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    Subject[PATCH v2] usb: core: don't try to reset_device() a port that got just disconnected
    Date
    The USB hub driver's event handler contains a check to catch SuperSpeed
    devices that transitioned into the SS.Inactive state and tries to fix
    them with a reset. It decides whether to do a plain hub port reset or
    call the usb_reset_device() function based on whether there was a device
    attached to the port.

    However, there are device/hub combinations (found with a JetFlash
    Transcend mass storage stick (8564:1000) on the root hub of an Intel
    LynxPoint PCH) which can transition to the SS.Inactive state on
    disconnect (and stay there long enough for the host to notice). In this
    case, above-mentioned reset check will call usb_reset_device() on the
    stale device data structure. The kernel will send pointless LPM control
    messages to the no longer connected device address and can even cause
    several 5 second khubd stalls on some (buggy?) host controllers, before
    finally accepting the device's fate amongst a flurry of error messages.

    This patch makes the choice of reset dependent on the port status that
    has just been read from the hub in addition to the existence of an
    in-kernel data structure for the device, and only proceeds with the more
    extensive reset if both are valid.

    Signed-off-by: Julius Werner <jwerner@chromium.org>
    ---
    drivers/usb/core/hub.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
    index 4a8a1d6..558313d 100644
    --- a/drivers/usb/core/hub.c
    +++ b/drivers/usb/core/hub.c
    @@ -4798,7 +4798,8 @@ static void hub_events(void)
    hub->ports[i - 1]->child;

    dev_dbg(hub_dev, "warm reset port %d\n", i);
    - if (!udev) {
    + if (!udev || !(portstatus &
    + USB_PORT_STAT_CONNECTION)) {
    status = hub_port_reset(hub, i,
    NULL, HUB_BH_RESET_TIME,
    true);
    @@ -4808,8 +4809,8 @@ static void hub_events(void)
    usb_lock_device(udev);
    status = usb_reset_device(udev);
    usb_unlock_device(udev);
    + connect_change = 0;
    }
    - connect_change = 0;
    }

    if (connect_change)
    --
    1.7.12.4


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