usb: gadget: udc-core: Rescan pending list on driver unbind

Since:

commit 855ed04a3758 ("usb: gadget: udc-core: independent registration
of gadgets and gadget drivers")

if we load gadget module but there is no free udc available
then it will be stored on a pending gadgets list.

$ modprobe g_zero.ko
$ modprobe g_ether.ko
[] udc-core: couldn't find an available UDC - added [g_ether] to list
of pending drivers

We scan this list each time when new UDC appears in system.
But we can get a free UDC each time after gadget unbind.
This commit add scanning of that list directly after unbinding
gadget from udc.

Thanks to this, when we unload first gadget:

$ rmmod g_zero.ko

gadget which is pending is automatically
attached to that UDC (if name matches).

Fixes: 855ed04a3758  ("usb: gadget: udc-core: independent registration of gadgets and gadget drivers")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/udc/core.c

@@ -1080,6 +1080,24 @@ static void usb_udc_nop_release(struct device *dev)
 	dev_vdbg(dev, "%s\n", __func__);
 }
 
+/* should be called with udc_lock held */
+static int check_pending_gadget_drivers(struct usb_udc *udc)
+{
+	struct usb_gadget_driver *driver;
+	int ret = 0;
+
+	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 != -EPROBE_DEFER)
+				list_del(&driver->pending);
+			break;
+		}
+
+	return ret;
+}
+
 /**
  * usb_add_gadget_udc_release - adds a new gadget to the udc class driver list
  * @parent: the parent device to this udc. Usually the controller driver's
@@ -1093,7 +1111,6 @@ 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);
@@ -1136,17 +1153,9 @@ int usb_add_gadget_udc_release(struct device *parent, struct usb_gadget *gadget,
 	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 != -EPROBE_DEFER)
-				list_del(&driver->pending);
-			if (ret)
-				goto err5;
-			break;
-		}
-	}
+	ret = check_pending_gadget_drivers(udc);
+	if (ret)
+		goto err5;
 
 	mutex_unlock(&udc_lock);
 
@@ -1356,14 +1365,22 @@ int usb_gadget_unregister_driver(struct usb_gadget_driver *driver)
 		return -EINVAL;
 
 	mutex_lock(&udc_lock);
-	list_for_each_entry(udc, &udc_list, list)
+	list_for_each_entry(udc, &udc_list, list) {
 		if (udc->driver == driver) {
 			usb_gadget_remove_driver(udc);
 			usb_gadget_set_state(udc->gadget,
-					USB_STATE_NOTATTACHED);
+					     USB_STATE_NOTATTACHED);
+
+			/* Maybe there is someone waiting for this UDC? */
+			check_pending_gadget_drivers(udc);
+			/*
+			 * For now we ignore bind errors as probably it's
+			 * not a valid reason to fail other's gadget unbind
+			 */
 			ret = 0;
 			break;
 		}
+	}
 
 	if (ret) {
 		list_del(&driver->pending);