Re: [PATCH net 1/2] net: ethernet: ti: am65-cpsw-nuss: Update port_mask while adding multicast entry

[Siddharth Vadapalli <s-vadapalli@ti.com>]

On Thu, 2026-02-05 at 12:39 +0530, Chintan Vankar wrote:
> Multicast entry rules are mainly evaluated for receiving traffic and do not
> require MAC ports to be explicitly associated with them. However, setting
> associated MAC port's bit to the port_mask of the ALE entry ensures
> technical correctness and helps maintaining ALE entries linked to MAC
> ports.
> 
> Signed-off-by: Chintan Vankar <c-vankar@ti.com>
> ---
>  drivers/net/ethernet/ti/am65-cpsw-nuss.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/ti/am65-cpsw-nuss.c b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> index 5924db6be3fe..967918050433 100644
> --- a/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> +++ b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> @@ -391,7 +391,7 @@ static void am65_cpsw_nuss_ndo_slave_set_rx_mode(struct net_device *ndev)
>  	cpsw_ale_set_allmulti(common->ale,
>  			      ndev->flags & IFF_ALLMULTI, port->port_id);
>  
> -	port_mask = ALE_PORT_HOST;
> +	port_mask = BIT(port->port_id) | ALE_PORT_HOST;

Since the port_mask setup above is passed to 'cpsw_ale_flush_multicast()'
below, wouldn't it temporarily cause the forwarded multicast traffic to be
dropped?

>  	/* Clear all mcast from ALE */
>  	cpsw_ale_flush_multicast(common->ale, port_mask, -1);
> 
> 

The code in the driver following the above function call is:

	if (!netdev_mc_empty(ndev)) {
		struct netdev_hw_addr *ha;

		/* program multicast address list into ALE register */
		netdev_for_each_mc_addr(ha, ndev) {
			cpsw_ale_add_mcast(common->ale, ha->addr,
					   port_mask, 0, 0, 0);
		}
	}

So we do add back the multicast entries for the same 'port_mask' that we
removed earlier during cpsw_ale_flush_multicast(), but, there is a delay
between flushing the entries in cpsw_ale_flush_multicast() and adding them
back via cpsw_ale_add_mcast(). During that period, the multicast traffic on
the forwarding path between MAC Ports will be momentarily dropped. Please
clarify if that isn't the case.

Regards,
Siddharth.