Hello,

Recently, my usb-serial converter has become unusable. Attempts to open
the device always fail with:
open("/dev/ttyUSB0", O_RDONLY)          = -1 EAGAIN (Resource temporarily unavailable)

The device is a:
ID 0c52:2101 Sealevel Systems, Inc. Serial Converter
and uses the ftdi_sio driver.

I've bisected this problem to
commit 1bfee5bc86fdaecc912e06080583eddab7263df2
Author: Alan Stern <stern@rowland.harvard.edu>
Date:   Sat Sep 25 23:35:00 2010 +0200

    PM / Runtime: Merge synchronous and async runtime routines

I have other usb-serial converters that use other drivers and that are
unaffected. I have noticed the problem on a x86_64 machine (.config
here: http://pastebin.ca/2006414) and can reproduce it in kvm (with usb
passthrough, .config here: http://pastebin.ca/2006416).

I'll be glad to provide more info or try patches.

Thanks,
-Ben
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