of: base: add function to get highest id of an alias stem

I2C supports adding adapters using either a dynamic or fixed id. The
latter is provided by aliases in the DT case. To prevent id collisions
of those two types, install this function which gives us the highest
fixed id, so we can then let the dynamically created ones come after
this highest number.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

1 files changed, 26 insertions, 0 deletions

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 0a8aeb8523fe..63cba04aacf6 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -1958,6 +1958,32 @@ int of_alias_get_id(struct device_node *np, const char *stem)
 }
 EXPORT_SYMBOL_GPL(of_alias_get_id);
 
+/**
+ * of_alias_get_highest_id - Get highest alias id for the given stem
+ * @stem:       Alias stem to be examined
+ *
+ * The function travels the lookup table to get the highest alias id for the
+ * given alias stem.  It returns the alias id if found.
+ */
+int of_alias_get_highest_id(const char *stem)
+{
+        struct alias_prop *app;
+        int id = -ENODEV;
+
+        mutex_lock(&of_mutex);
+        list_for_each_entry(app, &aliases_lookup, link) {
+                if (strcmp(app->stem, stem) != 0)
+                        continue;
+
+                if (app->id > id)
+                        id = app->id;
+        }
+        mutex_unlock(&of_mutex);
+
+        return id;
+}
+EXPORT_SYMBOL_GPL(of_alias_get_highest_id);
+
 const __be32 *of_prop_next_u32(struct property *prop, const __be32 *cur,
                                u32 *pu)
 {