umcs (4-Port-USB-serial) triggering way too much ehci IRQs

Harald Schmalzbauer h.schmalzbauer at
Mon Sep 16 16:11:53 UTC 2013


I have some of these 4-Port-Serial-USB-Hubs:
They have the MosChip MCS7840 inside, wich also understands RS485/422
besides RS232.

FreeBSDs umcs(4) supports the RS232 mode with standard baudrates and
works with that device.

Unfortunately, as soon as I open any of the 4 cuaU0.x ports, there are
500irq/s from ehci.
These irqs also accur if the port is closed again (until I unload the
umcs module).
These irqs prevent virtual machines and also real hardware from deeper
sleeping. In my case, it's a huge ammount of lost power saving.
I also saw that the windows driver of the MCS7840 consuming a lot of
CPU-cycles (XP-ESXi guest).
Is there any chance to tranquilize?

The 4-Port prolific model
doesn't show these unneccessary irqs btw.!



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