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Date:   Wed, 14 Jul 2021 22:48:12 +0300
From:   Vladimir Oltean <olteanv@gmail.com>
To:     Lino Sanfilippo <LinoSanfilippo@gmx.de>
Cc:     woojung.huh@microchip.com, UNGLinuxDriver@microchip.com,
        andrew@lunn.ch, vivien.didelot@gmail.com, f.fainelli@gmail.com,
        davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] net: dsa: tag_ksz: dont let the hardware process the
 layer 4 checksum
Message-ID: <20210714194812.stay3oqyw3ogshhj@skbuf>
References: <20210714191723.31294-1-LinoSanfilippo@gmx.de>
 <20210714191723.31294-3-LinoSanfilippo@gmx.de>
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In-Reply-To: <20210714191723.31294-3-LinoSanfilippo@gmx.de>
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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@gmx.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.