USB: skip Set-Interface(0) if already in altsetting 0

When a driver unbinds from an interface, usbcore always sends a
Set-Interface request to reinstall altsetting 0.  Unforunately, quite
a few devices have buggy firmware that crashes when it receives this
request.

To avoid such problems, this patch (as1180) arranges to send the
Set-Interface request only when the interface is not already in
altsetting 0.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index 3d7793d93031..8c081308b0e2 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -279,7 +279,9 @@ static int usb_unbind_interface(struct device *dev)
          * altsetting means creating new endpoint device entries).
          * When either of these happens, defer the Set-Interface.
          */
-        if (!error && intf->dev.power.status == DPM_ON)
+        if (intf->cur_altsetting->desc.bAlternateSetting == 0)
+                ;       /* Already in altsetting 0 so skip Set-Interface */
+        else if (!error && intf->dev.power.status == DPM_ON)
                 usb_set_interface(udev, intf->altsetting[0].
                                 desc.bInterfaceNumber, 0);
         else