net: stmmac: dwmac100: Add MAC loopback support

In preparation for the addition of stmmac selftests we implement the MAC
loopback callback in dwmac100 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/dwmac100_core.c

@@ -160,6 +160,18 @@ static void dwmac100_pmt(struct mac_device_info *hw, unsigned long mode)
 	return;
 }
 
+static void dwmac100_set_mac_loopback(void __iomem *ioaddr, bool enable)
+{
+	u32 value = readl(ioaddr + MAC_CONTROL);
+
+	if (enable)
+		value |= MAC_CONTROL_OM;
+	else
+		value &= ~MAC_CONTROL_OM;
+
+	writel(value, ioaddr + MAC_CONTROL);
+}
+
 const struct stmmac_ops dwmac100_ops = {
 	.core_init = dwmac100_core_init,
 	.set_mac = stmmac_set_mac,
@@ -171,6 +183,7 @@ const struct stmmac_ops dwmac100_ops = {
 	.pmt = dwmac100_pmt,
 	.set_umac_addr = dwmac100_set_umac_addr,
 	.get_umac_addr = dwmac100_get_umac_addr,
+	.set_mac_loopback = dwmac100_set_mac_loopback,
 };
 
 int dwmac100_setup(struct stmmac_priv *priv)