According to "i.MX 7Dual Applications Processor Reference Manual, Rev. 1, 01/2018" part 188.8.131.52 "Power Modes" there are two ways to enter "SNVS" mode from "RUN" mode: ONOFF long press, or SW.
Could you specify exactly the SW way? What register accesses are required to do this?
In tested design I have no ONOFF button and I would make sure that the imx7 would always be able to return to "RUN" mode without user intervention, but I want to keep SNVS battery backup to still have SNVS security features.