usb/gadget: Add an EP dispose() callback for EP lifetime tracking

Some UDC may want to allocate endpoints dynamically, either because
the HW supports an arbitrary large number or because (like the Aspeed
BMC SoCs), the pool of HW endpoints is shared between multiple gadgets.

The allocation side can be done rather easily using the existing
match_ep() UDC hook.

However we have no good place to "free" them.

This implements a "simple" variant of this, which calls an EP dispose
callback on all EPs associated with a gadget when the composite device
gets unbound.

This is required by my upcoming Aspeed vHub driver.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/composite.c

@@ -2142,6 +2142,7 @@ int composite_os_desc_req_prepare(struct usb_composite_dev *cdev,
 void composite_dev_cleanup(struct usb_composite_dev *cdev)
 {
 	struct usb_gadget_string_container *uc, *tmp;
+	struct usb_ep			   *ep, *tmp_ep;
 
 	list_for_each_entry_safe(uc, tmp, &cdev->gstrings, list) {
 		list_del(&uc->list);
@@ -2163,6 +2164,21 @@ void composite_dev_cleanup(struct usb_composite_dev *cdev)
 	}
 	cdev->next_string_id = 0;
 	device_remove_file(&cdev->gadget->dev, &dev_attr_suspended);
+
+	/*
+	 * Some UDC backends have a dynamic EP allocation scheme.
+	 *
+	 * In that case, the dispose() callback is used to notify the
+	 * backend that the EPs are no longer in use.
+	 *
+	 * Note: The UDC backend can remove the EP from the ep_list as
+	 *	 a result, so we need to use the _safe list iterator.
+	 */
+	list_for_each_entry_safe(ep, tmp_ep,
+				 &cdev->gadget->ep_list, ep_list) {
+		if (ep->ops->dispose)
+			ep->ops->dispose(ep);
+	}
 }
 
 static int composite_bind(struct usb_gadget *gadget,

include/linux/usb/gadget.h

@@ -129,6 +129,7 @@ struct usb_ep_ops {
 	int (*enable) (struct usb_ep *ep,
 		const struct usb_endpoint_descriptor *desc);
 	int (*disable) (struct usb_ep *ep);
+	void (*dispose) (struct usb_ep *ep);
 
 	struct usb_request *(*alloc_request) (struct usb_ep *ep,
 		gfp_t gfp_flags);