USB: Enable LPM after a failed probe.

Before a driver is probed, we want to disable USB 3.0 Link Power
Management (LPM), in case the driver needs hub-initiated LPM disabled.
After the probe finishes, we want to attempt to re-enable LPM, order to
balance the LPM ref count.

When a probe fails (such as when libusual doesn't want to bind to a USB
3.0 mass storage device), make sure to balance the LPM ref counts by
re-enabling LPM.

This patch should be backported to kernels as old as 3.5, that contain
the commit 8306095fd2c1100e8244c09bf560f97aca5a311d "USB: Disable USB
3.0 LPM in critical sections."

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: stable@vger.kernel.org

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index ddd820d25288b57da71336bf4eed397a4cc16410..6056db7af410fac833ed00d8c5f793773f628931 100644 (file)
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -367,6 +367,10 @@ static int usb_probe_interface(struct device *dev)
        intf->condition = USB_INTERFACE_UNBOUND;
        usb_cancel_queued_reset(intf);
 
+       /* If the LPM disable succeeded, balance the ref counts. */
+       if (!lpm_disable_error)
+               usb_unlocked_enable_lpm(udev);
+
        /* Unbound interfaces are always runtime-PM-disabled and -suspended */
        if (driver->supports_autosuspend)
                pm_runtime_disable(dev);