[PATCH 1/2] of: base: add function to get highest id of an alias stem

[Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>]

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-z923LK4zBo2bacvFa/9K2g@public.gmane.org>
---

Because this function is so similar to of_alias_get_id(), I thought of merging
them into __of_alias_get_id(np, stem, bool get_highest) and have two call
wrappers but then decided the decreased readability is not worth the hazzle.

 drivers/of/base.c  | 26 ++++++++++++++++++++++++++
 include/linux/of.h |  6 ++++++
 2 files changed, 32 insertions(+)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 0a8aeb8523fe7d..63cba04aacf686 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)
 {
diff --git a/include/linux/of.h b/include/linux/of.h
index dfde07e77a632b..9bfcc18ceab3bf 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -332,6 +332,7 @@ extern int of_count_phandle_with_args(const struct device_node *np,
 
 extern void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align));
 extern int of_alias_get_id(struct device_node *np, const char *stem);
+extern int of_alias_get_highest_id(const char *stem);
 
 extern int of_machine_is_compatible(const char *compat);
 
@@ -594,6 +595,11 @@ static inline int of_alias_get_id(struct device_node *np, const char *stem)
 	return -ENOSYS;
 }
 
+static inline int of_alias_get_highest_id(const char *stem)
+{
+	return -ENOSYS;
+}
+
 static inline int of_machine_is_compatible(const char *compat)
 {
 	return 0;
-- 
2.1.4