Hi Andrew, On Thu, Aug 9, 2018 at 6:23 PM Andrew Lunn <and...@lunn.ch> wrote: > > > Its coming from the switch lan4 I have attached the png, where > > C4:F3:12:08:FE:7F is > > the mac of lan4, which is broadcast to ff:ff:ff:ff:ff:ff, which is > > causing rx counter on > > PC to go up. > > So, big packets are making it from the switch to the PC. But the small > ARP packets are not. > > This is what Florian was suggesting. > > ARP packets are smaller than 64 bytes, which is the minimum packet > size for Ethernet. Any packets smaller than 64 bytes are called runt > packets. They have to be padded upto 64 bytes in order to make them > valid. Otherwise the destination, or any switch along the path, might > throw them away. > > What could be happening is that the CSPW driver or hardware is padding > the packet to 64 bytes. But that packet has a DSA header in it. The > switch removes the header, recalculate the checksum and sends the > packet. It is now either 4 or 8 bytes smaller, depending on what DSA > header was used. It then becomes a runt packet. > Thank you for the clarification, this really helped me out.
> Florian had to fix this problem recently. > > http://patchwork.ozlabs.org/patch/836534/ > But seems like this patch was never accepted, instead brcm_tag_xmit_ll() does it if I am understanding it correctly. similarly to this ksz_xmit() is taking care of padding. > You probably need something similar for the cpsw. > looking at the tag_ksz.c in xmit function this is taken care of /* For Ingress (Host -> KSZ), 2 bytes are added before FCS. * --------------------------------------------------------------------------- * DA(6bytes)|SA(6bytes)|....|Data(nbytes)|tag0(1byte)|tag1(1byte)|FCS(4bytes) * --------------------------------------------------------------------------- * tag0 : Prioritization (not used now) * tag1 : each bit represents port (eg, 0x01=port1, 0x02=port2, 0x10=port5) * * For Egress (KSZ -> Host), 1 byte is added before FCS. * --------------------------------------------------------------------------- * DA(6bytes)|SA(6bytes)|....|Data(nbytes)|tag0(1byte)|FCS(4bytes) * --------------------------------------------------------------------------- * tag0 : zero-based value represents port * (eg, 0x00=port1, 0x02=port3, 0x06=port7) */ #define KSZ_INGRESS_TAG_LEN 2 #define KSZ_EGRESS_TAG_LEN 1 static struct sk_buff *ksz_xmit(struct sk_buff *skb, struct net_device *dev) { struct dsa_slave_priv *p = netdev_priv(dev); struct sk_buff *nskb; int padlen; u8 *tag; padlen = (skb->len >= ETH_ZLEN) ? 0 : ETH_ZLEN - skb->len; if (skb_tailroom(skb) >= padlen + KSZ_INGRESS_TAG_LEN) { /* Let dsa_slave_xmit() free skb */ if (__skb_put_padto(skb, skb->len + padlen, false)) return NULL; nskb = skb; } else { nskb = alloc_skb(NET_IP_ALIGN + skb->len + padlen + KSZ_INGRESS_TAG_LEN, GFP_ATOMIC); if (!nskb) return NULL; skb_reserve(nskb, NET_IP_ALIGN); skb_reset_mac_header(nskb); skb_set_network_header(nskb, skb_network_header(skb) - skb->head); skb_set_transport_header(nskb, skb_transport_header(skb) - skb->head); skb_copy_and_csum_dev(skb, skb_put(nskb, skb->len)); /* Let skb_put_padto() free nskb, and let dsa_slave_xmit() free * skb */ if (skb_put_padto(nskb, nskb->len + padlen)) return NULL; consume_skb(skb); } tag = skb_put(nskb, KSZ_INGRESS_TAG_LEN); tag[0] = 0; tag[1] = 1 << p->dp->index; /* destination port */ return nskb; } Cheers, --Prabhakar Lad
