From: David Miller <davem@davemloft.net>
To: alexei.starovoitov@gmail.com
Cc: therbert@google.com, Yuval.Mintz@qlogic.com, netdev@vger.kernel.org
Subject: Re: How exactly does CHECKSUM_COMPLETE works?
Date: Tue, 30 Sep 2014 14:48:19 -0400 (EDT) [thread overview]
Message-ID: <20140930.144819.890888642079982128.davem@davemloft.net> (raw)
In-Reply-To: <CAADnVQLxX4LGFfqd6x+krfEMB57y_o80xW_3brkPvEJueDNWVg@mail.gmail.com>
From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date: Tue, 30 Sep 2014 09:58:32 -0700
> On Tue, Sep 30, 2014 at 7:59 AM, Tom Herbert <therbert@google.com> wrote:
>>
>>> So, to summarize my questions -
>>> 1. What should a driver set as the SKBs csum value when passing CHECKSUM_COMPLETE?
>>
>> This ones complete checksum of the Ethernet payload (start of IP
>> header to the end of the packet).
>
> I think it's confusing to describe CHECKSUM_COMPLETE this way.
> It is such only because driver pulls eth header before passing skb to stack.
> CHECKSUM_COMPLETE should cover the whole packet. If there are multiple
> vlan headers in front of IP they should be part of csum, since not all
> drivers may
> have hw offloading for vlan. The most simplistic HW would compute csum over
> the whole packet including eth header and driver will do
> eth_type_trans+skb_postpull_rcsum
The sungem computes the checksum over the entire frame. Here are the relevant
parts from the programmer's manual:
RX Descriptor Fields
...
TCP Pseudo-Checksum - Contains the 16-bit TCP checksum calculated over
the entire frame, starting at an offset programmable in the RX
Configuration Register.
In the gengem driver this is the RXDMA_CFG_CSUMOFF field of the RXDMA_CFG
register.
The driver seems to set this to the size of the ethernet header, which has
the problems you mention.
next prev parent reply other threads:[~2014-09-30 18:48 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-30 12:51 How exactly does CHECKSUM_COMPLETE works? Yuval Mintz
2014-09-30 14:59 ` Tom Herbert
2014-09-30 16:58 ` Alexei Starovoitov
2014-09-30 18:48 ` David Miller [this message]
2014-09-30 19:05 ` Yuval Mintz
2014-09-30 19:22 ` Eric Dumazet
2014-09-30 19:37 ` Eric Dumazet
2014-09-30 20:14 ` David Miller
2014-10-01 5:12 ` [PATCH net-next] ipv4: mentions skb_gro_postpull_rcsum() in inet_gro_receive() Eric Dumazet
2014-10-01 17:44 ` David Miller
2014-09-30 20:19 ` How exactly does CHECKSUM_COMPLETE works? Yuval Mintz
2014-09-30 20:32 ` Yuval Mintz
2014-10-01 5:15 ` Tom Herbert
2014-10-01 5:17 ` Yuval Mintz
2014-10-01 5:25 ` David Miller
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