xhci: refuse loading if nousb is used

commit 1eaf35e4 upstream.

The module should fail to load.
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ luis: backported to 3.16:
  - moved usb_disabled() check to the top of the function so that there's
    no need to invoke xhci_unregister_pci() before returning.  Suggested
    by gregkh. ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/usb/host/xhci.c

@@ -4928,6 +4928,9 @@ static int __init xhci_hcd_init(void)
 {
 	int retval;
 
+	if (usb_disabled())
+		return -ENODEV;
+
 	retval = xhci_register_pci();
 	if (retval < 0) {
 		pr_debug("Problem registering PCI driver.\n");
@@ -4955,6 +4958,7 @@ static int __init xhci_hcd_init(void)
 	BUILD_BUG_ON(sizeof(struct xhci_intr_reg) != 8*32/8);
 	/* xhci_run_regs has eight fields and embeds 128 xhci_intr_regs */
 	BUILD_BUG_ON(sizeof(struct xhci_run_regs) != (8+8*128)*32/8);
+
 	return 0;
 unreg_pci:
 	xhci_unregister_pci();