net: ravb: Enable SW IRQ Coalescing for GbEth

Software IRQ Coalescing is required to improve network stack performance
in the RZ/G2L SoC family and the RZ/G3S SoC, i.e. the SoCs which use the
GbEth IP.

This patch gives the following improvements during testing with iperf3:

  * RZ/G2L:
    * TCP RX: same bandwidth with -6% CPU load (76% -> 71%)
    * UDP RX: same bandwidth with -10% CPU load (99% -> 89%)

  * RZ/G2UL:
    * UDP RX: +4200% bandwidth (1.23Mbps -> 53Mbps)

  * RZ/G3S:
    * UDP RX: +425% bandwidth (1.23Mbps -> 6.46Mbps)

The improvement of UDP RX bandwidth for the single core SoCs (RZ/G2UL &
RZ/G3S) is particularly critical.

Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/ethernet/renesas/ravb.h

@@ -1054,6 +1054,7 @@ struct ravb_hw_info {
 	u32 rx_max_desc_use;
 	u32 rx_desc_size;
 	unsigned aligned_tx: 1;
+	unsigned coalesce_irqs:1;	/* Needs software IRQ coalescing */
 
 	/* hardware features */
 	unsigned internal_delay:1;	/* AVB-DMAC has internal delays */

drivers/net/ethernet/renesas/ravb_main.c

@@ -2667,6 +2667,7 @@ static const struct ravb_hw_info gbeth_hw_info = {
 	.rx_max_desc_use = 4080,
 	.rx_desc_size = sizeof(struct ravb_rx_desc),
 	.aligned_tx = 1,
+	.coalesce_irqs = 1,
 	.tx_counters = 1,
 	.carrier_counters = 1,
 	.half_duplex = 1,
@@ -2943,6 +2944,9 @@ static int ravb_probe(struct platform_device *pdev)
 	if (info->nc_queues)
 		netif_napi_add(ndev, &priv->napi[RAVB_NC], ravb_poll);
 
+	if (info->coalesce_irqs)
+		netdev_sw_irq_coalesce_default_on(ndev);
+
 	/* Network device register */
 	error = register_netdev(ndev);
 	if (error)