If I understand the USB Serial code correctly, at least open devices are 
constantly polled by 2 active URBs replaced immediately upon completion, 
except when the tty layer throttles them.

With many of these devices, this creates significant USB bandwidth usage. At 
least one report found that it starts creating practical problems after 12 
devices (on a BeagleBone), while adding a delay allows up to 60.

Is there any reason not to have some small delay (perhaps user-configurable) 
between URB requests, at least while the device is not actively receiving 
data? If a patch is needed to implement this, what would be the recommended 
approach for a kernel complete-newbie?

Thanks,

Luke
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