net: stmmac: dwmac4/5: Add MAC loopback support

In preparation for the addition of stmmac selftests we implement the MAC
loopback callback in dwmac4/5 cores.
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/dwmac4.h

@@ -160,6 +160,7 @@ enum power_event {
 #define GMAC_CONFIG_PS			BIT(15)
 #define GMAC_CONFIG_FES			BIT(14)
 #define GMAC_CONFIG_DM			BIT(13)
+#define GMAC_CONFIG_LM			BIT(12)
 #define GMAC_CONFIG_DCRS		BIT(9)
 #define GMAC_CONFIG_TE			BIT(1)
 #define GMAC_CONFIG_RE			BIT(0)

drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c

@@ -703,6 +703,18 @@ static void dwmac4_debug(void __iomem *ioaddr, struct stmmac_extra_stats *x,
 		x->mac_gmii_rx_proto_engine++;
 }
 
+static void dwmac4_set_mac_loopback(void __iomem *ioaddr, bool enable)
+{
+	u32 value = readl(ioaddr + GMAC_CONFIG);
+
+	if (enable)
+		value |= GMAC_CONFIG_LM;
+	else
+		value &= ~GMAC_CONFIG_LM;
+
+	writel(value, ioaddr + GMAC_CONFIG);
+}
+
 const struct stmmac_ops dwmac4_ops = {
 	.core_init = dwmac4_core_init,
 	.set_mac = stmmac_set_mac,
@@ -732,6 +744,7 @@ const struct stmmac_ops dwmac4_ops = {
 	.pcs_get_adv_lp = dwmac4_get_adv_lp,
 	.debug = dwmac4_debug,
 	.set_filter = dwmac4_set_filter,
+	.set_mac_loopback = dwmac4_set_mac_loopback,
 };
 
 const struct stmmac_ops dwmac410_ops = {
@@ -763,6 +776,7 @@ const struct stmmac_ops dwmac410_ops = {
 	.pcs_get_adv_lp = dwmac4_get_adv_lp,
 	.debug = dwmac4_debug,
 	.set_filter = dwmac4_set_filter,
+	.set_mac_loopback = dwmac4_set_mac_loopback,
 };
 
 const struct stmmac_ops dwmac510_ops = {
@@ -799,6 +813,7 @@ const struct stmmac_ops dwmac510_ops = {
 	.safety_feat_dump = dwmac5_safety_feat_dump,
 	.rxp_config = dwmac5_rxp_config,
 	.flex_pps_config = dwmac5_flex_pps_config,
+	.set_mac_loopback = dwmac4_set_mac_loopback,
 };
 
 int dwmac4_setup(struct stmmac_priv *priv)