s390/ccwgroup: add get_ccwgroupdev_by_busid()

Provide function to find a ccwgroup device by its busid.
Acked-by: Sebastian Ott <sebott@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/ccwgroup.h

@@ -64,6 +64,8 @@ extern int  ccwgroup_driver_register   (struct ccwgroup_driver *cdriver);
 extern void ccwgroup_driver_unregister (struct ccwgroup_driver *cdriver);
 int ccwgroup_create_dev(struct device *root, struct ccwgroup_driver *gdrv,
 			int num_devices, const char *buf);
+struct ccwgroup_device *get_ccwgroupdev_by_busid(struct ccwgroup_driver *gdrv,
+						 char *bus_id);
 
 extern int ccwgroup_set_online(struct ccwgroup_device *gdev);
 extern int ccwgroup_set_offline(struct ccwgroup_device *gdev);

drivers/s390/cio/ccwgroup.c

@@ -608,6 +608,36 @@ void ccwgroup_driver_unregister(struct ccwgroup_driver *cdriver)
 }
 EXPORT_SYMBOL(ccwgroup_driver_unregister);
 
+static int __ccwgroupdev_check_busid(struct device *dev, void *id)
+{
+	char *bus_id = id;
+
+	return (strcmp(bus_id, dev_name(dev)) == 0);
+}
+
+/**
+ * get_ccwgroupdev_by_busid() - obtain device from a bus id
+ * @gdrv: driver the device is owned by
+ * @bus_id: bus id of the device to be searched
+ *
+ * This function searches all devices owned by @gdrv for a device with a bus
+ * id matching @bus_id.
+ * Returns:
+ *  If a match is found, its reference count of the found device is increased
+ *  and it is returned; else %NULL is returned.
+ */
+struct ccwgroup_device *get_ccwgroupdev_by_busid(struct ccwgroup_driver *gdrv,
+						 char *bus_id)
+{
+	struct device *dev;
+
+	dev = driver_find_device(&gdrv->driver, NULL, bus_id,
+				 __ccwgroupdev_check_busid);
+
+	return dev ? to_ccwgroupdev(dev) : NULL;
+}
+EXPORT_SYMBOL_GPL(get_ccwgroupdev_by_busid);
+
 /**
  * ccwgroup_probe_ccwdev() - probe function for slave devices
  * @cdev: ccw device to be probed