USB: don't touch sysfs stuff when altsetting is unchanged

This patch (as955) prevents the interface-related sysfs files and
endpoint pseudo-devices from being deleted and recreated when a call
to usb_set_interface() specifies the current altsetting.  Since the
altsetting doesn't get changed, there's no need to do anything.

Furthermore, avoiding changes to the endpoint devices will be
necessary in the future.  This code is called from usb_reset_device(),
which gets invoked for reset-resume processing, but upcoming changes
to the PM and driver cores will make it impossible to register devices
while a suspend/resume transition is in progress.  Since we don't need
to re-register those endpoint devices anyhow, it's best to skip the
whole thing.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/message.c

@@ -1173,6 +1173,7 @@ int usb_set_interface(struct usb_device *dev, int interface, int alternate)
 	struct usb_host_interface *alt;
 	int ret;
 	int manual = 0;
+	int changed;
 
 	if (dev->state == USB_STATE_SUSPENDED)
 		return -EHOSTUNREACH;
@@ -1212,7 +1213,8 @@ int usb_set_interface(struct usb_device *dev, int interface, int alternate)
 	 */
 
 	/* prevent submissions using previous endpoint settings */
-	if (device_is_registered(&iface->dev))
+	changed = (iface->cur_altsetting != alt);
+	if (changed && device_is_registered(&iface->dev))
 		usb_remove_sysfs_intf_files(iface);
 	usb_disable_interface(dev, iface);
 
@@ -1249,7 +1251,7 @@ int usb_set_interface(struct usb_device *dev, int interface, int alternate)
 	 * (Likewise, EP0 never "halts" on well designed devices.)
 	 */
 	usb_enable_interface(dev, iface);
-	if (device_is_registered(&iface->dev))
+	if (changed && device_is_registered(&iface->dev))
 		usb_create_sysfs_intf_files(iface);
 
 	return 0;