Subject: Re: [PATCH iwl-next v2] igc: Add MQPRIO offload support

From: Simon Horman <[email-masked]>
Date: Thu, 28 Mar 2024 11:46:33 +0000

On Tue, Mar 26, 2024 at 02:34:54PM +0100, Kurt Kanzenbach wrote:
> Add support for offloading MQPRIO. The hardware has four priorities as well
> as four queues. Each queue must be a assigned with a unique priority.
> 
> However, the priorities are only considered in TSN Tx mode. There are two
> TSN Tx modes. In case of MQPRIO the Qbv capability is not required.
> Therefore, use the legacy TSN Tx mode, which performs strict priority
> arbitration.
> 
> Example for mqprio with hardware offload:
> 
> |tc qdisc replace dev ${INTERFACE} handle 100 parent root mqprio num_tc 4 \
> |   map 0 0 0 0 0 1 2 3 0 0 0 0 0 0 0 0 \
> |   queues 1@0 1@1 1@2 1@3 \
> |   hw 1
> 
> The mqprio Qdisc also allows to configure the `preemptible_tcs'. However,
> frame preemption is not supported yet.
> 
> Tested on Intel i225 and implemented by following data sheet section 7.5.2,
> Transmit Scheduling.
> 
> Signed-off-by: Kurt Kanzenbach <[email-masked]>

...

> diff --git a/drivers/net/ethernet/intel/igc/igc_defines.h b/drivers/net/ethernet/intel/igc/igc_defines.h
> index 5f92b3c7c3d4..73502a0b4df7 100644
> --- a/drivers/net/ethernet/intel/igc/igc_defines.h
> +++ b/drivers/net/ethernet/intel/igc/igc_defines.h
> @@ -547,6 +547,15 @@
>  
>  #define IGC_MAX_SR_QUEUES		2
>  
> +#define IGC_TXARB_TXQ_PRIO_0_SHIFT	0
> +#define IGC_TXARB_TXQ_PRIO_1_SHIFT	2
> +#define IGC_TXARB_TXQ_PRIO_2_SHIFT	4
> +#define IGC_TXARB_TXQ_PRIO_3_SHIFT	6
> +#define IGC_TXARB_TXQ_PRIO_0_MASK	GENMASK(1, 0)
> +#define IGC_TXARB_TXQ_PRIO_1_MASK	GENMASK(3, 2)
> +#define IGC_TXARB_TXQ_PRIO_2_MASK	GENMASK(5, 4)
> +#define IGC_TXARB_TXQ_PRIO_3_MASK	GENMASK(7, 6)
> +
>  /* Receive Checksum Control */
>  #define IGC_RXCSUM_CRCOFL	0x00000800   /* CRC32 offload enable */
>  #define IGC_RXCSUM_PCSD		0x00002000   /* packet checksum disabled */
> diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c

...

> diff --git a/drivers/net/ethernet/intel/igc/igc_tsn.c b/drivers/net/ethernet/intel/igc/igc_tsn.c

...

> @@ -106,7 +109,26 @@ static int igc_tsn_disable_offload(struct igc_adapter *adapter)
>  	wr32(IGC_QBVCYCLET_S, 0);
>  	wr32(IGC_QBVCYCLET, NSEC_PER_SEC);
>  
> +	/* Reset mqprio TC configuration. */
> +	netdev_reset_tc(adapter->netdev);
> +
> +	/* Restore the default Tx arbitration: Priority 0 has the highest
> +	 * priority and is assigned to queue 0 and so on and so forth.
> +	 */
> +	txarb = rd32(IGC_TXARB);
> +	txarb &= ~(IGC_TXARB_TXQ_PRIO_0_MASK |
> +		   IGC_TXARB_TXQ_PRIO_1_MASK |
> +		   IGC_TXARB_TXQ_PRIO_2_MASK |
> +		   IGC_TXARB_TXQ_PRIO_3_MASK);
> +
> +	txarb |= 0x00 << IGC_TXARB_TXQ_PRIO_0_SHIFT;
> +	txarb |= 0x01 << IGC_TXARB_TXQ_PRIO_1_SHIFT;
> +	txarb |= 0x02 << IGC_TXARB_TXQ_PRIO_2_SHIFT;
> +	txarb |= 0x03 << IGC_TXARB_TXQ_PRIO_3_SHIFT;
> +	wr32(IGC_TXARB, txarb);

Hi Kurt,

It looks like the above would be a good candidate for using FIELD_PREP,
in which case the _SHIFT #defines can likely be removed.

Also, the logic above seems to be replicated in igc_tsn_enable_offload.
Perhaps a helper is appropriate.

> +
>  	adapter->flags &= ~IGC_FLAG_TSN_QBV_ENABLED;
> +	adapter->flags &= ~IGC_FLAG_TSN_LEGACY_ENABLED;
>  
>  	return 0;
>  }
> @@ -123,6 +145,50 @@ static int igc_tsn_enable_offload(struct igc_adapter *adapter)
>  	wr32(IGC_DTXMXPKTSZ, IGC_DTXMXPKTSZ_TSN);
>  	wr32(IGC_TXPBS, IGC_TXPBSIZE_TSN);
>  
> +	if (adapter->strict_priority_enable) {
> +		u32 txarb;
> +		int err;
> +
> +		err = netdev_set_num_tc(adapter->netdev, adapter->num_tc);
> +		if (err)
> +			return err;
> +
> +		for (i = 0; i < adapter->num_tc; i++) {
> +			err = netdev_set_tc_queue(adapter->netdev, i, 1,
> +						  adapter->queue_per_tc[i]);
> +			if (err)
> +				return err;
> +		}
> +
> +		/* In case the card is configured with less than four queues. */
> +		for (; i < IGC_MAX_TX_QUEUES; i++)
> +			adapter->queue_per_tc[i] = i;
> +
> +		/* Configure queue priorities according to the user provided
> +		 * mapping.
> +		 */
> +		txarb = rd32(IGC_TXARB);
> +		txarb &= ~(IGC_TXARB_TXQ_PRIO_0_MASK |
> +			   IGC_TXARB_TXQ_PRIO_1_MASK |
> +			   IGC_TXARB_TXQ_PRIO_2_MASK |
> +			   IGC_TXARB_TXQ_PRIO_3_MASK);
> +		txarb |= adapter->queue_per_tc[3] << IGC_TXARB_TXQ_PRIO_0_SHIFT;
> +		txarb |= adapter->queue_per_tc[2] << IGC_TXARB_TXQ_PRIO_1_SHIFT;
> +		txarb |= adapter->queue_per_tc[1] << IGC_TXARB_TXQ_PRIO_2_SHIFT;
> +		txarb |= adapter->queue_per_tc[0] << IGC_TXARB_TXQ_PRIO_3_SHIFT;
> +		wr32(IGC_TXARB, txarb);
> +
> +		/* Enable legacy TSN mode which will do strict priority without
> +		 * any other TSN features.
> +		 */
> +		tqavctrl = rd32(IGC_TQAVCTRL);
> +		tqavctrl |= IGC_TQAVCTRL_TRANSMIT_MODE_TSN;
> +		tqavctrl &= ~IGC_TQAVCTRL_ENHANCED_QAV;
> +		wr32(IGC_TQAVCTRL, tqavctrl);
> +
> +		return 0;
> +	}
> +
>  	for (i = 0; i < adapter->num_tx_queues; i++) {
>  		struct igc_ring *ring = adapter->tx_ring[i];
>  		u32 txqctl = 0;

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