Re: [PATCH net-next] net: stmmac: add tc-ets qdisc offload

[Davide Caratti <dcaratti@redhat.com>]

On Tue, Aug 04, 2026 at 08:17:35PM +0200, Lorenzo Bianconi wrote:

[...]

> When all bands are strict priority, the MTL scheduler is programmed with
> SP scheduling; 

... and I replied too early _ sorry for the noise _ there is another small thing
w.r.t. SP scheduling:

> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
> @@ -1210,6 +1210,73 @@ static int tc_setup_etf(struct stmmac_priv *priv,
>  	return 0;
>  }
>  
> +static int tc_setup_sp_sched(struct stmmac_priv *priv)
> +{
> +	struct plat_stmmacenet_data *pdata = priv->plat;
> +	int i;
> +
> +	for (i = 0; i < pdata->tx_queues_to_use; i++)
> +		pdata->tx_queues_cfg[i].weight = 0;
> +	stmmac_set_tx_queue_weight(priv);
> +
> +	pdata->tx_sched_algorithm = MTL_TX_ALGORITHM_SP;
> +	stmmac_prog_mtl_tx_algorithms(priv, priv->hw,
> +				      pdata->tx_sched_algorithm);
> +
> +	return 0;
> +}

The above function configures the stmmac SP queues to a well-known state where all
queues are SP. However,

[...]

> +
> +static int tc_setup_ets_sched(struct stmmac_priv *priv,
> +			      struct tc_ets_qopt_offload *qopt)
> +{
> +	struct tc_ets_qopt_offload_replace_params *p = &qopt->replace_params;
> +	struct plat_stmmacenet_data *pdata = priv->plat;
> +	int i, nstrict = 0;
> +
> +	if (p->bands > priv->plat->tx_queues_to_use)
> +		return -EOPNOTSUPP;
> +
> +	for (i = 0; i < p->bands; i++) {
> +		if (!p->quanta[i])
> +			nstrict++;
> +	}
> +
> +	if (p->bands && nstrict)
> +		return -EOPNOTSUPP;
> +
> +	if (nstrict) {
> +		tc_setup_sp_sched(priv);

This is not necessarily what the user wants when setting up the ETS qdisc.
The driver should parse 'priomap' (like in [1] or [2]) so that only 'nstrict'
queues are involved, and selected based on the packet priority. Otherwise, the
offloaded ETS is going to behave very differently from its full-software
implementation _ which is something we probably want to avoid.

[1] https://elixir.bootlin.com/linux/v7.1.5/source/drivers/net/ethernet/microchip/lan966x/lan966x_ets.c#L36
[2] https://elixir.bootlin.com/linux/v7.1.5/source/drivers/net/ethernet/airoha/airoha_eth.c#L2281
	
WDYT? Any feedback appreciated!

-- 
davide