libfdt: Add new maximum phandle lookup function

The fdt_get_max_phandle() function has some shortcomings. On one hand
it returns just a uint32_t which means to check for the "negative"
error code a caller has to explicitly check against the error code
(uint32_t)-1. In addition, the -1 is the only error code that can be
returned, so a caller cannot tell the difference between the various
failures.

Fix this by adding a new fdt_find_max_phandle() function that returns an
error code on failure and 0 on success, just like other APIs, and stores
the maximum phandle value in an output argument on success.

This also refactors fdt_get_max_phandle() to use the new function. Add a
note pointing out that the new fdt_find_max_phandle() function should be
preferred over fdt_get_max_phandle().

Signed-off-by: Thierry Reding <treding@nvidia.com>
Message-Id: <20190326153302.17109-1-thierry.reding@gmail.com>
[dwg: Reword for some inaccuracies in the commit message]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 29 insertions, 15 deletions

diff --git a/libfdt/fdt_ro.c b/libfdt/fdt_ro.c
index eafc142..1d0335e 100644
--- a/libfdt/fdt_ro.c
+++ b/libfdt/fdt_ro.c
@@ -144,32 +144,46 @@ static int fdt_string_eq_(const void *fdt, int stroffset,
 	return p && (slen == len) && (memcmp(p, s, len) == 0);
 }
 
-uint32_t fdt_get_max_phandle(const void *fdt)
+int fdt_find_max_phandle(const void *fdt, uint32_t *phandle)
 {
-	uint32_t max_phandle = 0;
-	int offset;
+	uint32_t max = 0;
+	int offset = -1;
 
-	for (offset = fdt_next_node(fdt, -1, NULL);;
-	     offset = fdt_next_node(fdt, offset, NULL)) {
-		uint32_t phandle;
+	while (true) {
+		uint32_t value;
 
-		if (offset == -FDT_ERR_NOTFOUND)
-			return max_phandle;
+		offset = fdt_next_node(fdt, offset, NULL);
+		if (offset < 0) {
+			if (offset == -FDT_ERR_NOTFOUND)
+				break;
 
-		if (offset < 0)
-			return (uint32_t)-1;
+			return offset;
+		}
 
-		phandle = fdt_get_phandle(fdt, offset);
-		if (phandle == (uint32_t)-1)
-			continue;
+		value = fdt_get_phandle(fdt, offset);
 
-		if (phandle > max_phandle)
-			max_phandle = phandle;
+		if (value > max)
+			max = value;
 	}
 
+	if (phandle)
+		*phandle = max;
+
 	return 0;
 }
 
+uint32_t fdt_get_max_phandle(const void *fdt)
+{
+	uint32_t phandle;
+	int err;
+
+	err = fdt_find_max_phandle(fdt, &phandle);
+	if (err < 0)
+		return (uint32_t)-1;
+
+	return phandle;
+}
+
 static const struct fdt_reserve_entry *fdt_mem_rsv(const void *fdt, int n)
 {
 	int offset = n * sizeof(struct fdt_reserve_entry);