USB reset fails when using a LimeSDR Mini on FreeBSD

[Jan Behrens]

On Fri, 26 Jun 2020 14:47:13 +0200
Hans Petter Selasky <hps at selasky.org> wrote:

> Hi,
> 
> On 2020-06-26 13:51, Jan Behrens wrote:
> > I made the discovery that running the library as root works just fine!
> 
> The libusb_reset_device() function needs root permissions! This is 
> expected. There are specific checks in the kernel for this.

I might have misunderstood your earlier post:

On Thu, 25 Jun 2020 20:16:14 +0200
Hans Petter Selasky <hps at selasky.org> wrote:

> Unless the device requires it, libusb_reset_device(), will only 
> re-enumerate the device. Beware that this only is allowed if you are 
> running the application as root. Else libusb_reset_device() will be a 
> no-operation.
> 
> --HPS

Does this mean that depending on the device, it will either be a
no-operation or a re-enumeration, and in the latter case, root
privileges are required, otherwise not?

Or did you mean that if you are non-root, it will/should always be a
no-operation?

What I don't understand is that the Lime Suite SoapySDR module seems to
work fine on Linux and other operating systems but makes trouble with
FreeBSD. Is it a FreeBSD specific thing that libusb_reset_device()
fails if called as non-root?

> Can you run this app as root, and then change to non-root after 
> libusb_reset_device() has been executed?
> 
> --HPS

It's not really practical. I'd have to patch every program using the
module. But maybe libusb_reset_device() isn't necessary to call?

I could give recommendation to the Lime Suite developers to remove the
libusb_reset_device() call on FreeBSD systems if it is not neccessary.
However, I would like to understand why it is called and what's its
usual purpose, and if there are side effects when removing the call, or
whether the call should/could be replaced by a different call that
"only" requires device privileges. Also: Why does this work on Linux
but fails on FreeBSD? Is the API differently defined?

Sorry for my confusion, I'm really not experienced with USB programming.


Regards,
Jan Behrens