diff --git a/drivers/net/ethernet/airoha/airoha_eth.c b/drivers/net/ethernet/airoha/airoha_eth.c
index 09acbe669536..7b47d9e066ce 100644
--- a/drivers/net/ethernet/airoha/airoha_eth.c
+++ b/drivers/net/ethernet/airoha/airoha_eth.c
@@ -1729,10 +1729,12 @@ static int airhoha_set_gdm2_loopback(struct airoha_gdm_port *port)
 		      SP_CPORT_MASK(val),
 		      __field_prep(SP_CPORT_MASK(val), FE_PSE_PORT_CDM2));
 
-	if (port->id != AIROHA_GDM3_IDX && airoha_is_7581(eth))
-		airoha_fe_rmw(eth, REG_SRC_PORT_FC_MAP6,
-			      FC_ID_OF_SRC_PORT24_MASK,
-			      FIELD_PREP(FC_ID_OF_SRC_PORT24_MASK, 2));
+	if (port->id == AIROHA_GDM4_IDX && airoha_is_7581(eth)) {
+		u32 mask = FC_ID_OF_SRC_PORT_MASK(nbq);
+
+		airoha_fe_rmw(eth, REG_SRC_PORT_FC_MAP6, mask,
+			      __field_prep(mask, AIROHA_GDM2_IDX));
+	}
 
 	return 0;
 }
diff --git a/drivers/net/ethernet/airoha/airoha_regs.h b/drivers/net/ethernet/airoha/airoha_regs.h
index ed4e3407f4a0..29878b954c77 100644
--- a/drivers/net/ethernet/airoha/airoha_regs.h
+++ b/drivers/net/ethernet/airoha/airoha_regs.h
@@ -376,10 +376,7 @@
 #define SP_CPORT_MASK(_n)		GENMASK(3 + ((_n) << 2), ((_n) << 2))
 
 #define REG_SRC_PORT_FC_MAP6		0x2298
-#define FC_ID_OF_SRC_PORT27_MASK	GENMASK(28, 24)
-#define FC_ID_OF_SRC_PORT26_MASK	GENMASK(20, 16)
-#define FC_ID_OF_SRC_PORT25_MASK	GENMASK(12, 8)
-#define FC_ID_OF_SRC_PORT24_MASK	GENMASK(4, 0)
+#define FC_ID_OF_SRC_PORT_MASK(_n)	GENMASK(4 + ((_n) << 3), ((_n) << 3))
 
 #define REG_CDM5_RX_OQ1_DROP_CNT	0x29d4