Port configuration fails because offload flags don't match the expected
value when max-pkt-len is set to a value that should enable receive port
offloading but doesn't.

There are two cases to consider:

1. VIRTIO_NET_F_MTU is set. Then we need to check if the requested
   max-pkt-len fits into the MTU plus header. If yes we set the
   offload flag.
2. VIRTIO_NET_F_MTU is not set. We can set the offload flag.

Fixes: a4996bd89c42 ("ethdev: new Rx/Tx offloads API")
Cc: sta...@dpdk.org

Signed-off-by: Jens Freimann <jfreim...@redhat.com>
---
v3->v4:
 * make use of hw-max_mtu which is calculated during device init. This
   way we don't have to re-read the mtu from config space again. This
   is safe because hw->max_mtu is not changed after init.

v2->v3:
 * remove unnecessary brackets (Maxime)
 * fix commit message (David)

v1->v2:
 * include virtnet hdr, ethernet header, vlan tag when comparing against
   max-rx-pkt-len (Maxime)

 drivers/net/virtio/virtio_ethdev.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/net/virtio/virtio_ethdev.c 
b/drivers/net/virtio/virtio_ethdev.c
index 7c4c1df00..4cf91909d 100644
--- a/drivers/net/virtio/virtio_ethdev.c
+++ b/drivers/net/virtio/virtio_ethdev.c
@@ -2351,6 +2351,16 @@ virtio_dev_info_get(struct rte_eth_dev *dev, struct 
rte_eth_dev_info *dev_info)
        if ((host_features & tso_mask) == tso_mask)
                dev_info->rx_offload_capa |= DEV_RX_OFFLOAD_TCP_LRO;
 
+       if (host_features & (1ULL << VIRTIO_NET_F_MTU)) {
+               uint32_t ether_hdr_len = ETHER_HDR_LEN + VLAN_TAG_LEN +
+                       hw->vtnet_hdr_size;
+               if (dev->data->dev_conf.rxmode.max_rx_pkt_len <=
+                               hw->max_mtu + ether_hdr_len)
+                       dev_info->rx_offload_capa |= DEV_RX_OFFLOAD_JUMBO_FRAME;
+       } else {
+               dev_info->rx_offload_capa |= DEV_RX_OFFLOAD_JUMBO_FRAME;
+       }
+
        dev_info->tx_offload_capa = DEV_TX_OFFLOAD_MULTI_SEGS |
                                    DEV_TX_OFFLOAD_VLAN_INSERT;
        if (host_features & (1ULL << VIRTIO_NET_F_CSUM)) {
-- 
2.17.2

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