net: ethernet: mtk_eth_soc: fix parsing packets in GDM

When using DSA, set the special tag in GDM ingress control to allow the MAC
to parse packets properly earlier. This affects rx DMA source port reporting.
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mediatek/mtk_eth_soc.c

@@ -19,6 +19,7 @@
 #include <linux/interrupt.h>
 #include <linux/pinctrl/devinfo.h>
 #include <linux/phylink.h>
+#include <net/dsa.h>
 
 #include "mtk_eth_soc.h"
 
@@ -1264,13 +1265,12 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
 			break;
 
 		/* find out which mac the packet come from. values start at 1 */
-		if (MTK_HAS_CAPS(eth->soc->caps, MTK_SOC_MT7628)) {
+		if (MTK_HAS_CAPS(eth->soc->caps, MTK_SOC_MT7628) ||
+		    (trxd.rxd4 & RX_DMA_SPECIAL_TAG))
 			mac = 0;
-		} else {
-			mac = (trxd.rxd4 >> RX_DMA_FPORT_SHIFT) &
-				RX_DMA_FPORT_MASK;
-			mac--;
-		}
+		else
+			mac = ((trxd.rxd4 >> RX_DMA_FPORT_SHIFT) &
+			       RX_DMA_FPORT_MASK) - 1;
 
 		if (unlikely(mac < 0 || mac >= MTK_MAC_COUNT ||
 			     !eth->netdev[mac]))
@@ -2233,6 +2233,9 @@ static void mtk_gdm_config(struct mtk_eth *eth, u32 config)
 
 		val |= config;
 
+		if (!i && eth->netdev[0] && netdev_uses_dsa(eth->netdev[0]))
+			val |= MTK_GDMA_SPECIAL_TAG;
+
 		mtk_w32(eth, val, MTK_GDMA_FWD_CFG(i));
 	}
 	/* Reset and enable PSE */

drivers/net/ethernet/mediatek/mtk_eth_soc.h

@@ -82,6 +82,7 @@
 
 /* GDM Exgress Control Register */
 #define MTK_GDMA_FWD_CFG(x)	(0x500 + (x * 0x1000))
+#define MTK_GDMA_SPECIAL_TAG	BIT(24)
 #define MTK_GDMA_ICS_EN		BIT(22)
 #define MTK_GDMA_TCS_EN		BIT(21)
 #define MTK_GDMA_UCS_EN		BIT(20)
@@ -305,6 +306,7 @@
 #define RX_DMA_L4_VALID_PDMA	BIT(30)		/* when PDMA is used */
 #define RX_DMA_FPORT_SHIFT	19
 #define RX_DMA_FPORT_MASK	0x7
+#define RX_DMA_SPECIAL_TAG	BIT(22)
 
 /* PHY Indirect Access Control registers */
 #define MTK_PHY_IAC		0x10004