netdev - Re: [PATCH net-next v2] docs: net: dsa: describe issues with checksum offload

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Date:   Thu, 14 Apr 2022 15:22:12 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Kurt Kanzenbach <kurt@...utronix.de>
CC:     Luiz Angelo Daros de Luca <luizluca@...il.com>,
        George McCollister <george.mccollister@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "corbet@....net" <corbet@....net>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [PATCH net-next v2] docs: net: dsa: describe issues with checksum
 offload

On Thu, Apr 14, 2022 at 08:29:12AM +0200, Kurt Kanzenbach wrote:
> On Wed Apr 13 2022, Vladimir Oltean wrote:
> > I've copied a bunch of new people to this email.
> >
> > TL;DR: Kurt/George/Andrew, on your systems with hellcreek/xrs700x/mv88e6060,
> > does the DSA master declare any of the following features as "on"?
> >
> > ethtool -k eth0 | grep tx-checksum-ip
> 
> It's a Cyclone V with stmmac as master:
> 
> |root@tsn:~# ethtool -k eth0 | grep tx-checksum-ip
> |        tx-checksum-ipv4: on
> |        tx-checksum-ip-generic: off [fixed]
> |        tx-checksum-ipv6: on
> 
> >
> > I would expect not. Otherwise, we've either found a bug, or discovered
> > the Sasquatch.
> 
> Now, I'm wondering how this actually works. Anyway, I'll send a patch to
> add the missing skb_checksum_help().
> 
> Thanks,
> Kurt

Thanks, Kurt.

It works because stmmac declares NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM in
ndev->hw_features but not in ndev->vlan_features. Whereas DSA inherits
what it inherits from ndev->vlan_features.

It's good to fix this in hellcreek anyway.