From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jesse Brandeburg <jesse.brandeburg@intel.com>
Date: Tue, 2 Feb 2016 15:10:00 -0800
Subject: [Intel-wired-lan] [next PATCH v3 11/15] i40e/i40evf: Enable
 support for SKB_GSO_UDP_TUNNEL_CSUM
In-Reply-To: <20160202144924.0000795d@unknown>
References: <20160125050602.12004.38884.stgit@localhost.localdomain>
 <20160125051729.12004.54009.stgit@localhost.localdomain>
 <20160202144924.0000795d@unknown>
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To: intel-wired-lan@osuosl.org
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On Tue, 2 Feb 2016 14:49:24 -0800
Jesse Brandeburg <jesse.brandeburg@intel.com> wrote:

> On Sun, 24 Jan 2016 21:17:29 -0800
> Alexander Duyck <aduyck@mirantis.com> wrote:
> 
> > The XL722 has support for providing the outer UDP tunnel checksum on
> 
> X722, not XL722
> 
> > transmits.  Make use of this feature to support segmenting UDP tunnels with
> > outer checksums enabled.
> > 
> > Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
> > ---
> 
> ...
> 
> > +		if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_TUNNEL_CSUM) {
> > +			/* determine offset of outer transport header */
> > +			l4_offset = l4.hdr - skb->data;
> > +
> > +			/* remove payload length from outer checksum */
> > +			paylen = (__force u16)l4.udp->check;
> > +			paylen += ntohs(1) * (u16)~(skb->len - l4_offset);
> 
> Can we get a comment about how this is supposed to work?  Doesn't it
> have endian problems?  I understand these lines are removing the payload
> length from the checksum by getting the length of the payload,
> inverting it and removing it from the checksum, and then below,
> updating the checksum, but it is really hard to follow why you use
> ntohs(1) without some explanation.
> 
> > +			l4.udp->check = ~csum_fold((__force __wsum)paylen);
> > +		}
> > +
> 

And, isn't this patch missing the check that enables outer UDP only in
the case of X722?

I expected to see an i40e_main.c change to tell the stack we support
UDP_TUNNEL_CSUM only on X722.