netdev - Re: [PATCH net-next v3 1/1] net: fec: Enable imx6 enet checksum acceleration.

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Date:	Thu, 18 Apr 2013 18:07:32 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Jim Baxter <jim_baxter@...tor.com>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Frank Li <Frank.Li@...escale.com>,
	Fugang Duan <B38611@...escale.com>, <netdev@...r.kernel.org>,
	Fabio Estevam <festevam@...il.com>,
	Francois Romieu <romieu@...zoreil.com>
Subject: Re: [PATCH net-next v3 1/1] net: fec: Enable imx6 enet checksum
 acceleration.

On Thu, 2013-04-18 at 17:16 +0100, Ben Hutchings wrote:
[...]
> But you don't actually need to check protocol numbers at all, as the
> kernel already specifies where the checksum should be.
> 
> So I think this function should look like:
> {
> 	if (skb->ip_summed != CHECKSUM_PARTIAL)
> 		return 0;
> 
> 	if (unlikely(skb_cow_head(skb, 0)))
> 		return -1;
> 
> 	*(__sum16 *)(skb->head + skb->csum_start + skb->csum_offset) = 0;
> 	return 0;
> }
> 
> The caller needs to check for the failure, and free the skb
> (kfree_skb()) rather than transmitting it.

Oh, presumably you still need to clear the IPv4 header checksum as well.
But it might be better to enable only TCP/UDP checksumming, because
Linux always calculates the IPv4 header checksum in software.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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