USB: gadget: Document that certain ep operations can be called in interrupt context

This documentation patch specifies that certain USB gadget endpoint
operations may be called in interrupt context:

	usb_ep_queue, usb_ep_dequeue, usb_ep_set_halt,
	usb_ep_clear_halt, usb_ep_set_wedge, usb_ep_fifo_status,
	and usb_ep_fifo_flush;

while others must be called in process context:

	usb_ep_enable and usb_ep_disable.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NFelipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/udc/core.c

@@ -87,6 +87,8 @@ EXPORT_SYMBOL_GPL(usb_ep_set_maxpacket_limit);
  * configurable, with more generic names like "ep-a".  (remember that for
  * USB, "in" means "towards the USB master".)
  *
+ * This routine must be called in process context.
+ *
  * returns zero, or a negative error code.
  */
 int usb_ep_enable(struct usb_ep *ep)
@@ -119,6 +121,8 @@ EXPORT_SYMBOL_GPL(usb_ep_enable);
  * gadget drivers must call usb_ep_enable() again before queueing
  * requests to the endpoint.
  *
+ * This routine must be called in process context.
+ *
  * returns zero, or a negative error code.
  */
 int usb_ep_disable(struct usb_ep *ep)
@@ -241,6 +245,8 @@ EXPORT_SYMBOL_GPL(usb_ep_free_request);
  * Note that @req's ->complete() callback must never be called from
  * within usb_ep_queue() as that can create deadlock situations.
  *
+ * This routine may be called in interrupt context.
+ *
  * Returns zero, or a negative error code.  Endpoints that are not enabled
  * report errors; errors will also be
  * reported when the usb peripheral is disconnected.
@@ -284,6 +290,8 @@ EXPORT_SYMBOL_GPL(usb_ep_queue);
  * at the head of the queue) except as part of disconnecting from usb. Such
  * restrictions prevent drivers from supporting configuration changes,
  * even to configuration zero (a "chapter 9" requirement).
+ *
+ * This routine may be called in interrupt context.
  */
 int usb_ep_dequeue(struct usb_ep *ep, struct usb_request *req)
 {
@@ -311,6 +319,8 @@ EXPORT_SYMBOL_GPL(usb_ep_dequeue);
  * current altsetting, see usb_ep_clear_halt().  When switching altsettings,
  * it's simplest to use usb_ep_enable() or usb_ep_disable() for the endpoints.
  *
+ * This routine may be called in interrupt context.
+ *
  * Returns zero, or a negative error code.  On success, this call sets
  * underlying hardware state that blocks data transfers.
  * Attempts to halt IN endpoints will fail (returning -EAGAIN) if any
@@ -336,6 +346,8 @@ EXPORT_SYMBOL_GPL(usb_ep_set_halt);
  * for endpoints that aren't reconfigured, after clearing any other state
  * in the endpoint's i/o queue.
  *
+ * This routine may be called in interrupt context.
+ *
  * Returns zero, or a negative error code.  On success, this call clears
  * the underlying hardware state reflecting endpoint halt and data toggle.
  * Note that some hardware can't support this request (like pxa2xx_udc),
@@ -360,6 +372,8 @@ EXPORT_SYMBOL_GPL(usb_ep_clear_halt);
  * requests. If the gadget driver clears the halt status, it will
  * automatically unwedge the endpoint.
  *
+ * This routine may be called in interrupt context.
+ *
  * Returns zero on success, else negative errno.
  */
 int usb_ep_set_wedge(struct usb_ep *ep)
@@ -388,6 +402,8 @@ EXPORT_SYMBOL_GPL(usb_ep_set_wedge);
  * written OUT to it by the host.  Drivers that need precise handling for
  * fault reporting or recovery may need to use this call.
  *
+ * This routine may be called in interrupt context.
+ *
  * This returns the number of such bytes in the fifo, or a negative
  * errno if the endpoint doesn't use a FIFO or doesn't support such
  * precise handling.
@@ -415,6 +431,8 @@ EXPORT_SYMBOL_GPL(usb_ep_fifo_status);
  * an endpoint fifo after abnormal transaction terminations.  The call
  * must never be used except when endpoint is not being used for any
  * protocol translation.
+ *
+ * This routine may be called in interrupt context.
  */
 void usb_ep_fifo_flush(struct usb_ep *ep)
 {