[PATCH v1] doc: update mlx4 flow limitations

[Ophir Munk <ophirmu@mellanox.com>]

From: Moti Haimovsky <motih@mellanox.com>

This patch updates mlx4 documentation with flow
configuration limitations imposed by NIC hardware and
PMD implementation

Signed-off-by: Ophir Munk <ophirmu@mellanox.com>
---
 doc/guides/nics/mlx4.rst | 77 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)

diff --git a/doc/guides/nics/mlx4.rst b/doc/guides/nics/mlx4.rst
index 98b9716..b81a875 100644
--- a/doc/guides/nics/mlx4.rst
+++ b/doc/guides/nics/mlx4.rst
@@ -515,3 +515,80 @@ devices managed by librte_pmd_mlx4.
       Port 3 Link Up - speed 40000 Mbps - full-duplex
       Done
       testpmd>
+
+Limitations
+-----------
+
+Flow rules
+~~~~~~~~~~
+
+L2 (eth)
+^^^^^^^^
+
+- Can only use real destination MAC
+- Source MAC is not taken into consideration
+
+  For example using testpmd command - src mask must be 00:00:00:00:00:00
+  otherwise the following command will fail
+
+.. code-block:: console
+
+     testpmd> flow create 1 ingress pattern eth
+              src spec 00:16:3e:2b:e6:47 src mask FF:FF:FF:FF:FF:FF
+              / end actions drop / end
+
+- Supports only full MASK
+
+  For example the following testpmd command will fail
+
+.. code-block:: console
+
+     testpmd> flow create 1 ingress pattern eth
+              src spec 00:16:3e:2b:e6:47
+              dst spec 4A:11:6C:FA:60:D0 dst mask FF:00:FF:FF:FF:00
+              / end actions drop / end
+
+
+- When configured to run in promiscuous or all-multicast modes does
+  not support additional rules
+- Does not support the explicit exclusion of all multicast traffic
+- Does not support partial VLAN TCI VID matching
+
+L3 (ipv4)
+^^^^^^^^^
+
+- Supports only 0 or full mask. Prerequisites: Need to have eth dst spec
+
+L4 (tcp/udp)
+^^^^^^^^^^^^
+
+- Supports only full mask
+
+  For example the following testpmd command will fail
+
+.. code-block:: console
+
+     testpmd> flow create 0 ingress pattern eth
+              src spec e4:1d:2d:2d:8d:22
+              dst spec 00:15:5D:10:8D:00 dst mask FF:FF:FF:FF:FF:FF
+              / ipv4 src spec 144.144.92.0 src prefix 16
+              / end actions drop  / end
+
+  Prerequisites: Need to have eth dst spec and IPv4 before it with all
+  its limitations
+
+Flow actions
+~~~~~~~~~~~~
+
+RSS
+^^^
+
+RSS is performed on packets to spread them among several queues based on hash
+function calculation and according to provided parameters.
+
+- RSS hash is calculated on fixed packet fields including: L3 source and
+  destination addresses (ipv4 or ipv6) and L4 source and destination addresses
+  (upd or tcp ports)
+- Uses default constant RSS key
+- Only power of two number of queues is supported
+- Every Rx queue can be specified only once in RSS action
-- 
2.7.4