usb: Iterator for ports

Introducing usb_for_each_port(). It works the same way as
usb_for_each_dev(), but instead of going through every USB
device in the system, it walks through the USB ports in the
system.
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20210407065555.88110-4-heikki.krogerus@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/usb.c

@@ -398,6 +398,52 @@ int usb_for_each_dev(void *data, int (*fn)(struct usb_device *, void *))
 }
 EXPORT_SYMBOL_GPL(usb_for_each_dev);
 
+struct each_hub_arg {
+	void *data;
+	int (*fn)(struct device *, void *);
+};
+
+static int __each_hub(struct usb_device *hdev, void *data)
+{
+	struct each_hub_arg *arg = (struct each_hub_arg *)data;
+	struct usb_hub *hub;
+	int ret = 0;
+	int i;
+
+	hub = usb_hub_to_struct_hub(hdev);
+	if (!hub)
+		return 0;
+
+	mutex_lock(&usb_port_peer_mutex);
+
+	for (i = 0; i < hdev->maxchild; i++) {
+		ret = arg->fn(&hub->ports[i]->dev, arg->data);
+		if (ret)
+			break;
+	}
+
+	mutex_unlock(&usb_port_peer_mutex);
+
+	return ret;
+}
+
+/**
+ * usb_for_each_port - interate over all USB ports in the system
+ * @data: data pointer that will be handed to the callback function
+ * @fn: callback function to be called for each USB port
+ *
+ * Iterate over all USB ports and call @fn for each, passing it @data. If it
+ * returns anything other than 0, we break the iteration prematurely and return
+ * that value.
+ */
+int usb_for_each_port(void *data, int (*fn)(struct device *, void *))
+{
+	struct each_hub_arg arg = {data, fn};
+
+	return usb_for_each_dev(&arg, __each_hub);
+}
+EXPORT_SYMBOL_GPL(usb_for_each_port);
+
 /**
  * usb_release_dev - free a usb device structure when all users of it are finished.
  * @dev: device that's been disconnected

include/linux/usb.h

@@ -882,6 +882,15 @@ extern struct usb_host_interface *usb_find_alt_setting(
 		unsigned int iface_num,
 		unsigned int alt_num);
 
+#if IS_REACHABLE(CONFIG_USB)
+int usb_for_each_port(void *data, int (*fn)(struct device *, void *));
+#else
+static inline int usb_for_each_port(void *data, int (*fn)(struct device *, void *))
+{
+	return 0;
+}
+#endif
+
 /* port claiming functions */
 int usb_hub_claim_port(struct usb_device *hdev, unsigned port1,
 		struct usb_dev_state *owner);