Re: [PATCH net 4/4] net: ti: icssg: Fix XSK zero copy TX during application wakeup

[Meghana Malladi]

Hi Jakub,

On 6/16/26 04:51, Jakub Kicinski wrote:
> On Fri, 12 Jun 2026 00:27:44 +0530 Meghana Malladi wrote:
> > @@ -169,9 +169,6 @@ static int emac_xsk_xmit_zc(struct prueth_emac *emac,
> >   
> >   		num_tx++;
> >   	}
> > -
> > -	xsk_tx_release(tx_chn->xsk_pool);
> > -	return num_tx;
>
> Why are you deleting this?

xsk_sendmsg() also calls this without an rcu-lock when transmitting the 
packets if the xmit was successful, so I was assuming it is not required 
and I removed this.

> >   }
> >   
> >   void prueth_xmit_free(struct prueth_tx_chn *tx_chn,
> > @@ -279,9 +276,6 @@ int emac_tx_complete_packets(struct prueth_emac *emac, int chn,
> >   		num_tx++;
> >   	}
> >   
> > -	if (!num_tx)
> > -		return 0;
>
> Does something prevent us from running all this code if budget is 0?
> If budget is 0 we can complete normal Tx with skbs but we must
> not touch any AF-XDP related state.

Can you elaborate more, I couldn't interpret your comment here

> >   	netif_txq = netdev_get_tx_queue(ndev, chn);
> >   	netdev_tx_completed_queue(netif_txq, num_tx, total_bytes);
> >   
> > @@ -306,7 +300,9 @@ int emac_tx_complete_packets(struct prueth_emac *emac, int chn,
> >   
> >   		netif_txq = netdev_get_tx_queue(ndev, chn);
> >   		txq_trans_cond_update(netif_txq);
>
> This looks misplaced, now we will hit it even if we didn't complete
> or submit any Tx.

This code needs to be hit for packet transmission in zero copy mode.
emac_xsk_xmit_zc() submits the packets to the DMA in NAPI context,
when application wakes up the driver and triggers NAPI. Once DMA 
transfer is done, irq gets triggered NAPI gets called which will handle 
the tx packet completion + submit next Tx batch packets to the DMA.

if (tx_chn->xsk_pool) -> check ensure this hits and runs for zero copy 
only. Also above check (!num_tx) returns early during the application 
wakeup (where budget is zero), hence it is removed.

> > +		__netif_tx_lock(netif_txq, smp_processor_id());
> >   		emac_xsk_xmit_zc(emac, chn);
> > +		__netif_tx_unlock(netif_txq);
> >   	}