net: stmmac: dwmac1000: Add MAC loopback support

In preparation for the addition of stmmac selftests we implement the MAC
loopback callback in dwmac1000 core.
Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Cc: Joao Pinto <jpinto@synopsys.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c

@@ -499,6 +499,18 @@ static void dwmac1000_debug(void __iomem *ioaddr, struct stmmac_extra_stats *x,
 		x->mac_gmii_rx_proto_engine++;
 }
 
+static void dwmac1000_set_mac_loopback(void __iomem *ioaddr, bool enable)
+{
+	u32 value = readl(ioaddr + GMAC_CONTROL);
+
+	if (enable)
+		value |= GMAC_CONTROL_LM;
+	else
+		value &= ~GMAC_CONTROL_LM;
+
+	writel(value, ioaddr + GMAC_CONTROL);
+}
+
 const struct stmmac_ops dwmac1000_ops = {
 	.core_init = dwmac1000_core_init,
 	.set_mac = stmmac_set_mac,
@@ -518,6 +530,7 @@ const struct stmmac_ops dwmac1000_ops = {
 	.pcs_ctrl_ane = dwmac1000_ctrl_ane,
 	.pcs_rane = dwmac1000_rane,
 	.pcs_get_adv_lp = dwmac1000_get_adv_lp,
+	.set_mac_loopback = dwmac1000_set_mac_loopback,
 };
 
 int dwmac1000_setup(struct stmmac_priv *priv)