2 files changed, 73 insertions, 2 deletions

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 85c876c1f150..f79fdb839cb8 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -128,6 +128,70 @@ done:
 }
 
 /**
+ * usb_function_deactivate - prevent function and gadget enumeration
+ * @function: the function that isn't yet ready to respond
+ *
+ * Blocks response of the gadget driver to host enumeration by
+ * preventing the data line pullup from being activated.  This is
+ * normally called during @bind() processing to change from the
+ * initial "ready to respond" state, or when a required resource
+ * becomes available.
+ *
+ * For example, drivers that serve as a passthrough to a userspace
+ * daemon can block enumeration unless that daemon (such as an OBEX,
+ * MTP, or print server) is ready to handle host requests.
+ *
+ * Not all systems support software control of their USB peripheral
+ * data pullups.
+ *
+ * Returns zero on success, else negative errno.
+ */
+int usb_function_deactivate(struct usb_function *function)
+{
+        struct usb_composite_dev        *cdev = function->config->cdev;
+        int                             status = 0;
+
+        spin_lock(&cdev->lock);
+
+        if (cdev->deactivations == 0)
+                status = usb_gadget_disconnect(cdev->gadget);
+        if (status == 0)
+                cdev->deactivations++;
+
+        spin_unlock(&cdev->lock);
+        return status;
+}
+
+/**
+ * usb_function_activate - allow function and gadget enumeration
+ * @function: function on which usb_function_activate() was called
+ *
+ * Reverses effect of usb_function_deactivate().  If no more functions
+ * are delaying their activation, the gadget driver will respond to
+ * host enumeration procedures.
+ *
+ * Returns zero on success, else negative errno.
+ */
+int usb_function_activate(struct usb_function *function)
+{
+        struct usb_composite_dev        *cdev = function->config->cdev;
+        int                             status = 0;
+
+        spin_lock(&cdev->lock);
+
+        if (WARN_ON(cdev->deactivations == 0))
+                status = -EINVAL;
+        else {
+                cdev->deactivations--;
+                if (cdev->deactivations == 0)
+                        status = usb_gadget_connect(cdev->gadget);
+        }
+
+        spin_unlock(&cdev->lock);
+        return status;
+}
+
+/**
  * usb_interface_id() - allocate an unused interface ID
  * @config: configuration associated with the interface
  * @function: function handling the interface
diff --git a/include/linux/usb/composite.h b/include/linux/usb/composite.h
index c932390c6da0..935c380ffe47 100644
--- a/include/linux/usb/composite.h
+++ b/include/linux/usb/composite.h
@@ -130,6 +130,9 @@ struct usb_function {
 
 int usb_add_function(struct usb_configuration *, struct usb_function *);
 
+int usb_function_deactivate(struct usb_function *);
+int usb_function_activate(struct usb_function *);
+
 int usb_interface_id(struct usb_configuration *, struct usb_function *);
 
 /**
@@ -316,9 +319,13 @@ struct usb_composite_dev {
         struct usb_composite_driver     *driver;
         u8                              next_string_id;
 
-        spinlock_t                      lock;
+        /* the gadget driver won't enable the data pullup
+         * while the deactivation count is nonzero.
+         */
+        unsigned                        deactivations;
 
-        /* REVISIT use and existence of lock ... */
+        /* protects at least deactivation count */
+        spinlock_t                      lock;
 };
 
 extern int usb_string_id(struct usb_composite_dev *c);