[PATCH v2] doc: update match with compare result item limitation

[Suanming Mou <suanmingm@nvidia.com>]

In switch mode, when ``repr_matching_en`` flag is enabled in the devarg,
the match with compare result item is not supported to the ``ingress``
rule as an implicit REPRESENTED_PORT need to be added to the matcher.
That REPRESENTED_PORT item conflicts with the single item limitation for
match with compare result item.

Fixes: cb25df7ce9d6 ("net/mlx5: support comparison matching")
Cc: stable@dpdk.org

Signed-off-by: Suanming Mou <suanmingm@nvidia.com>
---

v2: Add `repr_matching_en`` enabled by default explanation.

---
 doc/guides/nics/mlx5.rst | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst
index 7ced6ca8f9..64933a0823 100644
--- a/doc/guides/nics/mlx5.rst
+++ b/doc/guides/nics/mlx5.rst
@@ -460,6 +460,11 @@ Limitations
   - The field type ``RTE_FLOW_FIELD_VALUE`` must be the base (``b``) field.
   - The field type ``RTE_FLOW_FIELD_RANDOM`` can only be compared with
     ``RTE_FLOW_FIELD_VALUE``.
+  - In switch mode, when ``repr_matching_en`` flag is enabled (by default)
+    in the devarg, the match with compare result item is not supported to
+    the ``ingress`` rule as an implicit REPRESENTED_PORT need to be added to
+    the matcher. That REPRESENTED_PORT item conflicts with the single item
+    limitation for match with compare result item.
 
 - No Tx metadata go to the E-Switch steering domain for the Flow group 0.
   The flows within group 0 and set metadata action are rejected by hardware.
-- 
2.34.1