[PLUG] How to make my laptop look like a USB charger?

[Eric House]

> Eric House wrote:
> > I have a Dell laptop running Ubuntu and a Virgin Mobile "MiFi"
> > cellular wifi hotspot.  The MiFi is great but for one bug: when you
> > plug its USB cable into the laptop to charge it stops being a hotspot,
> > so you have to carry a separate USB wallwart to charge it.
> >
> > I'm pretty sure this is unnecessary -- that if I could get my laptop
> > to pretend to be a mere USB wallwart I could prevent the loss of wifi.
> > Googling on the subject turns up instructions for fixing this by
> > disabling USB Mass Storage mode on windows thus:
> >
> > # KB823732 explains how you can disable USB device support by changing
> > # the Start value of
> > # HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\UsbStor to 4
> >
> > The closest I could think to try on GNU/Linux was to prevent the
> > usb_storage module from loading, but this didn't work.  The MiFi still
> > shuts down, meaning it's been signalled in some way by the laptop.
> >
> > Can anybody suggest how to do this, or where to read or ask for
> > further information?  I'm happy to hack the drivers if that's what
> > it's going to take.  It's apparently possible to fix this by removing
> > the two inner contacts from a USB cable end, but I don't want to carry
> > a second cable either -- if I can avoid it.

> Eric House
> Googling on
>     linux disable mass storage
> At 
> <http://www.linuxquestions.org/questions/linux-newbie-8/how-to-disable-usb-mass-storage-device-usb-drive-in-linux-651262/> 
> it says ...
> "In linux it's even more easily done, by unloading the usb_storage module:
> 
> modprobe -r usb_storage
> 
> from the command line"
> ... then it goes on about how to do that permanently, if that is of any 
> interest.
> Does that help?

No.  That's the first thing I tried.  Another reply suggested
disabling the core USB module, which I *can* do on my laptop, but that
doesn't help either.

BTW, the MiFi presents itself as an ISO 9600 FS -- i.e. it looks like
a CD-ROM to Ubuntu.  I'm not even sure what the point of that is, but
then I haven't looked at what files are there -- and can't or I'll
lose the connection over which I'm writing this. :-)

> The inner contacts are the data lines, and the outer contacts are
> power.  I'm not sure of the data lines even exist on a wall wart.  The
> USB standard requires that initialization happens within milliseconds
> of connecting the cable, and some of that has to happen before the
> computer even knows that it's a USB Mass storage device.  Depending on
> how the MiFi device responds to this disabling USB Mass Storage might
> be too late.  Have you confirmed that it actually works in Windows?

No.  That's an excellent question/idea.  Before I chase this much
further I'll find myself a windows box.

> Modern Linux will typically load this driver automatically as soon as
> it's detected, and in some cases may be built into the kernel rather
> than loaded on use.
> 
> On my ubuntu system the place to prevent loading the driver would be.
> /etc/modprobe.d/blacklist.conf

I did that, and confirmed with lsusb that it was not being loaded.  If
I rmmod'd it and did not add it to the blacklist it would get reloaded
when I connected the USB cable, but with the blacklist mod that was
prevented.  Wifi still shuts down, though.

Thanks!

--Eric
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