	for (offset = fdt_first_subnode(fdt, parent_offset);
+	     offset >= 0;
+	     offset = fdt_next_subnode(fdt, offset))
+		count++;
+
+	if (count != subnodes) {
+		FAIL("Node '%s': Expected %d subnodes, got %d\n",
+		     fdt_get_name(fdt, parent_offset, NULL), subnodes,
+		     count);
+	}
+}
+
+static void check_fdt_next_subnode(void *fdt)
+{
+	int offset;
+	int count = 0;
+
+	for (offset = fdt_first_subnode(fdt, 0);
+	     offset >= 0;
+	     offset = fdt_next_subnode(fdt, offset)) {
+		test_node(fdt, offset);
+		count++;
+	}
+
+	if (count != 2)
+		FAIL("Expected %d tests, got %d\n", 2, count);
+}
+
+int main(int argc, char *argv[])
+{
+	void *fdt;
+
+	test_init(argc, argv);
+	if (argc != 2)
+		CONFIG("Usage: %s <dtb file>", argv[0]);
+
+	fdt = load_blob(argv[1]);
+	if (!fdt)
+		FAIL("No device tree available");
+
+	check_fdt_next_subnode(fdt);
+
+	PASS();
+}

tests/subnode_iterate.dts

@@ -0,0 +1,44 @@
+/dts-v1/;
+
+/ {
+	#address-cells = <1>;
+	#size-cells = <0>;
+
+	test1 {
+		subnodes = <2>;
+		linux,phandle = <0x1>;
+		#address-cells = <1>;
+		#size-cells = <0>;
+		PowerPC,970@0 {
+			name = "PowerPC,970";
+			device_type = "cpu";
+			reg = <0x00000000>;
+			clock-frequency = <1600000000>;
+			timebase-frequency = <33333333>;
+			linux,boot-cpu;
+			i-cache-size = <65536>;
+			d-cache-size = <32768>;
+			another-sub-node {
+				should-be-ignored;
+				yet-another {
+					should-also-be-ignored;
+				};
+			};
+		};
+
+		PowerPC,970@1 {
+			name = "PowerPC,970";
+			device_type = "cpu";
+			reg = <0x00000001>;
+			clock-frequency = <1600000000>;
+			timebase-frequency = <33333333>;
+			i-cache-size = <65536>;
+			d-cache-size = <32768>;
+		};
+	};
+
+	test2 {
+		subnodes = <0>;
+	};
+};
+