[PATCH] USB: otg hub support is optional

USB OTG devices are not required to support external hubs.  This adds a
configuration option to disable that support.
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/Kconfig

@@ -99,4 +99,11 @@ config USB_OTG_WHITELIST
 	  normal Linux-USB hosts do (other than the warning), and is
 	  convenient for many stages of product development.
 
+config USB_OTG_BLACKLIST_HUB
+	bool "Disable external hubs"
+	depends on USB_OTG
+	help
+	  If you say Y here, then Linux will refuse to enumerate
+	  external hubs.  OTG hosts are allowed to reduce hardware
+	  and software costs by not supporting external hubs.
 

drivers/usb/core/hub.c

@@ -836,6 +836,13 @@ static int hub_probe(struct usb_interface *intf, const struct usb_device_id *id)
 	desc = intf->cur_altsetting;
 	hdev = interface_to_usbdev(intf);
 
+#ifdef	CONFIG_USB_OTG_BLACKLIST_HUB
+	if (hdev->parent) {
+		dev_warn(&intf->dev, "ignoring external hub\n");
+		return -ENODEV;
+	}
+#endif
+
 	/* Some hubs have a subclass of 1, which AFAICT according to the */
 	/*  specs is not defined, but it works */
 	if ((desc->desc.bInterfaceSubClass != 0) &&