greybus: usb: implement hub_control callback

static int hub_control(struct usb_hcd *hcd, u16 typeReq, u16 wValue, u16 wIndex,

		       char *buf, u16 wLength)

{

	struct gb_usb_hub_control_request request;

	struct gb_usb_device *dev = to_gb_usb_device(hcd);

	struct gb_operation *operation;

	struct gb_usb_hub_control_request *request;

	struct gb_usb_hub_control_response *response;

	size_t response_size;

	int ret;

	request.typeReq = cpu_to_le16(typeReq);

	request.wValue = cpu_to_le16(wValue);

	request.wIndex = cpu_to_le16(wIndex);

	request.wLength = cpu_to_le16(wLength);

	// FIXME - buf needs to come back in struct gb_usb_hub_control_response

	// for some types of requests, depending on typeReq.  Do we do this in a

	// "generic" way, or only ask for a response for the ones we "know" need

	// a response (a small subset of all valid typeReq, thankfully.)

	ret = gb_operation_sync(dev->connection, GB_USB_TYPE_HUB_CONTROL,

				&request, sizeof(request), NULL, 0);

	/* FIXME: handle unspecified lengths */

	response_size = sizeof(*response) + wLength;

	operation = gb_operation_create(dev->connection,

					GB_USB_TYPE_HUB_CONTROL,

					sizeof(*request),

					response_size,

					GFP_KERNEL);

	if (!operation)

		return -ENOMEM;

	request = operation->request->payload;

	request->typeReq = cpu_to_le16(typeReq);

	request->wValue = cpu_to_le16(wValue);

	request->wIndex = cpu_to_le16(wIndex);

	request->wLength = cpu_to_le16(wLength);

	ret = gb_operation_request_send_sync(operation);

	if (ret)

		goto out;

	if (wLength) {

		/* Greybus core has verified response size */

		response = operation->response->payload;

		memcpy(buf, response->buf, wLength);

	}

out:

	gb_operation_put(operation);

	return ret;

}