Comment # 18 on bug 1177973 from Takashi Iwai

The bug is likely intermittent.  It's caused by the concurrent access to the
GPIO to get / write some EDID thingy, so sometimes it hits, sometimes not.
I was afraid that it caused some deep loop, but apparently it's a one-off
thing, and we can fix it properly just by dropping the ASSERT*() call there.

I'm going to submit the patch to upstream after a bit more discussion with
them.

About the invocation of xcmddc: no worries, I checked xcm package, and found
that it contains a udev rule to invoke the command.

I guess you might be able to trigger the bug by running like
  xcmddc --i2c /dev/$I2C --identify
where $I2C is i2c-0 or such existing device file.  Run the above from multiple
places at the same time, and you might see the kernel warning again.