Regression since 4.1

[Tobias Geiger <tobias.geiger-9woOUGhjKTphl2p70BpVqQ@public.gmane.org>]

Hello!

in short:
No Kernel since 4.1 boots on my machine.

I can make newer kernels boot, but ONLY when i remove "iommu=on 
intel_iommu=on" from the cmdline.
If i leave it in, as with all the kernels before and including 4.1, newer 
kernels dont boot, and in a really not very informative way:
They dont even print a single message to the console, i only see the grub-
messages (like "loading kernel" and "loading initial ramdisk") - after these 
messages NO more output of any kind - also no SysRQ keys working - nothing.

Because of this complete lack of information, i guess its hard to debug for 
you the cause of this.
Perhaps i can help - but how?

i'm writing from a pure IOMMU-User perspective - i can compile kernels, but 
never git-bisected, so maybe a hint to a tutorial for that would be great!

Greetings and thanks for your insight!
Tobias