Re: [PATCH net-next v2 3/4] net: macb: Add MQPRIO qdisc hardware offload support

["Théo Lebrun" <theo.lebrun@bootlin.com>]

Hello Vineeth,

On Wed Sep 9, 2026 at 4:20 PM CEST, Vineeth Karumanchi wrote:
> Add support for TC_SETUP_QDISC_MQPRIO hardware offload, allowing
> traffic class to queue mapping via the mqprio qdisc.
>
> Implement macb_setup_mqprio() which configures TC-to-queue mappings
> through netdev_set_num_tc() and netdev_set_tc_queue(), and resets
> them when num_tc is zero. The driver advertises TC_MQPRIO_HW_OFFLOAD_TCS
> offload level.
>
> Add macb_tc_query_caps() to report mqprio capabilities. Setting
> validate_queue_counts to true delegates queue count and overlap
> validation to the mqprio core via mqprio_validate_queue_counts(),
> avoiding redundant checks in the driver.
>
> Signed-off-by: Vineeth Karumanchi <vineeth.karumanchi@amd.com>
> ---
> Changes in v2:
> - No functional change; rebased on net-next, which renamed the
>   struct net_device pointer to "netdev" (was "dev"/"ndev").
>
>  drivers/net/ethernet/cadence/macb_main.c | 59 ++++++++++++++++++++++++
>  1 file changed, 59 insertions(+)
>
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index ff7e02d3fab8..67150ff03066 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -4492,6 +4492,60 @@ static int macb_setup_taprio(struct net_device *netdev,
>  	return err;
>  }
>  
> +static int macb_setup_mqprio(struct net_device *netdev,
> +			     struct tc_mqprio_qopt_offload *mqprio)
> +{
> +	struct tc_mqprio_qopt *qopt = &mqprio->qopt;
> +	u8 num_tc = qopt->num_tc;
> +	int err;
> +	u8 i;
> +
> +	/* Handle reset case early */
> +	if (!num_tc) {
> +		netdev_reset_tc(netdev);
> +		return 0;
> +	}
> +
> +	/* Configure traffic classes */
> +	qopt->hw = TC_MQPRIO_HW_OFFLOAD_TCS;
> +
> +	err = netdev_set_num_tc(netdev, num_tc);
> +	if (err)
> +		return err;
> +
> +	for (i = 0; i < num_tc; i++) {
> +		err = netdev_set_tc_queue(netdev, i, qopt->count[i],
> +					  qopt->offset[i]);
> +		if (err)
> +			goto err_reset_tc;
> +
> +		netdev_dbg(netdev, "MQPRIO: TC%d -> queue %u (count=%u)\n",
> +			   i, qopt->offset[i], qopt->count[i]);
> +	}

MACB queue N is always higher priority than queue M if N > M. Here we
should refuse the setup if mqprio->qopt->offset[i] isn't sorted no?

I asked an LLM and it found a precedent in igc:
igc_tsn_is_tc_to_queue_priority_ordered()
https://elixir.bootlin.com/linux/v7.2.5/source/drivers/net/ethernet/intel/igc/igc_main.c#L6797-L6801

> +
> +	return 0;
> +
> +err_reset_tc:
> +	netdev_reset_tc(netdev);
> +	return err;
> +}

Thanks,

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com