virtio-net: initially change the value of tx-frames

Background:
1. Commit 0c465be1 ("virtio_net: ethtool tx napi configuration") uses
   tx-frames to toggle napi_tx (0 off and 1 on) if notification coalescing
   is not supported.
2. Commit 31c03aef ("virtio_net: enable napi_tx by default") enables
   napi_tx for all txqs by default.

Status:
When virtio-net supports notification coalescing, after initialization,
tx-frames is 0 and napi_tx is true.

Problem:
When the user only wants to set rx coalescing params using
           ethtool -C eth0 rx-usecs 10, or
	   ethtool -Q eth0 queue_mask 0x1 -C rx-usecs 10,
these cmds will carry tx-frames as 0, causing the napi_tx switching condition
is satisfied. Then the user gets:
           netlink error: Device or resource busy.

The same happens when trying to set rx-frames, adaptive_rx, adaptive_tx...

How to fix:
When notification coalescing feature is negotiated, initially make the
value of tx-frames to be consistent with napi_tx.

For compatibility with the past, it is still supported to use tx-frames
to toggle napi_tx.
Reported-by: Xiaoming Zhao <zxm377917@alibaba-inc.com>
Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -4442,13 +4442,6 @@ static int virtnet_probe(struct virtio_device *vdev)
 		dev->xdp_features |= NETDEV_XDP_ACT_RX_SG;
 	}
 
-	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_NOTF_COAL)) {
-		vi->intr_coal_rx.max_usecs = 0;
-		vi->intr_coal_tx.max_usecs = 0;
-		vi->intr_coal_tx.max_packets = 0;
-		vi->intr_coal_rx.max_packets = 0;
-	}
-
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_HASH_REPORT))
 		vi->has_rss_hash_report = true;
 
@@ -4523,6 +4516,27 @@ static int virtnet_probe(struct virtio_device *vdev)
 	if (err)
 		goto free;
 
+	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_NOTF_COAL)) {
+		vi->intr_coal_rx.max_usecs = 0;
+		vi->intr_coal_tx.max_usecs = 0;
+		vi->intr_coal_rx.max_packets = 0;
+
+		/* Keep the default values of the coalescing parameters
+		 * aligned with the default napi_tx state.
+		 */
+		if (vi->sq[0].napi.weight)
+			vi->intr_coal_tx.max_packets = 1;
+		else
+			vi->intr_coal_tx.max_packets = 0;
+	}
+
+	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL)) {
+		/* The reason is the same as VIRTIO_NET_F_NOTF_COAL. */
+		for (i = 0; i < vi->max_queue_pairs; i++)
+			if (vi->sq[i].napi.weight)
+				vi->sq[i].intr_coal.max_packets = 1;
+	}
+
 #ifdef CONFIG_SYSFS
 	if (vi->mergeable_rx_bufs)
 		dev->sysfs_rx_queue_group = &virtio_net_mrg_rx_group;