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, 37 insertions, 0 deletions

diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
index d1e9440799de..99e54586a545 100644
--- a/drivers/usb/core/usb.c
+++ b/drivers/usb/core/usb.c
@@ -64,6 +64,43 @@ MODULE_PARM_DESC(autosuspend, "default autosuspend delay");
 
 
 /**
+ * usb_find_alt_setting() - Given a configuration, find the alternate setting
+ * for the given interface.
+ * @config - the configuration to search (not necessarily the current config).
+ * @iface_num - interface number to search in
+ * @alt_num - alternate interface setting number to search for.
+ *
+ * Search the configuration's interface cache for the given alt setting.
+ */
+struct usb_host_interface *usb_find_alt_setting(
+                struct usb_host_config *config,
+                unsigned int iface_num,
+                unsigned int alt_num)
+{
+        struct usb_interface_cache *intf_cache = NULL;
+        int i;
+
+        for (i = 0; i < config->desc.bNumInterfaces; i++) {
+                if (config->intf_cache[i]->altsetting[0].desc.bInterfaceNumber
+                                == iface_num) {
+                        intf_cache = config->intf_cache[i];
+                        break;
+                }
+        }
+        if (!intf_cache)
+                return NULL;
+        for (i = 0; i < intf_cache->num_altsetting; i++)
+                if (intf_cache->altsetting[i].desc.bAlternateSetting == alt_num)
+                        return &intf_cache->altsetting[i];
+
+        printk(KERN_DEBUG "Did not find alt setting %u for intf %u, "
+                        "config %u\n", alt_num, iface_num,
+                        config->desc.bConfigurationValue);
+        return NULL;
+}
+EXPORT_SYMBOL_GPL(usb_find_alt_setting);
+
+/**
  * usb_ifnum_to_if - get the interface object with a given interface number
  * @dev: the device whose current configuration is considered
  * @ifnum: the desired interface