USB: disable reset-resume when USB_QUIRK_RESET is set

The USB_QUIRK_RESET flag indicates that a USB device changes its
identity in some way when it is reset.  It may lose its firmware, its
descriptors may change, or it may switch back to a default mode of
operation.

If a device does this, the kernel needs to avoid resetting it.  Resets
are likely to fail, or worse, succeed while changing the device's
state in a way the system can't detect.

This means we should disable the reset-resume mechanism whenever this
quirk flag is present.  An attempted reset-resume will fail, the
device will be logically disconnected, and later on the hub driver
will rediscover and re-enumerate the device.  This will cause the
appropriate udev events to be generated, so that userspace will have a
chance to switch the device into its normal operating mode, if
necessary.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Oliver Neukum <oliver@neukum.org>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 12 insertions, 2 deletions

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 2d74dfb9c989..d670aaf13a3d 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -3105,9 +3105,19 @@ static int finish_port_resume(struct usb_device *udev)
          * operation is carried out here, after the port has been
          * resumed.
          */
-        if (udev->reset_resume)
+        if (udev->reset_resume) {
+                /*
+                 * If the device morphs or switches modes when it is reset,
+                 * we don't want to perform a reset-resume.  We'll fail the
+                 * resume, which will cause a logical disconnect, and then
+                 * the device will be rediscovered.
+                 */
  retry_reset_resume:
-                status = usb_reset_and_verify_device(udev);
+                if (udev->quirks & USB_QUIRK_RESET)
+                        status = -ENODEV;
+                else
+                        status = usb_reset_and_verify_device(udev);
+        }
 
         /* 10.5.4.5 says be sure devices in the tree are still there.
          * For now let's assume the device didn't go crazy on resume,