Some of the confusion probably comes from the fact that the rulings change fairly recently (within the last couple years).
It USED to be that both pilots could be without an IR.
NOW, the safety pilot must be IR (and rated in the aircraft as well, but since we're talking about a C152 this doesn't apply here)
You don't have to specify which pilot is PIC for logging, both can log PIC while the limiting device is in place. (You SHOULD define the PIC prior to the flight for purposes of who's in charge if something happens)
So, P1 is in either the left or right seat and will wear the limiting device.
P2 MUST be IR (but does NOT have to have a current medical), is in the other front seat.
If P1 has an IR, P1 can file the IFR flight plan. If not, P2 must be the pilot listed on the flight plan.
During taxi, take-off, and until the limiting device is in place, whoever is actually flying the plane logs PIC.
After the limiting device is in place, both log PIC.
When the limiting device is removed, only the pilot flying the plane logs PIC.
Things change when the aircraft requires SIC, but that's not applicable for a C152.
To 'split' the time and cost, both must be rated for the plane and have medicals, and the time without the limiting device in place is split between the two. For example, P1 does the take-off, P2 does the landing, the rest of the time P1 is 'under the hood' and P2 is the safety pilot.
Again, the rules have changed, P2 must be IR since the change became effective.