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 <[e-mail]>
Signed-off-by: Jerry Zhang <[e-mail]>
Signed-off-by: Felipe Balbi <[e-mail]>

drivers/usb/gadget/function/f_fs.c

···
 			     unsigned long value)
 {
 	struct ffs_epfile *epfile = file->private_data;
+	struct ffs_ep *ep;
 	int ret;
 
 	ENTER();
···
 	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)) {
-		switch (code) {
-		case FUNCTIONFS_FIFO_STATUS:
-			ret = usb_ep_fifo_status(epfile->ep->ep);
-			break;
-		case FUNCTIONFS_FIFO_FLUSH:
-			usb_ep_fifo_flush(epfile->ep->ep);
-			ret = 0;
-			break;
-		case FUNCTIONFS_CLEAR_HALT:
-			ret = usb_ep_clear_halt(epfile->ep->ep);
-			break;
-		case FUNCTIONFS_ENDPOINT_REVMAP:
-			ret = epfile->ep->num;
-			break;
-		case FUNCTIONFS_ENDPOINT_DESC:
-		{
-			int desc_idx;
-			struct usb_endpoint_descriptor *desc;
 
-			switch (epfile->ffs->gadget->speed) {
-			case USB_SPEED_SUPER:
-				desc_idx = 2;
-				break;
-			case USB_SPEED_HIGH:
-				desc_idx = 1;
-				break;
-			default:
-				desc_idx = 0;
-			}
-			desc = epfile->ep->descs[desc_idx];
+	/* In the meantime, endpoint got disabled or changed. */
+	if (epfile->ep != ep) {
+		spin_unlock_irq(&epfile->ffs->eps_lock);
+		return -ESHUTDOWN;
+	}
 
-			spin_unlock_irq(&epfile->ffs->eps_lock);
-			ret = copy_to_user((void *)value, desc, desc->bLength);
-			if (ret)
-				ret = -EFAULT;
-			return ret;
-		}
+	switch (code) {
+	case FUNCTIONFS_FIFO_STATUS:
+		ret = usb_ep_fifo_status(epfile->ep->ep);
+		break;
+	case FUNCTIONFS_FIFO_FLUSH:
+		usb_ep_fifo_flush(epfile->ep->ep);
+		ret = 0;
+		break;
+	case FUNCTIONFS_CLEAR_HALT:
+		ret = usb_ep_clear_halt(epfile->ep->ep);
+		break;
+	case FUNCTIONFS_ENDPOINT_REVMAP:
+		ret = epfile->ep->num;
+		break;
+	case FUNCTIONFS_ENDPOINT_DESC:
+	{
+		int desc_idx;
+		struct usb_endpoint_descriptor *desc;
+
+		switch (epfile->ffs->gadget->speed) {
+		case USB_SPEED_SUPER:
+			desc_idx = 2;
+			break;
+		case USB_SPEED_HIGH:
+			desc_idx = 1;
+			break;
 		default:
-			ret = -ENOTTY;
+			desc_idx = 0;
 		}
-	} else {
-		ret = -ENODEV;
+		desc = epfile->ep->descs[desc_idx];
+
+		spin_unlock_irq(&epfile->ffs->eps_lock);
+		ret = copy_to_user((void *)value, desc, desc->bLength);
+		if (ret)
+			ret = -EFAULT;
+		return ret;
+	}
+	default:
+		ret = -ENOTTY;
 	}
 	spin_unlock_irq(&epfile->ffs->eps_lock);
 

include/uapi/linux/usb/functionfs.h

···
 #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)