port-evbarm/49019: RPI: interrupt storm when url0 is up

[Takahiro HAYASHI <t.hash425%gmail.com@localhost>]

>Number:         49019
>Category:       port-evbarm
>Synopsis:       RPI: interrupt storm when url0 is up
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-evbarm-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Jul 18 21:00:00 +0000 2014
>Originator:     Takahiro HAYASHI
>Release:        NetBSD 6.99.47
>Organization:
>Environment:
System: NetBSD raspi 6.99.47 NetBSD 6.99.47 (MYRPI) #13: Fri Jul 18 20:50:08 
JST 2014  root@halt:/build/head/obj.evbarm/sys/arch/evbarm/compile/MYRPI evbarm
Architecture: earmhf
Machine: evbarm
>Description:
        I have noticed tty interaction gets slow and laggie when
        I turn up url0 plugged into Raspberry-Pi.
        "bcm2835 pic usb" intr rate shown by systat vm increases from
        about 8100 to more than 37000.
        It gets back to 8100 when ifconfig url0 down.

        This issue happens with kue and udav too, but does not w/ axe.
        url, kue, and udav are FS devices, axe is HS device.

>How-To-Repeat:
        Plug url, kue, or udav into RPI and ifconfig it up.
>Fix:
        Not known.