perf/marvell: cn10k DDR perfmon event overflow handling

CN10k DSS h/w perfmon does not support event overflow interrupt, so
periodic timer is being used. Each event counter is 48bit, which in worst
case scenario can increment at maximum 5.6 GT/s. At this rate it may take
many hours to overflow these counters. Therefore polling period for
overflow is set to 100 sec, which can be changed using sysfs parameter.

Two fixed event counters starts counting from zero on overflow, so
overflow condition is when new count less than previous count. While
eight programmable event counters freezes at maximum value. Also individual
counter cannot be restarted, so need to restart all eight counters.

Signed-off-by: Bharat Bhushan <bbhushan2@marvell.com>
Reviewed-by: Bhaskara Budiredla <bbudiredla@marvell.com>
Link: https://lore.kernel.org/r/20220211045346.17894-4-bbhushan2@marvell.com
Signed-off-by: Will Deacon <will@kernel.org>

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