net-next: ethernet: mediatek: add CDM able to recognize the tag for DSA

The patch adds the setup for allowing CDM can recognize these packets with
carrying port-distinguishing tag. Otherwise, these tagging packets will be
handled incorrectly by CDM. The setup is also working out for general
untag packets as well.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Landen Chao <Landen.Chao@mediatek.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.h b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
index 99b1c8e..996024d 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.h
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
@@ -70,6 +70,10 @@
 /* Frame Engine Interrupt Grouping Register */
 #define MTK_FE_INT_GRP		0x20
 
+/* CDMP Ingress Control Register */
+#define MTK_CDMQ_IG_CTRL	0x1400
+#define MTK_CDMQ_STAG_EN	BIT(0)
+
 /* CDMP Exgress Control Register */
 #define MTK_CDMP_EG_CTRL	0x404