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    SubjectRe: [PATCH net-next v2 4/7] net: dsa: vsc73xx: Add dsa tagging based on 8021q
    + Dan Carpenter

    On Sun, Jun 25, 2023 at 01:53:39PM +0200, Pawel Dembicki wrote:
    > This patch is simple implementation of 8021q tagging in vsc73xx driver.
    > At this moment devices with DSA_TAG_PROTO_NONE are useless. VSC73XX
    > family doesn't provide any tag support for external ethernet ports.
    >
    > The only way is vlan-based tagging. It require constant hardware vlan
    > filtering. VSC73XX family support provider bridging but QinQ only without
    > fully implemented 802.1AD. It allow only doubled 0x8100 TPID.
    >
    > In simple port mode QinQ is enabled to preserve forwarding vlan tagged
    > frames.
    >
    > Tag driver introduce most simple funcionality required for proper taging
    > support.
    >
    > Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
    > Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>

    ...

    > +static void vsc73xx_vlan_rcv(struct sk_buff *skb, int *source_port,
    > + int *switch_id, int *vbid, u16 *vid)
    > +{
    > + if (vid_is_dsa_8021q(skb_vlan_tag_get(skb) & VLAN_VID_MASK))
    > + return dsa_8021q_rcv(skb, source_port, switch_id, vbid);
    > +
    > + /* Try our best with imprecise RX */
    > + *vid = skb_vlan_tag_get(skb) & VLAN_VID_MASK;
    > +}
    > +
    > +static struct sk_buff *vsc73xx_rcv(struct sk_buff *skb,
    > + struct net_device *netdev)
    > +{
    > + int src_port = -1, switch_id = -1, vbid = -1;
    > + u16 vid;
    > +
    > + if (skb_vlan_tag_present(skb))
    > + /* Normal traffic path. */
    > + vsc73xx_vlan_rcv(skb, &src_port, &switch_id, &vbid, &vid);
    > +
    > + if (vbid >= 1)
    > + skb->dev = dsa_tag_8021q_find_port_by_vbid(netdev, vbid);
    > + else if (src_port == -1 || switch_id == -1)
    > + skb->dev = dsa_find_designated_bridge_port_by_vid(netdev, vid);

    Hi Pawel,

    Smatch warns that vid may be used uninitialised here.
    And it's not clear to me why that cannot be the case.

    > + else
    > + skb->dev = dsa_master_find_slave(netdev, switch_id, src_port);
    > + if (!skb->dev) {
    > + netdev_warn(netdev, "Couldn't decode source port\n");
    > + return NULL;
    > + }
    > +
    > + dsa_default_offload_fwd_mark(skb);
    > +
    > + if (dsa_port_is_vlan_filtering(dsa_slave_to_port(skb->dev)) &&
    > + eth_hdr(skb)->h_proto == htons(ETH_P_8021Q))
    > + __vlan_hwaccel_clear_tag(skb);
    > +
    > + return skb;
    > +}

    ...

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