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

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Message-ID: <trinity-3bd0a864-e313-4403-8f8b-46fa344c80a4-1626356052833@3c-app-gmx-bap31>
Date:   Thu, 15 Jul 2021 15:34:12 +0200
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>, woojung.huh@...rochip.com,
        UNGLinuxDriver@...rochip.com, vivien.didelot@...il.com,
        f.fainelli@...il.com, davem@...emloft.net, kuba@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Aw: Re: [PATCH 2/2] net: dsa: tag_ksz: dont let the hardware
 process the layer 4 checksum


> Gesendet: Donnerstag, 15. Juli 2021 um 15:12 Uhr
> Von: "Vladimir Oltean" <olteanv@...il.com>
> An: "Lino Sanfilippo" <LinoSanfilippo@....de>
> Cc: "Andrew Lunn" <andrew@...n.ch>, woojung.huh@...rochip.com, UNGLinuxDriver@...rochip.com, vivien.didelot@...il.com, f.fainelli@...il.com, davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
> Betreff: Re: [PATCH 2/2] net: dsa: tag_ksz: dont let the hardware process the layer 4 checksum
>
> On Thu, Jul 15, 2021 at 03:04:31PM +0200, Lino Sanfilippo wrote:
> > Please note that skb_put() asserts that the SKB is linearized. So I think we
> > should rather clear both NETIF_F_FRAGLIST and NETIF_F_SG unconditionally since also
> > header taggers use some form of skb_put() dont they?
>
> The tail taggers use skb_put() as part of the routine to make room for
> the tail tag.
>
> Some of the header taggers use __skb_put_padto() when the packets are
> too small (under ETH_ZLEN). When they are so small they are definitely
> linear already.
>
> We don't have a third form/use of skb_put().
>

Ah ok, I see. Then it should be fine do clear both flags only in case of
tail taggers.

Regards,
Lino