[dpdk-dev] [PATCH v2] doc: update multiple instance info for NULL crypto

[Vipin Varghese <vipin.varghese@intel.com>]

Add foot note & example to inform user how to use multiple instance.

Signed-off-by: Vipin Varghese <vipin.varghese@intel.com>
---

V2 Changes:
 - Updated Note for better wording - Pablo
 - Multiple instance information to Crypto Device Lib - Pablo
---
 doc/guides/cryptodevs/null.rst | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/doc/guides/cryptodevs/null.rst b/doc/guides/cryptodevs/null.rst
index 03a3ddc..f476e9d 100644
--- a/doc/guides/cryptodevs/null.rst
+++ b/doc/guides/cryptodevs/null.rst
@@ -41,6 +41,10 @@ each mbuf in the burst will be enqueued in an internal buffer for collection on
 a dequeue call as long as the mbuf has a valid rte_mbuf_offload operation with
 a valid rte_cryptodev_session or rte_crypto_xform chain of operations.
 
+.. Note::
+
+    In case of multiple NULL cryptos PMD instances, each should have unique id.
+
 Features
 --------
 
@@ -91,7 +95,9 @@ The following parameters (all optional) can be provided in the previous two call
 
 Example:
 
-.. code-block:: console
+-.. code-block:: console
+
+   ./l2fwd-crypto -l 1 -n 4 \
+   --vdev="crypto_null,socket_id=0,max_nb_sessions=128" \
+   -- -p 1 --cdev SW --chain CIPHER_ONLY --cipher_algo "null"
 
-    ./l2fwd-crypto -l 1 -n 4 --vdev="crypto_null,socket_id=0,max_nb_sessions=128" \
-    -- -p 1 --cdev SW --chain CIPHER_ONLY --cipher_algo "null"
-- 
1.9.1