net: stmmac: Disable automatic FCS/Pad stripping

The stmmac has the possibility to automatically strip the padding/FCS for IEEE
802.3 type frames. This feature is enabled conditionally. Therefore, the stmmac
receive path has to have a determination logic whether the FCS has to be
stripped in software or not.

In fact, for DSA this ACS feature is disabled and the determination logic
doesn't check for it properly. For instance, when using DSA in combination with
an older stmmac (pre version 4), the FCS is not stripped by hardware or software
which is problematic.

So either add another check for DSA to the fast path or simply disable ACS
feature completely. The latter approach has been chosen, because most of the
time the FCS is stripped in software anyway and it removes conditionals from the
receive fast path.
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/87v8q8jjgh.fsf@kurt/
Link: https://lore.kernel.org/r/20220905130155.193640-1-kurt@linutronix.deSigned-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/ethernet/stmicro/stmmac/dwmac100.h

@@ -56,7 +56,7 @@
 #define MAC_CONTROL_TE		0x00000008	/* Transmitter Enable */
 #define MAC_CONTROL_RE		0x00000004	/* Receiver Enable */
 
-#define MAC_CORE_INIT (MAC_CONTROL_HBD | MAC_CONTROL_ASTP)
+#define MAC_CORE_INIT (MAC_CONTROL_HBD)
 
 /* MAC FLOW CTRL defines */
 #define MAC_FLOW_CTRL_PT_MASK	0xffff0000	/* Pause Time Mask */

drivers/net/ethernet/stmicro/stmmac/dwmac1000.h

@@ -126,7 +126,7 @@ enum inter_frame_gap {
 #define GMAC_CONTROL_TE		0x00000008	/* Transmitter Enable */
 #define GMAC_CONTROL_RE		0x00000004	/* Receiver Enable */
 
-#define GMAC_CORE_INIT (GMAC_CONTROL_JD | GMAC_CONTROL_PS | GMAC_CONTROL_ACS | \
+#define GMAC_CORE_INIT (GMAC_CONTROL_JD | GMAC_CONTROL_PS | \
 			GMAC_CONTROL_BE | GMAC_CONTROL_DCRS)
 
 /* GMAC Frame Filter defines */

drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c

@@ -15,7 +15,6 @@
 #include <linux/crc32.h>
 #include <linux/slab.h>
 #include <linux/ethtool.h>
-#include <net/dsa.h>
 #include <asm/io.h>
 #include "stmmac.h"
 #include "stmmac_pcs.h"
@@ -24,7 +23,6 @@
 static void dwmac1000_core_init(struct mac_device_info *hw,
 				struct net_device *dev)
 {
-	struct stmmac_priv *priv = netdev_priv(dev);
 	void __iomem *ioaddr = hw->pcsr;
 	u32 value = readl(ioaddr + GMAC_CONTROL);
 	int mtu = dev->mtu;
@@ -32,13 +30,6 @@ static void dwmac1000_core_init(struct mac_device_info *hw,
 	/* Configure GMAC core */
 	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) || !priv->plat->enh_desc)
-		value &= ~GMAC_CONTROL_ACS;
-
 	if (mtu > 1500)
 		value |= GMAC_CONTROL_2K;
 	if (mtu > 2000)

drivers/net/ethernet/stmicro/stmmac/dwmac100_core.c

@@ -15,7 +15,6 @@
 *******************************************************************************/
 
 #include <linux/crc32.h>
-#include <net/dsa.h>
 #include <asm/io.h>
 #include "stmmac.h"
 #include "dwmac100.h"
@@ -28,13 +27,6 @@ static void dwmac100_core_init(struct mac_device_info *hw,
 
 	value |= MAC_CORE_INIT;
 
-	/* Clear ASTP 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 &= ~MAC_CONTROL_ASTP;
-
 	writel(value, ioaddr + MAC_CONTROL);
 
 #ifdef STMMAC_VLAN_TAG_USED

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

@@ -14,7 +14,6 @@
 #include <linux/slab.h>
 #include <linux/ethtool.h>
 #include <linux/io.h>
-#include <net/dsa.h>
 #include "stmmac.h"
 #include "stmmac_pcs.h"
 #include "dwmac4.h"

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

@@ -5076,16 +5076,8 @@ static int stmmac_rx_zc(struct stmmac_priv *priv, int limit, u32 queue)
 		buf1_len = stmmac_rx_buf1_len(priv, p, status, len);
 		len += buf1_len;
 
-		/* 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 (likely(!(status & rx_not_ls)) &&
-		    (likely(priv->synopsys_id >= DWMAC_CORE_4_00) ||
-		     unlikely(status != llc_snap))) {
+		/* ACS is disabled; strip manually. */
+		if (likely(!(status & rx_not_ls))) {
 			buf1_len -= ETH_FCS_LEN;
 			len -= ETH_FCS_LEN;
 		}
@@ -5262,16 +5254,8 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 		buf2_len = stmmac_rx_buf2_len(priv, p, status, len);
 		len += buf2_len;
 
-		/* 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 (likely(!(status & rx_not_ls)) &&
-		    (likely(priv->synopsys_id >= DWMAC_CORE_4_00) ||
-		     unlikely(status != llc_snap))) {
+		/* ACS is disabled; strip manually. */
+		if (likely(!(status & rx_not_ls))) {
 			if (buf2_len) {
 				buf2_len -= ETH_FCS_LEN;
 				len -= ETH_FCS_LEN;