[PATCH v3 6/6] doc: add feature for loopback mode

[Huisong Li]

Add feature for loopback mode.

Fixes: db0359256170 ("ixgbe: add Tx->Rx loopback mode for 82599")
Cc: stable at dpdk.org

Signed-off-by: Huisong Li <lihuisong at huawei.com>
Acked-by: Chengwen Feng <fengchengwen at huawei.com>
---
 doc/guides/nics/features.rst | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/doc/guides/nics/features.rst b/doc/guides/nics/features.rst
index c5c4dbf745..caf1258554 100644
--- a/doc/guides/nics/features.rst
+++ b/doc/guides/nics/features.rst
@@ -45,6 +45,18 @@ Supports configurating fixed speed and link autonegotiation.
 * **[related]  API**: ``rte_eth_dev_configure()``.
 
 
+.. _nic_features_loopback:
+
+Loopback configuration
+----------------------
+
+Supports configurating loopback mode. The default value 0 is to disable
+loopback mode and other value is defined by given Ethernet controller.
+
+* **[uses]     user config**: ``dev_conf.lpbk_mode``.
+* **[related]  API**: ``rte_eth_dev_configure()``.
+
+
 .. _nic_features_link_status:
 
 Link status
-- 
2.33.0