net: stmmac: Disable ACS Feature for GMAC >= 4

ACS Feature is currently enabled for GMAC >= 4 but the llc_snap status
is never checked in descriptor rx_status callback. This will cause
stmmac to always strip packets even that ACS feature is already
stripping them.

Lets be safe and disable the ACS feature for GMAC >= 4 and always strip
the packets for this GMAC version.

Fixes: 477286b53f55 ("stmmac: add GMAC4 core support")
Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Joao Pinto <jpinto@synopsys.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/dwmac4.h

@@ -347,7 +347,7 @@ enum power_event {
 #define MTL_RX_OVERFLOW_INT		BIT(16)
 
 /* Default operating mode of the MAC */
-#define GMAC_CORE_INIT (GMAC_CONFIG_JD | GMAC_CONFIG_PS | GMAC_CONFIG_ACS | \
+#define GMAC_CORE_INIT (GMAC_CONFIG_JD | GMAC_CONFIG_PS | \
 			GMAC_CONFIG_BE | GMAC_CONFIG_DCRS)
 
 /* To dump the core regs excluding  the Address Registers */

drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c

@@ -31,13 +31,6 @@ static void dwmac4_core_init(struct mac_device_info *hw,
 
 	value |= GMAC_CORE_INIT;
 
-	/* Clear ACS bit because Ethernet switch tagging formats such as
-	 * Broadcom tags can look like invalid LLC/SNAP packets and cause the
-	 * hardware to truncate packets on reception.
-	 */
-	if (netdev_uses_dsa(dev))
-		value &= ~GMAC_CONFIG_ACS;
-
 	if (mtu > 1500)
 		value |= GMAC_CONFIG_2K;
 	if (mtu > 2000)

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -3495,8 +3495,13 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 
 			/* ACS is set; GMAC core strips PAD/FCS for IEEE 802.3
 			 * Type frames (LLC/LLC-SNAP)
+			 *
+			 * llc_snap is never checked in GMAC >= 4, so this ACS
+			 * feature is always disabled and packets need to be
+			 * stripped manually.
 			 */
-			if (unlikely(status != llc_snap))
+			if (unlikely(priv->synopsys_id >= DWMAC_CORE_4_00) ||
+			    unlikely(status != llc_snap))
 				frame_len -= ETH_FCS_LEN;
 
 			if (netif_msg_rx_status(priv)) {