How long person can stay out of Italy with Permesso di soggiorno

Hi All Mentors,

I am now in Milan Italy with permesso di soggiorno.

I have to go my home country for some period.

I want to know how long time I can stay at my home country India with permesso di soggiorno with validaty  of 2 Year and Permesso di soggiorno Karta with unlimited validity.

Regards