Re: [PATCH net-next v19 06/10] net: dsa: tag_mtk: add Airoha variant usage of this TAG

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Introducing DSA_TAG_PROTO_AIROHA breaks DSA hardware offloading and tag processing in compatible Ethernet MAC drivers (Airoha and Mediatek).
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--- Patch [6]: [PATCH net-next v19 06/10] net: dsa: tag_mtk: add Airoha variant usage of this TAG ---
commit 2b8fd23ca8ea6ac3597ff1360a2ad1a9a14fa563
Author: Christian Marangi <[email protected]>

net: dsa: tag_mtk: add Airoha variant usage of this TAG

This commit introduces a new DSA tag protocol variant for Airoha switches,
documenting differences from the Mediatek tag bitmap. It also adds a
dedicated config, makefile entry, and "airoha" name for external tools
like libpcap.

> diff --git a/include/net/dsa.h b/include/net/dsa.h
> index 8c16ef23cc102..9957443e2907f 100644
> --- a/include/net/dsa.h
> +++ b/include/net/dsa.h
> @@ -73,6 +74,7 @@ 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]
Will this new tag protocol break hardware offloading and tag processing in
the Ethernet MAC drivers?

Looking at airoha_get_dsa_tag() in drivers/net/ethernet/airoha/airoha_eth.c, 
the driver requires DSA_TAG_PROTO_MTK to extract the tag into the DMA 
descriptor:

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

For DSA_TAG_PROTO_AIROHA, this fails and leaves the tag in the packet 
payload, which can break the PPE module that expects untagged packets.

Similarly, the Mediatek Ethernet driver checks strictly for DSA_TAG_PROTO_MTK
in mtk_uses_dsa() (mtk_eth_soc.c), __mtk_ppe_check_skb() (mtk_ppe.c), and
mtk_flow_get_dsa_port() (mtk_ppe_offload.c). Without DSA_TAG_PROTO_MTK,
hardware DSA untagging and PPE offloading will silently fail.

Do these host Ethernet drivers need to be updated to accept 
DSA_TAG_PROTO_AIROHA alongside DSA_TAG_PROTO_MTK?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=6