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@xxxxxxxxxxxxxxxxxxx>
CC: Oliver Neukum <oliver@xxxxxxxxxx>
---
[as1743]
drivers/usb/core/hub.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
Index: usb-3.14/drivers/usb/core/hub.c
===================================================================
--- usb-3.14.orig/drivers/usb/core/hub.c
+++ usb-3.14/drivers/usb/core/hub.c
@@ -3098,9 +3098,19 @@ static int finish_port_resume(struct usb
* 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,
--
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