usb: gadget: function: f_fs: Let ffs_epfile_ioctl wait for enable.

This allows users to make an ioctl call as the first action on a
connection. Ex, some functions might want to get endpoint size
before making any i/os.

Previously, calling ioctls before read/write would depending on the
timing of endpoints being enabled.

ESHUTDOWN is now a possible return value and ENODEV is not, so change
docs accordingly.
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Jerry Zhang <zhangjerry@google.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/function/f_fs.c

@@ -1189,6 +1189,7 @@ static long ffs_epfile_ioctl(struct file *file, unsigned code,
 			     unsigned long value)
 {
 	struct ffs_epfile *epfile = file->private_data;
+	struct ffs_ep *ep;
 	int ret;
 
 	ENTER();
@@ -1196,8 +1197,25 @@ static long ffs_epfile_ioctl(struct file *file, unsigned code,
 	if (WARN_ON(epfile->ffs->state != FFS_ACTIVE))
 		return -ENODEV;
 
+	/* Wait for endpoint to be enabled */
+	ep = epfile->ep;
+	if (!ep) {
+		if (file->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+
+		ret = wait_event_interruptible(epfile->wait, (ep = epfile->ep));
+		if (ret)
+			return -EINTR;
+	}
+
 	spin_lock_irq(&epfile->ffs->eps_lock);
-	if (likely(epfile->ep)) {
+
+	/* In the meantime, endpoint got disabled or changed. */
+	if (epfile->ep != ep) {
+		spin_unlock_irq(&epfile->ffs->eps_lock);
+		return -ESHUTDOWN;
+	}
+
 	switch (code) {
 	case FUNCTIONFS_FIFO_STATUS:
 		ret = usb_ep_fifo_status(epfile->ep->ep);
@@ -1238,9 +1256,6 @@ static long ffs_epfile_ioctl(struct file *file, unsigned code,
 	default:
 		ret = -ENOTTY;
 	}
-	} else {
-		ret = -ENODEV;
-	}
 	spin_unlock_irq(&epfile->ffs->eps_lock);
 
 	return ret;

include/uapi/linux/usb/functionfs.h

@@ -275,13 +275,14 @@ struct usb_functionfs_event {
 #define	FUNCTIONFS_INTERFACE_REVMAP	_IO('g', 128)
 
 /*
- * Returns real bEndpointAddress of an endpoint.  If function is not
- * active returns -ENODEV.
+ * Returns real bEndpointAddress of an endpoint. If endpoint shuts down
+ * during the call, returns -ESHUTDOWN.
  */
 #define	FUNCTIONFS_ENDPOINT_REVMAP	_IO('g', 129)
 
 /*
- * Returns endpoint descriptor. If function is not active returns -ENODEV.
+ * Returns endpoint descriptor. If endpoint shuts down during the call,
+ * returns -ESHUTDOWN.
  */
 #define	FUNCTIONFS_ENDPOINT_DESC	_IOR('g', 130, \
 					     struct usb_endpoint_descriptor)