nvmem: add a notifier chain

Add a blocking notifier chain with four events (add and remove for
both devices and cells) so that users can get notified about the
addition of nvmem resources they're waiting for.

We'll use this instead of the at24 setup callback in the mityomapl138
board file.
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/core.c

@@ -65,6 +65,8 @@ static LIST_HEAD(nvmem_cell_tables);
 static DEFINE_MUTEX(nvmem_lookup_mutex);
 static LIST_HEAD(nvmem_lookup_list);
 
+static BLOCKING_NOTIFIER_HEAD(nvmem_notifier);
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 static struct lock_class_key eeprom_lock_key;
 #endif
@@ -300,6 +302,7 @@ static struct nvmem_device *nvmem_find(const char *name)
 
 static void nvmem_cell_drop(struct nvmem_cell *cell)
 {
+	blocking_notifier_call_chain(&nvmem_notifier, NVMEM_CELL_REMOVE, cell);
 	mutex_lock(&nvmem_mutex);
 	list_del(&cell->node);
 	mutex_unlock(&nvmem_mutex);
@@ -319,6 +322,7 @@ static void nvmem_cell_add(struct nvmem_cell *cell)
 	mutex_lock(&nvmem_mutex);
 	list_add_tail(&cell->node, &cell->nvmem->cells);
 	mutex_unlock(&nvmem_mutex);
+	blocking_notifier_call_chain(&nvmem_notifier, NVMEM_CELL_ADD, cell);
 }
 
 static int nvmem_cell_info_to_nvmem_cell(struct nvmem_device *nvmem,
@@ -434,6 +438,32 @@ static int nvmem_setup_compat(struct nvmem_device *nvmem,
 	return 0;
 }
 
+/**
+ * nvmem_register_notifier() - Register a notifier block for nvmem events.
+ *
+ * @nb: notifier block to be called on nvmem events.
+ *
+ * Return: 0 on success, negative error number on failure.
+ */
+int nvmem_register_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&nvmem_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(nvmem_register_notifier);
+
+/**
+ * nvmem_unregister_notifier() - Unregister a notifier block for nvmem events.
+ *
+ * @nb: notifier block to be unregistered.
+ *
+ * Return: 0 on success, negative error number on failure.
+ */
+int nvmem_unregister_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&nvmem_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(nvmem_unregister_notifier);
+
 static int nvmem_add_cells_from_table(struct nvmem_device *nvmem)
 {
 	const struct nvmem_cell_info *info;
@@ -647,6 +677,10 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 	if (rval)
 		goto err_remove_cells;
 
+	rval = blocking_notifier_call_chain(&nvmem_notifier, NVMEM_ADD, nvmem);
+	if (rval)
+		goto err_remove_cells;
+
 	return nvmem;
 
 err_remove_cells:
@@ -669,6 +703,8 @@ static void nvmem_device_release(struct kref *kref)
 
 	nvmem = container_of(kref, struct nvmem_device, refcnt);
 
+	blocking_notifier_call_chain(&nvmem_notifier, NVMEM_REMOVE, nvmem);
+
 	if (nvmem->flags & FLAG_COMPAT)
 		device_remove_bin_file(nvmem->base_dev, &nvmem->eeprom);
 

include/linux/nvmem-consumer.h

@@ -14,6 +14,7 @@
 
 #include <linux/err.h>
 #include <linux/errno.h>
+#include <linux/notifier.h>
 
 struct device;
 struct device_node;
@@ -47,6 +48,13 @@ struct nvmem_cell_lookup {
 	struct list_head	node;
 };
 
+enum {
+	NVMEM_ADD = 1,
+	NVMEM_REMOVE,
+	NVMEM_CELL_ADD,
+	NVMEM_CELL_REMOVE,
+};
+
 #if IS_ENABLED(CONFIG_NVMEM)
 
 /* Cell based interface */
@@ -80,6 +88,9 @@ void nvmem_add_cell_lookups(struct nvmem_cell_lookup *entries,
 void nvmem_del_cell_lookups(struct nvmem_cell_lookup *entries,
 			    size_t nentries);
 
+int nvmem_register_notifier(struct notifier_block *nb);
+int nvmem_unregister_notifier(struct notifier_block *nb);
+
 #else
 
 static inline struct nvmem_cell *nvmem_cell_get(struct device *dev,
@@ -179,6 +190,16 @@ nvmem_add_cell_lookups(struct nvmem_cell_lookup *entries, size_t nentries) {}
 static inline void
 nvmem_del_cell_lookups(struct nvmem_cell_lookup *entries, size_t nentries) {}
 
+static inline int nvmem_register_notifier(struct notifier_block *nb)
+{
+	return -ENOSYS;
+}
+
+static inline int nvmem_unregister_notifier(struct notifier_block *nb)
+{
+	return -ENOSYS;
+}
+
 #endif /* CONFIG_NVMEM */
 
 #if IS_ENABLED(CONFIG_NVMEM) && IS_ENABLED(CONFIG_OF)