usb: gadget: udc-core: move sysfs_notify() to a workqueue

usb_gadget_set_state() will call sysfs_notify()
which might sleep. Some users might want to call
usb_gadget_set_state() from the very IRQ handler
which actually changes the gadget state.

Instead of having every UDC driver add their own
workqueue for such a simple notification, we're
adding it generically to our struct usb_gadget,
so the details are hidden from all UDC drivers.
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/udc-core.c

@@ -23,6 +23,7 @@
 #include <linux/list.h>
 #include <linux/err.h>
 #include <linux/dma-mapping.h>
+#include <linux/workqueue.h>
 
 #include <linux/usb/ch9.h>
 #include <linux/usb/gadget.h>
@@ -105,11 +106,18 @@ EXPORT_SYMBOL_GPL(usb_gadget_unmap_request);
 
 /* ------------------------------------------------------------------------- */
 
+static void usb_gadget_state_work(struct work_struct *work)
+{
+	struct usb_gadget	*gadget = work_to_gadget(work);
+
+	sysfs_notify(&gadget->dev.kobj, NULL, "status");
+}
+
 void usb_gadget_set_state(struct usb_gadget *gadget,
 		enum usb_device_state state)
 {
 	gadget->state = state;
-	sysfs_notify(&gadget->dev.kobj, NULL, "status");
+	schedule_work(&gadget->work);
 }
 EXPORT_SYMBOL_GPL(usb_gadget_set_state);
 
@@ -196,6 +204,7 @@ int usb_add_gadget_udc_release(struct device *parent, struct usb_gadget *gadget,
 		goto err1;
 
 	dev_set_name(&gadget->dev, "gadget");
+	INIT_WORK(&gadget->work, usb_gadget_state_work);
 	gadget->dev.parent = parent;
 
 #ifdef	CONFIG_HAS_DMA
@@ -315,6 +324,7 @@ void usb_del_gadget_udc(struct usb_gadget *gadget)
 		usb_gadget_remove_driver(udc);
 
 	kobject_uevent(&udc->dev.kobj, KOBJ_REMOVE);
+	flush_work(&gadget->work);
 	device_unregister(&udc->dev);
 	device_unregister(&gadget->dev);
 }

include/linux/usb/gadget.h

@@ -22,6 +22,7 @@
 #include <linux/slab.h>
 #include <linux/scatterlist.h>
 #include <linux/types.h>
+#include <linux/workqueue.h>
 #include <linux/usb/ch9.h>
 
 struct usb_ep;
@@ -475,6 +476,7 @@ struct usb_gadget_ops {
 
 /**
  * struct usb_gadget - represents a usb slave device
+ * @work: (internal use) Workqueue to be used for sysfs_notify()
  * @ops: Function pointers used to access hardware-specific operations.
  * @ep0: Endpoint zero, used when reading or writing responses to
  *	driver setup() requests
@@ -520,6 +522,7 @@ struct usb_gadget_ops {
  * device is acting as a B-Peripheral (so is_a_peripheral is false).
  */
 struct usb_gadget {
+	struct work_struct		work;
 	/* readonly to gadget driver */
 	const struct usb_gadget_ops	*ops;
 	struct usb_ep			*ep0;
@@ -538,6 +541,7 @@ struct usb_gadget {
 	unsigned			out_epnum;
 	unsigned			in_epnum;
 };
+#define work_to_gadget(w)	(container_of((w), struct usb_gadget, work))
 
 static inline void set_gadget_data(struct usb_gadget *gadget, void *data)
 	{ dev_set_drvdata(&gadget->dev, data); }