usb: gadget: composite: add req_match method to usb_function

Non-standard requests can encode the actual interface number in a
non-standard way. For example composite_setup() assumes
that it is w_index && 0xFF, but the printer function encodes the interface
number in a context-dependet way (either w_index or w_index >> 8).
This can lead to such requests being directed to wrong functions.

This patch adds req_match() method to usb_function. Its purpose is to
verify that a given request can be handled by a given function.
If any function within a configuration provides the method and it returns
true, then it is assumed that the right function is found.

If a function uses req_match(), it should try as hard as possible to
determine if the request is meant for it.

If no functions in a configuration provide req_match or none of them
returns true, then fall back to the usual approach.

Signed-off-by: Andrzej Pietrasiewicz <[e-mail]>
Signed-off-by: Felipe Balbi <[e-mail]>

drivers/usb/gadget/composite.c

···
 		 * take such requests too, if that's ever needed:  to work
 		 * in config 0, etc.
 		 */
+		list_for_each_entry(f, &cdev->config->functions, list)
+			if (f->req_match && f->req_match(f, ctrl))
+				goto try_fun_setup;
+		f = NULL;
 		switch (ctrl->bRequestType & USB_RECIP_MASK) {
 		case USB_RECIP_INTERFACE:
 			if (!cdev->config || intf >= MAX_CONFIG_INTERFACES)
···
 				f = NULL;
 			break;
 		}
-
+try_fun_setup:
 		if (f && f->setup)
 			value = f->setup(f, ctrl);
 		else {

include/linux/usb/composite.h

···
  * @disable: (REQUIRED) Indicates the function should be disabled.  Reasons
  *	include host resetting or reconfiguring the gadget, and disconnection.
  * @setup: Used for interface-specific control requests.
+ * @req_match: Tests if a given class request can be handled by this function.
  * @suspend: Notifies functions when the host stops sending USB traffic.
  * @resume: Notifies functions when the host restarts USB traffic.
  * @get_status: Returns function status as a reply to
···
 					unsigned interface);
 	void			(*disable)(struct usb_function *);
 	int			(*setup)(struct usb_function *,
+					const struct usb_ctrlrequest *);
+	bool			(*req_match)(struct usb_function *,
 					const struct usb_ctrlrequest *);
 	void			(*suspend)(struct usb_function *);
 	void			(*resume)(struct usb_function *);