extcon : register for cable interest by cable name

There are some scnearios where a driver/framework needs to register
interest for a particular cable without specifying the extcon device
name. One such scenario is charger notifications. The platform will
have charger cabel which will be bound to any extcon device. It's
not mandatory for the charger driver to know which extcon device
it should use. This patch enables the support for registering
interest for a cable just by cable name wihtout specifying the
extcon device name

Signed-off-by: Jenny TC <jenny.tc@intel.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Tested-by: Chanwoo Choi <cw00.choi@samsung.com>

--
Kernel-doc comment added by MyungJoo Ham

drivers/extcon/extcon-class.c

@@ -441,6 +441,8 @@ static int _call_per_cable(struct notifier_block *nb, unsigned long val,
  *			      extcon device.
  * @obj:	an empty extcon_specific_cable_nb object to be returned.
  * @extcon_name:	the name of extcon device.
+ *			if NULL, extcon_register_interest will register
+ *			every cable with the target cable_name given.
  * @cable_name:		the target cable name.
  * @nb:		the notifier block to get notified.
  *
@@ -460,22 +462,44 @@ int extcon_register_interest(struct extcon_specific_cable_nb *obj,
 			     const char *extcon_name, const char *cable_name,
 			     struct notifier_block *nb)
 {
-	if (!obj || !extcon_name || !cable_name || !nb)
+	if (!obj || !cable_name || !nb)
 		return -EINVAL;
 
-	obj->edev = extcon_get_extcon_dev(extcon_name);
-	if (!obj->edev)
-		return -ENODEV;
+	if (extcon_name) {
+		obj->edev = extcon_get_extcon_dev(extcon_name);
+		if (!obj->edev)
+			return -ENODEV;
 
-	obj->cable_index = extcon_find_cable_index(obj->edev, cable_name);
-	if (obj->cable_index < 0)
-		return -EINVAL;
+		obj->cable_index = extcon_find_cable_index(obj->edev, cable_name);
+		if (obj->cable_index < 0)
+			return -ENODEV;
 
-	obj->user_nb = nb;
+		obj->user_nb = nb;
 
-	obj->internal_nb.notifier_call = _call_per_cable;
+		obj->internal_nb.notifier_call = _call_per_cable;
 
-	return raw_notifier_chain_register(&obj->edev->nh, &obj->internal_nb);
+		return raw_notifier_chain_register(&obj->edev->nh, &obj->internal_nb);
+	} else {
+		struct class_dev_iter iter;
+		struct extcon_dev *extd;
+		struct device *dev;
+
+		if (!extcon_class)
+			return -ENODEV;
+		class_dev_iter_init(&iter, extcon_class, NULL, NULL);
+		while ((dev = class_dev_iter_next(&iter))) {
+			extd = (struct extcon_dev *)dev_get_drvdata(dev);
+
+			if (extcon_find_cable_index(extd, cable_name) < 0)
+				continue;
+
+			class_dev_iter_exit(&iter);
+			return extcon_register_interest(obj, extd->name,
+						cable_name, nb);
+		}
+
+		return -ENODEV;
+	}
 }
 
 /**