[PATCH 2/6] usb: gadget: uvc: enqueue usb request in setup handler for control OUT

[Paul Elder <paul.elder@ideasonboard.com>]

Currently, for uvc class-specific control IN and OUT requests, in the
setup handler a UVC_EVENT_SETUP with the setup control is enqueued to
userspace. In response to this, the uvc function driver expects
userspace to call ioctl UVCIOC_SEND_RESPONSE containing uvc request
data.

In the case of control IN this is fine, but for control OUT it causes a
problem. Since the host sends data immediately after the setup stage
completes, it is possible that the empty uvc request data is not
enqueued in time for the UDC driver to put the data stage data into
(this causes some UDC drivers, such as MUSB, to reply with a STALL).
This problem is remedied by having the setup handler enqueue the empty
uvc request data, instead of waiting for userspace to do it.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
---
 drivers/usb/gadget/function/f_uvc.c    | 25 +++++++++++++++++++------
 drivers/usb/gadget/function/uvc_v4l2.c |  7 +++++++
 2 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/gadget/function/f_uvc.c b/drivers/usb/gadget/function/f_uvc.c
index dc12d868f9e8..8452de3dfccc 100644
--- a/drivers/usb/gadget/function/f_uvc.c
+++ b/drivers/usb/gadget/function/f_uvc.c
@@ -223,8 +223,6 @@ static int
 uvc_function_setup(struct usb_function *f, const struct usb_ctrlrequest *ctrl)
 {
 	struct uvc_device *uvc = to_uvc(f);
-	struct v4l2_event v4l2_event;
-	struct uvc_event *uvc_event = (void *)&v4l2_event.u.data;
 
 	if ((ctrl->bRequestType & USB_TYPE_MASK) != USB_TYPE_CLASS) {
 		uvcg_info(f, "invalid request type\n");
@@ -241,10 +239,25 @@ uvc_function_setup(struct usb_function *f, const struct usb_ctrlrequest *ctrl)
 	uvc->event_setup_out = !(ctrl->bRequestType & USB_DIR_IN);
 	uvc->event_length = le16_to_cpu(ctrl->wLength);
 
-	memset(&v4l2_event, 0, sizeof(v4l2_event));
-	v4l2_event.type = UVC_EVENT_SETUP;
-	memcpy(&uvc_event->req, ctrl, sizeof(uvc_event->req));
-	v4l2_event_queue(&uvc->vdev, &v4l2_event);
+	if (uvc->event_setup_out) {
+		struct usb_request *req = uvc->control_req;
+
+		/*
+		 * Enqueue the request immediately for control OUT as the
+		 * host will start the data stage straight away.
+		 */
+		req->length = uvc->event_length;
+		req->zero = 0;
+		usb_ep_queue(f->config->cdev->gadget->ep0, req, GFP_KERNEL);
+	} else {
+		struct v4l2_event v4l2_event;
+		struct uvc_event *uvc_event = (void *)&v4l2_event.u.data;
+
+		memset(&v4l2_event, 0, sizeof(v4l2_event));
+		v4l2_event.type = UVC_EVENT_SETUP;
+		memcpy(&uvc_event->req, ctrl, sizeof(uvc_event->req));
+		v4l2_event_queue(&uvc->vdev, &v4l2_event);
+	}
 
 	return 0;
 }
diff --git a/drivers/usb/gadget/function/uvc_v4l2.c b/drivers/usb/gadget/function/uvc_v4l2.c
index 038482ff40e8..2e2251bdef03 100644
--- a/drivers/usb/gadget/function/uvc_v4l2.c
+++ b/drivers/usb/gadget/function/uvc_v4l2.c
@@ -35,6 +35,13 @@ uvc_send_response(struct uvc_device *uvc, struct uvc_request_data *data)
 	struct usb_composite_dev *cdev = uvc->func.config->cdev;
 	struct usb_request *req = uvc->control_req;
 
+	/*
+	 * For control OUT transfers the request has been enqueued synchronously
+	 * by the setup handler, there's nothing to be done here.
+	 */
+	if (uvc->event_setup_out)
+		return 0;
+
 	if (data->length < 0)
 		return usb_ep_set_halt(cdev->gadget->ep0);
 
-- 
2.18.0