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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , linux-ppp@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Felix Fietkau Subject: [RFC PATCH net-next v2] ppp: enable TX scatter-gather Date: Tue, 9 Sep 2025 09:27:42 +0800 Message-ID: <20250909012742.424771-1-dqfext@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" When chan->direct_xmit is true, and no compressors are in use, PPP prepends its header to a skb, and calls dev_queue_xmit directly. In this mode the skb does not need to be linearized. Enable NETIF_F_SG and NETIF_F_FRAGLIST, and add .ndo_fix_features() callback to conditionally disable them if a linear skb is required. This is required to support PPPoE GSO. Signed-off-by: Qingfang Deng --- RFC v2: Dynamically update netdev features with ndo_fix_features() callback. Link to RFC v1: https://lore.kernel.org/netdev/20250904021328.24329-1-dqfe= xt@gmail.com/ drivers/net/ppp/ppp_generic.c | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c index f9f0f16c41d1..22e17f8fb61f 100644 --- a/drivers/net/ppp/ppp_generic.c +++ b/drivers/net/ppp/ppp_generic.c @@ -835,6 +835,10 @@ static long ppp_ioctl(struct file *file, unsigned int = cmd, unsigned long arg) ppp_unlock(ppp); if (cflags & SC_CCP_OPEN) ppp_ccp_closed(ppp); + + rtnl_lock(); + netdev_update_features(ppp->dev); + rtnl_unlock(); err =3D 0; break; =20 @@ -1545,6 +1549,22 @@ ppp_get_stats64(struct net_device *dev, struct rtnl_= link_stats64 *stats64) dev_fetch_sw_netstats(stats64, dev->tstats); } =20 +static netdev_features_t +ppp_fix_features(struct net_device *dev, netdev_features_t features) +{ + struct ppp *ppp =3D netdev_priv(dev); + + ppp_lock(ppp); + /* Allow SG/FRAGLIST only when we have direct-xmit, and no compression + * path that wants a linear skb. + */ + if (!(dev->priv_flags & IFF_NO_QUEUE) || + (ppp->flags & (SC_COMP_TCP | SC_CCP_OPEN | SC_CCP_UP))) + features &=3D ~(NETIF_F_SG | NETIF_F_FRAGLIST); + ppp_unlock(ppp); + return features; +} + static int ppp_dev_init(struct net_device *dev) { struct ppp *ppp; @@ -1619,6 +1639,7 @@ static const struct net_device_ops ppp_netdev_ops =3D= { .ndo_start_xmit =3D ppp_start_xmit, .ndo_siocdevprivate =3D ppp_net_siocdevprivate, .ndo_get_stats64 =3D ppp_get_stats64, + .ndo_fix_features =3D ppp_fix_features, .ndo_fill_forward_path =3D ppp_fill_forward_path, }; =20 @@ -1641,6 +1662,8 @@ static void ppp_setup(struct net_device *dev) dev->flags =3D IFF_POINTOPOINT | IFF_NOARP | IFF_MULTICAST; dev->priv_destructor =3D ppp_dev_priv_destructor; dev->pcpu_stat_type =3D NETDEV_PCPU_STAT_TSTATS; + dev->hw_features =3D NETIF_F_SG | NETIF_F_FRAGLIST; + dev->features =3D dev->hw_features; netif_keep_dst(dev); } =20 @@ -3537,6 +3560,12 @@ ppp_connect_channel(struct channel *pch, int unit) spin_unlock(&pch->upl); out: mutex_unlock(&pn->all_ppp_mutex); + if (ret =3D=3D 0) { + rtnl_lock(); + netdev_update_features(ppp->dev); + rtnl_unlock(); + } + return ret; } =20 --=20 2.43.0