usb: add devicetree helpers for determining dr_mode and phy_type

This adds two little devicetree helper functions for determining the
dr_mode (host, peripheral, otg) and phy_type (utmi, ulpi,...) from
the devicetree.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/include/linux/usb/of.h b/include/linux/usb/of.h
new file mode 100644
index 0000000..e460a24
--- /dev/null
+++ b/include/linux/usb/of.h
@@ -0,0 +1,28 @@
+/*
+ * OF helpers for usb devices.
+ *
+ * This file is released under the GPLv2
+ */
+
+#ifndef __LINUX_USB_OF_H
+#define __LINUX_USB_OF_H
+
+#include <linux/usb/otg.h>
+#include <linux/usb/phy.h>
+
+#ifdef CONFIG_OF
+enum usb_phy_interface of_usb_get_phy_mode(struct device_node *np);
+enum usb_dr_mode of_usb_get_dr_mode(struct device_node *np);
+#else
+static inline enum usb_phy_interface of_usb_get_phy_mode(struct device_node *np)
+{
+	return USBPHY_INTERFACE_MODE_UNKNOWN;
+}
+
+static inline enum usb_dr_mode of_usb_get_dr_mode(struct device_node *np)
+{
+	return USB_DR_MODE_UNKNOWN;
+}
+#endif
+
+#endif /* __LINUX_USB_OF_H */