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Subject: Re: [PATCH] Revert "net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are
 friends"
To:     Andreas Schwab <schwab@linux-m68k.org>,
        Eric Dumazet <eric.dumazet@gmail.com>
Cc:     Mathieu Malaterre <malat@debian.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Christophe LEROY <christophe.leroy@c-s.fr>,
        Meelis Roos <mroos@linux.ee>, netdev@vger.kernel.org,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
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From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <e1790720-911b-4d04-2215-752ec612e3d7@gmail.com>
Date:   Tue, 19 Jun 2018 13:10:55 -0700
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On 06/19/2018 12:10 PM, Andreas Schwab wrote:
> On Jun 18 2018, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> 
>> DUMP_PREFIX_ADDRESS might give us more information (say alignment problem, or crossing page boundaries)
> 
> DUMP_PREFIX_ADDRESS is useless for that purpose.
> 
> Here are some samples of broken csums:
> 
> [  853.849225] sungem: sungem wrong csum : 9886/07be, len 94 bytes, c0000001fa187e02
> [  853.849232] raw data: 00000000: 00 0d 93 43 81 62 18 d6 c7 51 b8 1c 08 00 45 10  ...C.b...Q....E.
> [  853.849235] raw data: 00000010: 00 4c cb a0 40 00 40 11 d9 97 c0 a8 0a 01 c0 a8  .L..@.@.........
> [  853.849237] raw data: 00000020: 0a 07 00 7b 00 7b 00 38 69 e1 1c 03 0c f7 00 00  ...{.{.8i.......
> [  853.849240] raw data: 00000030: 08 f0 00 00 15 f0 c0 35 67 67 de d3 ca c9 d9 5b  .......5gg.....[
> [  853.849242] raw data: 00000040: 1f ff de d3 d2 86 8f 67 fa f2 de d3 d2 86 8f 38  .......g.......8
> [  853.849244] raw data: 00000050: 2f ff de d3 d2 86 8f 3b ff ff d1 93 bc 50        /......;.....P

Thanks.

4 bytes in excess.

Might be the FCS, and it does not look like provided csum has a relation with it.

For some reason FCS stripping was disabled by :

commit 3e32011d4da6424b3bc65b1e1a047e30ac9882c7
Author: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date:   Mon May 19 09:39:11 2003 -0700

    [SUNGEM]: Updates from PowerPC people.
    
    Support more chips and split out all the complex PHY
    handling into a seperate file.


Since this NIC never had CHECKSUM_COMPLETE support (since we have to trim each skb,
thus were forcing ip_summed to CHECKSUM_NONE) we probably should remove it and be happy.

Unless you guys find a way to let the NIC strip the FCS, and double check the csum is a real csum ;)

diff --git a/drivers/net/ethernet/sun/sungem.c b/drivers/net/ethernet/sun/sungem.c
index 7a16d40a72d13cf1d522e8a3a396c826fe76f9b9..85439308375e95c3854e4a1561697d69ec85399b 100644
--- a/drivers/net/ethernet/sun/sungem.c
+++ b/drivers/net/ethernet/sun/sungem.c
@@ -760,7 +760,6 @@ static int gem_rx(struct gem *gp, int work_to_do)
        struct net_device *dev = gp->dev;
        int entry, drops, work_done = 0;
        u32 done;
-       __sum16 csum;
 
        if (netif_msg_rx_status(gp))
                printk(KERN_DEBUG "%s: rx interrupt, done: %d, rx_new: %d\n",
@@ -855,9 +854,6 @@ static int gem_rx(struct gem *gp, int work_to_do)
                        skb = copy_skb;
                }
 
-               csum = (__force __sum16)htons((status & RXDCTRL_TCPCSUM) ^ 0xffff);
-               skb->csum = csum_unfold(csum);
-               skb->ip_summed = CHECKSUM_COMPLETE;
                skb->protocol = eth_type_trans(skb, gp->dev);
 
                napi_gro_receive(&gp->napi, skb);