net: fec: ptp: Use the 31-bit ptp timer.

When ptp switches from software adjustment to hardware ajustment, linux ptp can't converge.
It is caused by the IP limit. Hardware adjustment logcial have issue when ptp counter
runs over 0x80000000(31 bit counter). The internal IP reference manual already remove 32bit
free-running count support. This patch replace the 32-bit PTP timer with 31-bit.

Signed-off-by: Luwei Zhou <b45643@freescale.com>
Signed-off-by: Frank Li <Frank.Li@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/fec_ptp.c

@@ -70,6 +70,7 @@
 #define FEC_TS_TIMESTAMP	0x418
 
 #define FEC_CC_MULT	(1 << 31)
+#define FEC_COUNTER_PERIOD	(1 << 31)
 /**
  * fec_ptp_read - read raw cycle counter (to be used by time counter)
  * @cc: the cyclecounter structure
@@ -113,14 +114,15 @@ void fec_ptp_start_cyclecounter(struct net_device *ndev)
 	/* 1ns counter */
 	writel(inc << FEC_T_INC_OFFSET, fep->hwp + FEC_ATIME_INC);
 
-	/* use free running count */
-	writel(0, fep->hwp + FEC_ATIME_EVT_PERIOD);
+	/* use 31-bit timer counter */
+	writel(FEC_COUNTER_PERIOD, fep->hwp + FEC_ATIME_EVT_PERIOD);
 
-	writel(FEC_T_CTRL_ENABLE, fep->hwp + FEC_ATIME_CTRL);
+	writel(FEC_T_CTRL_ENABLE | FEC_T_CTRL_PERIOD_RST,
+		fep->hwp + FEC_ATIME_CTRL);
 
 	memset(&fep->cc, 0, sizeof(fep->cc));
 	fep->cc.read = fec_ptp_read;
-	fep->cc.mask = CLOCKSOURCE_MASK(32);
+	fep->cc.mask = CLOCKSOURCE_MASK(31);
 	fep->cc.shift = 31;
 	fep->cc.mult = FEC_CC_MULT;