usb: gadget: udc-core: independent registration of gadgets and gadget drivers

Change behavior during registration of gadgets and
gadget drivers in udc-core. Instead of previous
approach when for successful probe of usb gadget driver
at least one usb gadget should be already registered
use another one where gadget drivers and gadgets
can be registered in udc-core independently.

Independent registration of gadgets and gadget drivers
is useful for built-in into kernel gadget and gadget
driver case - because it's possible that gadget is
really probed only on late_init stage (due to deferred
probe) whereas gadget driver's probe is silently failed
on module_init stage due to no any UDC added.

Also it is useful for modules case - now there is no
difference what module to insert first: gadget module
or gadget driver one.
Tested-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
[simplified code as requested by Alan Stern and Felipe Balbi,
 fixed checkpatch issues]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/udc/udc-core.c

@@ -51,8 +51,12 @@ struct usb_udc {
 
 static struct class *udc_class;
 static LIST_HEAD(udc_list);
+static LIST_HEAD(gadget_driver_pending_list);
 static DEFINE_MUTEX(udc_lock);
 
+static int udc_bind_to_driver(struct usb_udc *udc,
+		struct usb_gadget_driver *driver);
+
 /* ------------------------------------------------------------------------- */
 
 #ifdef	CONFIG_HAS_DMA
@@ -356,6 +360,7 @@ int usb_add_gadget_udc_release(struct device *parent, struct usb_gadget *gadget,
 		void (*release)(struct device *dev))
 {
 	struct usb_udc		*udc;
+	struct usb_gadget_driver *driver;
 	int			ret = -ENOMEM;
 
 	udc = kzalloc(sizeof(*udc), GFP_KERNEL);
@@ -403,6 +408,18 @@ int usb_add_gadget_udc_release(struct device *parent, struct usb_gadget *gadget,
 	usb_gadget_set_state(gadget, USB_STATE_NOTATTACHED);
 	udc->vbus = true;
 
+	/* pick up one of pending gadget drivers */
+	list_for_each_entry(driver, &gadget_driver_pending_list, pending) {
+		if (!driver->udc_name || strcmp(driver->udc_name,
+						dev_name(&udc->dev)) == 0) {
+			ret = udc_bind_to_driver(udc, driver);
+			if (ret)
+				goto err4;
+			list_del(&driver->pending);
+			break;
+		}
+	}
+
 	mutex_unlock(&udc_lock);
 
 	return 0;
@@ -473,10 +490,14 @@ void usb_del_gadget_udc(struct usb_gadget *gadget)
 
 	mutex_lock(&udc_lock);
 	list_del(&udc->list);
-	mutex_unlock(&udc_lock);
 
-	if (udc->driver)
+	if (udc->driver) {
+		struct usb_gadget_driver *driver = udc->driver;
+
 		usb_gadget_remove_driver(udc);
+		list_add(&driver->pending, &gadget_driver_pending_list);
+	}
+	mutex_unlock(&udc_lock);
 
 	kobject_uevent(&udc->dev.kobj, KOBJ_REMOVE);
 	flush_work(&gadget->work);
@@ -535,11 +556,7 @@ int usb_gadget_probe_driver(struct usb_gadget_driver *driver)
 			if (!ret)
 				break;
 		}
-		if (ret)
-			ret = -ENODEV;
-		else if (udc->driver)
-			ret = -EBUSY;
-		else
+		if (!ret && !udc->driver)
 			goto found;
 	} else {
 		list_for_each_entry(udc, &udc_list, list) {
@@ -549,9 +566,11 @@ int usb_gadget_probe_driver(struct usb_gadget_driver *driver)
 		}
 	}
 
-	pr_debug("couldn't find an available UDC\n");
+	list_add_tail(&driver->pending, &gadget_driver_pending_list);
+	pr_info("udc-core: couldn't find an available UDC - added [%s] to list of pending drivers\n",
+		driver->function);
 	mutex_unlock(&udc_lock);
-	return ret;
+	return 0;
 found:
 	ret = udc_bind_to_driver(udc, driver);
 	mutex_unlock(&udc_lock);
@@ -577,6 +596,10 @@ int usb_gadget_unregister_driver(struct usb_gadget_driver *driver)
 			break;
 		}
 
+	if (ret) {
+		list_del(&driver->pending);
+		ret = 0;
+	}
 	mutex_unlock(&udc_lock);
 	return ret;
 }

include/linux/usb/gadget.h

@@ -1014,6 +1014,7 @@ static inline int usb_gadget_activate(struct usb_gadget *gadget)
  * @driver: Driver model state for this driver.
  * @udc_name: A name of UDC this driver should be bound to. If udc_name is NULL,
  *	this driver will be bound to any available UDC.
+ * @pending: UDC core private data used for deferred probe of this driver.
  *
  * Devices are disabled till a gadget driver successfully bind()s, which
  * means the driver will handle setup() requests needed to enumerate (and
@@ -1076,6 +1077,7 @@ struct usb_gadget_driver {
 	struct device_driver	driver;
 
 	char			*udc_name;
+	struct list_head	pending;
 };