net: dsa: mt7530: Enable Rx sptag for EN7581 SoC

Packet Processor Engine (PPE) module used for hw acceleration on EN7581
mac block, in order to properly parse packets, requires DSA untagged
packets on TX side and read DSA tag from DMA descriptor on RX side.
For this reason, enable RX Special Tag (SPTAG) for EN7581 SoC.
This is a preliminary patch to enable netfilter flowtable hw offloading
on EN7581 SoC.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/dsa/mt7530.c

@@ -2586,6 +2586,11 @@ mt7531_setup_common(struct dsa_switch *ds)
 	/* Allow mirroring frames received on the local port (monitor port). */
 	mt7530_set(priv, MT753X_AGC, LOCAL_EN);
 
+	/* Enable Special Tag for rx frames */
+	if (priv->id == ID_EN7581)
+		mt7530_write(priv, MT753X_CPORT_SPTAG_CFG,
+			     CPORT_SW2FE_STAG_EN | CPORT_FE2SW_STAG_EN);
+
 	/* Flush the FDB table */
 	ret = mt7530_fdb_cmd(priv, MT7530_FDB_FLUSH, NULL);
 	if (ret < 0)

drivers/net/dsa/mt7530.h

@@ -627,6 +627,10 @@ enum mt7531_xtal_fsel {
 #define  MT7531_GPIO12_RG_RXD3_MASK	GENMASK(19, 16)
 #define  MT7531_EXT_P_MDIO_12		(2 << 16)
 
+#define MT753X_CPORT_SPTAG_CFG		0x7c10
+#define  CPORT_SW2FE_STAG_EN		BIT(1)
+#define  CPORT_FE2SW_STAG_EN		BIT(0)
+
 /* Registers for LED GPIO control (MT7530 only)
  * All registers follow this pattern:
  * [ 2: 0]  port 0