netdev - Re: [PATCH 2/2] net: dsa: tag_ksz: dont let the hardware process the layer 4 checksum

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Message-ID: <20210714194812.stay3oqyw3ogshhj@skbuf>
Date:   Wed, 14 Jul 2021 22:48:12 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
Cc:     woojung.huh@...rochip.com, UNGLinuxDriver@...rochip.com,
        andrew@...n.ch, vivien.didelot@...il.com, f.fainelli@...il.com,
        davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] net: dsa: tag_ksz: dont let the hardware process the
 layer 4 checksum

Hi Lino,

On Wed, Jul 14, 2021 at 09:17:23PM +0200, Lino Sanfilippo wrote:
> If the checksum calculation is offloaded to the network device (e.g due to
> NETIF_F_HW_CSUM inherited from the DSA master device), the calculated
> layer 4 checksum is incorrect. This is since the DSA tag which is placed
> after the layer 4 data is seen as a part of the data portion and thus
> errorneously included into the checksum calculation.
> To avoid this, always calculate the layer 4 checksum in software.
> 
> Signed-off-by: Lino Sanfilippo <LinoSanfilippo@....de>
> ---

This needs to be solved more generically for all tail taggers. Let me
try out a few things tomorrow and come with a proposal.