device filtering support

[Segher Boessenkool]

>> The firmware is buggy since after it transfers some endpoint data
>> and then all subsequent device descriptor request will fail and then
>> the device goes to an unstable state.
>>
>> We changed libusb-win32 driver in 1.2.5.0 to cache the
>> device descriptor to solve the issue.
>
> Is compensating for buggy firmwares something we really want to  
> consider doing with libusbx?

Not at all costs no.  But it would be good if libusbx worked with
not-fully-standard-compliant devices: there aren't very many devices
that *are* standard compliant in all details!

If we do weird things no one else does, it has a bigger chance of
hitting a bug on a device.  So we should try to avoid asking for
the device descriptor a zillion times, since no OS does that, so
it isn't tested.  It's also a rather stupid thing to do in any
case ;-)


Segher