net: ethernet: ti: am65-cpsw: use napi_complete_done() in TX completion

This patch enables support for hard irqs deferral feature from Eric Dumazet
[1] for TI K3 CPSW driver by using napi_complete_done() in TX completion
path.

Depending on gro_flush_timeout and napi_defer_hard_irqs at gives up to 30%
CPU utilization reduction:

gro_flush_timeout=50000
napi_defer_hard_irqs=2

netperf -l 10 -H 192.168.1.1  -t UDP_STREAM -c -C -- -m 1470
MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.1.1 () port 0 AF_INET
Socket  Message  Elapsed      Messages                   CPU      Service
Size    Size     Time         Okay Errors   Throughput   Util     Demand
bytes   bytes    secs            #      #   10^6bits/sec % SS     us/KB

before:
212992    1470   10.00      809632      0      952.0     42.98    14.792
212992           10.00      809630             952.0     50.66    8.719

after:
212992    1470   10.00      813686      0      956.8     32.14    11.009
212992           10.00      813686             956.8     50.05    8.570

[1] https://lore.kernel.org/netdev/20200422161329.56026-1-edumazet@google.com/Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/ti/am65-cpsw-nuss.c

@@ -1086,13 +1086,13 @@ static int am65_cpsw_nuss_tx_poll(struct napi_struct *napi_tx, int budget)
 	else
 		num_tx = am65_cpsw_nuss_tx_compl_packets(tx_chn->common, tx_chn->id, budget);
 
-	num_tx = min(num_tx, budget);
-	if (num_tx < budget) {
-		napi_complete(napi_tx);
+	if (num_tx >= budget)
+		return budget;
+
+	if (napi_complete_done(napi_tx, num_tx))
 		enable_irq(tx_chn->irq);
-	}
 
-	return num_tx;
+	return 0;
 }
 
 static irqreturn_t am65_cpsw_nuss_rx_irq(int irq, void *dev_id)