http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff...
A driver writer from another operating system hinted that the versions of Yukon 2 chip with rambuffer (EC and XL) have a hardware bug that if the FIFO ever gets completely full it will hang. Sounds like a classic ring full vs ring empty wrap around bug.
As a workaround, use the existing watchdog timer to check for ring full lockup.