net: systemport: tell RXCHK if we are using Broadcom tags

When Broadcom tags are enabled, e.g: when interfaced to an Ethernet
switch, make sure that we tell the RXCHK engine that it should be
expecting a 4-bytes Broadcom tag after the Ethernet MAC Source Address.

Use netdev_uses_dsa() to check for that condition since that will tell
us if a switch is attached to our network interface.

Fixes: 80105befdb4b ("net: systemport: add Broadcom SYSTEMPORT Ethernet MAC driver")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bcmsysport.c

@@ -139,6 +139,15 @@ static int bcm_sysport_set_rx_csum(struct net_device *dev,
 	else
 		reg &= ~RXCHK_SKIP_FCS;
 
+	/* If Broadcom tags are enabled (e.g: using a switch), make
+	 * sure we tell the RXCHK hardware to expect a 4-bytes Broadcom
+	 * tag after the Ethernet MAC Source Address.
+	 */
+	if (netdev_uses_dsa(dev))
+		reg |= RXCHK_BRCM_TAG_EN;
+	else
+		reg &= ~RXCHK_BRCM_TAG_EN;
+
 	rxchk_writel(priv, reg, RXCHK_CONTROL);
 
 	return 0;