netdev - Re: [PATCH] net: fec: remove HW IP header checksum for IPV6 frame

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Date:	Tue, 17 Jun 2014 17:31:21 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Fugang Duan <b38611@...escale.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH] net: fec: remove HW IP header checksum for IPV6 frame

On Tue, Jun 17, 2014 at 04:31:35PM +0800, Fugang Duan wrote:
> The commit 96c50caa5148 (net: fec: Enable IP header hardware checksum)
> enable HW IP header checksum for IPV4 and IPV6, which causes IPV6 TCP/UDP
> cannot work. (The issue is reported by Russell King)
> 
> The reason is that FEC HW IP cannot detect the transmit frame type (can
> detect received frame type), and treats all packets as IPv4, overwrites
> the point in the packet which would be the IPv4 checksum field. Since IPV6
> don't have IP header checksum, so this results in the frame being corrupted.
> 
> The patch just add software detect the current packet type, if it is IPV6
> frame, it don't enable IP header checksum.
> 
> Cc: Russell King <linux@....linux.org.uk>
> Signed-off-by: Fugang Duan <B38611@...escale.com>
> ---
>  drivers/net/ethernet/freescale/fec_main.c |   36 +++++++++++++++++++++-------
>  1 files changed, 27 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
> index 38d9d27..c13185a 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -320,6 +320,11 @@ static void *swap_buffer(void *bufaddr, int len)
>  	return bufaddr;
>  }
>  
> +static inline bool is_ipv4_pkt(struct sk_buff *skb)
> +{
> +	return skb->protocol == htons(ETH_P_IP) && ip_hdr(skb)->version == 4;
> +}
> +
>  static int
>  fec_enet_clear_csum(struct sk_buff *skb, struct net_device *ndev)
>  {
> @@ -330,7 +335,8 @@ fec_enet_clear_csum(struct sk_buff *skb, struct net_device *ndev)
>  	if (unlikely(skb_cow_head(skb, 0)))
>  		return -1;
>  
> -	ip_hdr(skb)->check = 0;
> +	if (is_ipv4_pkt(skb))
> +		ip_hdr(skb)->check = 0;
>  	*(__sum16 *)(skb->head + skb->csum_start + skb->csum_offset) = 0;
>  
>  	return 0;

As I suspected, just applying the above two hunks fixes the problem
I was seeing.

-- 
FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly
improving, and getting towards what was expected from it.
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