On 12/10/2018 09:04 PM, tristram...@microchip.com wrote: >>>>>> - padlen = (skb->len >= ETH_ZLEN) ? 0 : ETH_ZLEN - skb->len; >>>>>> + padlen = (skb->len >= VLAN_ETH_ZLEN) ? 0 : VLAN_ETH_ZLEN - skb- >>>>>>> len; >>> Oh so they add the internal VLAN at the end of the frame, not the >>> beginning? That is quite surprising but that would not be the one single >>> oddity found with CPSW I am afraid.. The way I would approach this is >>> with layering where the padding needs to occur: >>> >>> - within the tag driver you need to make sure there is enough room to >>> insert the KSZ tag >>> >>> - within the ethernet MAC driver (which comes last in the transmit >>> path), you need to make sure there is enough room to insert that trailer >>> VLAN tag to permit internal transmission >> >> So you think this is a bug in the CPSW instead ? >> > > I think what causes this problem. In the MAC controller driver cpsw.c > the buffer is always padded to CPSW_MIN_PACKET_SIZE. Normally that > size is 60 bytes, but after Linux 4.14 kernel it was changed to VLAN_ETH_ZLEN. > The original size should work, but I do not know why it was changed. It seems > there is a new function using the CPSW_RX_VLAN_ENCAP bit. > > It is similar to what I experienced with the Atmel MAC driver. The newer > kernels > added some changes that introduced a bug and broke the tail tagging code. I > had > to submit a fix to the MAC driver to correct that. > > I do not think this patch should apply generally, but I do not know how to > fix the > MAC driver to work in all cases. > > You can try temporarily to change CPSW_MIN_PACKET_SIZE back to 60. > > It is only used to assign to min_packet_size. It may be possible to use a > different > size like 60 instead of 64 in the skb_padto function.
I am not looking for a hack-around, I am looking for a proper solution. -- Best regards, Marek Vasut
