Hello! On 01/11/2019 06:48 PM, Simon Horman wrote:
>>>>> EtherAVB may provide a checksum of packet data appended to packet data. In >>>>> order to allow this checksum to be received by the host descriptor data >>>>> needs to be enlarged by 2 bytes to accommodate the checksum. >>>>> >>>>> In the case of MTU-sized packets without a VLAN tag the >>>>> checksum were already accommodated by virtue of the space reserved for the >>>>> VLAN tag. However, a packet of MTU-size with a VLAN tag consumed all >>>>> packet data space provided by a descriptor leaving no space for the >>>>> trailing checksum. >>>> >>>> Wait! The gen3 manual is rather clear about the auto-checksumming not >>>> working >>>> right in the presence of the VLAN tag. Where do you check for that case? >>> >>> In my testing on E3 this works correctly. Which portion of >>> the manual are you referring to? >> >> Section 50.4.1 in R-Car Series, 3rd Generation User’s Manual: Hardware, >> Rev 1.00, >> section 45A.3.14.1 in R-Car Series, 2nd Generation User’s Manual: Hardware, >> Rev 2.00. >> The problem is that the checksum is always calculated starting at byte >> 14, i.e. amidst the VLAN header (if present). > > Yes, I understand that. What I'm unclear on is why that is a problem. > Empirically I have observed that RX csum offload works in the presence > of a VLAN tag and offers a significant benefit in terms of reduced CPU > utilisation. OK, after having looked a the networking code, I agree there shouldn't be issues with VLAN packets. [...] MBR, Sergei
