Add notifier framework

This is loosely based on the Linux notifier framework, but
stripped down to the bare minimum.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

include/notifier.h

@@ -0,0 +1,35 @@
+#ifndef __NOTIFIER_H
+#define __NOTIFIER_H
+
+/*
+ * Notifer chains loosely based on the according Linux framework
+ */
+
+struct notifier_block {
+	int (*notifier_call)(struct notifier_block *, unsigned long, void *);
+	struct list_head list;
+};
+
+struct notifier_head {
+	struct list_head blocks;
+};
+
+int notifier_chain_register(struct notifier_head *nh, struct notifier_block *n);
+
+int notifier_call_chain(struct notifier_head *nh, unsigned long val, void *v);
+
+/*
+ * Register a function which is called upon changes of
+ * clock frequencies in the system.
+ */
+int clock_register_client(struct notifier_block *nb);
+int clock_unregister_client(struct notifier_block *nb);
+int clock_notifier_call_chain(void);
+
+#define NOTIFIER_HEAD(name)					\
+	struct notifier_head name = {				\
+		.blocks = LIST_HEAD_INIT((name).blocks),	\
+	};
+
+#endif /* __NOTIFIER_H */
+

lib/Makefile

@@ -26,3 +26,5 @@ obj-$(CONFIG_SIMPLE_READLINE)	+= readline_simple.o
 obj-$(CONFIG_GLOB)		+= fnmatch.o
 obj-$(CONFIG_GENERIC_FIND_NEXT_BIT) += find_next_bit.o
 obj-y			+= glob.o
+obj-y			+= notifier.o
+

lib/notifier.c

@@ -0,0 +1,59 @@
+#include <common.h>
+#include <list.h>
+#include <notifier.h>
+
+int notifier_chain_register(struct notifier_head *nh, struct notifier_block *n)
+{
+	list_add_tail(&n->list, &nh->blocks);
+	return 0;
+}
+
+int notifier_chain_unregister(struct notifier_head *nh, struct notifier_block *n)
+{
+	list_del(&n->list);
+	return 0;
+}
+
+int notifier_call_chain(struct notifier_head *nh, unsigned long val, void *v)
+{
+	struct notifier_block *entry;
+
+	list_for_each_entry(entry, &nh->blocks, list)
+		entry->notifier_call(entry, val, v);
+
+	return 0;
+}
+
+/*
+ *	Notifier list for code which wants to be called at clock
+ *	frequency changes.
+ */
+static NOTIFIER_HEAD(clock_notifier_list);
+
+/**
+ *	clock_register_client - register a client notifier
+ *	@nb: notifier block to callback on events
+ */
+int clock_register_client(struct notifier_block *nb)
+{
+	return notifier_chain_register(&clock_notifier_list, nb);
+}
+
+/**
+ *	clock_register_client - unregister a client notifier
+ *	@nb: notifier block to callback on events
+ */
+int clock_unregister_client(struct notifier_block *nb)
+{
+	return notifier_chain_unregister(&clock_notifier_list, nb);
+}
+
+/**
+ * clock_register_client - notify clients of clock frequency changes
+ *
+ */
+int clock_notifier_call_chain(void)
+{
+	return notifier_call_chain(&clock_notifier_list, 0, NULL);
+}
+