net: ena: Advertise TX push support

LLQ is auto enabled by the device and disabling it isn't supported on
new ENA generations while on old ones causes sub-optimal performance.

This patch adds advertisement of push-mode when LLQ mode is used, but
rejects an attempt to modify it.
Reviewed-by: Michal Kubiak <michal.kubiak@intel.com>
Signed-off-by: Shay Agroskin <shayagr@amazon.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/amazon/ena/ena_ethtool.c

@@ -479,12 +479,14 @@ static void ena_get_ringparam(struct net_device *netdev,
 	if (adapter->ena_dev->tx_mem_queue_type == ENA_ADMIN_PLACEMENT_POLICY_DEV) {
 		bool large_llq_supported = adapter->large_llq_header_supported;
 
+		kernel_ring->tx_push = true;
 		kernel_ring->tx_push_buf_len = adapter->ena_dev->tx_max_header_size;
 		if (large_llq_supported)
 			kernel_ring->tx_push_buf_max_len = ENA_LLQ_LARGE_HEADER;
 		else
 			kernel_ring->tx_push_buf_max_len = ENA_LLQ_HEADER;
 	} else {
+		kernel_ring->tx_push = false;
 		kernel_ring->tx_push_buf_max_len = 0;
 		kernel_ring->tx_push_buf_len = 0;
 	}
@@ -516,6 +518,12 @@ static int ena_set_ringparam(struct net_device *netdev,
 	/* This value is ignored if LLQ is not supported */
 	new_tx_push_buf_len = adapter->ena_dev->tx_max_header_size;
 
+	if ((adapter->ena_dev->tx_mem_queue_type == ENA_ADMIN_PLACEMENT_POLICY_DEV) !=
+	    kernel_ring->tx_push) {
+		NL_SET_ERR_MSG_MOD(extack, "Push mode state cannot be modified");
+		return -EINVAL;
+	}
+
 	/* Validate that the push buffer is supported on the underlying device */
 	if (kernel_ring->tx_push_buf_len) {
 		enum ena_admin_placement_policy_type placement;
@@ -957,7 +965,8 @@ static int ena_set_tunable(struct net_device *netdev,
 static const struct ethtool_ops ena_ethtool_ops = {
 	.supported_coalesce_params = ETHTOOL_COALESCE_USECS |
 				     ETHTOOL_COALESCE_USE_ADAPTIVE_RX,
-	.supported_ring_params	= ETHTOOL_RING_USE_TX_PUSH_BUF_LEN,
+	.supported_ring_params	= ETHTOOL_RING_USE_TX_PUSH_BUF_LEN |
+				  ETHTOOL_RING_USE_TX_PUSH,
 	.get_link_ksettings	= ena_get_link_ksettings,
 	.get_drvinfo		= ena_get_drvinfo,
 	.get_msglevel		= ena_get_msglevel,