of: Add helper for getting the maximum alias index for a stem

of_alias_max_index will return the maximum number for which an
alias of a given stem exists. This is useful for frameworks
whishing to reserve a number of device slots from dynamic
allocation.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
(cherry picked from commit 18ae7362e9822993436c1a544e49cfd58fa175b2)

1 files changed, 29 insertions, 0 deletions

diff --git a/drivers/of/base.c b/drivers/of/base.c
index c258df42b002..5e713b42621f 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -1588,6 +1588,35 @@ static void of_alias_add(struct alias_prop *ap, struct device_node *np,
                  ap->alias, ap->stem, ap->id, of_node_full_name(np));
 }
 
+/*
+ * of_alias_max_index() - get the maximum index for a given alias stem
+ * @stem:   The alias stem for which the maximum index is searched for
+ *
+ * Given an alias stem (the alias without the number) this function
+ * returns the maximum number for which an alias exists.
+ *
+ * Return: The maximum existing alias index or -ENODEV if no alias
+ *         exists for this stem.
+ */
+int of_alias_max_index(const char *stem)
+{
+        struct alias_prop *app;
+        int max = -ENODEV;
+
+        mutex_lock(&of_aliases_mutex);
+
+        list_for_each_entry(app, &aliases_lookup, link) {
+                if (strcmp(app->stem, stem))
+                        continue;
+                if (app->id > max)
+                        max = app->id;
+        }
+
+        mutex_unlock(&of_aliases_mutex);
+
+        return max;
+}
+
 /**
  * of_alias_scan - Scan all properties of 'aliases' node
  *