net: systemport: only update UMAC_CMD if something changed

The link adjustment callback can be called as frequently as desired by
the PHY library, as such, let's avoid doing a Read/Modify/Write sequence
if nothing changed, which is more than likely since we are interfaced
with a switch device.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bcmsysport.c

@@ -959,15 +959,16 @@ static void bcm_sysport_adj_link(struct net_device *dev)
 	if (!phydev->pause)
 		cmd_bits |= CMD_RX_PAUSE_IGNORE | CMD_TX_PAUSE_IGNORE;
 
-	reg = umac_readl(priv, UMAC_CMD);
-	reg &= ~((CMD_SPEED_MASK << CMD_SPEED_SHIFT) |
+	if (changed) {
+		reg = umac_readl(priv, UMAC_CMD);
+		reg &= ~((CMD_SPEED_MASK << CMD_SPEED_SHIFT) |
 			CMD_HD_EN | CMD_RX_PAUSE_IGNORE |
 			CMD_TX_PAUSE_IGNORE);
-	reg |= cmd_bits;
-	umac_writel(priv, reg, UMAC_CMD);
+		reg |= cmd_bits;
+		umac_writel(priv, reg, UMAC_CMD);
 
-	if (changed)
 		phy_print_status(priv->phydev);
+	}
 }
 
 static int bcm_sysport_init_tx_ring(struct bcm_sysport_priv *priv,