Re: [PATCH v3 net-next 04/10] net: dsa: tag_ksz: add tag handling for Microchip LAN937x

Vladimir Oltean
2021-07-23T19:23:55Z

On Fri, Jul 23, 2021 at 11:01:02PM +0530, Prasanna Vengateshan wrote:
> --- a/net/dsa/tag_ksz.c
> +++ b/net/dsa/tag_ksz.c
> @@ -187,10 +187,66 @@ static const struct dsa_device_ops ksz9893_netdev_ops = {
> DSA_TAG_DRIVER(ksz9893_netdev_ops);
> MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_KSZ9893);
>
> +/* For xmit, 2 bytes are added before FCS.
> + * ---------------------------------------------------------------------------
> + * DA(6bytes)|SA(6bytes)|....|Data(nbytes)|tag0(1byte)|tag1(1byte)|FCS(4bytes)
> + * ---------------------------------------------------------------------------
> + * tag0 : represents tag override, lookup and valid
> + * tag1 : each bit represents port (eg, 0x01=port1, 0x02=port2, 0x80=port8)
> + *
> + * For rcv, 1 byte is added before FCS.
> + * ---------------------------------------------------------------------------
> + * DA(6bytes)|SA(6bytes)|....|Data(nbytes)|tag0(1byte)|FCS(4bytes)
> + * ---------------------------------------------------------------------------
> + * tag0 : zero-based value represents port
> + * (eg, 0x00=port1, 0x02=port3, 0x07=port8)
> + */
> +#define LAN937X_EGRESS_TAG_LEN 2
> +
> +#define LAN937X_TAIL_TAG_BLOCKING_OVERRIDE BIT(11)
> +#define LAN937X_TAIL_TAG_LOOKUP BIT(12)
> +#define LAN937X_TAIL_TAG_VALID BIT(13)
> +#define LAN937X_TAIL_TAG_PORT_MASK 7
> +
> +static struct sk_buff *lan937x_xmit(struct sk_buff *skb,
> + struct net_device *dev)
> +{
> + struct dsa_port *dp = dsa_slave_to_port(dev);
> + const struct ethhdr *hdr = eth_hdr(skb);
> + __be16 *tag;
> + u16 val;

There was a recent patch on net.git to fix an issue with DSA master
drivers which set NETIF_F_HW_CSUM in dev->vlan_features, which DSA
inherits.
https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=37120f23ac8998c250573ea3247ff77426551f69
Until we fix the issue at the DSA layer, could you also apply that fix
here please?

> +
> + tag = skb_put(skb, LAN937X_EGRESS_TAG_LEN);
> +
> + val = BIT(dp->index);
> +
> + if (is_link_local_ether_addr(hdr->h_dest))
> + val |= LAN937X_TAIL_TAG_BLOCKING_OVERRIDE;
> +
> + /* Tail tag valid bit - This bit should always be set by the CPU*/
> + val |= LAN937X_TAIL_TAG_VALID;

Please add an extra space here between "CPU" and the comment ending
delimiter.

> +
> + *tag = cpu_to_be16(val);

This probably works for the arch you are testing on, but it is better to
avoid unaligned accesses when the skb->len is odd:
https://www.kernel.org/doc/Documentation/unaligned-memory-access.txt

You can use put_unaligned_be16().

> +
> + return skb;
> +}