USB: Refactor code to find alternate interface settings.

Refactor out the code to find alternate interface settings into
usb_find_alt_setting().  Print a debugging message and return null if the
alt setting is not found.

While we're at it, correct a bug in the refactored code.  The interfaces
in the configuration's interface cache are not necessarily in numerical
order, so we can't just use the interface number as an array index.  Loop
through the interface caches, looking for the correct interface.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/usb.h b/include/linux/usb.h
index 6af3581e1114..e101a2d04d75 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -619,6 +619,10 @@ extern struct usb_interface *usb_ifnum_to_if(const struct usb_device *dev,
                 unsigned ifnum);
 extern struct usb_host_interface *usb_altnum_to_altsetting(
                 const struct usb_interface *intf, unsigned int altnum);
+extern struct usb_host_interface *usb_find_alt_setting(
+                struct usb_host_config *config,
+                unsigned int iface_num,
+                unsigned int alt_num);
 
 
 /**