Comment 4 for bug 1783746

It started after upgrade from X to B. This may only show up on Tegra2, which does not have an IOMMU, and which creates problems if one is registered. Sorry, I don't understand the technical details. AFAICT, the whole driver is still broken in mainline kernel (since 3.20). An upstream fixed is currently proposed. See:
https://git.kernel.org/pub/scm/linux/kernel/git/joro/iommu.git/commit/?h=next&id=5c5c87411488af3cd082221e567498d813d0fe83