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Old 02-17-2012, 11:22 PM
Ben Hutchings
Default Bug#660291: Excessive USB disconnects (continuous udev add/remove cycles)

On Fri, Feb 17, 2012 at 03:33:38PM -0600, Hecker, Richard (DFRC-ME)[ARCATA ASSOCIATES INC] wrote:
> Package: linux-image-amd64
> Severity: normal
> I have been tracking down a udev problem on an Edgeport/416 USB to serial
> adapter. At intervals of about a minute, a USB disconnect event initiates
> the removal of all the serial devices and udev events immediately add them
> again. I have used linux-image-2.6.32-5-amd64 and linux-image-3.2.0-1-rt-amd64
> with the same results. I have a similar RHEL box with a 2.6 kernel that does
> not have this problem when we plug in these USB to serial adapters. Older
> Solaris boxes with sparc chips work fine too.

USB disconnect means either (1) the USB device stopped responding
or (2) the kernel was instructed to shut it up. In either case,
naturally the kernel should remove any child devices.

1. I assume the device isn't somehow being electrically disconnected
at such regular intervals. Other possibilies are a mode switch (not
likely, it never appears as a storage device), the device's firmware
crashing, a faulty USB cable or port, or excessive electrical noise in
the environment. Can you try using a different cable, a different
port, or running RHEL on the same physical system?

2. udev won't tell the kernel to shut it up, but I can imagine that
some other software might. However, if it's shut up then it
shouldn't immediately reconnect, so this doesn't seem very likely.


Ben Hutchings
We get into the habit of living before acquiring the habit of thinking.
- Albert Camus

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