Not much of an answer, only what I know.
That missile was fitted with various means of control and guidance over its long use (>40y) - in fact, as it's still in use today by some navies as P-35.
Before going into details it's important to understand that it was designed to attack a carrier group and here if possible the carrier itself. So a fairly large target with a massive radar signature in an almost 'flat' surrounding with nothing but the target (group).
The very first (early 1960s) version didn't have any real kind of 'data' link, at least not in a sense like we would call it today. It's main control was an inertia system. The guidance system was feed a vector and a distance. This was done locally from SIGINT data received from a TU-16 or TU95. The starting sub was roughly pointed in that direction as well. The missile was started and climbed to high altitude, heading toward the target. After droping the start rockets and reaching cruise speed an analog TV link was established with the sub. The transmitted radar information was used to guide and at some point lock the final target and let go. Now the cruise missile dropped to low altitude and followed the locked direction.
In later versions this TV link could be hand over between the submarine and a TU-95 long range targeter. The TU-96 was a special version equipped with a long range target radar. The advantage of using that TU-95 was it's higher energy and ranging. When feed from the airplane, the analogue radar data was send toward the cruise missile and insed as input much if it was taken from the onboard radar. This allowed to drop to low (safe) altitude quite early - if necessary. At some point again (or whenever jammed) it reverted to on board radar for the final aproach.
Next to all of this was done analogue. So 'data' has to be understood in a broader sense than we would today.
Of course, the P6 and it's offsprings has had many updates in electronics in more than 40 years of service, so today's versions can be assumed as fully digital.