net: ethernet: ti: cpts: fix overflow check period

The CPTS drivers uses 8sec period for overflow checking with
assumption that CPTS retclk will not exceed 500MHz. But that's not
true on some TI platforms (Kesytone 2). As result, it is possible that
CPTS counter will overflow more than once between two readings.

Hence, fix it by selecting overflow check period dynamically as
max_sec_before_overflow/2, where
 max_sec_before_overflow = max_counter_val / rftclk_freq.

Cc: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/ti/cpts.h

@@ -97,9 +97,6 @@ enum {
 	CPTS_EV_TX,   /* Ethernet Transmit Event */
 };
 
-/* This covers any input clock up to about 500 MHz. */
-#define CPTS_OVERFLOW_PERIOD (HZ * 8)
-
 #define CPTS_FIFO_DEPTH 16
 #define CPTS_MAX_EVENTS 32
 
@@ -127,6 +124,7 @@ struct cpts {
 	struct list_head events;
 	struct list_head pool;
 	struct cpts_event pool_data[CPTS_MAX_EVENTS];
+	unsigned long ov_check_period;
 };
 
 void cpts_rx_timestamp(struct cpts *cpts, struct sk_buff *skb);