libfdt: Add phandle generation helper

The new fdt_generate_phandle() function can be used to generate a new,
unused phandle given a specific device tree blob. The implementation is
somewhat naive in that it simply walks the entire device tree to find
the highest phandle value and then returns a phandle value one higher
than that. A more clever implementation might try to find holes in the
current set of phandle values and fill them. But this implementation is
relatively simple and works reliably.

Also add a test that validates that phandles generated by this new API
are indeed unique.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Message-Id: <20190326153302.17109-3-thierry.reding@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

libfdt/fdt_ro.c

@@ -184,6 +184,24 @@ uint32_t fdt_get_max_phandle(const void *fdt)
 	return phandle;
 }
 
+int fdt_generate_phandle(const void *fdt, uint32_t *phandle)
+{
+	uint32_t max;
+	int err;
+
+	err = fdt_find_max_phandle(fdt, &max);
+	if (err < 0)
+		return err;
+
+	if (max == FDT_MAX_PHANDLE)
+		return -FDT_ERR_NOPHANDLES;
+
+	if (phandle)
+		*phandle = max + 1;
+
+	return 0;
+}
+
 static const struct fdt_reserve_entry *fdt_mem_rsv(const void *fdt, int n)
 {
 	int offset = n * sizeof(struct fdt_reserve_entry);

libfdt/libfdt.h

@@ -140,6 +140,10 @@
 
 #define FDT_ERR_MAX		17
 
+/* constants */
+#define FDT_MAX_PHANDLE 0xfffffffe
+	/* Valid values for phandles range from 1 to 2^32-2. */
+
 /**********************************************************************/
 /* Low-level functions (you probably don't need these)                */
 /**********************************************************************/
@@ -416,6 +420,21 @@ int fdt_find_max_phandle(const void *fdt, uint32_t *phandle);
  */
 uint32_t fdt_get_max_phandle(const void *fdt);
 
+/**
+ * fdt_generate_phandle - return a new, unused phandle for a device tree blob
+ * @fdt: pointer to the device tree blob
+ * @phandle: return location for the new phandle
+ *
+ * Walks the device tree blob and looks for the highest phandle value. On
+ * success, the new, unused phandle value (one higher than the previously
+ * highest phandle value in the device tree blob) will be returned in the
+ * @phandle parameter.
+ *
+ * Returns:
+ *   0 on success or a negative error-code on failure
+ */
+int fdt_generate_phandle(const void *fdt, uint32_t *phandle);
+
 /**
  * fdt_num_mem_rsv - retrieve the number of memory reserve map entries
  * @fdt: pointer to the device tree blob

libfdt/version.lds

@@ -68,6 +68,7 @@ LIBFDT_1.2 {
 		fdt_get_string;
 		fdt_find_max_phandle;
 		fdt_get_max_phandle;
+		fdt_generate_phandle;
 		fdt_check_full;
 		fdt_setprop_placeholder;
 		fdt_property_placeholder;

tests/get_phandle.c

@@ -17,6 +17,7 @@
  * 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 <stdbool.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
@@ -42,9 +43,30 @@ static void check_phandle(void *fdt, const char *path, uint32_t checkhandle)
 		     path, phandle, checkhandle);
 }
 
+static void check_phandle_unique(const void *fdt, uint32_t checkhandle)
+{
+	uint32_t phandle;
+	int offset = -1;
+
+	while (true) {
+		offset = fdt_next_node(fdt, offset, NULL);
+		if (offset < 0) {
+			if (offset == -FDT_ERR_NOTFOUND)
+				break;
+
+			FAIL("error looking for phandle %#x", checkhandle);
+		}
+
+		phandle = fdt_get_phandle(fdt, offset);
+
+		if (phandle == checkhandle)
+			FAIL("generated phandle already exists");
+	}
+}
+
 int main(int argc, char *argv[])
 {
-	uint32_t max;
+	uint32_t max, phandle;
 	void *fdt;
 	int err;
 
@@ -68,5 +90,11 @@ int main(int argc, char *argv[])
 		FAIL("fdt_get_max_phandle returned 0x%x instead of 0x%x\n",
 		     max, PHANDLE_2);
 
+	err = fdt_generate_phandle(fdt, &phandle);
+	if (err < 0)
+		FAIL("failed to generate phandle: %d", err);
+
+	check_phandle_unique(fdt, phandle);
+
 	PASS();
 }

tests/multilabel.dts

@@ -41,4 +41,9 @@ m1: mq: /memreserve/ 0 0x1000;
 		n2 = &n2;
 		n3 = &n3;
 	};
+
+	node6 {
+		linux,phandle = <0xfffffffe>;
+		phandle = <0xfffffffe>;
+	};
 };

tests/multilabel_merge.dts

@@ -39,6 +39,11 @@ m1: mq: /memreserve/ 0 0x1000;
 		n2 = &n2;
 		n3 = &n3;
 	};
+
+	node6 {
+		linux,phandle = <0xfffffffe>;
+		phandle = <0xfffffffe>;
+	};
 };
 
 / {

tests/references.c

@@ -76,8 +76,8 @@ static void check_rref(const void *fdt)
 int main(int argc, char *argv[])
 {
 	void *fdt;
-	int n1, n2, n3, n4, n5;
+	int n1, n2, n3, n4, n5, n6, err;
-	uint32_t h1, h2, h4, h5;
+	uint32_t h1, h2, h4, h5, h6, hn;
 
 	test_init(argc, argv);
 	fdt = load_blob_arg(argc, argv);
@@ -97,11 +97,15 @@ int main(int argc, char *argv[])
 	n5 = fdt_path_offset(fdt, "/node5");
 	if (n5 < 0)
 		FAIL("fdt_path_offset(/node5): %s", fdt_strerror(n5));
+	n6 = fdt_path_offset(fdt, "/node6");
+	if (n6 < 0)
+		FAIL("fdt_path_offset(/node6): %s", fdt_strerror(n6));
 
 	h1 = fdt_get_phandle(fdt, n1);
 	h2 = fdt_get_phandle(fdt, n2);
 	h4 = fdt_get_phandle(fdt, n4);
 	h5 = fdt_get_phandle(fdt, n5);
+	h6 = fdt_get_phandle(fdt, n6);
 
 	if (h1 != 0x2000)
 		FAIL("/node1 has wrong phandle, 0x%x instead of 0x%x",
@@ -109,6 +113,9 @@ int main(int argc, char *argv[])
 	if (h2 != 0x1)
 		FAIL("/node2 has wrong phandle, 0x%x instead of 0x%x",
 		     h2, 0x1);
+	if (h6 != FDT_MAX_PHANDLE)
+		FAIL("/node6 has wrong phandle, 0x%x instead of 0x%x",
+		     h6, FDT_MAX_PHANDLE);
 	if ((h4 == 0x2000) || (h4 == 0x1) || (h4 == 0))
 		FAIL("/node4 has bad phandle, 0x%x", h4);
 
@@ -117,6 +124,14 @@ int main(int argc, char *argv[])
 	if ((h5 == h4) || (h5 == h2) || (h5 == h1))
 		FAIL("/node5 has duplicate phandle, 0x%x", h5);
 
+	/*
+	 * /node6 has phandle FDT_MAX_PHANDLE, so fdt_generate_phandle() is
+	 * expected to fail.
+	 */
+	err = fdt_generate_phandle(fdt, &hn);
+	if (err != -FDT_ERR_NOPHANDLES)
+		FAIL("generated invalid phandle 0x%x\n", hn);
+
 	check_ref(fdt, n1, h2);
 	check_ref(fdt, n2, h1);
 	check_ref(fdt, n3, h4);

tests/references.dts

@@ -33,4 +33,9 @@
 		linux,phandle = <&n5>;
 		phandle = <&n5>;
 	};
+
+	node6 {
+		linux,phandle = <0xfffffffe>;
+		phandle = <0xfffffffe>;
+	};
 };