Still know little about it, but have DDG'd it & read many pages, including https://superuser.com/questions/1170280/should-i-disable-the-hardware-iommu-when-booting-with-iommu-soft and https://bbs.archlinux.org/viewtopic.php?id=168555.
Given it was linked in an earlier post in this current thread, i also read https://forum.giga-byte.co.uk/index.php?PHPSESSID=8h47qhnhvhl9mjed9k82o0r721&topic=14802.msg105102#msg1051022, which was a horror-show!
However, none of the pages i read seem applicable to my scenario, hence i struggle to comprehend exactly what perceived "problem" of mine now this "solution" is intended to resolve...? Some of those pages mentioned USB problems... but i do not have any such problems. Other pages mentioned that IOMMU can help with either allowing, or improving, Virtual Machine performance... but i do not have any such problems. My 1st pasted link above mentions boot problems, & memory problems... but i do not have any such problems. My 2nd pasted link above mentions sound problems & again memory problems... but i do not have any such problems.
Puzzled but moderately undaunted, i dug a bit deeper. I opened my MoB User Guide in Okular, did an initial dummy search with a simple keyword to confirm the search function works [yes], then searched for "IOMMU" ... zero hits. Hmmm. Next i thought i'd see if any nasty IOMMU messages have been accruing in the journal, so...
[kdemeoz@GA-Z97-HD3-Tower ~]$ dmesg --level=err,warn -T | grep IOMMU
[kdemeoz@GA-Z97-HD3-Tower ~]$ dmesg | grep IOMMU
I absolutely do not want to sound like an ingrate, as i truly value the nice help i get here, but i have to say that at this stage i do not feel inclined [sorry] to proceed @tbg with your clever-looking grub edit:
...without a clear idea of what specifically is the objective here. When you said:
... & again with no disrespect meant, but atm i don't see evidence of this fabled beastie at all, in as much as my Tower is once again correctly Suspend-Resume networking, now that it uses the newer driver. Unless i'm overlooking something, atm my Tower seems to be all nice & happy once more.