Should i tell my mom about my dad's porn?

Ok my parent's have a great marriage. They have been married 25 years and are still happy and love each other. Now my dad has an office and whenver i go in to talk to him or ask him something i see him staring intently at the screen and then quickly click the mouse like he's trying to close the web browser. So one day while he is not home i log onto his computer and check his favorites and among them is porn. I expected as much. But then i get suspicious of a cabinet he keeps locked in his closet (my parents have seperate closets). So i dig through his many keys and finally find the one that unlocks it. And it is full of porn magazines. Like im talking stacks. So i have no idea if my mom knows he has all this porn. We moved into our house about 3 years ago and before that we moved from a different state so i don't see how she couldn't have known about this. So what should i do? Confront my dad? My mom? Or just keep it to myself?