net: ethernet: mvneta: Add 2500BaseX support for SoCs without comphy

The older SoCs like Armada XP support a 2500BaseX mode in the datasheets
referred to as DR-SGMII (Double rated SGMII) or HS-SGMII (High Speed
SGMII). This is an upclocked 1000BaseX mode, thus
PHY_INTERFACE_MODE_2500BASEX is the appropriate mode define for it.
adding support for it merely means writing the correct magic value into
the MVNETA_SERDES_CFG register.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/mvneta.c

@@ -110,6 +110,7 @@
 #define MVNETA_SERDES_CFG			 0x24A0
 #define      MVNETA_SGMII_SERDES_PROTO		 0x0cc7
 #define      MVNETA_QSGMII_SERDES_PROTO		 0x0667
+#define      MVNETA_HSGMII_SERDES_PROTO		 0x1107
 #define MVNETA_TYPE_PRIO                         0x24bc
 #define      MVNETA_FORCE_UNI                    BIT(21)
 #define MVNETA_TXQ_CMD_1                         0x24e4
@@ -3564,6 +3565,11 @@ static int mvneta_config_interface(struct mvneta_port *pp,
 			mvreg_write(pp, MVNETA_SERDES_CFG,
 				    MVNETA_SGMII_SERDES_PROTO);
 			break;
+
+		case PHY_INTERFACE_MODE_2500BASEX:
+			mvreg_write(pp, MVNETA_SERDES_CFG,
+				    MVNETA_HSGMII_SERDES_PROTO);
+			break;
 		default:
 			return -EINVAL;
 		}