DisplayLink USB3.0 to HDMI converter doesn't work when intel_iommu is enabled

[YuZhang]

Hi,
I don't know why I post new thread several times but I still can not find it in this forum. I just register this account. Do I have the permission to start a new thread?

I have a DisplayLink product, i.e., WAVLINK UG35H5, which is a multi-display HDMI adapter or a USB3.0 to HDMI converter.
I encounter a problem with this DisplayLink adapter.
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 plugging to DVI-I-1-1 doesn't work. It shows a black screen while the primary monitor plugging to onboard DP port displays in a bad status of very low resolution. Besides, everytime when intel_iommu is enabled, there appears an error message at the Ubuntu user-login interface, i.e., “Could not switch the monitor configuration could not set the configuration for CRTC 226”.
There is one similar thread on the forum pertaining to iommu. But the solution is not useful for me since I need to enable intel_iommu but not to disable it.
Could anyone tell me how can I use this DisplayLink adapter with intel_iommu enabled?
Attached are log files collected by DLSupportTool.

Thanks.
Yu Zhang