Your Perc. Did you do the well known SMbios 'fix/mod' on the card.
No, didn't need it.
BTW; I am not saying or suggesting the kext is wrong, since there are a million different DSDT's out there, and they could easily be the cause of malfunctioning legacy support.
The kext can't be completely wrong for sure since it behaves, but can haz bugs and problems, like any software. Some were uncovered (thanks to people in this thread) and fixed.
Plus hardware & it's firmware may have dark corners too. For example, by link i provided:
To make matters worse, it appears that certain OEM firmware causes a
deadlock in the megaraid_sas probe function if you try to enable MSI
interrupts, which possibly explains why the driver never tries to enable
them in the first place (I have still not had any response from LSI)
BTW, as we figured out, it's not a DMA issue you had, so it's not much worry about. Since MSI work for you, stay on 'em, they will provide you will better I/O.