The MaxLinear GSW1xx family got a single (R)(G)MII port at index 5 but
the registers MII_PCDU and MII_CFG are those of port 0.
Allow applying an offset for the port index to access those registers.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
---
 drivers/net/dsa/lantiq_gswip.c | 12 ++++++++++--
 drivers/net/dsa/lantiq_gswip.h |  1 +
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/net/dsa/lantiq_gswip.c b/drivers/net/dsa/lantiq_gswip.c
index 7ffaa6481271..f9b03fb5f57b 100644
--- a/drivers/net/dsa/lantiq_gswip.c
+++ b/drivers/net/dsa/lantiq_gswip.c
@@ -183,21 +183,29 @@ static void gswip_mii_mask(struct gswip_priv *priv, u32 clear, u32 set,
 static void gswip_mii_mask_cfg(struct gswip_priv *priv, u32 clear, u32 set,
 			       int port)
 {
+	int reg_port;
+
 	/* MII_CFG register only exists for MII ports */
 	if (!(priv->hw_info->mii_ports & BIT(port)))
 		return;
 
-	gswip_mii_mask(priv, clear, set, GSWIP_MII_CFGp(port));
+	reg_port = port + priv->hw_info->mii_port_reg_offset;
+
+	gswip_mii_mask(priv, clear, set, GSWIP_MII_CFGp(reg_port));
 }
 
 static void gswip_mii_mask_pcdu(struct gswip_priv *priv, u32 clear, u32 set,
 				int port)
 {
+	int reg_port;
+
 	/* MII_PCDU register only exists for MII ports */
 	if (!(priv->hw_info->mii_ports & BIT(port)))
 		return;
 
-	switch (port) {
+	reg_port = port + priv->hw_info->mii_port_reg_offset;
+
+	switch (reg_port) {
 	case 0:
 		gswip_mii_mask(priv, clear, set, GSWIP_MII_PCDU0);
 		break;
diff --git a/drivers/net/dsa/lantiq_gswip.h b/drivers/net/dsa/lantiq_gswip.h
index 19bbe6fddf04..2df9c8e8cfd0 100644
--- a/drivers/net/dsa/lantiq_gswip.h
+++ b/drivers/net/dsa/lantiq_gswip.h
@@ -233,6 +233,7 @@ struct gswip_hw_info {
 	int max_ports;
 	unsigned int allowed_cpu_ports;
 	unsigned int mii_ports;
+	int mii_port_reg_offset;
 	const struct gswip_pce_microcode (*pce_microcode)[];
 	size_t pce_microcode_size;
 	enum dsa_tag_protocol tag_protocol;
-- 
2.50.1