Hi Florian, On Fri, Aug 10, 2018 at 6:36 PM Florian Fainelli <f.faine...@gmail.com> wrote: > > On 08/10/2018 04:26 AM, Lad, Prabhakar wrote: > > 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. > > net/dsa/tag_brcm.c ended up doing the padding because that was a more > generic and central location: > > https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/tree/net/dsa/tag_brcm.c#n73 > > > > >> You probably need something similar for the cpsw. > >> > > looking at the tag_ksz.c in xmit function this is taken care of > > I agree, this should be padding packets correctly, can you still > instrument cpsw to make sure that what comes to its ndo_start_xmit() is > ETH_ZLEN + tag_len or more? > Yes I can confirm the skb->len is always >= 62 (ETH_ZLEN + 2)
Cheers, --Prabhakar
