Resetting USB devices (was Re: making me autocratically logged in?)
On Mon, 2017-09-18 at 17:49 -0400, Gene Heskett wrote:
> On Monday 18 September 2017 11:39:26 Tixy wrote:
>
> > On Mon, 2017-09-18 at 11:13 -0400, Gene Heskett wrote:
> > [...]
> >
> > > My instant problem, a disappearing usb camera, could also be solved
> > > I think, by power cycling the usb port its plugged into, as it will
> > > re-appear after a powerdown reboot, but I do not know how to do that
> > > short of a powerdown reset. If there is such an ability the user,
> > > or a sudo can do, that would also be helpfull.
> >
> > I don't know if this is useful, but the method I found for resetting a
> > USB device was to unbind then rebind it with something like:
> >
> > echo '3-1.4' >/sys/bus/usb/drivers/usb/unbind
> > echo '3-1.4' >/sys/bus/usb/drivers/usb/bind
> >
> > Where '3-1.4' is the endpoint name for the device found by looking in
> > the kernel log. E.g. for this example I ran the 'dmesg' command and
> > looked for my web camera and found these entries:
> >
> > usb 3-1.4: new high-speed USB device number 3 using ehci-pci
> > usb 3-1.4: New USB device found, idVendor=2232, idProduct=1018
> > usb 3-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=0
> > usb 3-1.4: Product: WebCam SC-13HDL11431N
> >
> > I don't know if this will help with your particular problem.
>
> Wheezy apparently isn't organized in quite that manner. So the best I
> could do, even as root, was elicit no permissions messages.
Strange, I'm using Jessie, but looks like unbinding has been supported
in the kernel for over 10 years [1] so would expect a Wheezy kernel to
support it, perhaps the path is different. Does a file at that path
exist? For me I get
#ls -l /sys/bus/usb/drivers/usb/unbind
--w------- 1 root root 4096 Sep 19 06:28 /sys/bus/usb/drivers/usb/unbind
Actually, looking at that old article [1] the path is different
(/sys/bus/usb/drivers/ub/) so perhaps you might try that, or any other
likely path you may have under /sys/bus/usb/drivers/
BTW, I'm sure you realised this, but to make it explicit, the magic
string '3-1.4' in my example is specific to my machine and yours will be
different depending on the USB hub/device topography.
I have no experience with webcam problems so can't help with that
specificly. (I use this USB driver unbind/bind trick to get an FTDI
development module to toggle it's power enable output)
[1] https://lwn.net/Articles/143397/
--
Tixy
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