usb: cdns3: gadget: Fix g_audio use case when connected to Super-Speed host

Take into account gadget driver's speed limit when programming
controller speed.

Fixes: 7733f6c32e ("usb: cdns3: Add Cadence USB3 DRD Driver")
Signed-off-by: Roger Quadros <rogerq@ti.com>
Acked-by: Peter Chen <peter.chen@nxp.com>
Link: https://lore.kernel.org/r/20191030121607.21739-1-rogerq@ti.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/cdns3/gadget.c

@@ -2343,9 +2343,35 @@ static int cdns3_gadget_udc_start(struct usb_gadget *gadget,
 {
 	struct cdns3_device *priv_dev = gadget_to_cdns3_device(gadget);
 	unsigned long flags;
+	enum usb_device_speed max_speed = driver->max_speed;
 
 	spin_lock_irqsave(&priv_dev->lock, flags);
 	priv_dev->gadget_driver = driver;
+
+	/* limit speed if necessary */
+	max_speed = min(driver->max_speed, gadget->max_speed);
+
+	switch (max_speed) {
+	case USB_SPEED_FULL:
+		writel(USB_CONF_SFORCE_FS, &priv_dev->regs->usb_conf);
+		writel(USB_CONF_USB3DIS, &priv_dev->regs->usb_conf);
+		break;
+	case USB_SPEED_HIGH:
+		writel(USB_CONF_USB3DIS, &priv_dev->regs->usb_conf);
+		break;
+	case USB_SPEED_SUPER:
+		break;
+	default:
+		dev_err(priv_dev->dev,
+			"invalid maximum_speed parameter %d\n",
+			max_speed);
+		/* fall through */
+	case USB_SPEED_UNKNOWN:
+		/* default to superspeed */
+		max_speed = USB_SPEED_SUPER;
+		break;
+	}
+
 	cdns3_gadget_config(priv_dev);
 	spin_unlock_irqrestore(&priv_dev->lock, flags);
 	return 0;
@@ -2575,12 +2601,7 @@ static int cdns3_gadget_start(struct cdns3 *cdns)
 	/* Check the maximum_speed parameter */
 	switch (max_speed) {
 	case USB_SPEED_FULL:
-		writel(USB_CONF_SFORCE_FS, &priv_dev->regs->usb_conf);
-		writel(USB_CONF_USB3DIS, &priv_dev->regs->usb_conf);
-		break;
 	case USB_SPEED_HIGH:
-		writel(USB_CONF_USB3DIS, &priv_dev->regs->usb_conf);
-		break;
 	case USB_SPEED_SUPER:
 		break;
 	default: