usb: gadget: composite: Allow function drivers to pause control transfers

Some USB function drivers (e.g. f_mass_storage.c) need to delay or defer the
data/status stages of standard control requests like SET_CONFIGURATION or
SET_INTERFACE till they are done with their bookkeeping and are actually ready
for accepting new commands to their interface.

They can now achieve this functionality by returning USB_GADGET_DELAYED_STATUS
in their setup handlers (e.g. set_alt()). The composite framework will then
defer completion of the control transfer by not completing the data/status stages.

This ensures that the host does not send new packets to the interface till the
function driver is ready to take them.

When the function driver that requested for USB_GADGET_DELAYED_STATUS is done
with its bookkeeping, it should signal the composite framework to continue with
the data/status stages of the control transfer. It can do so by invoking
the new API usb_composite_setup_continue(). This is where the control transfer's
data/status stages are completed and host can initiate new transfers.

The DELAYED_STATUS mechanism is currently only supported if the expected data phase
is 0 bytes (i.e. w_length == 0). Since SET_CONFIGURATION and SET_INTERFACE are the
only cases that will use this mechanism, this is not a limitation.

Signed-off-by: Roger Quadros <roger.quadros@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 61 insertions, 1 deletions

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 82314ed..5cbb1a4 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -461,12 +461,23 @@ static int set_config(struct usb_composite_dev *cdev,
 			reset_config(cdev);
 			goto done;
 		}
+
+		if (result == USB_GADGET_DELAYED_STATUS) {
+			DBG(cdev,
+			 "%s: interface %d (%s) requested delayed status\n",
+					__func__, tmp, f->name);
+			cdev->delayed_status++;
+			DBG(cdev, "delayed_status count %d\n",
+					cdev->delayed_status);
+		}
 	}
 
 	/* when we return, be sure our power usage is valid */
 	power = c->bMaxPower ? (2 * c->bMaxPower) : CONFIG_USB_GADGET_VBUS_DRAW;
 done:
 	usb_gadget_vbus_draw(gadget, power);
+	if (result >= 0 && cdev->delayed_status)
+		result = USB_GADGET_DELAYED_STATUS;
 	return result;
 }
 
@@ -895,6 +906,14 @@ composite_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
 		if (w_value && !f->set_alt)
 			break;
 		value = f->set_alt(f, w_index, w_value);
+		if (value == USB_GADGET_DELAYED_STATUS) {
+			DBG(cdev,
+			 "%s: interface %d (%s) requested delayed status\n",
+					__func__, intf, f->name);
+			cdev->delayed_status++;
+			DBG(cdev, "delayed_status count %d\n",
+					cdev->delayed_status);
+		}
 		break;
 	case USB_REQ_GET_INTERFACE:
 		if (ctrl->bRequestType != (USB_DIR_IN|USB_RECIP_INTERFACE))
@@ -958,7 +977,7 @@ unknown:
 	}
 
 	/* respond with data transfer before status phase? */
-	if (value >= 0) {
+	if (value >= 0 && value != USB_GADGET_DELAYED_STATUS) {
 		req->length = value;
 		req->zero = value < w_length;
 		value = usb_ep_queue(gadget->ep0, req, GFP_ATOMIC);
@@ -967,6 +986,10 @@ unknown:
 			req->status = 0;
 			composite_setup_complete(gadget->ep0, req);
 		}
+	} else if (value == USB_GADGET_DELAYED_STATUS && w_length != 0) {
+		WARN(cdev,
+			"%s: Delayed status not supported for w_length != 0",
+			__func__);
 	}
 
 done:
@@ -1289,3 +1312,40 @@ void usb_composite_unregister(struct usb_composite_driver *driver)
 		return;
 	usb_gadget_unregister_driver(&composite_driver);
 }
+
+/**
+ * usb_composite_setup_continue() - Continue with the control transfer
+ * @cdev: the composite device who's control transfer was kept waiting
+ *
+ * This function must be called by the USB function driver to continue
+ * with the control transfer's data/status stage in case it had requested to
+ * delay the data/status stages. A USB function's setup handler (e.g. set_alt())
+ * can request the composite framework to delay the setup request's data/status
+ * stages by returning USB_GADGET_DELAYED_STATUS.
+ */
+void usb_composite_setup_continue(struct usb_composite_dev *cdev)
+{
+	int			value;
+	struct usb_request	*req = cdev->req;
+	unsigned long		flags;
+
+	DBG(cdev, "%s\n", __func__);
+	spin_lock_irqsave(&cdev->lock, flags);
+
+	if (cdev->delayed_status == 0) {
+		WARN(cdev, "%s: Unexpected call\n", __func__);
+
+	} else if (--cdev->delayed_status == 0) {
+		DBG(cdev, "%s: Completing delayed status\n", __func__);
+		req->length = 0;
+		value = usb_ep_queue(cdev->gadget->ep0, req, GFP_ATOMIC);
+		if (value < 0) {
+			DBG(cdev, "ep_queue --> %d\n", value);
+			req->status = 0;
+			composite_setup_complete(cdev->gadget->ep0, req);
+		}
+	}
+
+	spin_unlock_irqrestore(&cdev->lock, flags);
+}
+