Re: [RFC net-next 3/5] net: dsa: mv88e6xxx: MQPRIO support

[Luke Howard <lukeh@padl.com>]

Hi Andrew,

> On 28 Sep 2025, at 04:14, Luke Howard <lukeh@padl.com> wrote:
> 
> I guess we need a new attribute or flag when adding a MDB or FDB entry, and also a way to indicate that a TC is SRP-managed. The kernel bridge could then be modified to reject or reclassify packets that are classified into a TC with the SRP flag set, unless a MDB/FDB entry exists for the DA that also has that flag set.

I have looked into this once more (disclosure: this time, LLM-aided).

* adding a MDB entry can now take a nested MDBE_ATTR_FLAGS attribute; the only one defined is MDB_FLAGS_STREAM_RESERVED
* this is propagated to MDB_PG_FLAGS_STREAM_RESERVED in br_mdb_config’s pg_flags
* MDB_PG_FLAGS_STREAM_RESERVED is propagated, in turn, to SWITCHDEV_MDB_F_STREAM_RESERVED

I intentionally avoided FDB entries as they’re not typically used in AVB/TSN, and this would have involved more intrusive API changes (port_fdb_add takes just the address/VID as distinct parameters).

If mv88e6xxx_port_mdb_add() is called with SWITCHDEV_MDB_F_STREAM_RESERVED set, it adds the ATU entry as MV88E6XXX_G1_ATU_DATA_STATE_MC_STATIC_AVB_NRL instead of MV88E6XXX_G1_ATU_DATA_STATE_MC_STATIC. For a given destination MAC, the AVB_NRL state must match across ports (otherwise -EINVAL is returned).

For the software bridge, if a frame arrives with PCP 3 or 2 (Class A/B traffic per IEEE 802.1Q-2018 Annex L) and the destination MDB entry has at least one port group marked STREAM_RESERVED, the unflagged port groups are skipped and router ports are suppressed. MDB entries with no flagged port groups follow the existing br_multicast_flood() path unchanged. The PCP set is hard-coded for now as an example and probably needs a configuration knob.

Cheers,
Luke