usb: roles: add helper usb_role_string()

Introduces usb_role_string() function, which returns a
human-readable name of provided usb role, it's useful to
make the log readable.
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1621932786-9335-1-git-send-email-chunfeng.yun@mediatek.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/roles/class.c

@@ -214,6 +214,15 @@ static const char * const usb_roles[] = {
 	[USB_ROLE_DEVICE]	= "device",
 };
 
+const char *usb_role_string(enum usb_role role)
+{
+	if (role < 0 || role >= ARRAY_SIZE(usb_roles))
+		return "unknown";
+
+	return usb_roles[role];
+}
+EXPORT_SYMBOL_GPL(usb_role_string);
+
 static ssize_t
 role_show(struct device *dev, struct device_attribute *attr, char *buf)
 {

include/linux/usb/role.h

@@ -65,6 +65,7 @@ void usb_role_switch_unregister(struct usb_role_switch *sw);
 
 void usb_role_switch_set_drvdata(struct usb_role_switch *sw, void *data);
 void *usb_role_switch_get_drvdata(struct usb_role_switch *sw);
+const char *usb_role_string(enum usb_role role);
 #else
 static inline int usb_role_switch_set_role(struct usb_role_switch *sw,
 		enum usb_role role)
@@ -109,6 +110,11 @@ static inline void *usb_role_switch_get_drvdata(struct usb_role_switch *sw)
 	return NULL;
 }
 
+static inline const char *usb_role_string(enum usb_role role)
+{
+	return "unknown";
+}
+
 #endif
 
 #endif /* __LINUX_USB_ROLE_H */