doc: clarify L3 Tx checksum prerequisite

Based on PKT_TX_IP_CKSUM definition the user needs
to fill l2_len and l3_len mbuf fields before issuing
HW Tx checksum request.

Fixes: dad1ec72a377 ("doc: document NIC features")
Cc: stable@dpdk.org
Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>

diff --git a/doc/guides/nics/features.rst b/doc/guides/nics/features.rst
index 4a94625..a211466 100644 (file)
--- a/doc/guides/nics/features.rst
+++ b/doc/guides/nics/features.rst
@@ -563,6 +563,7 @@ Supports L3 checksum offload.
 * **[uses]     rte_eth_txconf,rte_eth_txmode**: ``offloads:DEV_TX_OFFLOAD_IPV4_CKSUM``.
 * **[uses]     mbuf**: ``mbuf.ol_flags:PKT_TX_IP_CKSUM``,
   ``mbuf.ol_flags:PKT_TX_IPV4`` | ``PKT_TX_IPV6``.
+* **[uses]     mbuf**: ``mbuf.l2_len``, ``mbuf.l3_len``.
 * **[provides] mbuf**: ``mbuf.ol_flags:PKT_RX_IP_CKSUM_UNKNOWN`` |
   ``PKT_RX_IP_CKSUM_BAD`` | ``PKT_RX_IP_CKSUM_GOOD`` |
   ``PKT_RX_IP_CKSUM_NONE``.