USB: UDC: Implement udc_async_callbacks in net2280

This patch adds a udc_async_callbacks handler to the net2280 UDC
driver, which will prevent a theoretical race during gadget unbinding.

The net2280 driver is sufficiently complicated that I didn't want to
mess around with IRQ settings.  Instead, the patch simply adds a new
flag to control async callbacks, and checks the flag before issuing
any of them.
Acked-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20210520202200.GE1216852@rowland.harvard.eduSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/udc/net2280.c

@@ -1617,6 +1617,7 @@ static struct usb_ep *net2280_match_ep(struct usb_gadget *_gadget,
 static int net2280_start(struct usb_gadget *_gadget,
 		struct usb_gadget_driver *driver);
 static int net2280_stop(struct usb_gadget *_gadget);
+static void net2280_async_callbacks(struct usb_gadget *_gadget, bool enable);
 
 static const struct usb_gadget_ops net2280_ops = {
 	.get_frame	= net2280_get_frame,
@@ -1625,6 +1626,7 @@ static const struct usb_gadget_ops net2280_ops = {
 	.pullup		= net2280_pullup,
 	.udc_start	= net2280_start,
 	.udc_stop	= net2280_stop,
+	.udc_async_callbacks = net2280_async_callbacks,
 	.match_ep	= net2280_match_ep,
 };
 
@@ -2472,7 +2474,7 @@ static void stop_activity(struct net2280 *dev, struct usb_gadget_driver *driver)
 		nuke(&dev->ep[i]);
 
 	/* report disconnect; the driver is already quiesced */
-	if (driver) {
+	if (dev->async_callbacks && driver) {
 		spin_unlock(&dev->lock);
 		driver->disconnect(&dev->gadget);
 		spin_lock(&dev->lock);
@@ -2502,6 +2504,15 @@ static int net2280_stop(struct usb_gadget *_gadget)
 	return 0;
 }
 
+static void net2280_async_callbacks(struct usb_gadget *_gadget, bool enable)
+{
+	struct net2280	*dev = container_of(_gadget, struct net2280, gadget);
+
+	spin_lock_irq(&dev->lock);
+	dev->async_callbacks = enable;
+	spin_unlock_irq(&dev->lock);
+}
+
 /*-------------------------------------------------------------------------*/
 
 /* handle ep0, ep-e, ep-f with 64 byte packets: packet per irq.
@@ -3042,10 +3053,12 @@ static void handle_stat0_irqs_superspeed(struct net2280 *dev,
 				readl(&ep->cfg->ep_cfg));
 
 		ep->responded = 0;
+		if (dev->async_callbacks) {
 			spin_unlock(&dev->lock);
 			tmp = dev->driver->setup(&dev->gadget, &r);
 			spin_lock(&dev->lock);
 		}
+	}
 do_stall3:
 	if (tmp < 0) {
 		ep_vdbg(dev, "req %02x.%02x protocol STALL; stat %d\n",
@@ -3284,10 +3297,12 @@ static void handle_stat0_irqs(struct net2280 *dev, u32 stat)
 				w_value, w_index, w_length,
 				readl(&ep->cfg->ep_cfg));
 			ep->responded = 0;
+			if (dev->async_callbacks) {
 				spin_unlock(&dev->lock);
 				tmp = dev->driver->setup(&dev->gadget, &u.r);
 				spin_lock(&dev->lock);
 			}
+		}
 
 		/* stall ep0 on error */
 		if (tmp < 0) {
@@ -3391,14 +3406,14 @@ __acquires(dev->lock)
 			if (disconnect || reset) {
 				stop_activity(dev, dev->driver);
 				ep0_start(dev);
+				if (dev->async_callbacks) {
 					spin_unlock(&dev->lock);
 					if (reset)
-					usb_gadget_udc_reset
-						(&dev->gadget, dev->driver);
+						usb_gadget_udc_reset(&dev->gadget, dev->driver);
 					else
-					(dev->driver->disconnect)
-						(&dev->gadget);
+						(dev->driver->disconnect)(&dev->gadget);
 					spin_lock(&dev->lock);
+				}
 				return;
 			}
 		}
@@ -3419,12 +3434,12 @@ __acquires(dev->lock)
 		writel(tmp, &dev->regs->irqstat1);
 		spin_unlock(&dev->lock);
 		if (stat & BIT(SUSPEND_REQUEST_INTERRUPT)) {
-			if (dev->driver->suspend)
+			if (dev->async_callbacks && dev->driver->suspend)
 				dev->driver->suspend(&dev->gadget);
 			if (!enable_suspend)
 				stat &= ~BIT(SUSPEND_REQUEST_INTERRUPT);
 		} else {
-			if (dev->driver->resume)
+			if (dev->async_callbacks && dev->driver->resume)
 				dev->driver->resume(&dev->gadget);
 			/* at high speed, note erratum 0133 */
 		}

drivers/usb/gadget/udc/net2280.h

@@ -162,6 +162,7 @@ struct net2280 {
 					ltm_enable:1,
 					wakeup_enable:1,
 					addressed_state:1,
+					async_callbacks:1,
 					bug7734_patched:1;
 	u16				chiprev;
 	int enhanced_mode;