jme: Fix FIFO flush issue

commit ba9adbe6 upstream.

Set the RX FIFO flush watermark lower.
According to Federico and JMicron's reply,
setting it to 16QW would be stable on most platforms.
Otherwise, user might experience packet drop issue.
Reported-by: Federico Quagliata <federico@quagliata.org>
Fixed-by: Federico Quagliata <federico@quagliata.org>
Signed-off-by: Guo-Fu Tseng <cooldavid@cooldavid.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/net/jme.c

@@ -2228,19 +2228,11 @@ jme_change_mtu(struct net_device *netdev, int new_mtu)
 		((new_mtu) < IPV6_MIN_MTU))
 		return -EINVAL;
 
-	if (new_mtu > 4000) {
-		jme->reg_rxcs &= ~RXCS_FIFOTHNP;
-		jme->reg_rxcs |= RXCS_FIFOTHNP_64QW;
-		jme_restart_rx_engine(jme);
-	} else {
-		jme->reg_rxcs &= ~RXCS_FIFOTHNP;
-		jme->reg_rxcs |= RXCS_FIFOTHNP_128QW;
-		jme_restart_rx_engine(jme);
-	}
 
 	netdev->mtu = new_mtu;
 	netdev_update_features(netdev);
 
+	jme_restart_rx_engine(jme);
 	jme_reset_link(jme);
 
 	return 0;

drivers/net/jme.h

@@ -734,7 +734,7 @@ enum jme_rxcs_values {
 	RXCS_RETRYCNT_60	= 0x00000F00,
 
 	RXCS_DEFAULT		= RXCS_FIFOTHTP_128T |
-				  RXCS_FIFOTHNP_128QW |
+				  RXCS_FIFOTHNP_16QW |
 				  RXCS_DMAREQSZ_128B |
 				  RXCS_RETRYGAP_256ns |
 				  RXCS_RETRYCNT_32,