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From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH 01/10] ftgmac100: Upgrade to NETIF_F_HW_CSUM
Date: Tue, 11 Apr 2017 20:03:47 -0400 (EDT)
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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Wed, 12 Apr 2017 09:36:05 +1000

> I should call the helper when I don't recognize the protocol type in
> the IP header, not just when the main skb protocol type is not IP.

That's correct.

> BTW. I'm not too familiar with how encapsulation works these days. I
> wouldn't throw at that HW anything other than unencapsulated packets
> for HW checksumming. Is checking skb->protocol to be IP and
> ip_hdr(skb)->protocol to be IP, UDP or TCP enough ? IE. Will the latter
> especially return the outer header ?

If skb->protocol is IP then yes ip_hdr() will point at the outermost
header.