USB: fix interface runtime-PM settings

This patch (as1379) reworks the logic for handling USB interface
runtime-PM settings -- hopefully it's right this time!  The problem is
that when a driver is unbound or binding fails, runtime PM for the
interface always gets disabled.  But pm_runtime_disable() nests, so it
shouldn't be called unless the interface was previously enabled for
runtime PM.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Rob Duncan <Robert.Duncan@exar.com>
Tested-by: Rob Duncan <Robert.Duncan@exar.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/driver.c

@@ -334,7 +334,8 @@ static int usb_probe_interface(struct device *dev)
 	usb_cancel_queued_reset(intf);
 
 	/* Unbound interfaces are always runtime-PM-disabled and -suspended */
-	pm_runtime_disable(dev);
+	if (driver->supports_autosuspend)
+		pm_runtime_disable(dev);
 	pm_runtime_set_suspended(dev);
 
 	usb_autosuspend_device(udev);
@@ -389,7 +390,8 @@ static int usb_unbind_interface(struct device *dev)
 	intf->needs_remote_wakeup = 0;
 
 	/* Unbound interfaces are always runtime-PM-disabled and -suspended */
-	pm_runtime_disable(dev);
+	if (driver->supports_autosuspend)
+		pm_runtime_disable(dev);
 	pm_runtime_set_suspended(dev);
 
 	/* Undo any residual pm_autopm_get_interface_* calls */
@@ -438,14 +440,17 @@ int usb_driver_claim_interface(struct usb_driver *driver,
 
 	iface->condition = USB_INTERFACE_BOUND;
 
-	/* Claimed interfaces are initially inactive (suspended).  They are
-	 * runtime-PM-enabled only if the driver has autosuspend support.
-	 * They are sensitive to their children's power states.
+	/* Claimed interfaces are initially inactive (suspended) and
+	 * runtime-PM-enabled, but only if the driver has autosuspend
+	 * support.  Otherwise they are marked active, to prevent the
+	 * device from being autosuspended, but left disabled.  In either
+	 * case they are sensitive to their children's power states.
 	 */
-	pm_runtime_set_suspended(dev);
 	pm_suspend_ignore_children(dev, false);
 	if (driver->supports_autosuspend)
 		pm_runtime_enable(dev);
+	else
+		pm_runtime_set_active(dev);
 
 	/* if interface was already added, bind now; else let
 	 * the future device_add() bind it, bypassing probe()