Visit visa for Parents

I am U.K. citizen living in Dublin since 2013, naturalised as Irish in the ceremony couple of weeks ago.
My parents visit me here every year. I heard from someone that if you have been to Ireland on visits visa for more than two times. You can get multi entry visit visa. I confirmed it in inis website as well. But it doesn’t say anywhere what is the duration of total visa. Is it 5 years, with 90 day max stay at a time.
Thanks guys

There are two type of visit visa.

short term visa is for 90 days max
long term visa is for 1 year

for short term visa its mention that
"A multi entry visa permits you to travel to Ireland on a number of occasions during the dates shown on you visa, for short trips only. It is not permitted to use this category of visa to bypass immigration rules governing residency in the State i.e. it is not possible to remain in Ireland for a period of 90 days and then seek to re-enter the country for a further period of up to 90 days. Any abuse of this may result in you being refused entry at the port of entry or future visa applications being refused."

More detail on link below

http://www.inis.gov.ie/en/INIS/Pages/Single%20Multi%20Entry%20Visas

Hi there, I am very interested on this topic as well, please let us know if you find out more information. I think you are better off emailing the visa section in INIS about this scenario. Emailed them myself a couple of times and they replied in reasonable time.