net: airoha: Disable GDM2 forwarding before configuring GDM2 loopback

[ Upstream commit 985d4a55e64e43bd86eeb896b81ceba453301989 ]

Hw design requires to disable GDM2 forwarding before configuring GDM2
loopback in airoha_set_gdm2_loopback routine.

Fixes: 9cd451d ("net: airoha: Add loopback support for GDM2")
Tested-by: Madhur Agrawal <madhur.agrawal@airoha.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20260520-airoha-disable-gdm2-fwd-v1-1-1eeea5dffc2f@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit d1d76bbb6d7af470fa57bf4888d4912109c72bd2)
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>

Author: LorenzoBianconi

drivers/net/ethernet/airoha/airoha_eth.c

@@ -1800,11 +1800,8 @@ static int airhoha_set_gdm2_loopback(struct airoha_gdm_port *port)
 	u32 val, pse_port, chan;
 	int src_port;
 
-	/* Forward the traffic to the proper GDM port */
-	pse_port = port->id == AIROHA_GDM3_IDX ? FE_PSE_PORT_GDM3
-					       : FE_PSE_PORT_GDM4;
 	airoha_set_gdm_port_fwd_cfg(eth, REG_GDM_FWD_CFG(AIROHA_GDM2_IDX),
-				    pse_port);
+				    FE_PSE_PORT_DROP);
 	airoha_fe_clear(eth, REG_GDM_FWD_CFG(AIROHA_GDM2_IDX),
 			GDM_STRIP_CRC_MASK);
 
@@ -1822,6 +1819,11 @@ static int airhoha_set_gdm2_loopback(struct airoha_gdm_port *port)
 		      GDM_SHORT_LEN_MASK | GDM_LONG_LEN_MASK,
 		      FIELD_PREP(GDM_SHORT_LEN_MASK, 60) |
 		      FIELD_PREP(GDM_LONG_LEN_MASK, AIROHA_MAX_MTU));
+	/* Forward the traffic to the proper GDM port */
+	pse_port = port->id == AIROHA_GDM3_IDX ? FE_PSE_PORT_GDM3
+					       : FE_PSE_PORT_GDM4;
+	airoha_set_gdm_port_fwd_cfg(eth, REG_GDM_FWD_CFG(AIROHA_GDM2_IDX),
+				    pse_port);
 
 	/* Disable VIP and IFC for GDM2 */
 	airoha_fe_clear(eth, REG_FE_VIP_PORT_EN, BIT(AIROHA_GDM2_IDX));