Re: [PATCH net-next v22 6/9] net: dsa: tag_mtk: add Airoha variant usage of this TAG

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] net: dsa: missing DSA_TAG_PROTO_AIROHA in eth drivers breaks offloads
--

commit aaecc61a677f69e71544a1c2a64947df3cc03f58
Author: Christian Marangi <ansuelsmth@gmail.com>

net: dsa: tag_mtk: add Airoha variant usage of this TAG
    
Add variant of the MTK TAG for Airoha Switch and comments about difference
between Airoha AN8855 and Mediatek tag bitmap.

> diff --git a/include/net/dsa.h b/include/net/dsa.h
> index 7507d632e7c6d..c5659e9ab6d35 100644
> --- a/include/net/dsa.h
> +++ b/include/net/dsa.h
> @@ -75,6 +76,7 @@ enum dsa_tag_protocol {
>  	DSA_TAG_PROTO_KSZ9893		= DSA_TAG_PROTO_KSZ9893_VALUE,
>  	DSA_TAG_PROTO_LAN9303		= DSA_TAG_PROTO_LAN9303_VALUE,
>  	DSA_TAG_PROTO_MTK		= DSA_TAG_PROTO_MTK_VALUE,
> +	DSA_TAG_PROTO_AIROHA		= DSA_TAG_PROTO_AIROHA_VALUE,

[Severity: High]
Does adding this new protocol break hardware offloads in the ethernet MAC
drivers?

The Mediatek and Airoha ethernet drivers explicitly check for
DSA_TAG_PROTO_MTK to enable hardware DSA tag extraction and PPE offloading.

For example, in airoha_get_dsa_tag() in
drivers/net/ethernet/airoha/airoha_eth.c:

    if (dev->dsa_ptr->tag_ops->proto != DSA_TAG_PROTO_MTK)
        return 0;

Because DSA_TAG_PROTO_AIROHA is not matched, the MAC drivers will skip DSA
tag extraction, leaving the tag in the payload. Will this cause the hardware
to miscalculate IP header offsets and break checksum offloads?

Similar checks exist in mtk_uses_dsa() in
drivers/net/ethernet/mediatek/mtk_eth_soc.c:

    return netdev_uses_dsa(dev) &&
           dev->dsa_ptr->tag_ops->proto == DSA_TAG_PROTO_MTK;

And in mtk_foe_entry_commit_subflow() in
drivers/net/ethernet/mediatek/mtk_ppe.c:

    if (!netdev_uses_dsa(skb->dev) ||
        skb->dev->dsa_ptr->tag_ops->proto != DSA_TAG_PROTO_MTK)
        goto out;

This could entirely disable PPE hardware offloading for the new Airoha switch
protocol. Should these drivers be updated to also match DSA_TAG_PROTO_AIROHA?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260915123812.14747-1-ansuelsmth@gmail.com?part=6