diff --git a/drivers/net/ethernet/cadence/macb.h b/drivers/net/ethernet/cadence/macb.h
index 6ff123da6a140042b69b21420ee3e753b7e210aa..98735584570db7a98ea21149b000e5077d8f7b51 100644
--- a/drivers/net/ethernet/cadence/macb.h
+++ b/drivers/net/ethernet/cadence/macb.h
@@ -496,7 +496,11 @@
 
 /* Bitfields in TISUBN */
 #define GEM_SUBNSINCR_OFFSET			0
-#define GEM_SUBNSINCR_SIZE			16
+#define GEM_SUBNSINCRL_OFFSET			24
+#define GEM_SUBNSINCRL_SIZE			8
+#define GEM_SUBNSINCRH_OFFSET			0
+#define GEM_SUBNSINCRH_SIZE			16
+#define GEM_SUBNSINCR_SIZE			24
 
 /* Bitfields in TI */
 #define GEM_NSINCR_OFFSET			0
@@ -834,6 +838,9 @@ struct gem_tx_ts {
 /* limit RX checksum offload to TCP and UDP packets */
 #define GEM_RX_CSUM_CHECKED_MASK		2
 
+/* Scaled PPM fraction */
+#define PPM_FRACTION	16
+
 /* struct macb_tx_skb - data about an skb which is being transmitted
  * @skb: skb currently being transmitted, only set for the last buffer
  *       of the frame
diff --git a/drivers/net/ethernet/cadence/macb_ptp.c b/drivers/net/ethernet/cadence/macb_ptp.c
index 0a8aca8d3634b5322b7b53bf58b7f763674fdf44..43a3f0dbf857c1a44db0093b80330e5905107e99 100644
--- a/drivers/net/ethernet/cadence/macb_ptp.c
+++ b/drivers/net/ethernet/cadence/macb_ptp.c
@@ -104,7 +104,10 @@ static int gem_tsu_incr_set(struct macb *bp, struct tsu_incr *incr_spec)
 	 * to take effect.
 	 */
 	spin_lock_irqsave(&bp->tsu_clk_lock, flags);
-	gem_writel(bp, TISUBN, GEM_BF(SUBNSINCR, incr_spec->sub_ns));
+	/* RegBit[15:0] = Subns[23:8]; RegBit[31:24] = Subns[7:0] */
+	gem_writel(bp, TISUBN, GEM_BF(SUBNSINCRL, incr_spec->sub_ns) |
+		   GEM_BF(SUBNSINCRH, (incr_spec->sub_ns >>
+			  GEM_SUBNSINCRL_SIZE)));
 	gem_writel(bp, TI, GEM_BF(NSINCR, incr_spec->ns));
 	spin_unlock_irqrestore(&bp->tsu_clk_lock, flags);
 
@@ -135,7 +138,7 @@ static int gem_ptp_adjfine(struct ptp_clock_info *ptp, long scaled_ppm)
 	 * (temp / USEC_PER_SEC) + 0.5
 	 */
 	adj += (USEC_PER_SEC >> 1);
-	adj >>= GEM_SUBNSINCR_SIZE; /* remove fractions */
+	adj >>= PPM_FRACTION; /* remove fractions */
 	adj = div_u64(adj, USEC_PER_SEC);
 	adj = neg_adj ? (word - adj) : (word + adj);