driver core: implement device_for_each_child_reverse()

The new function device_for_each_child_reverse() is helpful to traverse the
registered devices in a reversed order, e.g. in the case when an operation on
each device should be done first on the last added device, then on one before
last and so on.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

2 files changed, 45 insertions, 0 deletions

diff --git a/drivers/base/core.c b/drivers/base/core.c
index dafae6d2f7ac..7d6279554afc 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1252,6 +1252,19 @@ void device_unregister(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(device_unregister);
 
+static struct device *prev_device(struct klist_iter *i)
+{
+        struct klist_node *n = klist_prev(i);
+        struct device *dev = NULL;
+        struct device_private *p;
+
+        if (n) {
+                p = to_device_private_parent(n);
+                dev = p->device;
+        }
+        return dev;
+}
+
 static struct device *next_device(struct klist_iter *i)
 {
         struct klist_node *n = klist_next(i);
@@ -1341,6 +1354,36 @@ int device_for_each_child(struct device *parent, void *data,
 EXPORT_SYMBOL_GPL(device_for_each_child);
 
 /**
+ * device_for_each_child_reverse - device child iterator in reversed order.
+ * @parent: parent struct device.
+ * @fn: function to be called for each device.
+ * @data: data for the callback.
+ *
+ * Iterate over @parent's child devices, and call @fn for each,
+ * passing it @data.
+ *
+ * We check the return of @fn each time. If it returns anything
+ * other than 0, we break out and return that value.
+ */
+int device_for_each_child_reverse(struct device *parent, void *data,
+                                  int (*fn)(struct device *dev, void *data))
+{
+        struct klist_iter i;
+        struct device *child;
+        int error = 0;
+
+        if (!parent->p)
+                return 0;
+
+        klist_iter_init(&parent->p->klist_children, &i);
+        while ((child = prev_device(&i)) && !error)
+                error = fn(child, data);
+        klist_iter_exit(&i);
+        return error;
+}
+EXPORT_SYMBOL_GPL(device_for_each_child_reverse);
+
+/**
  * device_find_child - device iterator for locating a particular device.
  * @parent: parent struct device
  * @match: Callback function to check device
diff --git a/include/linux/device.h b/include/linux/device.h
index 5a31bf3a4024..af6fbc35d8a6 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -958,6 +958,8 @@ extern int __must_check device_add(struct device *dev);
 extern void device_del(struct device *dev);
 extern int device_for_each_child(struct device *dev, void *data,
                      int (*fn)(struct device *dev, void *data));
+extern int device_for_each_child_reverse(struct device *dev, void *data,
+                     int (*fn)(struct device *dev, void *data));
 extern struct device *device_find_child(struct device *dev, void *data,
                                 int (*match)(struct device *dev, void *data));
 extern int device_rename(struct device *dev, const char *new_name);