Can I reboot a USB device within a driver's probe function?

Thierry Seegers thierry.seegers at
Mon Sep 14 04:03:49 EDT 2020

Hi, thanks for the reply.

> > One can even have this script executed automatically through a
> > ".rules" file. So far so good. My question is: can I write a driver
> > that will perform the same thing?
> Yes, but why?  We pushed most of this logic out to userspace as it is
> easier to handle there.  Why do you want a kernel driver for this?

Here's my (perhaps incorrect thought) as to why doing this in a driver would
be desirable. In the case of the Python script executed through a .rules file,
the script can't know which device this is in response to. It is only launched
because "some" device with product ID "0580" has been connected. Then,
it just searches the system for "a" device with product ID "0580" and talks to
*the first one it finds*. In the case where two devices would be plugged in to
the computer at roughly the same time, I think this mechanism would break
because there's a chance both scripts would attempt to talk to the same
device and fail to update it. You end up with a device in a bad state and a
second "0580" device that wouldn't even be spoken to ever.

Contrast with a driver where if two devices are connected at the same time, two
separate instances of the driver code would be executed for each
specific device.
There would be no chance of both probe() functions talking to the same device
because the probe() function would be invoked for a specific device.

> Did your problem function return an error (saying the driver is not in
> control of the device), or 0, saying it is?  I recommend sending an
> error, that should free up the reference counting properly.

I'll keep hacking at it but I agree with you that regardless of
anything else, the
probe() function ought to return an error code.

> Are you sure you sent the proper data to the device?

I'm sure in so far as I straight copy pasted the code from a
user-executed program
that did the exact same thing successfully.

Thanks for your help!


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