ptp_qoriq: fix overflow in ptp_qoriq_adjfine() u64 calcalation

Current calculation for diff of TMR_ADD register value may have
64-bit overflow in this code line, when long type scaled_ppm is
large.

adj *= scaled_ppm;

This patch is to resolve it by using mul_u64_u64_div_u64().

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/ptp/ptp_qoriq.c

@@ -189,15 +189,16 @@ int ptp_qoriq_adjfine(struct ptp_clock_info *ptp, long scaled_ppm)
 	tmr_add = ptp_qoriq->tmr_add;
 	adj = tmr_add;
 
-	/* calculate diff as adj*(scaled_ppm/65536)/1000000
-	 * and round() to the nearest integer
+	/*
+	 * Calculate diff and round() to the nearest integer
+	 *
+	 * diff = adj * (ppb / 1000000000)
+	 *      = adj * scaled_ppm / 65536000000
 	 */
-	adj *= scaled_ppm;
-	diff = div_u64(adj, 8000000);
-	diff = (diff >> 13) + ((diff >> 12) & 1);
+	diff = mul_u64_u64_div_u64(adj, scaled_ppm, 32768000000);
+	diff = DIV64_U64_ROUND_UP(diff, 2);
 
 	tmr_add = neg_adj ? tmr_add - diff : tmr_add + diff;
-
 	ptp_qoriq->write(&regs->ctrl_regs->tmr_add, tmr_add);
 
 	return 0;