[PATCH] USB: revert "fix" to usb_set_interface()

This reverts a recent change to usb_set_interface().  The change worked
around a quirk in certain devices, but doing this in usbcore creates
needless regressions for other devices.  More appropriate fixes won't
put such handling in usbcore.

Basically it's tricky to do a full software reset of USB device state, since
the devices don't all act the same.  This adds a note to the kerneldoc for
the usb_reset_configuration() call to highlight the quirk this was working
around:  endpoint data toggles not being reset.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/message.c

@@ -1133,29 +1133,10 @@ int usb_set_interface(struct usb_device *dev, int interface, int alternate)
 	/* prevent submissions using previous endpoint settings */
 	usb_disable_interface(dev, iface);
 
-	/* 9.1.1.5 says:
-	 *
-	 *	Configuring a device or changing an alternate setting
-	 *	causes all of the status and configuration values
-	 *	associated with endpoints in the affected interfaces to
-	 *	be set to their default values. This includes setting
-	 *	the data toggle of any endpoint using data toggles to
-	 *	the value DATA0.
-	 *
-	 * Some devices take this too literally and don't reset the data
-	 * toggles if the new altsetting is the same as the old one (the
-	 * command isn't "changing" an alternate setting).  We will manually
-	 * reset the toggles when the new and old altsettings are the same.
-	 * Most devices won't need this, but fortunately it doesn't happen
-	 * often.
-	 */
-	if (iface->cur_altsetting == alt)
-		manual = 1;
 	iface->cur_altsetting = alt;
 
 	/* If the interface only has one altsetting and the device didn't
-	 * accept the request (or whenever the old altsetting is the same
-	 * as the new one), we attempt to carry out the equivalent action
+	 * accept the request, we attempt to carry out the equivalent action
 	 * by manually clearing the HALT feature for each endpoint in the
 	 * new altsetting.
 	 */
@@ -1202,7 +1183,9 @@ int usb_set_interface(struct usb_device *dev, int interface, int alternate)
  *
  * Because this affects multiple interfaces, avoid using this with composite
  * (multi-interface) devices.  Instead, the driver for each interface may
- * use usb_set_interface() on the interfaces it claims.  Resetting the whole
+ * use usb_set_interface() on the interfaces it claims.  Be careful though;
+ * some devices don't support the SET_INTERFACE request, and others won't
+ * reset all the interface state (notably data toggles).  Resetting the whole
  * configuration would affect other drivers' interfaces.
  *
  * The caller must own the device lock.