DisplayLink doesn't work when intel_iommu is enabled

[YuZhang]

I have a DisplayLink product, i.e., a WAVLINK multi-display HDMI adapter, i.e., USB3.0 to HDMI converter.
I run Ubuntu16.04.1 on i3-6100U machine. I need to turn on intel_iommu, however, it seems as if DisplayLink is not compatible with intel_iommu. When intel_iommu is enabled(intel_iommu=on), the extended monitor (DVI-I-1-1) doesn't work. It keeps a black screen while the primary monitor is in a bad status of very low resolution. There is one similar thread on the forum. But the solution is not useful for me since I need to enable intel_iommu but not to disable it.
(http://displaylink.org/forum/showthr...ighlight=iommu)
Could anyone tell me how can I use DisplayLink with intel_iommu enabled?
I have attached the log files collected by DLSupportTool.

Thanks.

[GolemIII]

I need also to set enable intel_iommu for Virtualization reason : share network card
do we have any reason to have no displaylink work with this setting ?

[geostar1024]

I've run into the same issue on both 16.04 and 18.04, with the latest version of the driver (5.1.26). I've tried various combinations of kernel parameters, but end up with the same error in dmesg whenever I try to activate a DisplayLink adapter:

DMAR: Allocating domain for evdi.0 failed

It looks like the driver isn't handling DMA correctly or something like that. Since it seems like the odds of someone wanting to pass one of these adapters through to a VM is quite low (considerably lower than simply wanting to have virtualization active), I'd suggest that the fix be to simply disable iommu capability in the driver until a better fix can be devised.