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

[Karumanchi, Vineeth]

Hi Théo,

On 9/17/2026 2:52 PM, Théo Lebrun wrote:
> 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@xxxxxxx>
>> ---
>> 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?
> 

yes, thanks for pointing it out.
I will fix in next version.

Thanks,
> 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
> 

-- 
🙏 Vineeth